AsyncTask 异步加载网络图片简单应用

来源：互联网发布：编码器编程程序接线图编辑：程序博客网时间：2024/05/29 19:29

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 = "http://img.my.csdn.net/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);        }    }}

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