android-原因：android.view.ViewRootImpl $ CalledFromWrongThreadException

Question

我试图从我的URL获取图像并在应用程序中显示，但引发错误， 原因如下：android.view.ViewRootImpl $
CalledFromWrongThreadException：只有创建视图层次结构的原始线程才能触摸其视图
。下面是我的代码

码

package com.smartag.bird.dev;

public class MainActivity extends Activity {
    static String ndefMsg = null;
    static String ndefMsg1 = null;
    NfcAdapter mNfcAdapter;
    PendingIntent mNfcPendingIntent;
    IntentFilter[] mNdefExchangeFilters;
    static final String TAG = "Read Tag";
    TextView mTitle;
    private static ImageView imageView;
    static String url = "http://sposter.smartag.my/images/chicken_soup.jpg";
    private static Bitmap downloadBitmap;
    private static BitmapDrawable bitmapDrawable;
    private static boolean largerImg = false;

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);            
        //setContentView(R.layout.main);
        mNfcAdapter = NfcAdapter.getDefaultAdapter(this);
        mNfcPendingIntent = PendingIntent.getActivity(this, 0,
                new Intent(this, getClass()).addFlags(Intent.FLAG_ACTIVITY_SINGLE_TOP), 0);
        IntentFilter ndefDetected = new IntentFilter(NfcAdapter.ACTION_NDEF_DISCOVERED);
        try {
            ndefDetected.addDataType("text/plain");
        } catch (MalformedMimeTypeException e) { }
        mNdefExchangeFilters = new IntentFilter[] { ndefDetected };  
        if (NfcAdapter.ACTION_NDEF_DISCOVERED.equals(getIntent().getAction())) {
            NdefMessage[] messages = getNdefMessages(getIntent());
            byte[] payload = messages[0].getRecords()[0].getPayload();
            ndefMsg = new String(payload);           
            setIntent(new Intent()); // Consume this intent.
        }

        ConnectivityManager connManager = (ConnectivityManager) getSystemService(CONNECTIVITY_SERVICE);
        NetworkInfo mWifi = connManager.getNetworkInfo(ConnectivityManager.TYPE_WIFI);

        if(ndefMsg == null || ndefMsg.length() == 0)
        {               
            startActivity(new Intent(MainActivity.this, MainMenu.class));               
        }            
        else
        {
            setContentView(R.layout.main);
            if (mWifi.isConnected()) {              
                ndefMsg1 = ndefMsg;
                 new DownloadFilesTask().execute(); 
                  ndefMsg = null;
            }
            else
            {                        
                AlertDialog.Builder dialog = new AlertDialog.Builder(this);
                dialog.setTitle("Attention");
                dialog.setMessage("No Internet Connection. Please enable the wifi.");
                dialog.setPositiveButton("OK", new DialogInterface.OnClickListener() {
                    public void onClick(DialogInterface dialog, int whichButton) 
                    {
                    }
                });
                dialog.show();
            }
        }           
    }
    private class DownloadFilesTask extends AsyncTask<Void, Void, Void> {
        protected void onPostExecute(Void result) {             
        }           
        @Override
        protected Void doInBackground(Void... params) {             
            try {
                URL myFileUrl = new URL("http://sposter.smartag.my/images/chicken_soup.jpg");
                HttpURLConnection conn= (HttpURLConnection)myFileUrl.openConnection();
                conn.setDoInput(true);
                conn.connect();
                InputStream is = conn.getInputStream();
                downloadBitmap = BitmapFactory.decodeStream(is);
                            } catch (FileNotFoundException e) {             
                e.printStackTrace();
            }
            catch (IOException e) {         
                e.printStackTrace();
            }               
            ImageView image = (ImageView) findViewById(R.id.imview);            
            image.setImageBitmap(downloadBitmap);
            return null;
        }
    }
}

Answer 1

使用 AsyncTask的 错误做法，

您正在尝试从更新主UI线程，doInBackGround()因为AsyncTask从未允许这样做。

切勿从doInBackGround()AsyncTask的唯一工作线程中更新UI。因此onPostExecute()，使用AsyncTask方法编写您的Main UI更新数据。

@Override
        protected Void doInBackground(Void... params) {             
            try {
                URL myFileUrl = new URL("http://sposter.smartag.my/images/chicken_soup.jpg");
                HttpURLConnection conn= (HttpURLConnection)myFileUrl.openConnection();
                conn.setDoInput(true);
                conn.connect();
                InputStream is = conn.getInputStream();
                downloadBitmap = BitmapFactory.decodeStream(is);
                            } catch (FileNotFoundException e) {             
                e.printStackTrace();
            }
            catch (IOException e) {         
                e.printStackTrace();
            }               
            return null;
        }

@Override
onPostExecute()
{
 ImageView image = (ImageView) findViewById(R.id.imview);            
            image.setImageBitmap(downloadBitmap);
}