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POlaunchModes, singleTask: how to switch between "screens"? Is Intents the only way, and if so I think I have a problem
 

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  1. POlaunchModes, singleTask: how to switch between "screens"? Is Intents the only way, and if so I think I have a problem
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    <p>In a number of questions (<a href="https://stackoverflow.com/questions/2013865/header-views-and-buttons-how-do-i-attach-listeners-to-buttons-in-a-header-th">like this one</a>) I have been looking into how to "change screens" in my app. I have a "header" on top, with 4 buttons. Each button is meant to replace the "content" (ie change screen):</p> <pre><code>+--------------------+ | menu with buttons | +--------------------+ | | | | | C O N T E N T | | | | | +--------------------+ </code></pre> <p>When I click a Menu button, I run the following code:</p> <pre><code>@Override public void onClick(View v) { Intent myIntent = new Intent(BaseActivity.this, ActivityMain.class); BaseActivity.this.startActivity(myIntent); } </code></pre> <p>As you can see, the <i>startActivity</i> is executed. Now, if I do not specify <i>"launchMode"</i> for the Activity that means that launchMode = normal. If launchMode == normal that means that the Activity will be re-created each and every time I navigate using the top header buttons, and that means that all data entered in "form elements" are gone (or at least hidden).</p> <p>So, I found the launchMode "singleTask" that sounded sort of nice. If I add that launchMode to my Activity, it will not be re-created when I navigate with the buttons, thus keeping state. Great! Well, until I read <a href="http://developer.android.com/guide/topics/fundamentals.html#acttask" rel="nofollow noreferrer">this</a>:</p> <p><i>As noted above, there's never more than one instance of a "singleTask" or "singleInstance" activity, so that instance is expected to handle all new intents.</i></p> <p>I found out that the sentence mean that <b>there can be only one</b> Activity that has the launchMode set to "singleTask" - if I have more than one it wont work (no compiler error though). </p> <p><b>This means that I can only "keep the state" for one Activity, when switching back and forth (navigating) between my screens!</b></p> <p><a href="https://stackoverflow.com/questions/2032173/configuration-changed-orientation-change-and-destroying-activities-is-this-th">Once again</a>, is this really how it supposed to work?</p>
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    1. COIt sounds like you want to use `singleInstance` more than `singleTask` -- there will be only one task anyway, then with only one instance of each of your activities.
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    2. COIm not following... a "singleInstance" is "always at the root", but I have 4 different screens an they cant all be at the root? Also singleInstance "permits no other activities to be part of its task"... How am I suppose to buil an app with that? The more I learn about Android, the less I understand it seems... =(
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    3. COChristpher: hmm, I tried the "singleInstance" instead, as you suggested, and that works a lot better. Now I dont loose my state in the second Activity. I dont understand why... but it looks alright. hmm... Does that mean that for each Activity with the *singleTask* flag, I get a new Task? from android.com: " A "singleInstance" activity stands alone as the only activity in its task. If it starts another activity, that activity will be launched into a different task..."
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