1 @Override 2     public boolean onKeyDown(int keyCode, KeyEvent event) 3     { 4         if(keyCode == KeyEvent.KEYCODE_BACK){ 5             quitApp(); 6             return false; 7         }else{ 8             return super.onKeyDown(keyCode, event); 9         }10     }11     /**12      * 退出APP13      */14     private void quitApp(){15         if(isExit){16             Intent intent = new Intent(Intent.ACTION_MAIN);17             intent.addCategory(Intent.CATEGORY_HOME);18             startActivity(intent);19             System.exit(0);20         }else{21             isExit = true;22             Tools.showText(mContext, "再按一次退出应用");23             mHandler.sendEmptyMessageDelayed(0, 2000);24         }25     }26     Handler mHandler = new Handler(){27         public void handleMessage(android.os.Message msg) {28             super.handleMessage(msg);29             isExit = false;30         };31     };

第二种：

1 @Override 2     public boolean onKeyDown(int keyCode, KeyEvent event) 3     { 4         if(keyCode == KeyEvent.KEYCODE_BACK && event.getRepeatCount() == 0) 5             quitApp(); 6         return false; 7     } 8     private long exitTime = 0; 9     private void quitApp(){10         if(System.currentTimeMillis() - exitTime > 2000){11             Tools.showText(mContext, "再按一次退出应用");12             exitTime = System.currentTimeMillis();13         }else{14             finish();15         }16     }