Question

我是App开发的新手，我正在尝试使用JSONParser创建一个登录应用，但问题是每当我尝试login时它都会崩溃。

 06-30 15:06:32.415  16009-16052/com.zaid.sling.mysqltest E/AndroidRuntime﹕ FATAL EXCEPTION: AsyncTask #1
    java.lang.RuntimeException: An error occured while executing doInBackground()
            ......
     Caused by: java.lang.NullPointerException

代码如下

public class Login extends Activity implements OnClickListener{

    private EditText user, pass;
    private Button mSubmit, mRegister;

    // Progress Dialog
    private ProgressDialog pDialog;

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

    private static final String LOGIN_URL = "http://10.0.2.2:1234/webservice/login.php";

    private static final String TAG_SUCCESS = "success";
    private static final String TAG_MESSAGE = "message";

    @Override
    protected void onCreate(Bundle savedInstanceState) {

        // TODO Auto-generated method stub
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_login);

        //setup input fields
        user = (EditText)findViewById(R.id.username);
        pass = (EditText)findViewById(R.id.password);

        //setup buttons
        mSubmit = (Button)findViewById(R.id.login);
        mRegister = (Button)findViewById(R.id.register);

        //register listeners
        mSubmit.setOnClickListener(this);
        mRegister.setOnClickListener(this);

    }
    @Override
    public void onPause(){

        super.onPause();
        if(pDialog != null)
            pDialog.dismiss();
    }
    @Override
    protected void onStop() {

        super.onStop();

        if (pDialog != null) {
            pDialog.dismiss();
            pDialog = null;
        }

    }

    @Override
    public void onClick(View v) {
        // TODO Auto-generated method stub
        switch (v.getId()) {
            case R.id.login:
                new AttemptLogin().execute("username", "password");
                break;
            case R.id.register:
                Intent i = new Intent(this, Register.class);
                startActivity(i);
                break;

            default:
                break;
        }

    }

   class AttemptLogin extends AsyncTask<String, String, String> {

    boolean failure;

    @Override
    protected void onPreExecute() {
        super.onPreExecute();
        pDialog = new ProgressDialog(Login.this);
        pDialog.setMessage("Attempting login...");
        pDialog.setIndeterminate(false);
        pDialog.setCancelable(true);
        pDialog.show();
    }

    @Override
    protected String doInBackground(String... args) {

        int success;
        String username = args[0];
        String password = args[1];


        try {
            // Building Parameters
            List<NameValuePair> params = new ArrayList<NameValuePair>();
            params.add(new BasicNameValuePair("name", username));
            params.add(new BasicNameValuePair("password", password));

            Log.d("request!", "starting");
            // getting product details by making HTTP request
            JSONObject json = jsonParser.makeHttpRequest(
                    LOGIN_URL, params);

            // check your log for json response
            Log.d("Login attempt", json.toString());

            // json success tag
            success = json.getInt(TAG_SUCCESS);
            if (success == 1) {
                failure = false;
                Log.d("Login Successful!", json.toString());

            }else{
                failure = true;
                Log.d("Login Failure!", json.getString(TAG_MESSAGE));
            }
            return json.getString(TAG_MESSAGE);

        } catch (JSONException e) {
            e.printStackTrace();
        }

        return null;

    }

    protected void onPostExecute(String file_url) {
        // dismiss the dialog once product deleted
        pDialog.dismiss();
        if (file_url != null){
            Toast.makeText(Login.this, file_url, Toast.LENGTH_LONG).show();
        }


        if (failure == false) {
            Intent i = new Intent(Login.this, ReadComment.class);
           finish();
            Login.this.startActivity(i);
        }

    }
}
}

用@Daniel更新我的代码后，我在logcat中获得了以下内容。

07-01 14:28:35.969  12758-12876/com.zaid.sling.mysqltest E/AndroidRuntime﹕ FATAL EXCEPTION: AsyncTask #1
    java.lang.RuntimeException: An error occured while executing doInBackground()
            at android.os.AsyncTask$3.done(AsyncTask.java:299)
            ......
     Caused by: java.lang.NullPointerException
            at com.zaid.sling.mysqltest.Login$AttemptLogin.doInBackground(Login.java:143)

Answer 1

这是错误

 new AttemptLogin().execute();

这是错误的。您需要在此处传递用户名和密码。

 new AttemptLogin().execute("user_name", "password");

您收到ArrayIndexOutOfBoundsException错误。因为没有args传递给AsyncTask但是你试着像这样阅读

String username = args[0];
        String password = args[1];

所以你需要将值传递给AsyncTask。

Answer 2

您可能缺少必需的参数作为数组传递。使用以下：

new AttemptLogin().execute(your_string_array);

例如，请参阅AsyncTask_Example。

AndroidRuntime：FATAL EXCEPTION：AsyncTask＃1

2 个答案: