AsyncTask 异步加载网络图片简单应用

     这个是一个加载网络图片资源的小Demo可以很好地解释AsyncTask的工作流程 

      布局文件如下所示

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:padding="16dp"
    android:layout_width="match_parent"
    android:layout_height="match_parent">
<ImageView
    android:id="@+id/asyimg"
    android:layout_width="match_parent"
    android:layout_height="match_parent" />

    <ProgressBar
        android:id="@+id/asyprog"
        android:visibility="gone"
        android:foregroundGravity="center"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_centerVertical="true"
        android:layout_centerHorizontal="true" />
</RelativeLayout>

MainActivity代码

package com.imooc.www.moocdemo;

import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.os.AsyncTask;
import android.os.Bundle;
import android.os.PersistableBundle;
import android.support.v7.app.AppCompatActivity;
import android.view.View;
import android.widget.ImageView;
import android.widget.ProgressBar;

import java.io.BufferedInputStream;
import java.net.URL;
import java.io.IOException;
import java.io.InputStream;
import java.net.URLConnection;

/**
 * Created by Administrator on 2016/5/12.
 */
public class AsyncImageActivity extends AppCompatActivity {
    private ImageView mImageView;
    private ProgressBar mProgressBar;
    private static String URL = "https://img-my.youkuaiyun.com/uploads/201504/12/1428806103_9476.png";

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.asyncimageactivity);
        mImageView = (ImageView) findViewById(R.id.asyimg);
        mProgressBar = (ProgressBar) findViewById(R.id.asyprog);

        //设置传递进来的参数
        new MyImageAsyncTask().execute(URL);
    }

    class MyImageAsyncTask extends AsyncTask<String, Void, Bitmap> {

        @Override
        protected Bitmap doInBackground(String... params) {
            //获取传进来的参数 params为参数的意思 参数的个数不确定 params【0】表示获取第一个参数要注意一下
            String url = params[0];
            Bitmap bitmap = null;
            URLConnection connection;
            InputStream is;
            try {
                connection = new URL(url).openConnection();
                is = connection.getInputStream();
                BufferedInputStream bis = new BufferedInputStream(is);
                //通过decodeStream将输入流解析成bitmap
                bitmap = BitmapFactory.decodeStream(bis);
                //关闭输入流
                is.close();
                bis.close();
            } catch (IOException e) {
                e.printStackTrace();
            }
               //将bitmap作为返回值返回
            return bitmap;
        }

        @Override
        protected void onPreExecute() {
            super.onPreExecute();
            mProgressBar.setVisibility(View.VISIBLE);
        }

        @Override
        protected void onPostExecute(Bitmap bitmap) {
            super.onPostExecute(bitmap);
            mProgressBar.setVisibility(View.GONE);
            mImageView.setImageBitmap(bitmap);
        }

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