Android之AsyncTask異步任務下載網絡圖片

xml代碼

<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"
    android:paddingBottom="@dimen/activity_vertical_margin"
    android:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:paddingTop="@dimen/activity_vertical_margin"
    tools:context="com.example.asynctask_downloadpicture2.MainActivity$PlaceholderFragment" >

    <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="10dp"/>

    <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="14dp"
        android:text="下載網絡圖片" />

</RelativeLayout>

一個activity：

package com.example.asynctask_downloadpicture2;

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.support.v7.app.ActionBarActivity;
import android.support.v7.app.ActionBar;
import android.support.v4.app.Fragment;
import android.app.ProgressDialog;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.os.AsyncTask;
import android.os.Bundle;
import android.view.LayoutInflater;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.view.View.OnClickListener;
import android.view.ViewGroup;
import android.widget.Button;
import android.widget.ImageView;
import android.widget.ProgressBar;
import android.os.Build;

public class MainActivity extends ActionBarActivity {
	private Button button;
	private ImageView imageView;
	private ProgressDialog dialog;
	private final String PIC_PATH="http://www.bz55.com/uploads/allimg/150309/139-150309101F7.jpg";
	@Override
	protected void onCreate(Bundle savedInstanceState) {
		super.onCreate(savedInstanceState);
		setContentView(R.layout.fragment_main);
		button=(Button) findViewById(R.id.button1);
		imageView=(ImageView) findViewById(R.id.imageView1);
		dialog=new ProgressDialog(MainActivity.this);
		dialog.setTitle("提示");
		dialog.setMessage("下載圖片中,請稍後....");
		dialog.setCancelable(false);
		dialog.setProgressStyle(ProgressDialog.STYLE_HORIZONTAL);
		button.setOnClickListener(new OnClickListener() {
			
			@Override
			public void onClick(View v) {
				// TODO Auto-generated method stub
				new MyAsyncTask().execute(PIC_PATH);
			}
		});
	}
	
	public class MyAsyncTask extends AsyncTask<String, Integer, Bitmap>{

		@Override
		protected Bitmap doInBackground(String... params) {
			// TODO Auto-generated method stub
			Bitmap bitmap=null;
			HttpClient httpClient=new DefaultHttpClient();
			HttpGet httpGet=new HttpGet(params[0]);
			ByteArrayOutputStream outputStream=new ByteArrayOutputStream();
			InputStream inputStream=null;
			try {
				HttpResponse respone=httpClient.execute(httpGet);
				inputStream=respone.getEntity().getContent();
				long pic_length=respone.getEntity().getContentLength();
				byte[] data=new byte[1024];
				int len=0;
				int totoal_length=0;
				while((len=inputStream.read(data))!=-1){
					totoal_length+=len;
					publishProgress((int) ((totoal_length / (float) pic_length) * 100));
					outputStream.write(data, 0, len);
				}
				byte[] bitmapByte=outputStream.toByteArray();
				bitmap=BitmapFactory.decodeByteArray(bitmapByte, 0, bitmapByte.length);
				
			} catch (ClientProtocolException e) {
				// TODO Auto-generated catch block
				e.printStackTrace();
			} catch (IOException e) {
				// TODO Auto-generated catch block
				e.printStackTrace();
			}
			return bitmap;
		}
		@Override
		protected void onPreExecute() {
			// TODO Auto-generated method stub
			super.onPreExecute();
			dialog.show();
		}
		@Override
		protected void onProgressUpdate(Integer... values) {
			// TODO Auto-generated method stub
			super.onProgressUpdate(values);
			dialog.setProgress(values[0]);
		}
		@Override
		protected void onPostExecute(Bitmap result) {
			// TODO Auto-generated method stub
			super.onPostExecute(result);
			dialog.dismiss();
			imageView.setImageBitmap(result);
		}
	}


}