Android 实现返回键退出弹出确认对话框

实现效果：

实现代码：

package com.example.android12_zhangkai;

import android.content.DialogInterface;
import android.support.v7.app.AlertDialog;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.KeyEvent;
import android.widget.Toast;

public class MainActivity extends AppCompatActivity {

    private long firstTime=0;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);


    }

    @Override
    public boolean onKeyDown(int keyCode, KeyEvent event) {
        if (keyCode==KeyEvent.KEYCODE_BACK){
            AlertDialog.Builder builder=new AlertDialog.Builder(this);
            builder.setTitle("提示：");
            builder.setMessage("您确定退出？");

            //设置确定按钮
            builder.setNegativeButton("确定", new DialogInterface.OnClickListener() {
                @Override
                public void onClick(DialogInterface dialog, int which) {
                    finish();
                }
            });
            //设置取消按钮
            builder.setPositiveButton("容我再想想",null);
            //显示提示框
            builder.show();
        }
        return super.onKeyDown(keyCode, event);
    }


}