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(upbeat music)

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Alright, so we added two

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more menu items in the last video.

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Now we need to write the code

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to make these menu items work.

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So we're going to go back to main activities,

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I'm going to close down this design.

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The feed on manual XML

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(mouse clicks)

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Go to my main activity.

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Bring it on the screen,

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And we need to add the new items

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in the on options items selected function.

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This one here.

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Now this takes a bit of thought,

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because these two options are going to

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keep most of the euro unchanged,

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they just alter the limit perimeter.

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So that means we have to store

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the base part of the yearout

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as a class variable

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rather than a private variable.

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Now at the moment,

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we've got to feedUrl

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private in the onOptionsItemSelected method.

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So we need to move it into the class

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so we that we can use it's value

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from one quarter to the next

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as different limits are chosen.

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And we also need to store the current limit size,

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so I'm going to add two variables

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to the top of the class.

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So what I'm going to do also is

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just take a copy of that

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feedUrl.

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Well actually I'll cut it out of there,

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Go back up to the top of the class,

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and just below the tag,

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you're going to put the code in there.

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Tidy this up a little bit,

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I'll put it below the download data,

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So instead of just val now

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it's going to be private.

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(typing)

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It's going to be a ver,

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equals, and we're going to get the

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default value in a minute.

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For the next line we need to add this feed limit

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so I'm going to set that to private var

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feedlimit = 10.

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Alright so then we're going to take a copy,

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of this line at the top of the application

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We're just going to copy that.

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Let's paste it in our feedUrl.

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But, instead of where it's got 10,

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you'll change that to percent d.

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That's a lower case d.

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Now, this is a way of specifying an integer value

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that's going to be replaced by an actual value

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using a string dot format function.

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Now, the string dot format function takes a string

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containing special format codes like we said d

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and a number of values that are used

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to replace the format codes.

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You can do the same thing

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by concatenating strings using plus.

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But, this is a bit later.

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Alright and to avoid duplicating the Url,

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I'm going to change the oncreate code

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so that is uses these two fields

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to create the Url that's downloaded initially.

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So, to do that we're going to come down to oncreate method.

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We're going to change the download to euro method core.

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Going to delete out that hard code

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feed euro we have to replace that with

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feedeuro

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.format

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feedlimit

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(typing)

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So, that now uses the string dot format method

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to replace the percent d in the feed euro

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which we added on line 37

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with the current value of feed limit.

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The other thing that we're going to do

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is with our on options item created,

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we also want to fix that there as well.

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So, let's do the same thing.

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Now I'm going to take a copy of that,

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that line that download euro line.

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Come down here, we're going to replace it there.

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The other thing we need to do

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is we need to replace the percent d in three places

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in our on options item selected.

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So let's do that.

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Percent d.

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Percent d

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and percent d.

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Alright, so that's done.

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And, all we have to do now

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is change the value of feed limit

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when one of the two menu options is chosen.

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So, to do that we need another brant in our when expression.

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So, let's go ahead and do that.

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We're going to put this before the else.

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So, down here.

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And what we're going to type

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is r.id.mnu10

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,r.id.mnu25

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arrowtoken right blockade block

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and then we're going to put our logic in here

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to define whether to select 25 or 10.

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We'll do that by putting if not item.ischecked

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not is checkable but is checked.

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Then we put item.ischecked=true

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so if it's not checked

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we're setting it equal to checked.

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In other words we're setting it to true to do that.

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And we're going to put

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feedlimit=35takefeedlimit.

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Then, we're going to do a log

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so a log.d(tag,"onOptions

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(typing)

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itemselected, we'll put a colon there space

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a dollar sign left to right curly brackets

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item.title left side of the curly brackets setting

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feed limit to dollar feed limit.

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Then we'll put an else there.

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Let's just copy that line to save a bit of time.

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(typing)

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And this time, will be onOptionsItemSelectedItem feed limit

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and because it's an else, there wasn't any change

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so we're just going to put the text unchanged.

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So, we want them to perform pretty much

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the same actions whichever of the two options is selected.

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The only difference here is that

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the new value assigned to feed limit.

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And, you can see here that there's a neat little way

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to toggle between two different numerical values

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and that's just to subtract the current value

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from the sum of the two.

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So, in other words, 35 minus 25 is 10

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and 35 minus 10 is 25.

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So, that's how the limit changed here.

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Now, if an item was already checked

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then we don't need to do anything.

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Let's just test here on line 72.

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But, actually what we're doing we're making sure

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that it's not checked.

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So, if it's already checked we're going to ignore that

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and then the else code will be handled.

