[Android]android.view.ViewRoot$CalledFromWrongThreadException

今日寫軟體中的某個畫面，我使用了new thread來加速圖片的處理以及使用Progressbar，原本以為應該很快就可以寫好的程式，在測試時卻一直跳出exception：android.view.ViewRoot$CalledFromWrongThreadException: Only the original thread that created a view hierarchy can touch its views.


問了孤狗大神才知道原來不能在major thread以外的thread更新使用者介面，所以需先在thread中，download圖片至手機中，download完畢時，sendMessage to Handler，接著在把剛剛download下來的圖片設定至bitmap中，並更新使用者介面才能完成整個流程。

public class LocationDetail extends Activity implements Runnable{
private String imageUrl;
private ImageView content;
private ProgressBar myProgressBar;
int myProgress = 0;

@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.location_detail);

myProgressBar = (ProgressBar) findViewById(R.id.progressbar);
myProgressBar.setProgress(myProgress);
content = (ImageView) findViewById(R.id.content);
//開啟另一個Thread來download圖片至手機暫存資料夾中
new Thread(this).start();
}

@Override
public void run() {
String imageUrl = "abc.jpg";

URL picUrl = new URL("http://xxx.yyy.zzz/"+ imageUrl);
URLConnection imageConn = picUrl.openConnection();
imageConn.connect();

InputStream imageOnCloud = imageConn.getInputStream();
String outFileName = "手機存放圖片的路徑" + imageUrl;

OutputStream imageInPhone = new FileOutputStream(outFileName);

byte[] buffer = new byte[1024];
int length;
while ((length = imageOnCloud.read(buffer)) > 0) {
imageInPhone.write(buffer, 0, length);
}
imageInPhone.flush();
imageInPhone.close();
imageOnCloud.close();
//圖片下載完畢，sendMessage to Handler做接下來更新UI的動作

handler.sendEmptyMessage(0);
}

private Handler handler = new Handler() {
@Override
public void handleMessage(Message msg) {
Bitmap bitmap = BitmapFactory.decodeFile("手機存放圖片的路徑" + imageUrl);
content.setImageBitmap(bitmap);
myProgressBar.setVisibility(View.GONE);
}
};