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How to understand the Activity startup mode, many novices are not very clear about this, in order to help you solve this problem, the following editor will explain for you in detail, people with this need can come to learn, I hope you can gain something.

There are four startup modes of Activity, standard, singleTop, singleTask, singleInstance.

1.standard

Standard is the default startup mode for Activity, which is automatically used by all activities without the display specified.

Each time you start, a new Activity is at the top of the stack.

Android:launchMode= "standard", where each click of the button creates a new Activity

Now, let's write a simple button to jump to Activity

Private Button button; @ Override protected void onCreate (Bundle savedInstanceState) {super.onCreate (savedInstanceState); setContentView (R.layout.activity_main); Log.e ("MainActivity", this.toString ()); button = (Button) findViewById (R.id.button) Button.setOnClickListener (new View.OnClickListener () {@ Override public void onClick (View view) {Intent intent = new Intent (MainActivity.this, MainActivity.class); startActivity (intent);}});}

Although the jump page is the same, a new Activity is created with each click of the button in Task

Activity create Log

Startup example diagram

2.singleTop

When the startup mode of Activity is singleTop, when the launched Activity is already at the top of the Activity stack, it is used directly.

Android:launchMode= "singleTop"

We create the NextActivity and add button2 to the MainActivity

Private Button button1,button2; @ Override protected void onCreate (Bundle savedInstanceState) {super.onCreate (savedInstanceState); setContentView (R.layout.activity_main); Log.e ("MainActivity", this.toString ()); button1 = (Button) findViewById (R.id.button1); button2 = (Button) findViewById (R.id.button2); button1.setOnClickListener (this); button2.setOnClickListener (this) } @ Override public void onClick (View view) {switch (view.getId ()) {case R.id.button1: Intent intent = new Intent (MainActivity.this, MainActivity.class); startActivity (intent); break; case R.id.button2: Intent intent2 = new Intent (this, NextActivity.class) StartActivity (intent2); break;}}

At this point, if you start MainActivity in MainActivity, it will only be created once in the Activity stack, but if you start NextActivity first and then MainActivity, a new MainActivity will be created because at this time the top of the Activity stack is NextActivity.

MainActivity-> MainActivity-> MainActivity

MainActivity-> NextActivity-> MainActivity

Startup example diagram

3.singleTask

When the startup mode of the activity is singleTask, starting the Activity will now check whether it exists in the stack, and if so, all the Activity above the activity will be unstacked directly.

Android:launchMode= "singleTask"

Startup example diagram

4.singleInstance

In singleInstance mode, there is a separate return stack to manage activities. No matter which application accesses the activity, they all share the same stack, which allows other programs to call and implement to share the activity.

Android:launchMode= "singleInstance"

Startup example diagram

The startup process in the figure is: Main-> New-> Next. This process is easy to understand.

The return process is: Next-> Main-> New

It is obvious that the order is different. Why does this happen?

NextActivity and MainActivity are on the same stack. When we return, NextActivity leaves the stack, and there is still MainActivity in stack An and at the top of the stack, so we will see MainActivity.

When the MainActivity execution returns, stack An is emptied, and then we see the NewActivity at stack B.

After that, NewActivity exits the stack, and stack B is empty, and App exits.

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