android基础总结篇之一：Activity生命周期

package com.scott.lifecycle; 
 
import android.app.Activity; 
import android.content.Context; 
import android.content.Intent; 
import android.os.Bundle; 
import android.util.Log; 
import android.view.View; 
import android.widget.Button; 
 
public class LifeCycleActivity extends Activity { 
  
 private static final String TAG = "LifeCycleActivity"; 
 private Context context = this; 
 private int param = 1; 
  
 //Activity创建时被调用 
 @Override 
 public void onCreate(Bundle savedInstanceState) { 
  super.onCreate(savedInstanceState); 
  Log.i(TAG, "onCreate called."); 
   
  setContentView(R.layout.lifecycle); 
   
  Button btn = (Button) findViewById(R.id.btn); 
  btn.setOnClickListener(new View.OnClickListener() { 
   @Override 
   public void onClick(View v) { 
    Intent intent = new Intent(context, TargetActivity.class); 
    startActivity(intent); 
   } 
  }); 
 } 
  
 //Activity创建或者从后台重新回到前台时被调用 
 @Override 
 protected void onStart() { 
  super.onStart(); 
  Log.i(TAG, "onStart called."); 
 } 
  
 //Activity从后台重新回到前台时被调用 
 @Override 
 protected void onRestart() { 
  super.onRestart(); 
  Log.i(TAG, "onRestart called."); 
 } 
  
 //Activity创建或者从被覆盖、后台重新回到前台时被调用 
 @Override 
 protected void onResume() { 
  super.onResume(); 
  Log.i(TAG, "onResume called."); 
 } 
  
 //Activity窗口获得或失去焦点时被调用,在onResume之后或onPause之后 
 /*@Override 
 public void onWindowFocusChanged(boolean hasFocus) { 
  super.onWindowFocusChanged(hasFocus); 
  Log.i(TAG, "onWindowFocusChanged called."); 
 }*/ 
  
 //Activity被覆盖到下面或者锁屏时被调用 
 @Override 
 protected void onPause() { 
  super.onPause(); 
  Log.i(TAG, "onPause called."); 
  //有可能在执行完onPause或onStop后,系统资源紧张将Activity杀死,所以有必要在此保存持久数据 
 } 
  
 //退出当前Activity或者跳转到新Activity时被调用 
 @Override 
 protected void onStop() { 
  super.onStop(); 
  Log.i(TAG, "onStop called.");  
 } 
  
 //退出当前Activity时被调用,调用之后Activity就结束了 
 @Override 
 protected void onDestroy() { 
  super.onDestroy(); 
  Log.i(TAG, "onDestory called."); 
 } 
  
 /** 
  * Activity被系统杀死时被调用. 
  * 例如:屏幕方向改变时,Activity被销毁再重建;当前Activity处于后台,系统资源紧张将其杀死. 
  * 另外,当跳转到其他Activity或者按Home键回到主屏时该方法也会被调用,系统是为了保存当前View组件的状态. 
  * 在onPause之前被调用. 
  */ 
 @Override 
 protected void onSaveInstanceState(Bundle outState) { 
  outState.putInt("param", param); 
  Log.i(TAG, "onSaveInstanceState called. put param: " + param); 
  super.onSaveInstanceState(outState); 
 } 
  
 /** 
  * Activity被系统杀死后再重建时被调用. 
  * 例如:屏幕方向改变时,Activity被销毁再重建;当前Activity处于后台,系统资源紧张将其杀死,用户又启动该Activity. 
  * 这两种情况下onRestoreInstanceState都会被调用,在onStart之后. 
  */ 
 @Override 
 protected void onRestoreInstanceState(Bundle savedInstanceState) { 
  param = savedInstanceState.getInt("param"); 
  Log.i(TAG, "onRestoreInstanceState called. get param: " + param); 
  super.onRestoreInstanceState(savedInstanceState); 
 } 
} 

setRequestedOrientation(ActivityInfo.SCREEN_ORIENTATION_PORTRAIT); //竖屏 

setRequestedOrientation(ActivityInfo.SCREEN_ORIENTATION_LANDSCAPE); //横屏 

package com.scott.lifecycle; 
 
import android.app.Activity; 
import android.content.res.Configuration; 
import android.os.Bundle; 
import android.util.Log; 
 
public class OrientationActivity extends Activity { 
  
 private static final String TAG = "OrientationActivity"; 
 private int param = 1; 
  
 @Override 
 protected void onCreate(Bundle savedInstanceState) { 
  super.onCreate(savedInstanceState); 
  setContentView(R.layout.orientation_portrait); 
  Log.i(TAG, "onCreate called."); 
 } 
  
 @Override 
 protected void onStart() { 
  super.onStart(); 
  Log.i(TAG, "onStart called."); 
 } 
  
 @Override 
 protected void onRestart() { 
  super.onRestart(); 
  Log.i(TAG, "onRestart called."); 
 } 
  
 @Override 
 protected void onResume() { 
  super.onResume(); 
  Log.i(TAG, "onResume called."); 
 } 
  
 @Override 
 protected void onPause() { 
  super.onPause(); 
  Log.i(TAG, "onPause called."); 
 } 
  
 @Override 
 protected void onStop() { 
  super.onStop(); 
  Log.i(TAG, "onStop called."); 
 } 
  
 @Override 
 protected void onDestroy() { 
  super.onDestroy(); 
  Log.i(TAG, "onDestory called."); 
 } 
 
 @Override 
 protected void onSaveInstanceState(Bundle outState) { 
  outState.putInt("param", param); 
  Log.i(TAG, "onSaveInstanceState called. put param: " + param); 
  super.onSaveInstanceState(outState); 
 } 
  
 @Override 
 protected void onRestoreInstanceState(Bundle savedInstanceState) { 
  param = savedInstanceState.getInt("param"); 
  Log.i(TAG, "onRestoreInstanceState called. get param: " + param); 
  super.onRestoreInstanceState(savedInstanceState); 
 } 
  
 //当指定了android:configChanges="orientation"后,方向改变时onConfigurationChanged被调用 
 @Override 
 public void onConfigurationChanged(Configuration newConfig) { 
  super.onConfigurationChanged(newConfig); 
  Log.i(TAG, "onConfigurationChanged called."); 
  switch (newConfig.orientation) { 
  case Configuration.ORIENTATION_PORTRAIT: 
   setContentView(R.layout.orientation_portrait); 
   break; 
  case Configuration.ORIENTATION_LANDSCAPE: 
   setContentView(R.layout.orientation_landscape); 
   break; 
  } 
 } 
}