关于AsyncTask异步下载图片带有进度条更新 android

【关于AsyncTask异步下载图片带有进度条更新】首先定义一个ImageView 和一个Button：

需要添加访问网络权限。在AndroidManifest.xml中添加android.permission.INTERNET权限。
主要代码：

package com.example.http_dowloadview; import java.io.ByteArrayOutputStream; import java.io.IOException; import java.io.InputStream; import java.io.ObjectOutputStream.PutField; import org.apache.http.HttpEntity; 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 org.apache.http.util.ByteArrayBuffer; import org.apache.http.util.EntityUtils; import android.R.integer; import android.os.AsyncTask; import android.os.Bundle; import android.app.Activity; import android.app.ProgressDialog; import android.graphics.Bitmap; import android.graphics.BitmapFactory; import android.view.Menu; import android.view.View; import android.view.View.OnClickListener; import android.widget.Button; import android.widget.ImageView; public class MainActivity extends Activity {private Button button; private ImageView image; String picture = "http://static.statickksmg.com/image/2012/09/26/b120f8a66e5ab2a2c0263e02fba5cb9c.jpg"; private ProgressDialog dia; @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_main); button = (Button)findViewById(R.id.button); image = (ImageView)findViewById(R.id.image); //定义进度条 dia = new ProgressDialog(this); dia.setTitle("提示信息"); dia.setMessage("正在下载、、、"); dia.setProgressStyle(ProgressDialog.STYLE_HORIZONTAL); //设置点击进度条外部，不响应； dia.setCancelable(false); button.setOnClickListener(new OnClickListener() { @Override public void onClick(View arg0) { // TODO Auto-generated method stub new MyTask().execute(picture); } }); } //Sting 表示传入的值， Integer代表进度，Bitmap 代表返回的值 public class MyTask extends AsyncTask{//任务执行之前的准备工作。 @Override protected void onPreExecute() { // TODO Auto-generated method stub super.onPreExecute(); dia.show(); } //主要完成耗时操作 @Override protected Bitmap doInBackground(String... arg0) { // TODO Auto-generated method stub Bitmap bitmap = null; ByteArrayOutputStream outputStream = new ByteArrayOutputStream(); InputStream inputStream = null; try { HttpClient httpClient = new DefaultHttpClient(); HttpGet httpGet = new HttpGet(arg0[0]); HttpResponse httpResponse = httpClient.execute(httpGet); if(httpResponse.getStatusLine().getStatusCode() == 200){ inputStream = httpResponse.getEntity().getContent(); //先获得文件的总长度， long file_length = httpResponse.getEntity().getContentLength(); int len = 0; byte[] data = https://www.it610.com/article/new byte[1024]; int total_length = 0; int value = 0; while((len = inputStream.read(data)) != -1){ total_length += len; value = (int)((total_length/(float)file_length)*100); //调用update函数，更新进度 publishProgress(value); outputStream.write(data, 0, len); } byte[] result = outputStream.toByteArray(); ; bitmap = BitmapFactory.decodeByteArray(result, 0, result.length); } } catch (Exception e) { // TODO: handle exception e.printStackTrace(); }finally{ if(inputStream != null){ try { inputStream.close(); } catch (IOException e) { // TODO Auto-generated catch block e.printStackTrace(); } } } return bitmap; } //更新进度条 @Override protected void onProgressUpdate(Integer... values) { // TODO Auto-generated method stub super.onProgressUpdate(values); dia.setProgress(values[0]); } //主要完成耗时操作 @Override protected void onPostExecute(Bitmap result) { // TODO Auto-generated method stub super.onPostExecute(result); dia.dismiss(); image.setImageBitmap(result); } }}

软件截图：