运用AsyncTask下载图片并显示下载进度，下载完成后显示

执行主窗体的代码：

public class MainActivity extends AppCompatActivity {
    //下载图片的url
    private String url = "http://p4.so.qhmsg.com/t01ba3531d5c8665a69.jpg";
    private ImageView ivPicOne;
    
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        ivPicOne = (ImageView) findViewById(R.id.ivPicOne);
    }
    
    public void download(View view){

	//通过点击按钮启动AsyncTask
        new MyAsyncTask(ivPicOne,this).execute(url);
    }
}

这段代码很简单，主要就是一个通过点击按钮来启动AsyncTask进行下载任务；

布局文件：

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:id="@+id/activity_main"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical"
    tools:context="com.shen.fourth.MainActivity">
    <ImageView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:id="@+id/ivPicOne"
        android:src="@mipmap/ic_launcher"/>
    <Button
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="download"
        android:onClick="download"/>
LinearLayout>

线性布局里放置了一个ImageView用来显示下载的图片，一个按钮用来启动AsyncTask；

主要代码在AsyncTask自定义类里面：

public class MyAsyncTask extends AsyncTask {

    private ImageView ivPicOne;	

    //进度条对话框，用来显示进度

    private ProgressDialog dialog;
    private Context context;

    public MyAsyncTask(ImageView ivPicOne, Context context) {
        this.ivPicOne = ivPicOne;
        this.context = context;
    }

    //2.执行耗时操作，子线程
    @Override
    protected Bitmap doInBackground(String... strings) {
        HttpURLConnection conn = null;
        InputStream is = null;
        try {
            URL url = new URL(strings[0]);
            conn = (HttpURLConnection) url.openConnection();
            conn.setConnectTimeout(1000);
            conn.connect();
            if(conn.getResponseCode() == 200){
                is = conn.getInputStream();
                byte[] buff = new byte[1024];
                ByteArrayOutputStream baos = new ByteArrayOutputStream();
                int len = 0;

		//currentSize变量用来统计当前已经下载的数据的总大小
                int currentSize = 0;

		//totalSize变量用来获得将要下载图片的总大小

                int totalSize = conn.getContentLength();
                while((len = is.read(buff))!=-1){

		    //累加
                    currentSize += len;

		    //算出百分比
                    int progressSize = (int)(currentSize/(double)totalSize * 100);

		    //Log面板显示当前进度
                    Log.i("progressSize+++++++++",progressSize+"");

   		    //更新进度
                    publishProgress(progressSize);
                    baos.write(buff,0,len);
                    baos.flush();
                }
                byte[] datas = baos.toByteArray();
                baos.close();
                Bitmap bitmap = BitmapFactory.decodeByteArray(datas,0, datas.length);
                return bitmap;



            }
        } catch (MalformedURLException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        }
        return null;
    }

    //1.作一些准备工作，UI主线程
    @Override
    protected void onPreExecute() {
        super.onPreExecute();

	//创建进度条对话框
        dialog = new ProgressDialog(context);

	//设置对话框的属性
        dialog.setTitle("提示");
        dialog.setIcon(R.mipmap.ic_launcher);
        dialog.setMessage("正在下载中。。。");

	//设置为水平进度条
        dialog.setProgressStyle(ProgressDialog.STYLE_HORIZONTAL);

	//显示
        dialog.show();


    }
 

     //3.耗时操作执行完执行此方法，用于更新UI，UI主线程

@Override protected void onPostExecute(Bitmap bitmap) {

	//绑定图片信息
        ivPicOne.setImageBitmap(bitmap);

	//关闭进度条对话框
        dialog.dismiss();
        super.onPostExecute(bitmap);
    }
    

    //该方法会在执行耗时操作过程中多次被调用

    @Override
    protected void onProgressUpdate(Integer... values) {
        super.onProgressUpdate(values);

	//更新进度对话框中的进度值
        dialog.setProgress(values[0]);
    }
}

ok，完毕~欢迎大家讨论交流