安卓学习-HttpURLConnection-显示一张网络图片到手机上

<uses-permission android:name="android.permission.INTERNET"></uses-permission>

activity_image.xml

<?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="com.example.administrator.http.ImageActivity">

    <ImageView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
       android:scaleType="centerCrop"
        android:id="@+id/imageView"
        android:layout_centerVertical="true"
        android:layout_centerHorizontal="true" />

    <Button
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="显示网络上的图片"
        android:id="@+id/button2"
        android:onClick="showNetImageClick"
        android:layout_alignParentTop="true"
        android:layout_alignParentLeft="true"
        android:layout_alignParentStart="true" />
</RelativeLayout>

ImageActivity.java

package com.example.administrator.http;

import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.os.Bundle;
import android.os.Handler;
import android.os.Message;
import android.support.v7.app.ActionBarActivity;
import android.view.View;
import android.widget.ImageView;

import java.io.IOException;
import java.io.InputStream;
import java.lang.ref.WeakReference;
import java.net.MalformedURLException;
import java.net.URL;

/*访问网络操作必须在工作线程内访问*/
public class ImageActivity extends ActionBarActivity {
    private static final int LOAD_SUCCESS = 0x1;
    private static ImageView iv;
    private final MyHandler handler = new MyHandler(this);

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_image);
        iv = (ImageView) findViewById(R.id.imageView);
    }

    private static class MyHandler extends Handler {

        //进行软引用
        private final WeakReference<ImageActivity> weakReference;

        public MyHandler(ImageActivity imageActivity) {
            weakReference = new WeakReference<ImageActivity>(imageActivity);
        }

        @Override
        public void handleMessage(Message msg) {
            ImageActivity imageActivity = weakReference.get();
            if (imageActivity != null) {
                switch (msg.what) {
                    case LOAD_SUCCESS:
                        ImageActivity.iv.setImageBitmap((Bitmap) msg.obj);
                        break;
                }
            }

        }
    }


    //访问网络操作必须在线程内访问
    public void showNetImageClick(View view) {
        new Thread(new Runnable() {
            @Override
            public void run() {
                try {
                    URL uri = new URL("http://img4.duitang.com/uploads/item/201412/08/20141208225053_VcWwd.png");
                    InputStream in = uri.openStream();
                    Bitmap bitmap = BitmapFactory.decodeStream(in);
                    Message msg = handler.obtainMessage(LOAD_SUCCESS, bitmap);
                    handler.sendMessage(msg);

                } catch (MalformedURLException e) {
                    e.printStackTrace();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
        }).start();
    }
}