Question

我已经创建了一个Android应用程序，其中有登录表单，更新详细信息表单等。

每当我输入错误的细节时，应用程序就会停止工作，并出现强制关闭对话框。

这是我的代码：

Login.java

   public class AllProductsActivity extends ListActivity
   {
       private ProgressDialog pDialog;
       JSONParser jParser = new JSONParser();
       ArrayList<HashMap<String, String>> productsList;
       private static String url_all_products = "http://192.168.1.4/android_connect/get_all_products.php";

       // JSON Node names
       private static final String TAG_SUCCESS = "success";
       private static final String TAG_PRODUCTS = "products";
       private static final String TAG_PID = "pid";
       private static final String TAG_NAME = "name";

       // products JSONArray
       JSONArray products = null;

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

    // Hashmap for ListView
    productsList = new ArrayList<HashMap<String, String>>();

    // Loading products in Background Thread
    new LoadAllProducts().execute();

    // Get listview
    ListView lv = getListView();

    // on seleting single product
    // launching Edit Product Screen
    lv.setOnItemClickListener(new OnItemClickListener() {

        @Override
        public void onItemClick(AdapterView<?> parent, View view,
                int position, long id) {
            // getting values from selected ListItem
            String pid = ((TextView) view.findViewById(R.id.pid)).getText()
                    .toString();

            // Starting new intent
            Intent in = new Intent(getApplicationContext(),
                    EditProductActivity.class);
            // sending pid to next activity
            in.putExtra(TAG_PID, pid);

            // starting new activity and expecting some response back
            startActivityForResult(in, 100);
        }
    });

}

// Response from Edit Product Activity
@Override
protected void onActivityResult(int requestCode, int resultCode, Intent data) {
    super.onActivityResult(requestCode, resultCode, data);
    // if result code 100
    if (resultCode == 100) {
        // if result code 100 is received 
        // means user edited/deleted product
        // reload this screen again
        Intent intent = getIntent();
        finish();
        startActivity(intent);
    }

}

/**
 * Background Async Task to Load all product by making HTTP Request
 * */
class LoadAllProducts extends AsyncTask<String, String, String> 
    {
         /**
     * Before starting background thread Show Progress Dialog
     * */
    @Override
    protected void onPreExecute() {
        super.onPreExecute();
        pDialog = new ProgressDialog(AllProductsActivity.this);
        pDialog.setMessage("Loading products. Please wait...");
        pDialog.setIndeterminate(false);
        pDialog.setCancelable(false);
        pDialog.show();
    }

    /**
     * getting All products from url
     * */
    protected String doInBackground(String... args) {
        // Building Parameters
        List<NameValuePair> params = new ArrayList<NameValuePair>();
        // getting JSON string from URL
        JSONObject json = jParser.makeHttpRequest(url_all_products, "GET", params);

        // Check your log cat for JSON reponse
        Log.d("All Products: ", json.toString());

        try {
            // Checking for SUCCESS TAG
            int success = json.getInt(TAG_SUCCESS);

            if (success == 1) {
                // products found
                // Getting Array of Products
                products = json.getJSONArray(TAG_PRODUCTS);

                // looping through All Products
                for (int i = 0; i < products.length(); i++) {
                    JSONObject c = products.getJSONObject(i);

                    // Storing each json item in variable
                    String id = c.getString(TAG_PID);
                    String name = c.getString(TAG_NAME);

                    // creating new HashMap
                    HashMap<String, String> map = new HashMap<String, String>();

                    // adding each child node to HashMap key => value
                    map.put(TAG_PID, id);
                    map.put(TAG_NAME, name);

                    // adding HashList to ArrayList
                    productsList.add(map);
                }
            } else {
                // no products found
                // Launch Add New product Activity
                Intent i = new Intent(getApplicationContext(),
                        NewProductActivity.class);
                // Closing all previous activities
                i.addFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP);
                startActivity(i);
            }
        } catch (JSONException e) {
            e.printStackTrace();
        }

        return null;
    }

    /**
     * After completing background task Dismiss the progress dialog
     * **/
    protected void onPostExecute(String file_url) {
        // dismiss the dialog after getting all products
        pDialog.dismiss();
        // updating UI from Background Thread
        runOnUiThread(new Runnable() {
            public void run() {
                /**
                 * Updating parsed JSON data into ListView
                 * */
                ListAdapter adapter = new SimpleAdapter(
                        AllProductsActivity.this, productsList,
                        R.layout.list_item, new String[] { TAG_PID,
                                TAG_NAME},
                        new int[] { R.id.pid, R.id.name });
                // updating listview
                setListAdapter(adapter);
            }
        });
    }
}
}

