Android异步消息处理机制

安卓子线程无法直接更改UI，所以需要异步消息处理机制来解决

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical"
    >

    <Button
        android:id="@+id/change_text"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="change text"
        />

    <TextView
        android:id="@+id/text_content"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_gravity="center"
        android:text="Hello World"
        android:textSize="20sp"/>

</LinearLayout>

package com.example.contacttest;

import android.app.Activity;
import android.os.Bundle;
import android.os.Handler;
import android.os.Message;
import android.view.View;
import android.widget.Button;
import android.widget.TextView;

public class NotificationTest extends Activity implements View.OnClickListener{

    private Button changeText;
    private TextView textContent;

    private static final int UPDATE_TEXT = 1;

    private Handler handler = new Handler(){
        @Override
        public void handleMessage(Message msg) {
            switch (msg.what){
                case UPDATE_TEXT:
                    textContent.setText("Nice to meet you!");
                    break;
                default:
                    break;
            }
        }
    };

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

        changeText = (Button)findViewById(R.id.change_text);
        textContent = (TextView)findViewById(R.id.text_content);

        changeText.setOnClickListener(this);

    }

    @Override
    public void onClick(View v) {

        switch (v.getId())
        {
            case R.id.change_text:
                    new Thread(new Runnable() {
                        @Override
                        public void run() {
                            Message message = new Message();
                            message.what = UPDATE_TEXT;
                            handler.sendMessage(message);
                        }
                    }).start();
                    break;
            default:
                break;
        }
    }

}