AsyncTask与HttpURLConnection下载网络图片

来源：互联网发布：玫瑰花简笔画软件编辑：程序博客网时间：2024/06/05 18:27

下载的图片
使用AsyncTask可以更加方便的在子线程中对UI进行操作。

AsyncTask是个抽象类，使用它必须要创建一个子类去继承它。他有三个泛型的参数，

<?xml version="1.0" encoding="utf-8"?><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="yifang.zhsong.ansyctaskdemo.MainActivity">    <Button        android:layout_width="wrap_content"        android:layout_height="wrap_content"        android:text="Download"        android:id="@+id/bt_download"        android:layout_alignParentBottom="true"        android:layout_centerHorizontal="true"        android:layout_marginBottom="43dp" />    <ImageView        android:layout_width="500dp"        android:layout_height="500dp"        android:id="@+id/iv_picture" /></RelativeLayout>

MainActivity部分的代码package yifang.zhsong.ansyctaskdemo;import android.app.ProgressDialog;import android.graphics.Bitmap;import android.graphics.BitmapFactory;import android.os.AsyncTask;import android.support.v7.app.AppCompatActivity;import android.os.Bundle;import android.view.View;import android.widget.Button;import android.widget.ImageView;import java.io.ByteArrayOutputStream;import java.io.IOException;import java.io.InputStream;import java.net.HttpURLConnection;import java.net.URL;public class MainActivity extends AppCompatActivity {    private Button button;    private ImageView image;    private ProgressDialog dia;    @Override    protected void onCreate(Bundle savedInstanceState) {        super.onCreate(savedInstanceState);        setContentView(R.layout.activity_main);        button = (Button) findViewById(R.id.bt_download);        image = (ImageView) findViewById(R.id.iv_picture);//定义进度条        dia = new ProgressDialog(this);        dia.setTitle("提示信息");        dia.setMessage("下载中，请稍后");        dia.setProgressStyle(ProgressDialog.STYLE_HORIZONTAL);//设置点击进度条外部，不响应；        dia.setCancelable(false);        button.setOnClickListener(new View.OnClickListener() {            @Override            public void onClick(View arg0) {// TODO Auto-generated method stub                new MyTask().execute();            }        });    }    //Sting 表示传入的值， Integer  代表进度 ，  Bitmap 代表返回的值    public class MyTask extends AsyncTask<String, Integer, Bitmap> {        //任务执行之前的准备工作。        @Override        protected void onPreExecute() {// TODO Auto-generated method stub            dia.show();        }        //主要完成耗时操作        @Override        protected Bitmap doInBackground(String... arg0) {// TODO Auto-generated method stub            HttpURLConnection connection = null;            Bitmap bitmap = null;            ByteArrayOutputStream outputStream = new ByteArrayOutputStream();            InputStream inputStream = null;            try {                URL url = new URL("http://imglf0.nosdn.127.net/img/akF3Q3JLbzVNWExja3g3d1B5a0NRcW50OUFtNTBoNTRaYkRjdEo2WlBDeGRTRkNGUUVraGxnPT0.jpg?imageView&thumbnail=500x0&quality=96&stripmeta=0&type=jpg");                connection = (HttpURLConnection) url.openConnection();                connection.setRequestMethod("GET");                connection.setConnectTimeout(8000);                connection.setReadTimeout(8000);                inputStream = connection.getInputStream();//先获得文件的总长度，                int fileLength = connection.getContentLength();                int len = 0;                byte[] data = new byte[1024];                int total_length = 0;                int value = 0;                while ((len = inputStream.read(data)) != -1) {                    total_length += len;                    value = ((total_length / fileLength) * 100);//调用update函数，更新进度                    publishProgress(value);                    outputStream.write(data, 0, len);                    Thread.sleep(500);                }                byte[] result = outputStream.toByteArray();                bitmap = BitmapFactory.decodeByteArray(result, 0, result.length);                inputStream.close();                outputStream.close();                connection.disconnect();            } catch (Exception e) {// TODO: handle exception                e.printStackTrace();            } finally {                if (inputStream != null) {                    try {                        inputStream.close();                        outputStream.close();                        connection.disconnect();                    } 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            dia.setProgress(values[0]);        }        //主要完成耗时操作        @Override        protected void onPostExecute(Bitmap result) {// TODO Auto-generated method stub            dia.dismiss();            image.setImageBitmap(result);        }    }}

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