android KeyEvent事件机制

package im.weiyuan.com.viewutils;

import android.content.Intent;
import android.os.PersistableBundle;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.util.Log;
import android.view.KeyEvent;
import android.view.MotionEvent;
import android.view.View;
import android.widget.Button;
import android.widget.ImageView;
import android.widget.LinearLayout;
import android.widget.RelativeLayout;
import android.widget.TextView;
import android.widget.Toast;

public class MainActivity extends AppCompatActivity {

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

    }

    @Override
    public boolean dispatchKeyEvent(KeyEvent event) {
        Log.d("123456","activity dispatchKeyEvent  is called"+event.getAction());
        return super.dispatchKeyEvent(event);
    }

    @Override
    public boolean onKeyDown(int keyCode, KeyEvent event) {
        Log.d("123456","activity onKeyDown  is called"+event.getAction());
        return super.onKeyDown(keyCode, event);
    }

    @Override
    public boolean onKeyUp(int keyCode, KeyEvent event) {
        Log.d("123456","activity onKeyUp  is called"+event.getAction());
        return super.onKeyUp(keyCode, event);
    }

    @Override
    public boolean onKeyLongPress(int keyCode, KeyEvent event) {
        Log.d("123456","activity onKeyLongPress  is called"+event.getAction());
        return super.onKeyLongPress(keyCode, event);
    }
}

如果按键盘的返回按键：

日志的打印如下：

07-24 14:20:57.771 26412-26412/im.weiyuan.com.viewutils D/123456: activity dispatchKeyEvent is called0
07-24 14:20:57.772 26412-26412/im.weiyuan.com.viewutils D/123456: activity onKeyDown is called0
07-24 14:20:57.831 26412-26412/im.weiyuan.com.viewutils D/123456: activity dispatchKeyEvent is called1
07-24 14:20:57.831 26412-26412/im.weiyuan.com.viewutils D/123456: activity onKeyUp is called1

实现下面的一个需求：

当点击返回按钮的时候弹出一个对话框提示是否退出应用

package im.weiyuan.com.viewutils;

import android.content.DialogInterface;
import android.content.Intent;
import android.os.PersistableBundle;
import android.support.v7.app.AlertDialog;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.util.Log;
import android.view.KeyEvent;
import android.view.MotionEvent;
import android.view.View;
import android.widget.Button;
import android.widget.ImageView;
import android.widget.LinearLayout;
import android.widget.RelativeLayout;
import android.widget.TextView;
import android.widget.Toast;

public class MainActivity extends AppCompatActivity {

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

    }

    @Override
    public boolean dispatchKeyEvent(KeyEvent event) {
        Log.d("123456","activity dispatchKeyEvent  is called"+event.getAction());
        return super.dispatchKeyEvent(event);
    }

    @Override
    public boolean onKeyDown(int keyCode, KeyEvent event) {
        Log.d("123456","activity onKeyDown  is called"+event.getAction());
        if(event.getAction() == KeyEvent.ACTION_DOWN){
            new AlertDialog.Builder(this).setTitle("kldlskakl").setMessage(R.string.app_name)
                    .setPositiveButton("41414", new DialogInterface.OnClickListener() {

                        @Override
                        public void onClick(DialogInterface dialog, int which) {
                            // TODO Auto-generated method stub
                            //这里定义对话框按钮单击之后要运行的事件
                        }
                    }).show();
        }
        /**
         * 这里要将案件的事件消费掉，所以这里函数的返回值是true
         * */
        return true;
    }

    @Override
    public boolean onKeyUp(int keyCode, KeyEvent event) {
        Log.d("123456","activity onKeyUp  is called"+event.getAction());

        return super.onKeyUp(keyCode, event);
    }

    @Override
    public boolean onKeyLongPress(int keyCode, KeyEvent event) {
        Log.d("123456","activity onKeyLongPress  is called"+event.getAction());
        return super.onKeyLongPress(keyCode, event);
    }
}