Activity的生命周期

为了更加生动的阐述 Activity 的生命周期，我们采用一个小例子来看看吧

• 创建两个 Activity
• 界面 A 点击按钮跳转到界面 B
• 通过 Log 打印生命周期
  

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1.启动应用，显示界面 A

• 界面A>>>: onCreate()
• 界面A>>>: onStart()
• 界面A>>>: onResume()

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2.点击按钮，跳转到界面 B

• 界面A>>>: onPause()
• 界面B>>>: onCreate()
• 界面B>>>: onStart()
• 界面B>>>: onResume()
• 界面A>>>: onStop()

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3.返回界面 A

• 界面B>>>: onPause()
• 界面A>>>: onRestart()
• 界面A>>>: onStart()
• 界面A>>>: onResume()
• 界面B>>>: onStop()
• 界面B>>>: onDestroy()

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4.点击 Home 键

• 界面A>>>: onPause()
• 界面A>>>: onStop()

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5.重新打开 APP

• 界面A>>>: onRestart()
• 界面A>>>: onStart()
• 界面A>>>: onResume()

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6.点击 Back 键

• 界面A>>>: onPause()
• 界面A>>>: onStop()
• 界面A>>>: onDestroy()

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7.重新打开 APP

• 界面A>>>: onCreate()
• 界面A>>>: onStart()
• 界面A>>>: onResume()

---

MainActivity.java

public class MainActivity extends AppCompatActivity {
    private static final String TAG = "MainActivity";
    private Button button;


    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        Log.i(TAG, "界面A>>>: onCreate()");
        button = findViewById(R.id.main_btn);
        button.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                Intent intent = new Intent(MainActivity.this, MainActivity2.class);
                startActivity(intent);
            }
        });
    }

    @Override
    protected void onStart() {
        super.onStart();
        Log.i(TAG, "界面A>>>: onStart()");
    }

    @Override
    protected void onResume() {
        super.onResume();
        Log.i(TAG, "界面A>>>: onResume()");
    }

    @Override
    protected void onPause() {
        super.onPause();
        Log.i(TAG, "界面A>>>: onPause()");
    }

    @Override
    protected void onStop() {
        super.onStop();
        Log.i(TAG, "界面A>>>: onStop()");
    }

    @Override
    protected void onDestroy() {
        super.onDestroy();
        Log.i(TAG, "界面A>>>: onDestroy()");
    }

    @Override
    protected void onRestart() {
        super.onRestart();
        Log.i(TAG, "界面A>>>: onRestart()");
    }

}

MainActivity2.java

public class MainActivity2 extends AppCompatActivity {
    private static final String TAG = "MainActivity2";

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main2);
        Log.i(TAG, "界面B>>>: onCreate()");
    }

    @Override
    protected void onStart() {
        super.onStart();
        Log.i(TAG, "界面B>>>: onStart()");
    }

    @Override
    protected void onResume() {
        super.onResume();
        Log.i(TAG, "界面B>>>: onResume()");
    }

    @Override
    protected void onPause() {
        super.onPause();
        Log.i(TAG, "界面B>>>: onPause()");
    }

    @Override
    protected void onStop() {
        super.onStop();
        Log.i(TAG, "界面B>>>: onStop()");
    }

    @Override
    protected void onDestroy() {
        super.onDestroy();
        Log.i(TAG, "界面B>>>: onDestroy()");
    }

    @Override
    protected void onRestart() {
        super.onRestart();
        Log.i(TAG, "界面B>>>: onRestart()");
    }
}

activity_main.xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical"
    tools:context=".MainActivity">

    <TextView
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_marginTop="100dp"
        android:gravity="center"
        android:text="我是界面A"
        android:textColor="#000000"
        android:textSize="36sp" />

    <Button
        android:id="@+id/main_btn"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_margin="32dp"
        android:text="跳转到界面B"
        android:textColor="#000000"
        android:textSize="36sp" />


</LinearLayout>

activity_main2.xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"

    tools:context=".MainActivity2">

    <TextView
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_gravity="center_vertical"
        android:gravity="center"
        android:text="我是界面B"
        android:textColor="#000000"
        android:textSize="36sp" />


</LinearLayout>

本文地址：https://blog.csdn.net/Joker_LCL/article/details/107523779