android 添加对back按钮的处理，点击提示退出

@Override
public boolean dispatchKeyEvent(KeyEvent event){
if(event.getKeyCode()==KeyEvent.KEYCODE_BACK&&event.getAction()!=1){
   exit();
   return true;
   }
super.dispatchKeyEvent(event);

}

private void exit() {
new AlertDialog.Builder(MainActivity.this).setMessage(R.string.exit_confirm)
.setPositiveButton(R.string.button_ok, new OnClickListener() {

@Override
public void onClick(DialogInterface dialog, int which) {
finish();
android.os.Process.killProcess(android.os.Process.myPid());
}
}).setNegativeButton(R.string.button_cancel, null).show();
}

上面先重写dispatchKeyEvent事件，最后学exit（）函数，完成退出，并设置AlertDialog 属性两个按钮