入门异步任务之Handler-优快云博客

本文介绍了一个简单的Android应用示例，展示了如何通过网络加载图片到ImageView，并使用ProgressDialog显示加载进度。该示例包括了AndroidManifest.xml配置、activity_main.xml布局文件和MainActivity.java代码实现。

效果图如下：

1、AndroidManifest.xml

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.lesson"
    android:versionCode="1"
    android:versionName="1.0" >

    <uses-sdk
        android:minSdkVersion="7"
        android:targetSdkVersion="7" />
    <uses-permission android:name="android.permission.INTERNET"/>

    <application
        android:allowBackup="true"
        android:icon="@drawable/ic_launcher"
        android:label="@string/app_name"
        android:theme="@style/AppTheme" >
        <activity
            android:name=".MainActivity"
            android:label="@string/app_name" >
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />

                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>
    </application>

</manifest>

2、activity_main.xml

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context="${relativePackage}.${activityClass}" >

    <Button
        android:id="@+id/button1"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_alignParentBottom="true"
        android:layout_centerHorizontal="true"
        android:layout_marginBottom="18dp"
        android:text="加载图片" />

    <ImageView
        android:id="@+id/imageView1"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_alignParentTop="true"
        android:layout_centerHorizontal="true"
        android:layout_marginTop="20dp"
        
        />

</RelativeLayout>

3、MainActivity.java

package com.lesson;

import java.io.ByteArrayOutputStream;
import java.io.IOException;
import java.io.InputStream;

import org.apache.http.HttpResponse;
import org.apache.http.client.ClientProtocolException;
import org.apache.http.client.HttpClient;
import org.apache.http.client.methods.HttpGet;
import org.apache.http.impl.client.DefaultHttpClient;

import android.app.Activity;
import android.app.ProgressDialog;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.os.Bundle;
import android.os.Handler;
import android.os.Message;
import android.util.Log;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
import android.widget.ImageView;
import android.widget.ProgressBar;

public class MainActivity extends Activity {
	private Button button;
	private ProgressDialog progerssDialog;
	private ImageView imageView;//要加载的图片
	private int Thread1=1;
	private final String url="http://pic.4j4j.cn/upload/pic/20130701/d363891105.jpg";

	@Override
	protected void onCreate(Bundle savedInstanceState) {
		super.onCreate(savedInstanceState);
		setContentView(R.layout.activity_main);		
		button=(Button)findViewById(R.id.button1);
		imageView=(ImageView)findViewById(R.id.imageView1);
		
		button.setOnClickListener(new OnClickListener() {
			
			@Override
			public void onClick(View arg0) {
				
				//加载图片时的进度显示对话框
				progerssDialog=new ProgressDialog(MainActivity.this);
				progerssDialog.setTitle("loading");
				progerssDialog.setMessage("正在加载中...");
				
				//设置进度条水平加载
				progerssDialog.setProgressStyle(ProgressDialog.STYLE_HORIZONTAL);
				progerssDialog.show();
				//添加子线程，用于发送消息给主线程
			
				new Thread(new MyThread(url,Thread1,new MyHandler())).start();
			}
		});
	}
	
	
	class MyHandler extends Handler{
		@Override
		public void handleMessage(Message msg) {
			
			super.handleMessage(msg);
			if(msg.what==Thread1){
				imageView.setImageBitmap((Bitmap)msg.obj);
				progerssDialog.dismiss();
			}
		}
	}
	class MyThread implements Runnable{
		//声明用来标识url地址参数的变量
		private String url;
		//声明用来标识线程id的变量
		private int threadId=0;
		
		private Handler handler=null;
		
		//构造函数
		public MyThread(String url,int threadId,Handler handler){
			this.url=url;
			this.threadId=threadId;
			this.handler=handler;
		}
		@Override
		public void run() {
		
			HttpGet httpGet=new HttpGet(url);
			InputStream inputStream;
			byte[] result=null;
			byte[] data=new byte[1024];
			HttpClient client = new DefaultHttpClient();
			ByteArrayOutputStream outputStream = new ByteArrayOutputStream();
			try {
				HttpResponse httpResponse=client.execute(httpGet);//得到响应
				if(httpResponse.getStatusLine().getStatusCode()==200){
					
					inputStream=httpResponse.getEntity().getContent();
					//文件总长度
					int filelenth=(int) httpResponse.getEntity().getContentLength();
					int readlength=0;
					int totallenth=0;
					while((readlength=inputStream.read(data))!=-1){
						totallenth+=readlength;
						int progressValue= (int)((totallenth/(float)filelenth)*100);
						Log.i("progressValue",progressValue+"");
						
						progerssDialog.setProgress(progressValue);
						outputStream.write(data, 0, readlength);
					}
					result=outputStream.toByteArray();
					
					//向handler发送消息
					 	Message msg = new Message();  
				        msg.what = threadId;  
				        Bitmap bitmap=BitmapFactory.decodeByteArray(result, 0, result.length);
				        msg.obj=bitmap;
				        handler.sendMessage(msg);  
				}
				
			} catch (ClientProtocolException e) {
				
				e.printStackTrace();
			} catch (IOException e) {
				
				e.printStackTrace();
			}finally{
				client.getConnectionManager().shutdown();
			}
		}
		
	}
}

注：ProgressDialog加载几种方式及注意点

// 方式一：new Dialog
		final ProgressDialog dialog = new ProgressDialog(this);
		dialog.show();

	// 方式二：使用静态方式创建并显示，这种进度条只能是圆形条,设置title和Message提示内容
		ProgressDialog dialog2 = ProgressDialog.show(this, "提示", "正在登陆中");

	// 方式三 使用静态方式创建并显示，这种进度条只能是圆形条,这里最后一个参数boolean indeterminate设置是否是不明确的状态
		ProgressDialog dialog3 = ProgressDialog
				.show(this, "提示", "正在登陆中", false);

	// 方式四 使用静态方式创建并显示，这种进度条只能是圆形条,这里最后一个参数boolean cancelable 设置是否进度条是可以取消的
		ProgressDialog dialog4 = ProgressDialog.show(this, "提示", "正在登陆中",
				false, true);

	// 方式五 使用静态方式创建并显示，这种进度条只能是圆形条,这里最后一个参数 DialogInterface.OnCancelListener
		// cancelListener用于监听进度条被取消
		ProgressDialog dialog5 = ProgressDialog.show(this, "提示", "正在登陆中", true,
				true, cancelListener);