android退出activity提示再按一次返回键

通过重载onKeyDown方法实现：

private long tempTime = -1;@Override  public boolean onKeyDown(int keyCode, KeyEvent event){      // TODO Auto-generated method stub       if((keyCode == KeyEvent.KEYCODE_BACK)&&(event.getAction() == KeyEvent.ACTION_DOWN))      {          if (System.currentTimeMillis() - temptime > 2000) // 2s内再次选择back键有效          {              Toast.makeText(this, "请再按一次返回退出", Toast.LENGTH_LONG).show();              temptime = System.currentTimeMillis();          } else {              finish();               System.exit(0); //凡是非零都表示异常退出!0表示正常退出!          }          return true;          }      return super.onKeyDown(keyCode, event);  }

禁用返回键：

public boolean onKeyDown(int keyCode, KeyEvent event){      // TODO Auto-generated method stub       if((keyCode == KeyEvent.KEYCODE_BACK)&&(event.getAction() == KeyEvent.ACTION_DOWN))      {          return false;    }      return super.onKeyDown(keyCode, event);  }

参考自：http://blog.csdn.net/ritazuozuo/article/details/7879286

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