UpdateDetails.java

   public class UpdateDetails extends Activity
   {

        EditText inputName;
        EditText inputAddress;
        EditText inputPassword;
        EditText confirmPassword;
        EditText inputEmailId, inputMobileno;

        // Progress Dialog
        private ProgressDialog pDialog;

    // JSON parser class
        JSONParser jsonParser = new JSONParser();

        // JSON Node names
        private static final String resp = "success";
        //private static final String Flag = "flag";

protected void onCreate(Bundle savedInstanceState) {

    super.onCreate(savedInstanceState);
    requestWindowFeature(Window.FEATURE_NO_TITLE);
    getWindow().setFlags(WindowManager.LayoutParams.FLAG_FULLSCREEN,
            WindowManager.LayoutParams.FLAG_FULLSCREEN);
    setContentView(R.layout.updatedetails);

        // Edit Text
        inputName = (EditText) findViewById(R.id.editName);
        inputAddress = (EditText) findViewById(R.id.editAddress);
        inputPassword = (EditText) findViewById(R.id.editPassword);
        confirmPassword=(EditText) findViewById(R.id.editConfirmPassword);
        inputEmailId=(EditText) findViewById(R.id.editText2_emailid);
        inputMobileno=(EditText) findViewById(R.id.editText1_mobile);

        // Create button
        Button update_details = (Button) findViewById(R.id.buttonUpdate);

        // button click event
        update_details.setOnClickListener(new View.OnClickListener() {

            @Override
            public void onClick(View view) {
                if (inputPassword == confirmPassword){
                // updating user in background thread
                new UpdateUserDetails().execute();
                }
                else {
                    //Some Sort Of Alert Box
                    Toast.makeText(getApplicationContext(), "Please Enter Valid Details", Toast.LENGTH_SHORT).show();
                    }
            }
        });
    }

    /**
     * Background Async Task to Create new product
     * */
    class UpdateUserDetails extends AsyncTask<String, String, String> {
        /**
         * Before starting background thread Show Progress Dialog
         * */
        @Override
        protected void onPreExecute() {
            super.onPreExecute();
            pDialog = new ProgressDialog(UpdateDetails.this);
            pDialog.setMessage("Updating User Details.. Please wait");
            pDialog.setIndeterminate(false);
            pDialog.setCancelable(false);
            pDialog.show();
        }

        /**
         * Updating User
         * */
        protected String doInBackground(String... args) {
            String name = inputName.getText().toString();
            String address = inputAddress.getText().toString();
            String password = inputPassword.getText().toString();
            String mobileno = inputMobileno.getText().toString();
            String emailid = inputEmailId.getText().toString();

            // Building Parameters
            List<NameValuePair> params = new ArrayList<NameValuePair>();
            params.add(new BasicNameValuePair("name", name));
            params.add(new BasicNameValuePair("address", address));
            params.add(new BasicNameValuePair("password", password));
            params.add(new BasicNameValuePair("mobile_no", mobileno));
            params.add(new BasicNameValuePair("email_id",emailid));

            final String url_user = "http://"+ Login.serve +"/catxam/android_update.php";

            // getting JSON Object
            JSONObject json = jsonParser.makeHttpRequest(url_user,"POST", params);

            // check log cat from response
            Log.d("Update Response", json.toString());

            // check for success tag
            try {
                int success = json.getInt(resp);

                if (success == 1) {
                    // successfully update user
                    Intent i = new Intent(getApplicationContext(), MainActivity.class);
                    startActivity(i);

                    // closing this screen
                    finish();
                } else {
                    Toast.makeText(getApplicationContext(), "Unsuccessful Updation", Toast.LENGTH_SHORT).show();
                }
            } 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 done
            pDialog.dismiss();
        }

