Question

我正在尝试使用WiFi来检索数据，但应用程序正在崩溃。当我使用localHost仿真器时，它工作得很好但是当我使用移动数据或WiFi时它会崩溃。我可以使用WiFi将数据保存到localhost上的MySql，但我无法接收数据。有些时候我会android.os.NetworkonMainThreadException。我是一个非常新的程序员，只是借用了大部分代码，需要明确说明如何解决这个问题。

/**
 * Background Async Task to Get complete User details
 * */
class GetUserDetails extends AsyncTask<String, String, String> {

    /**
     * Before starting background thread Show Progress Dialog
     * */
    @Override
    protected void onPreExecute() {
        super.onPreExecute();
        pDialog = new ProgressDialog(MainActivity.this);
        pDialog.setMessage("Loading details. Please wait...");
        pDialog.setIndeterminate(false);
        pDialog.setCancelable(true);
        pDialog.show();
    }

    /**
     * Getting User details in background thread
     * */
    protected String doInBackground(String... params) {

        // updating UI from Background Thread
        runOnUiThread(new Runnable() {
            public void run() {
                // Check for success tag
                int success;
                try {
                    // Building Parameters
                    List<NameValuePair> params = new ArrayList<NameValuePair>();
                    params.add(new BasicNameValuePair("user_ID", "2"));

                    // getting User details by making HTTP request
                    // Note that User details url will use GET request
                    JSONObject json = jsonParser.makeHttpRequest(
                            LOGIN_URL, "GET", params);

                    // check your log for json response
                    Log.d("Single User Details", json.toString());

                    // json success tag
                    success = json.getInt(TAG_SUCCESS);
                    if (success == 1) {
                        // successfully received User details
                        JSONArray UserObj = json
                                .getJSONArray(TAG_User); // JSON Array

                        // get first User object from JSON Array
                        JSONObject User = UserObj.getJSONObject(0);

                        // User with this pid found
                        // Edit Text
                        txtlname = (EditText) findViewById(R.id.editText1);
                        txtfname = (EditText) findViewById(R.id.editText2);

                        // display User data in EditText
                        txtfname.setText(User.getString(TAG_FNAME));
                        txtlname.setText(User.getString(TAG_LNAME));

                    }else{
                        // User with pid not found
                    }
                } catch (JSONException e) {
                    e.printStackTrace();
                }
            }
        });
        return null;
    }
    /**
     * After completing background task Dismiss the progress dialog
     * **/
    protected void onPostExecute(String file_url) {
        // dismiss the dialog once got all details
        pDialog.dismiss();
    }
}

Answer 1

实际上你不应该在UI线程中连接到互联网。您通过JSONObject json = jsonParser.makeHttpRequest( LOGIN_URL, "GET", params);中的runOnUiThread( new Runnable....与互联网建立了连接。

/**
 * Background Async Task to Get complete User details
 * */
class GetUserDetails extends AsyncTask<String, String, String> {

/**
 * Before starting background thread Show Progress Dialog
 * */
@Override
protected void onPreExecute() {
    super.onPreExecute();
    pDialog = new ProgressDialog(MainActivity.this);
    pDialog.setMessage("Loading details. Please wait...");
    pDialog.setIndeterminate(false);
    pDialog.setCancelable(true);
    pDialog.show();
}

/**
 * Getting User details in background thread
 * */
protected String doInBackground(String... params) {

    // updating UI from Background Thread

    // Check for success tag
    int success;
    try {
        // Building Parameters
        List<NameValuePair> params = new ArrayList<NameValuePair>();
        params.add(new BasicNameValuePair("user_ID", "2"));

        // getting User details by making HTTP request
        // Note that User details url will use GET request
        JSONObject json = jsonParser.makeHttpRequest(
                LOGIN_URL, "GET", params);

        // check your log for json response
        Log.d("Single User Details", json.toString());

        // json success tag
        success = json.getInt(TAG_SUCCESS);
        if (success == 1) {
            // successfully received User details
            JSONArray UserObj = json
                    .getJSONArray(TAG_User); // JSON Array

            // get first User object from JSON Array
            final JSONObject User = UserObj.getJSONObject(0);
            runOnUiThread(new Runnable() {
                public void run() {
                    // User with this pid found
                    // Edit Text
                    txtlname = (EditText) findViewById(R.id.editText1);
                    txtfname = (EditText) findViewById(R.id.editText2);

                    // display User data in EditText
                    txtfname.setText(User.getString(TAG_FNAME));
                    txtlname.setText(User.getString(TAG_LNAME));
                }
            });

        }else{
            // User with pid not found
        }
    } catch (JSONException e) {
        e.printStackTrace();
    }


    return null;
}
/**
 * After completing background task Dismiss the progress dialog
 * **/
protected void onPostExecute(String file_url) {
    // dismiss the dialog once got all details
    pDialog.dismiss();
}
}

正如您所看到的，当我想处理视图（如文本视图）时，我刚刚返回UI线程。注意user变量。我最后决定让它在我用作Runnable方法参数的runOnUiThread对象中可以访问。

Answer 2

您不应该在doInBackground中执行与UI相关的代码，您应该将UI相关代码移动到AsyncTask的onPostExecute或onProgressUpdate方法。

这个答案可能对您有所帮助：

Android : Calling the methods on UI thread from AsyncTask doInBackground method

使用JSON和MySql使用Android应用程序重现数据

2 个答案: