理解 Activity 的生命周期

把Activity看成一个页面，在Android系统中，Activity 被作为 Activity 栈进行管理.
- 当前活动的Activity 处于栈顶.
- 非活动的Activity 压在栈中, 处于等待状况

 

一个Activity的状态有如下4种:
- 活动. (处于栈顶, 有焦点，可见)
- 暂停. (失去焦点，但可见)
- 停止. (失去焦点，不可见)
- 销毁. (被系统或进程结束)

 

一个Activity的方法有如下7个:
- .onCreate()    创建
- .onStart()      启动
- .onRestart()    重启.
- .onResume()  恢复
- .onPause()     暂停
- .onStop()      停止
- .onDestroy()   销毁

 

Activity 的生命周期的 Cases
a. Activiy1 启动
   - Code:

super.onCreate()

 
   - 运行顺序: ( Activity1 : onCreate() -> onStart() ->onResume() )

 

b. 从Activity1 跳转到 Activity2, 然后关闭Activity1.
   - Code: 
      

Intent intent = new Intent();  //新建一个Intent对象.
intent.setClass(Activity1.this, Activity2.class);  //设定Intent要启动的类. 
startActivity(intent); //启动一个新的Activity
Activity1.this.finish();  //关闭当前的Activity.

     - 运行顺序: (Activity1: onPause() )->  ( Activity2: onCreate() ->onStart() ->onResume()) -> (Activity1:onStop() ->onDestroy())

 

c. 关闭Activity1, 退出程序 , 或者按 "BACK" 键.
    - Code: 
      

Activity1.this.finish(); 

 
     -运行顺序: Activity1: onPause()->onStop()->onDestroy();

 

d. 按"HOME"键， 然后再运行程序.
     - 运行顺序: Activity1: onPause()->onStop()  => 运行其他程序 => 再运行本程序: Activity1: onRestart()->onStart()-)>onResume()

 

e. 刷新Activity1
    - Code:

  

public class LifeCycleActivity extends Activity {
    /** Called when the activity is first created. */
	private static final String TAG = "MainActivity"; 
    
    @Override 
    public void onCreate(Bundle savedInstanceState) { 
        super.onCreate(savedInstanceState); 
        setContentView(R.layout.main); 
        Log.i(TAG, "onCreate()"); 
         
        Button button = (Button) this.findViewById(R.id.button); 
        button.setOnClickListener(new View.OnClickListener() { 
            @Override 
            public void onClick(View v) { 
              //Intent intent = new Intent(LifeCycleActivity.this, Activity2.class); 
              //startActivity(intent); 
            	reload();
            } 
        }); 
    } 
 
    @Override 
    protected void onDestroy() { 
        Log.i(TAG, "onDestroy()"); 
        super.onDestroy(); 
    } 
 
    @Override 
    protected void onPause() { 
         Log.i(TAG, "onPause()"); 
        super.onPause(); 
    } 
 
    @Override 
    protected void onRestart() { 
         Log.i(TAG, "onRestart()"); 
        super.onRestart(); 
    } 
 
    @Override 
    protected void onResume() { 
         Log.i(TAG, "onResume()"); 
        super.onResume(); 
    } 
 
    @Override 
    protected void onStart() { 
         Log.i(TAG, "onStart()"); 
        super.onStart(); 
    } 
 
    @Override 
    protected void onStop() { 
         Log.i(TAG, "onStop()"); 
        super.onStop(); 
    } 
     
    public void reload(){
    	Intent intent = getIntent();
    	this.finish();
    	startActivity(intent);
    }
} 

 -运行顺序: onCreate()->onStart()->onResume() ==> 点按纽后 onPause()->onCreate()->onStart()->onResume()->onStop()->onDestroy()

 

更多的可以参考:

http://www.ibm.com/developerworks/cn/opensource/os-cn-android-actvt/