    }
}

任何人都可以帮助我找出错误并帮助我纠正项目中的错误。

感谢您的帮助。提前致谢

这是logCat窗口！

02-13 19:32:10.096: E/AndroidRuntime(7328): FATAL EXCEPTION: AsyncTask #2

02-13 19:32:10.096: E/AndroidRuntime(7328): java.lang.RuntimeException: An error occured while executing doInBackground()

02-13 19:32:10.096: E/AndroidRuntime(7328):     at android.os.AsyncTask$3.done(AsyncTask.java:299)

02-13 19:32:10.096: E/AndroidRuntime(7328):     at java.util.concurrent.FutureTask.finishCompletion(FutureTask.java:352)

02-13 19:32:10.096: E/AndroidRuntime(7328):     at java.util.concurrent.FutureTask.setException(FutureTask.java:219)

02-13 19:32:10.096: E/AndroidRuntime(7328):     at java.util.concurrent.FutureTask.run(FutureTask.java:239)

02-13 19:32:10.096: E/AndroidRuntime(7328):     at android.os.AsyncTask$SerialExecutor$1.run(AsyncTask.java:230)

02-13 19:32:10.096: E/AndroidRuntime(7328):     at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1080)

02-13 19:32:10.096: E/AndroidRuntime(7328):     at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:573)

02-13 19:32:10.096: E/AndroidRuntime(7328):     at java.lang.Thread.run(Thread.java:838)

02-13 19:32:10.096: E/AndroidRuntime(7328): Caused by: java.lang.NullPointerException
02-13 19:32:10.096: E/AndroidRuntime(7328):     at 
com.example.catxam.Login$CreateNewUser.doInBackground(Login.java:146)

02-13 19:32:10.096: E/AndroidRuntime(7328):     at com.example.catxam.Login$CreateNewUser.doInBackground(Login.java:1)

02-13 19:32:10.096: E/AndroidRuntime(7328):     at android.os.AsyncTask$2.call(AsyncTask.java:287)

02-13 19:32:10.096: E/AndroidRuntime(7328):     at java.util.concurrent.FutureTask.run(FutureTask.java:234)

02-13 19:32:10.096: E/AndroidRuntime(7328):     ... 4 more

抱歉无法发布图片:(

Answer 1

在postExecute中执行此操作。要显示或传递给另一个活动，请在postExecute中使用。只有在doInBackground中执行的主要操作。

        try {
            int success = json.getInt(resp);

            if (success == 1) {
                // successfully update user
                Intent i = new Intent(getApplicationContext(), MainActivity.class);
                startActivity(i);

                // closing this screen
                finish();
            } else {
                Toast.makeText(getApplicationContext(), "Unsuccessful Updation", Toast.LENGTH_SHORT).show();
            }
        } catch (JSONException e) {
            e.printStackTrace();
        }

Answer 2

您无法从doInBackground方法调用Toast.makeText，因为它需要在UI线程上完成。

在doInBackground结束时执行此操作：

// check for success tag
try {
    int success = json.getInt(resp);
    String success = success == 1 ? "success" : null;
    return success;
} catch (JSONException e) {
    e.printStackTrace();
    return null;
}

和onPostExecute：

protected void onPostExecute(String result) {
    if (result!= null) {
        // successfully update user
        Intent i = new Intent(getApplicationContext(), MainActivity.class);
        startActivity(i);
        // closing this screen
        finish();
    } else {
        Toast.makeText(getApplicationContext(), "Unsuccessful Updation", Toast.LENGTH_SHORT).show();
    }
    pDialog.dismiss();
}

此外，您不应在LoadAllProducts：

中执行此操作

// updating UI from Background Thread
runOnUiThread(new Runnable()

onPostExecute旨在让您在后台任务结束时更新UI，因此您无需创建额外的线程来执行该代码。

Answer 3

和其他答案一样，你的错误（虽然没有logcat ....）是你打电话：

Toast.makeText(getApplicationContext(), "Unsuccessful Updation", Toast.LENGTH_SHORT).show();

<{1>}中的

，仅在UI线程上允许UI操作。另一方面，你不需要：

doInBackground

<{1>}中的

因为它已经在UI线程上执行，所以你应该使用runOnUiThread(new Runnable() {作为你的toast消息。

强制关闭我的Android应用程序

3 个答案: