第四节--Activity生命周期里的方法介绍

Activity中的生命周期方法：

原意：

The entire lifecycle of an activity is defined by the following Activity methods. All of these are hooks that you can override to do appropriate work when the activity changes state. All activities will implement onCreate(Bundle) to do their initial setup; many will also implement onPause() to commit changes to data and otherwise prepare to stop interacting with the user. You should always call up to your superclass when implementing these methods.

译文：

一个Activity的整个生命周期被定义为下面的一些方法。当Activity的状态有所改变时，所有这些继承的方法都会去做比较适合自己的工作。对于所有的Activity都实现onCreate()进行初始化。很多Activity也实现onPause()方法来提交改变的数据或者是准备停止和用户交互。当我们实现这些方法时，要调用父类的onCreate方法通知父类。

 public class Activity extends ApplicationContext {
     protected void onCreate(Bundle savedInstanceState);

     protected void onStart();
     
     protected void onRestart();

     protected void onResume();

     protected void onPause();

     protected void onStop();

     protected void onDestroy();
 }

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示例代码：

主Activity public class FirstActivity extends Activity { private Button Button; /* * 当activity被初始启动是被调用 * */ @Override public void onCreate(Bundle savedInstanceState) { System.out.println("打印第一个的onCreate"); super.onCreate(savedInstanceState); setContentView(R.layout.main); Button = (Button)findViewById(R.id.myButton); Button.setText("启动第二个Activity"); Button.setOnClickListener(new View.OnClickListener() { @Override public void onClick(View v) { Intent intent = new Intent(); intent.setClass(FirstActivity.this,SecondActivity.class); startActivity(intent); } }); } @Override protected void onDestroy() { System.out.println("打印第一个的onDestory"); super.onDestroy(); } /* * Called when the system is about to start resuming a previous activity * 系统将要调用另一个Activity的onReusme的方式时，会调用当前Activity的onPause()方法 */ @Override protected void onPause() { System.out.println("打印第一个的onPause"); super.onPause(); } /* * Activity之前已经被停止了，现在从新被启动时会调用这个方法。 */ @Override protected void onRestart() { System.out.println("打印第一个的onRestart"); super.onRestart(); } /* * Called when the activity will start interacting with the user. * At this point your activity is at the top of the activity stack, * with user input going to it. * 方法被调用时表示将要开始与用户进行交互。此时你的活动是在堆栈顶部的活动，要与用户输入它。 */ @Override protected void onResume() { System.out.println("打印第一个的onResume"); super.onResume(); } /* * Called when the activity is becoming visible to the user. * Activity即将被显示给用户时，改方法会被调用 */ @Override protected void onStart() { System.out.println("打印第一个的onStart"); super.onStart(); } /* * Called when the activity is no longer visible to the user, * because another activity has been resumed and is covering this one. * 当Activity已经不对用户显示时onStop方法被调用，因为另一个Activity已经进入onResume或当前activity已经被覆盖 */ @Override protected void onStop() { System.out.println("打印第一个的onStop"); super.onStop(); } }

public class SecondActivity extends Activity { @Override protected void onCreate(Bundle savedInstanceState) { System.out.println("打印第二个的onCreate"); super.onCreate(savedInstanceState); } @Override protected void onDestroy() { System.out.println("打印第二个的onDestory"); super.onDestroy(); } @Override protected void onPause() { System.out.println("打印第二个的onPause"); super.onPause(); } @Override protected void onRestart() { System.out.println("打印第二个的onRestart"); super.onRestart(); } @Override protected void onResume() { System.out.println("打印第二个的onResume"); super.onResume(); } @Override protected void onStart() { System.out.println("打印第二个的onStart"); super.onStart(); } @Override protected void onStop() { System.out.println("打印第二个的onStop"); super.onStop(); } }