Android Waiting progress bar Can't create handler inside the thread that has not called Looper.prepare() 错误

Question

在我的 android 应用程序中，我将一些数据从服务器数据库复制到本地数据库。这可能需要 15 分钟以上。对于较慢的连接，它可能会被超过。所以我想显示一个等待进度条。

代码贴在下面。

refresh.setOnClickListener(new OnClickListener(){
public void onClick(View v) {
final ProgressDialog progressDialog = ProgressDialog.show(login.this, "", "Please wait...");
new Thread() {
public void run() {
try{
mySQLiteAdapter.openToWrite();
mySQLiteAdapter.deleteAll();
radapter.openToWrite();
radapter.deleteAll();
uadapter.openToWrite();
uadapter.deleteAll();
        try
            {
                 HttpClient httpclient = new DefaultHttpClient();
                 HttpPost httppost = new HttpPost("http://xxxxxxxxxxxxxxxxxxxxx");
                 HttpResponse response = httpclient.execute(httppost);
                 HttpEntity entity = response.getEntity();
                  is = entity.getContent();
            } catch (UnsupportedEncodingException e) {
                e.printStackTrace();
            } catch (ClientProtocolException e) {
                e.printStackTrace();
            } catch (IOException e) {
                e.printStackTrace();
            }
            try {
                BufferedReader reader = new BufferedReader(new InputStreamReader(
                        is, "iso-8859-1"), 8);
                StringBuilder sb = new StringBuilder();
                String line = null;
                while ((line = reader.readLine()) != null) {
                    sb.append(line + "\n");
                }
                is.close();
                json = sb.toString();
            } catch (Exception e) {
            Toast.makeText(getBaseContext(), e.toString(), Toast.LENGTH_LONG).show();
            }

            try {
                jObj = new JSONObject(json);
                contacts = jObj.getJSONArray("get");
                for(int i = 0; i < contacts.length(); i++){
                JSONObject c = contacts.getJSONObject(i);
                    if(!c.isNull("rname"))// || c.getString("rcode").equals(null))
                    {
                        rname = c.getString("rname");
                        rcode = c.getString("rcode");
                        radapter.insert(rcode, rname);
                    }
                    else
                    {
                        rname = "";
                        rcode = c.getString("rcode");
                        radapter.insert(rcode, rname);
                    }
                }
                Toast.makeText(getBaseContext(), " Ryot BackUp completed", Toast.LENGTH_SHORT).show();

            } catch (JSONException e) {
                Toast.makeText(getBaseContext(), "Error"+e.toString(), Toast.LENGTH_LONG).show();
            }
                   progressDialog.dismiss();
               }
            }.start();
            adapter.deleteAll();
            oadapter.deleteAll();
            e2.setText("Back Up completed");
        }
            catch (Exception e) {
               Log.e("tag", e.getMessage());
               }
                   progressDialog.dismiss();
               }
            }.start();
       }

   });

当我运行我的应用程序时，进度条只显示几秒钟，然后执行 Catch 块，显示 logcat 错误为

Logcat：

02-26 14:26:07.151: E/tag(301): Can't create handler inside thread that has not called Looper.prepare()

谁能解释我的代码中的错误以及如何解决它

Answer 1

Toast.makeText(getBaseContext(), " Ryot BackUp completed", Toast.LENGTH_SHORT).show();

问题是由上面的代码引起的，这个方法会改变UI，你不能在非ui线程中更新UI。所以你需要从主 ui 线程调用它。

由于这是一项耗时的工作，我强烈建议您在 Android 中使用AsyncTask。

但如果你只想对现有代码做一点改动，尝试使用

context.runOnUiThread(new Runnable() {
  public void run() {
    Toast.makeText(...).show();
  }
});

或者handler，你可以看看How Handler Work in Android。一个基本的例子：

public Handler mHandler = new Handler() {

    public void handleMessage(Message msg) {
           //show toast here
    }
}

protected void startLongRunningOperation() {

    Thread t = new Thread() {
        public void run() {
            //do something here
            //update the result
            mHandler.postDelayed(mUpdateResults, 200);}
            mHandler.post(mUpdateResults);
        }
    };
    t.start();
}

Answer 2

不要创建一个新线程，而是创建一个 HandlerThread - http://developer.android.com/reference/android/os/HandlerThread.html

只需将“new Thread()”替换为“new HandlerThread(“any string”)”就可以了。