Handler類主要有兩個作用：在新啟動的執行緒中傳送訊息。在主執行緒中獲取、處理訊息。當新啟動的執行緒傳送訊息時，Handler類中處理訊息的方法會被自動回撥。Handler類包含如下方法用於傳送、處理訊息：

下面通過一個簡單例項來演示Handler的使用，實現點選切換按鈕，圖片開始自動切換；點選停止按鈕，圖片停止切換，程式碼如下：

Activity：

package com.lovo;

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

public class ChangeImageActivity extends Activity {
	// 宣告Handler物件
	private Handler handler;
	// 切換顯示圖片陣列id的下標
	private int index;
	// 切換是否進行
	private boolean isRun = true;
	public static final int CHANGE_IMAGE = 1;
	// 切換的圖片id陣列
	private int[] images = new int[] { R.drawable.whatsnew_fornew_01,
			R.drawable.whatsnew_fornew_02, R.drawable.whatsnew_fornew_03,
			R.drawable.whatsnew_fornew_04, R.drawable.whatsnew_fornew_05 };

	@Override
	public void onCreate(Bundle savedInstanceState) {
		super.onCreate(savedInstanceState);
		setContentView(R.layout.main);
		handler = new Handler() {
			@Override
			public void handleMessage(Message msg) {
				super.handleMessage(msg);
				if (msg.what == CHANGE_IMAGE) {
					ImageView imageView = (ImageView) findViewById(R.id.image);
					// 動態改變ImageView裡面的圖片
					imageView.setImageResource(images[msg.getData().getInt(
							"index")]);
				}
			}
		};
		// 獲得按鈕
		Button btn1 = (Button) findViewById(R.id.btn1);
		Button btn2 = (Button) findViewById(R.id.btn2);
		btn2.setOnClickListener(new OnClickListener() {

			@Override
			public void onClick(View v) {
				isRun = false;
			}
		});
		btn1.setOnClickListener(new OnClickListener() {

			@Override
			public void onClick(View v) {
				isRun = true;
				new Thread() {

					public void run() {

						for (index = 0; isRun; index++) {
							Message msg = new Message();
							msg.what = CHANGE_IMAGE;
							// 建立Bundle物件，封裝資料
							Bundle bundle = new Bundle();
							bundle.putInt("index", index);
							msg.setData(bundle);
							// 傳送訊息
							handler.sendMessage(msg);
							// 迴圈切換
							if (index >= 4) {
								index = -1;
							}
							try {
								Thread.sleep(1000);
							} catch (InterruptedException e) {
								e.printStackTrace();
							}
						}

					}
				}.start();
			}
		});
	}
}
 

佈局XML：

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

    <Button
        android:id="@+id/btn1"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="切換" />

    <Button
        android:id="@+id/btn2"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_toRightOf="@id/btn1"
        android:text="停止" />

    <ImageView
        android:id="@+id/image"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:layout_below="@id/btn1" />

</RelativeLayout>