Android项目实战（二）：安卓应用程序退出的三种方法

 1  @Override  2 public boolean onKeyDown(int keyCode, KeyEvent event) {  3 // TODO Auto-generated method stub  4 //点击了后退键  5 if(keyCode == KeyEvent.KEYCODE_BACK)  6  {  7 //创建对话框构建器对象  8 AlertDialog.Builder builder = new AlertDialog.Builder(this);  9 builder.setTitle("温馨提示")//对话框标题 10 .setMessage("确定要退出么?")//对话框内容 11 .setIcon(R.drawable.ic_launcher)//对话框图标 12 .setCancelable(false) //点击对话框之外的部分是否取消对话框  13 .setPositiveButton("确定", new OnClickListener() { 14 15  @Override 16 public void onClick(DialogInterface dialog, int which) { 17 // TODO Auto-generated method stub 18 finish();//结束当前Activity 19  } 20  }) 21 .setNegativeButton("取消", new OnClickListener() { 22 23  @Override 24 public void onClick(DialogInterface dialog, int which) { 25 // TODO Auto-generated method stub 26 dialog.dismiss();//取消对话框 27  } 28  }); 29 //生成对话框 30 Dialog dialog = builder.create(); 31 //显示对话框 32  dialog.show(); 33  } 34 35 return super.onKeyDown(keyCode, event); 36 } 

 1 public class MainActivity extends Activity {  2 long timefirst = 0; //一定要是long类型的  3 long timesecond = 0;  4 boolean isKeyBack = false;//当为false ，为应用程序第一次按后退键，第一次按键之后 永为true ，  5  @Override  6 protected void onCreate(Bundle savedInstanceState) {  7  super.onCreate(savedInstanceState);  8  setContentView(R.layout.activity_main);  9  } 10 11  @Override 12 public boolean onKeyDown(int keyCode, KeyEvent event) { 13 // TODO Auto-generated method stub 14 15 if(keyCode == KeyEvent.KEYCODE_BACK)//如果点击了撤退键 16  { 17 if(isKeyBack==true) //如果isKeyBack==true 说明第二次点击后退键 18  { 19 timesecond = System.currentTimeMillis();//记录第二次按键的时间 20 System.out.println("2"+timesecond); 21 22 if(Math.abs(timesecond-timefirst)<2000)//说明两次按键间隔小于2秒，满足退出条件，退出Activity 23  { 24  finish(); 25  } 26 else 27  { 28 timefirst = System.currentTimeMillis();//记录第一次按键的时间 29 Toast.makeText(this, "再按一次退出程序", 1).show(); 30 //不满足条件，则设置此次为第一次按键，因为isKeyBack为true 31 //屏蔽后退键的撤销功能 32 return true; 33  } 34  } 35 else if(isKeyBack==false) //如果isKeyBack为false 说明第一次点击后退键 36  { 37 timefirst = System.currentTimeMillis();//记录第一次按键的时间 38 Toast.makeText(this, "再按一次退出程序", 1).show(); 39 System.out.println("1"+timefirst); 40 isKeyBack = true; 41 //屏蔽后退键的撤销功能 42 return true; 43 44  } 45  } 46 47 return super.onKeyDown(keyCode, event); 48 } 

 1 public class MainActivity extends Activity {  2 long timefirst = 0; //一定要是long类型的  3 long timesecond = 0;  4 boolean isKeyBack = false;  5  @Override  6 protected void onCreate(Bundle savedInstanceState) {  7  super.onCreate(savedInstanceState);  8  setContentView(R.layout.activity_main);  9  } 10 11  @Override 12 public boolean onKeyDown(int keyCode, KeyEvent event) { 13 // TODO Auto-generated method stub 14 if(keyCode==KeyEvent.KEYCODE_BACK) 15  { 16 timesecond = System.currentTimeMillis(); //记录当前按键时间，相当于上一次为第二次按键 17 if(timesecond-timefirst<2000) //如果两次按键时间小于2000毫秒,结束应用程序 18  { 19  finish(); 20  } 21 else 22  { 23 Toast.makeText(this, "再按一次退出程序", 1).show(); 24 timefirst = timesecond; //如果不能退出，则当前按键时间设为第一次，下一次为第二次 25 return true; //屏蔽后退键的效果 return false;也可以 ，只要不让方法执行super.onKeyDown(keyCode, event);即可

 26  } 27  } 28 return super.onKeyDown(keyCode, event); 29 }

 1 @Override  2 public boolean onKeyDown(int keyCode, KeyEvent event) {  3  4 switch (keyCode){  5  6  7 case KeyEvent.KEYCODE_BACK:  8  9 if(isExit){ 10 11 return super.onKeyDown(keyCode, event); 12 }else { 13 14 Toast.makeText(this, "再按一下退出程序", Toast.LENGTH_SHORT).show(); 15 isExit = true; 16 17 new Thread(new Runnable() { 18 19  @Override 20 public void run() { 21 22 try { 23 24 Thread.sleep(2000); 25 26 isExit = false; 27 28 } catch (InterruptedException e) { 29  e.printStackTrace(); 30  } 31 32  } 33 34  }).start(); 35 return false; 36  } 37 38 default: 39 return super.onKeyDown(keyCode, event); 40 41  } 42 }