AsyncTask & HttpClient 下载图片

精通Android4 书中例子

关键点

ThreadSafeClientConnManager 解决同一个HttpClient同时发出多个请求可能发生的多线程问题。

AsyncTask 三个参数含义，方法之类的很容易理解，固定模式

* AsyncTask是抽象类.AsyncTask定义了三种泛型类型 Params，Progress和Result。

* Params 启动任务执行的输入参数，比如HTTP请求的URL。

* Progress 后台任务执行的百分比。

* Result 后台执行任务最终返回的结果，比如String,Integer等。

新建CustomHttpClient

package com.example.httpasynctask;

import org.apache.http.HttpVersion;
import org.apache.http.client.HttpClient;
import org.apache.http.conn.ClientConnectionManager;
import org.apache.http.conn.params.ConnManagerParams;
import org.apache.http.conn.scheme.PlainSocketFactory;
import org.apache.http.conn.scheme.Scheme;
import org.apache.http.conn.scheme.SchemeRegistry;
import org.apache.http.conn.ssl.SSLSocketFactory;
import org.apache.http.impl.client.DefaultHttpClient;
import org.apache.http.impl.conn.tsccm.ThreadSafeClientConnManager;
import org.apache.http.params.BasicHttpParams;
import org.apache.http.params.HttpConnectionParams;
import org.apache.http.params.HttpParams;
import org.apache.http.params.HttpProtocolParams;
import org.apache.http.protocol.HTTP;

public class CustomHttpClient {
private static HttpClient customHttpClient;
private CustomHttpClient(){

}
public static synchronized HttpClient getHttpClient(){
if(customHttpClient == null){
HttpParams params = new BasicHttpParams();
HttpProtocolParams.setContentCharset(params,HTTP.DEFAULT_CONTENT_CHARSET);
HttpProtocolParams.setVersion(params,HttpVersion.HTTP_1_1);
HttpProtocolParams.setUseExpectContinue(params, true);

ConnManagerParams.setTimeout(params,1000);
HttpConnectionParams.setConnectionTimeout(params, 5000);
HttpConnectionParams.setSoTimeout(params,10000);

SchemeRegistry schReg = new SchemeRegistry();
schReg.register(new Scheme("http",PlainSocketFactory.getSocketFactory(),80));
schReg.register(new Scheme("https",SSLSocketFactory.getSocketFactory(),433));
ClientConnectionManager conMgr = new ThreadSafeClientConnManager(params,schReg);
customHttpClient = new DefaultHttpClient(conMgr,params);
}
return customHttpClient;
}

}

AsyncTask 类

package com.example.httpasynctask;

import java.io.IOException;

import org.apache.http.HttpResponse;
import org.apache.http.client.HttpClient;
import org.apache.http.client.methods.HttpGet;
import org.apache.http.params.BasicHttpParams;
import org.apache.http.params.HttpConnectionParams;
import org.apache.http.params.HttpParams;
import org.apache.http.util.EntityUtils;

import android.os.AsyncTask;
import android.os.Bundle;
import android.app.Activity;
import android.content.Context;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.view.Menu;
import android.widget.ImageView;
import android.widget.TextView;

public class HttpAsyncTaskTest extends AsyncTask<String,Integer,Bitmap> {
private Context mContext;
HttpAsyncTaskTest(Context context){
mContext = context;
}

protected void onPreExecute(){

}
@Override
protected Bitmap doInBackground(String... arg0) {
// TODO Auto-generated method stub
return downloadImage(arg0);
}
protected void onProgressUpdate(Integer...progress){
TextView mText = (TextView)((Activity)mContext).findViewById(R.id.text);
mText.setText("Progress so far: " + progress[0]);
}
protected void onPostExecute(Bitmap result){
if(result != null){
ImageView mImage = (ImageView)((Activity)mContext).findViewById(R.id.image);
mImage.setImageBitmap(result);
}else{
TextView errorMsg = (TextView)((Activity)mContext).findViewById(R.id.errorMsg);
errorMsg.setText("Problem downloading image.please try again later.");
}
}

private Bitmap downloadImage(String... urls){
HttpClient httpClient = CustomHttpClient.getHttpClient();
try{
HttpGet request = new HttpGet(urls[0]);
HttpParams params = new BasicHttpParams();
HttpConnectionParams.setSoTimeout(params,60000);
request.setParams(params);
publishProgress(25);
HttpResponse response = httpClient.execute(request);
publishProgress(50);
byte[] image = EntityUtils.toByteArray(response.getEntity());
publishProgress(75);
Bitmap mBitmap = BitmapFactory.decodeByteArray(image,0,image.length);
publishProgress(100);
return mBitmap;

}catch(IOException e){
e.printStackTrace();
}
return null;
}
}

Activity界面

package com.example.httpasynctask;

import android.app.Activity;
import android.os.AsyncTask;
import android.os.Bundle;
import android.view.View;

public class HttpActivity extends Activity{
private HttpAsyncTaskTest diTask;
public void onCreate(Bundle savedInstanceState){
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_http_async_task_test);
}
public void doClick(View view){
if(diTask != null){
AsyncTask.Status diStatus = diTask.getStatus();
if(diStatus != AsyncTask.Status.FINISHED){
return;
}
}
diTask = new HttpAsyncTaskTest(this);
diTask.execute("http://chart.apis.google.com/chart?&cht=p&chs=460x250&chd=t:15.3,20.3,0.2,59.7,4.5&chl=Android%201.5%7CAndroid%201.6%7COther*%7CAndroid%202.1%7CAndroid%202.2&chco=c4df9b,6fad0c");

}
}

XML布局

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="fill_parent"  android:layout_height="fill_parent"
android:orientation="vertical"
>
<LinearLayout
android:layout_width="fill_parent"  android:layout_height="wrap_content"
android:orientation="horizontal"
>
<Button android:id="@+id/button"  android:text="Get Image"
android:layout_width="wrap_content"  android:layout_height="wrap_content"
android:onClick="doClick"
/>
<TextView android:id="@+id/text"
android:layout_width="wrap_content"  android:layout_height="wrap_content"
/>
</LinearLayout>
<TextView android:id="@+id/errorMsg"
android:layout_width="wrap_content"  android:layout_height="wrap_content"
/>
<ImageView  android:id="@+id/image"
android:layout_width="fill_parent"  android:layout_height="0dip"
android:layout_weight="1" />
</LinearLayout>

AndroidManifest.xml 添加访问网络权限

<uses-permission android:name="android.permission.INTERNET"></uses-permission>