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

[java]
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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;  
    }     
  
}  

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);
}
retu
4000
rn customHttpClient;
}

}

AsyncTask 类

[java]
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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;  
    }  
}  

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

[java]
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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");  
          
    }  
}  

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

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<?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>  

<?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>