一个重写的android生命周期方法如何在超级调用之后运行代码，而无需使用其后续的生命周期方法

Question

Take a look at this.

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
}

@Override
protected void onStart() {
    super.onStart();
}

Assume this code is from a normal activity which is a child of Activity class. super.onCreate() is the first statement in onCreate() . This super call must the connecting point to notify the parent class that the onCreate() is called in derived class and the next lifecycle method can be called, which is onStart() obviously.

That is, the order of execution must be like this :

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);              <-- ( 1 )
    setContentView(R.layout.activity_main);          <-- ( 3 )
}

@Override
protected void onStart() {
    super.onStart();                                 <-- ( 2 )
}

But it looks like working this way instead :

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);              <-- ( 1 )
    setContentView(R.layout.activity_main);          <-- ( 2 )
}

@Override
protected void onStart() {
    super.onStart();                                 <-- ( 3 )
}

How is it possible?

Answer 1

Because onStart() is called after onCreate() , not from it.

Take a look here .

ActivityThread#startActivityNow() instantiates the Activity and calls onCreate() .

A few lines down you'll see a call to ActivityThread#handleStartActivity() which is what calls onStart() .

Since there's no async there, Java will wait for onCreate() to finish before it continues and eventually calls onStart() .

Check the source comments in Activity.java for more details on how Activity lifecycles work.