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And then we'll actually go through and just log some output

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to say that this setting of feed limit was unchanged.

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Otherwise, if the radiact button wasn't already selected

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or checked in other words,

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we're actually checking it and then we're updating

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feed limit then we're logging that output as well.

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Now, the way these radiact groups work

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isn't immediately obvious but it's actually quite clever.

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The menu items aren't checked or unchecked

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by the menu system when you click them.

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You have to do that yourself in code.

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So, if either one of those options is selected from the menu

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then we test the item to see if it was already selected.

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If it was, we don't need to do anything else

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or I'll have logged the fact that you can see

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with the else on line 77,

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so that we can see what's happening by checking the log cat.

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But, if the item wasn't checked,

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then we're setting it to checked.

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Now, the menu system does help here,

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it will automatically uncheck any other members

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of the same group for us.

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And that's handy because we only going to reference

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the one item passed into the method.

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And incidentally, that's why android passes

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in the item reference rather than just it's id.

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So, we have an item to manipulate when we need to

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like we're doing here.

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Now, if you want to you can find out more information

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about menu option groups in the documentation.

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Let me just bring that up on the screen.

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(typing)

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Now, this guide on screen actually covers

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quite a lot about using menus in general.

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The bit that's specific about groups

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is pretty well towards the bottom.

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About 4/5 of the way down.

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There's a section that should be there called

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something along the lines of using checkable menu items.

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(silence)

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See the card Using checkable menu items.

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Alright, so check that out

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if you want to find out more information.

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Alright, so let's go back to our app.

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So, essentially the app should toggle between

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showing the top 10 and top 25

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now that we've introduced as code.

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So, let's actually run it and see what happens.

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(clicking)

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Alright, so it starts off showing the top 10

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and what we can do is, we'll just scroll down

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and just confirm that it is the top 10.

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We're getting google maps to be the last one there.

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If you change this now to top 25.

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And have another look while scrolling down.

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Clearly, there's more applications showing now

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so that's good that the top 25 is now running as well.

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And we can also if we want to confirm that,

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have a look at log cat.

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And confirm that the change did actually occur.

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We can see the data being downloaded there.

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Just scroll up above that.

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Top 25 setting feed limit to 25.

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00:09:04,005 --> 00:09:06,645
Let's make it easy, we can filter our main activity.

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Let's do that.

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00:09:07,478 --> 00:09:08,645
Main activity.

217
00:09:09,847 --> 00:09:12,359
So, you can see now onOptionsItemSelected Top 25

218
00:09:12,359 --> 00:09:16,043
was selected and feed limit was set to 25.

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And just to confirm that,

220
00:09:17,066 --> 00:09:20,566
if you go back and set it to top 25 again.

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You can see this time, Top 25 setting feed limit unchanged.

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00:09:25,224 --> 00:09:28,095
So, it's logging the fact that the limit wasn't changed.

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But, there is a problem though.

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00:09:30,071 --> 00:09:32,248
And that's that it downloads the data again

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even though nothing's changed.

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And we can see that here,

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the fact that it's started the asynctask.

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Now, that's a good way to drain the device battery

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00:09:41,599 --> 00:09:44,014
or incur roaming data charges.

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So, we really should do something about that.

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Now, by thinking back to the activity life cycle,

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you should be able to work out what will happen

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00:09:52,254 --> 00:09:54,519
when I rotate the device into landscape.

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00:09:54,519 --> 00:09:57,957
What I'm going to do is just clear the log cat

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00:09:57,957 --> 00:09:59,394
so that we can see the log entry

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00:09:59,394 --> 00:10:02,655
so download data will pass applications.

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Going to remove the filter to main activity.

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Actually I'll clear the log cat again

239
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now that I've done that.

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Now let's go and open up the app

241
00:10:09,561 --> 00:10:12,938
or bring that back onto the screen and let's rotate that

242
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and see what happens.

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00:10:16,445 --> 00:10:18,974
So, when I do that you can see from the log cat here

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that it downloads the data again.

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And that's because the activity's destroyed and recreated.

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00:10:27,036 --> 00:10:30,541
But, also if we come over here and check out the code,

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you can see what's happened here

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00:10:32,295 --> 00:10:35,295
is that it set the limit back to 10,

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rather than 25.

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And that's again because the activities

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00:10:40,008 --> 00:10:41,968
got destroyed and recreated.

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00:10:41,968 --> 00:10:45,183
But, we know how to fix that by storing the value in these

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to state bundle is in the instant state function.

