AsyncTask Demo小记

来源：互联网发布：话吧软件编辑：程序博客网时间：2024/04/30 12:32

今天搞了一个AsyncTask下载图片的demo，发现下载好的图片失真都扭曲了，开始还以为是图片大小或是屏幕分辨率的问题，后来检查了一下在用ByteArrayOutputStream写数据的时候犯了错：baos.write(buffer); 后改为：baos.write(buffer, 0, len); 就没有问题了，其实在InputStream is = response.getEntity().getContent();获得输入流以后可以不用把它转换成字节数组就能转换为Bitmap，调用Bitmap bitMap = BitmapFactory.decodeStream(is);这个方法即可，但是直接调用这个方法貌似不能计算出下载进度了？

代码如下：

package com.ylj.asynctask;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.ProgressDialog;import android.graphics.Bitmap;import android.graphics.BitmapFactory;import android.os.AsyncTask;import android.os.Bundle;import android.support.v7.app.ActionBarActivity;import android.view.View;import android.view.View.OnClickListener;import android.widget.Button;import android.widget.ImageView;public class MainActivity extends ActionBarActivity implements OnClickListener{private Button btn_download;private ImageView iv_picture;private ProgressDialog pDialog;private String path = "http://img8.zol.com.cn/bbs/upload/20688/20687324_0800.jpg";@Overrideprotected void onCreate(Bundle savedInstanceState){super.onCreate(savedInstanceState);setContentView(R.layout.activity_main);iv_picture = (ImageView) findViewById(R.id.iv_picture);btn_download = (Button) findViewById(R.id.btn_download);btn_download.setOnClickListener(this);}@Overridepublic void onClick(View v){new DownloadTask().execute(path);}private class DownloadTask extends AsyncTask<String, Integer, Bitmap>{private Bitmap bitMap;@Overrideprotected void onPreExecute(){pDialog = new ProgressDialog(MainActivity.this);pDialog.setTitle("下载提示");pDialog.setMessage("正在下载中,请稍后...");pDialog.setProgressStyle(ProgressDialog.STYLE_HORIZONTAL);pDialog.setCancelable(false);pDialog.show();super.onPreExecute();}@Overrideprotected Bitmap doInBackground(String... params){HttpClient client = new DefaultHttpClient();HttpGet get = new HttpGet(params[0]);try{HttpResponse response = client.execute(get);if(response.getStatusLine().getStatusCode() == 200){long length = response.getEntity().getContentLength();InputStream is = response.getEntity().getContent();byte[] buffer = new byte[1024];int len;int count = 0;ByteArrayOutputStream baos = new ByteArrayOutputStream();while((len=is.read(buffer)) != -1){count += len;baos.write(buffer, 0, len);int progress = (int) (((float)count / (float)length) * 100);publishProgress(progress);}byte[] data = baos.toByteArray();

                                // byte[] buffer = EntityUtils.toByteArray(response.getEntity());bitMap = BitmapFactory.decodeByteArray(data, 0, data.length);//  可以直接用这个方法把InputStream转换为bitmap//  bitMap = BitmapFactory.decodeStream(is);}}catch (ClientProtocolException e){e.printStackTrace();}catch (IOException e){e.printStackTrace();}return bitMap;}@Overrideprotected void onPostExecute(Bitmap result){pDialog.dismiss();iv_picture.setImageBitmap(result);super.onPostExecute(result);}@Overrideprotected void onProgressUpdate(Integer... values){pDialog.setProgress(values[0]);super.onProgressUpdate(values);}}}

布局：

<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="com.ylj.asynctask.MainActivity" >    <ImageView  android:id="@+id/iv_picture"        android:layout_width="wrap_content"        android:layout_height="wrap_content"        android:layout_alignParentTop="true"        android:layout_centerHorizontal="true"/>    <Button        android:id="@+id/btn_download"        android:layout_width="wrap_content"        android:layout_height="wrap_content"        android:layout_alignParentBottom="true"        android:layout_centerHorizontal="true"        android:text="@string/download" /></RelativeLayout>

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