佈局檔案：

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"

    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical">

    <Button
        android:id="@+id/button"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_gravity="center"
        android:layout_marginTop="30dp"
        android:text="從網路獲取圖片"
        android:layout_marginLeft="120dp"
        />
    <ImageView
        android:id="@+id/img"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:layout_below="@+id/button"
        />


</RelativeLayout>

public class MainActivity extends AppCompatActivity {

    private  String imageUrl = "http://news.sciencenet.cn/upload/news/images/2011/3/20113301123128272.jpg";


    private Button button;
    private ImageView img;

    //在訊息佇列中實現對控制元件的更改
    private Handler handle = new Handler() {
        public void handleMessage(Message msg) {
            switch (msg.what) {
                case 0:
                    Bitmap bmp=(Bitmap)msg.obj;
                    img.setImageBitmap(bmp);
                    break;
            }
        };
    };


    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        button = (Button) findViewById(R.id.button);
        img = (ImageView) findViewById(R.id.img);
        button.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                //新建執行緒載入圖片資訊，傳送到訊息佇列中
                new Thread(new Runnable() {

                    @Override
                    public void run() {
                        // TODO Auto-generated method stub
                        Bitmap bmp = getURLimage(imageUrl);
                        Message msg = new Message();
                        msg.what = 0;
                        msg.obj = bmp;
                        handle.sendMessage(msg);
                    }
                }).start();
            }
        });
    }

    private Bitmap getURLimage(String imageUrl) {
        Bitmap bmp = null;
        try {
            URL myurl = new URL(imageUrl);
            // 獲得連線
            HttpURLConnection conn = (HttpURLConnection) myurl.openConnection();
            conn.setConnectTimeout(6000);//設定超時
            conn.setDoInput(true);
            conn.setUseCaches(false);//不快取
            conn.connect();
            InputStream is = conn.getInputStream();//獲得圖片的資料流
            bmp = BitmapFactory.decodeStream(is);
            is.close();
        } catch (Exception e) {
            e.printStackTrace();
        }
        return bmp;

    }


}