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00:10:49,122 --> 00:10:53,736
Now, ideally the code should store the last used Url

255
00:10:53,736 --> 00:10:55,120
and only download the data again

256
00:10:55,120 --> 00:10:57,377
if the Url is actually changed.

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If we do that, we need to provide some way

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for the user to refresh the data manually.

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00:11:02,406 --> 00:11:03,944
But, at least then, they'd be able to make

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a conscious decision to use their mobile data

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00:11:06,370 --> 00:11:08,228
or use up some of the battery life

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00:11:08,228 --> 00:11:10,842
rather than our app just doing it anyway.

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00:11:10,842 --> 00:11:13,234
Unfortunately though, saving something as complex

264
00:11:13,234 --> 00:11:16,150
as an adapter, isn't as straight forward as just storing it

265
00:11:16,150 --> 00:11:18,183
in the instant state bundle.

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And that probably wouldn't be the best approach anyway.

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If we wanted to save performing a download

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with a device orientation changed.

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It's probably better to cache the downloaded data

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in the same way that web browsers do.

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So, that way you can allow your activity

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to be destroyed and recreated when the device is rotated

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and the redownloading would read the data

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from the local cache instead of over the internet.

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Now, that's a bit much for only the 3rd app in the course.

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So, this app's just going to download the data again

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when the device is rotated.

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But, if you do want to learn more about caching downloads,

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there's a pretty decent Google article,

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which I'm just going to bring up on the screen to check out.

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(clicking)

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And basically, we can prevent redundant downloads

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when menu items are clicked though

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and can also make sure that the correct Url

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and feed limit are used when the device is rotated.

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So, that sounds like a good challenge.

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Now, one problem you'll have that I haven't covered

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is how to set the current menu limit

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once we've restored the feed limit value.

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Now, the place to do that

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is in the OnCreateOptionsMenu method.

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Now, the approach is very similar

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to working with widgets in a layout.

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But, here we're working with items in a menu.

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So, let's actually have a look at that.

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So, OnCreateOptionsMenu, you've got the menu.flatline

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and what we want to do after that

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is put in some code that says if

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feed limit is equal to 10

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then we're going to do a menu question mark

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find item

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R.id.mnu10 question mark outside of the parenthesis

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.ischecked is equal to true,

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we're going to add an else otherwise.

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And the else is going to be basically very similar

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but it's going to be the r and the mnu25,

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so the top 25 button.

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So, your else will be

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menu question mark.find item parenthesis r.id.mnu25

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then a question mark outside of the parenthesis

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.ischecked equals true.

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And then we just kind of return to what it was before.

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So, we used the menu.finditem method

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then set the ischecked property to check

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either the mnu10 or mnu25 item

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depending on the value of feed limit.

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Now, notice that we're using the safe call operator

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a lot here.

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Menu is a nullable type, so we have to use safe call

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when calling it's finditem method.

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And we also use it before accessing the ischecked property.

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Now, you might be wondering why I didn't just change

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the function signature, after all I've been doing so

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with apparent appeal up until now.

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Well, as I said, you need to think very carefully

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before doing that.

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Now in here, we can't be certain that we can do it.

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So, our app could use one of the no action bar themes

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which means it wouldn't have a menu.

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So, in that case menu would be null.

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Now, it's likely that OnCreateOptionsMenu

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won't be called in that case.

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You'd have to examine the android framework code

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to be sure which would take some time.

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So, it's easier just to use safe calls,

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at least in this scenario.

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If in doubt, don't modify the framework's signatures.

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Now, of course if Google added a non-null annotation

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then you'll know that we could've changed it.

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When that happens the code generator will generate

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the method without using a nullable type.

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Alright, so with that change, you should now be able

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to have a go at the challenge.

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So, here's the challenge.

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So, you want to modify the apps,

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so it doesn't download data from the same Url a second time

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unless the user specifically chooses to refresh the data.

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Now, you also store the current Url and limit

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so that they aren't reset

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when the device orientation changes,

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the data will still be downloaded again

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to follow the change in orientation.

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But, it should download from the same Url

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that the user was looking at before they rotated the device.

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So, to be clear, the only three events

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that should cause data to be downloaded

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are firstly, a change in orientation.

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Secondly, selecting a different Url or limit from the menu.

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So, if the same menu Url or limit is selected from

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the menu a second time, the data wouldn't be downloaded.

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Thirdly, if the user chooses to refresh the feed,

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with the refresh menu option

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that you're going to actually add.

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And just as a hint there,

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review the Activity Lifecycle before restoring

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the data from the bundle.

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Now, there's more than one way to achieve this challenge.

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So, the real test here is just that the app works.

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Alright, so I'll go over my solution to this

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in the next video.