Android default launchMode of LAUNCHER activity?

Question

does the launchMode of the launcher activity in the manifest get ignored? The android documentation says that the default launchMode is "standard" but this isn't logic for me if this would be applied to the main activity of an app because each time you start the app, another task would be created in the instance of the app.

Answer 1

Well, I delved into Android sources myself and found the following thing.

The launcher starts apps using the method startActivityAsUser in LauncherAppsService. The intent is constructed using these lines:

Intent launchIntent = new Intent(Intent.ACTION_MAIN);
launchIntent.addCategory(Intent.CATEGORY_LAUNCHER);
launchIntent.setComponent(component);
launchIntent.setSourceBounds(sourceBounds);
launchIntent.addFlags(Intent.FLAG_ACTIVITY_NEW_TASK);

---

According to Android documentation, the flag FLAG_ACTIVITY_NEW_TASK means:

When using this flag, if a task is already running for the activity you are now starting, then a new activity will not be started; instead, the current task will simply be brought to the front of the screen with the state it was last in.

This effectively and unconditionally overrides launchMode specified (or omitted to default behaviour) in the app, and ignores this attribute.

I think this demonstrates that the documentation is not clear (or complete) enough. Without such deep investigations of the core source codes everyone can get unexpected results now and then.

Answer 2

You are confusing two things. One is launchMode and the other is "what happens when the user selects an app icon from the HOME screen, or selects a task from the list of recent tasks". These are 2 completely different things.

launchMode

Each Activity has a specified launchMode (the default is "standard" or "multiple". This tells Android how to start this Activity, and there are many factors that can contribute to the "interpretation" of the launchMode. It depends on what other flags may have been specified in the Intent used. It depends on which task requested the launch of the Activity (or if the launch was requested from a non-activity context, like from a Service or BroadcastReceiver). It depends on whether or not an existing instance of the Activity is already active in the specified task, etc.

Behaviour on selecting an app icon from the HOME screen or list of installed applications

When the user selects an app icon, startActivity() is called with an Intent containing the following data:

• ACTION=MAIN
• CATEGORY=LAUNCHER
• Component is set to the package name and the class name of the Activity that is defined in the manifest with ACTION=MAIN and CATEGORY=LAUNCHER
• Flag FLAG_ACTIVITY_NEW_TASK and FLAG_ACTIVITY_RESET_TASK_IF_NEEDED are set.

Regardless of the launchMode definition of the Activity to be launched, calling startActivity() with an Intent like this causes the following behaviour:

If there is already an existing task whose task affinity matches the Activity being started (in simple terms, if the app is already running), Android will simply bring the existing task to the foreground. That's it. It doesn't create an instance of any Activity. It doesn't call onNewIntent() on any Activity. It does nothing other than bringing the existing task to the foreground. This is why, even if you specify launchMode="standard" for your launcher Activity, Android doesn't create a new instance every time you click on your app icon.

If there isn't already an existing task whose task affinity matches the Activity being started (in simple terms, if the app isn't already running), Android will create a new task and launch the Activity into that task. launchMode doesn't play a role here, since there is absolutely no difference between the launch modes when launching a single Activity into a new task. Android always creates a new task and always creates a new instance of the Activity as the root of that task.

This behaviour is also the same when the user selectsa task from the list of recent tasks. If the task is still running, Android just brings the task to the foreground, does not start any new Activity instances and does not call onNewIntent(). If the task is no longer running, Android creates a new task and launches the launcher Activity into that task. The only difference here is that the flag FLAG_ACTIVITY_LAUNCHED_FROM_HISTORY is also set in the Intent if the user selected a task from the list of recent tasks.

I hope this answers your question.

See this answer for a very detailed explanation of FLAG_ACTIVITY_RESET_TASK_IF_NEEDED and task reparenting in general.

Answer 3

Think of everything except the opening activity as an abstract implementation. Declaring an activity as

        <intent-filter>
            <action android:name="android.intent.action.MAIN" />

            <category android:name="android.intent.category.LAUNCHER" />
        </intent-filter>

Will cause it to open first. Subsequent activities are Overriden at the time an Intent is formed to navigate between activities. The overrides are represented as intent flags.

A list of intent extras: http://developer.android.com/reference/android/content/Intent.html

With flags being commands you'd otherwise have written in the Manifest.

Answer 4

You are right.The default mode is "standard".

According to android documentation

*In standard mode ,Every time there's a new intent for a "standard" activity, a new instance of the class is created to respond to that intent. Each instance handles a single intent.

*.If the parent activity has launch mode standard (and the up intent does not contain FLAG_ACTIVITY_CLEAR_TOP), the current activity and its parent are both popped off the stack, and a new instance of the parent activity is created to receive the navigation intent.

Answer 5

The behavior of Activity set to standard mode is a new Activity will always be created to work separately with each Intent sent. Imagine, if there are 10 Intents sent to compose an email, there should be 10 Activities launch to serve each Intent separately. As a result, there could be an unlimited number of this kind of Activity launched in a device.

Behavior on Android pre-Lollipop

standard Activity would be created and placed on top of stack in the same task as one that sent an Intent. For example, when we share an image from gallery to a standard Activity, It will be stacked in the same task as described although they are from the different application. If we switch the application to the another one and then switch back to Gallery, we will still see that standard launchMode place on top of Gallery's task. As a result, if we need to do anything with Gallery, we have to finish our job in that additional Activity first.

Behavior on Android Lollipop

If the Activities are from the same application, it will work just like on pre-Lollipop, stacked on top of the task. But in case that an Intent is sent from a different application. New task will be created and the newly created Activity will be placed as a root Activity like below.

Source from here