我似乎无法通过我的 android 应用程序连接到远程服务器答案

【问题标题】：I can`t seem to connect to a remote server through my android application我似乎无法通过我的 android 应用程序连接到远程服务器
【发布时间】：2014-02-04 16:08:17
【问题描述】：

我在android studio中做了一个登录和注册系统。每当我启动应用程序并登录或向数据库添加新用户时，我都会收到此错误：

java.lang.RuntimeException：执行doInBackground()时出错

代码如下：

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

private ProgressDialog pDialog;


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) {

    super.onCreate(savedInstanceState);
    setContentView(R.layout.login);


    user = (EditText) findViewById(R.id.username);
    pass = (EditText) findViewById(R.id.password);


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


    mSubmit.setOnClickListener(this);
    mRegister.setOnClickListener(this);

}

@Override
public void onClick(View v) {

    switch (v.getId()) {
    case R.id.login:
        new AttemptLogin().execute();
        break;
    case R.id.register:
        Intent i = new Intent(this, Register.class);
        startActivity(i);
        break;

    default:
        break;
    }
}

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

    @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 = user.getText().toString();
        String password = pass.getText().toString();
        try {

            List<NameValuePair> params = new ArrayList<NameValuePair>();
            params.add(new BasicNameValuePair("username", username));
            params.add(new BasicNameValuePair("password", password));

            Log.d("request!", "starting");

            JSONObject json = jsonParser.makeHttpRequest(LOGIN_URL, "POST",
                    params);

            Log.d("Login attempt", json.toString());


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

                SharedPreferences sp = PreferenceManager
                        .getDefaultSharedPreferences(Login.this);
                Editor edit = sp.edit();
                edit.putString("username", username);
                edit.commit();

                Intent i = new Intent(Login.this, ReadComments.class);
                finish();
                startActivity(i);
                return json.getString(TAG_MESSAGE);
            } else {
                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) {

        pDialog.dismiss();
        if (file_url != null) {
            Toast.makeText(Login.this, file_url, Toast.LENGTH_LONG).show();
        }

    }

}

}

这里是日志：

在此处输入代码 02-04 16:51:58.079 12363-12496/com.example.app E/AndroidRuntime：致命异常：AsyncTask #1 java.lang.RuntimeException：执行 doInBackground() 时发生错误在 android.os.AsyncTask$3.done(AsyncTask.java:299) 在 java.util.concurrent.FutureTask$Sync.innerSetException(FutureTask.java:273) 在 java.util.concurrent.FutureTask.setException(FutureTask.java:124) 在 java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:307) 在 java.util.concurrent.FutureTask.run(FutureTask.java:137) 在 android.os.AsyncTask$SerialExecutor$1.run(AsyncTask.java:230) 在 java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1076) 在 java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:569) 在 java.lang.Thread.run(Thread.java:856) 引起：java.lang.NullPointerException 在 com.example.app.Login$AttemptLogin.doInBackground(Login.java:124) 在 com.example.app.Login$AttemptLogin.doInBackground(Login.java:93) 在 android.os.AsyncTask$2.call(AsyncTask.java:287) 在 java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:305) 在 java.util.concurrent.FutureTask.run(FutureTask.java:137) 在 android.os.AsyncTask$SerialExecutor$1.run(AsyncTask.java:230) 在 java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1076) 在 java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:569) 在 java.lang.Thread.run(Thread.java:856)

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

// Progress Dialog
private ProgressDialog pDialog;

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



// testing on Emulator:
private static final String LOGIN_URL = "http://www.skloink.com//ugur/login.php";


// JSON element ids from repsonse of php script:
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.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 onClick(View v) {
    // TODO Auto-generated method stub
    switch (v.getId()) {
        case R.id.login:
            new AttemptLogin().execute();
            break;
        case R.id.register:
            Intent i = new Intent(this, Register.class);
            startActivity(i);
            break;

        default:
            break;
    }
}

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

    @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) {
        // TODO Auto-generated method stub
        // Check for success tag
        int success;
        String username = user.getText().toString();
        String password = pass.getText().toString();
        try {
            // Building Parameters
            List<NameValuePair> params = new ArrayList<NameValuePair>();
            params.add(new BasicNameValuePair("username", username));
            params.add(new BasicNameValuePair("password", password));

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

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

            // json success tag
            success = json.getInt(TAG_SUCCESS);
            if (success == 1) {
                Log.d("Login Successful!", json.toString());
                // save user data
                SharedPreferences sp = PreferenceManager
                        .getDefaultSharedPreferences(Login.this);
                Editor edit = sp.edit();
                edit.putString("username", username);
                edit.commit();

                Intent i = new Intent(Login.this, ReadComments.class);
                finish();
                startActivity(i);
                return json.getString(TAG_MESSAGE);
            } else {
                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();
        }

    }

}

}

【问题讨论】：

您的问题实际上在这里：com.example.app.Login$AttemptLogin.doInBackground(Login.java:124) at com.example.app.Login$AttemptLogin.doInBackground(Login.java:93 ) - 你在哪里获得 NPE。
但这意味着什么？它无法连接到我的服务器吗？
基本上 NPE 或 NullPointerException 意味着您正在尝试使用不存在或尚未初始化的东西。您能否在 Login.java 的第 93-124 行附近发布代码部分。还是更好，全部？
我在上面添加了 login.java。
只是出于好奇，这部分是否曾经工作过： Intent i = new Intent(Login.this, ReadComments.class);结束（）;开始活动（一）；返回 json.getString(TAG_MESSAGE);? - 看起来真的不应该。您正在设置要运行的 Intent，然后“关闭”父活动，然后再尝试启动另一个活动，同时从刚刚关闭的父活动返回：S

标签： java android mysql database-connection remote-server

【解决方案1】：

我试过这种方式，这里使用回调的原因是为了完成当前的活动。并且函数 startLogin(),in post execute 是一个函数，您可以在其中执行其他工作，例如保存在数据库或其他任务中，并且不要忘记在 startLogin 函数中做一件事是关闭进度条，如 progressDialog.dismiss(); 希望这会有所帮助:)。

private void authenticate(String phoneNumber, String countryCode) {

        ServerVerify verify = new ServerVerify(this,new TaskCallback() {

            @Override
            public void done() {
                finish();

            }
        });
        verify.execute("");
        progressDialog = new ProgressDialog(this);
        progressDialog.setMessage("Registering.....");
        progressDialog.show();
    }
    public static class ServerVerify extends  AsyncTask<Object, Object, Object>{
        Context context;
        private TaskCallback mCallback;
        private ServerVerify(Context appContext , TaskCallback callback) {
            context = appContext.getApplicationContext();
            mCallback = callback;

        }
        @Override
        protected Object doInBackground(Object... param) {
            DefaultHttpClient client = new DefaultHttpClient();
            HttpPost post = new HttpPost(url);

            List<NameValuePair> nameValuePairs = new ArrayList<NameValuePair>(4);
            nameValuePairs.add(new BasicNameValuePair(HTTPConstants.PHONE_NUMBER , phoneNo));

            nameValuePairs.add(new BasicNameValuePair(HTTPConstants.OS_VERSION, version));
            try {
                post.setEntity(new UrlEncodedFormEntity(nameValuePairs));
            }  catch (UnsupportedEncodingException e) {
                Log.e("UnsupportedEncodingException", "could not load url while registering user");
            }
            HttpResponse response = null;
            try {
                response =  client.execute(post);
            } catch (ClientProtocolException e) {
                Log.e("ClientProtocolException", "Error while registering user");
            } catch (IOException e) {   
                Log.e("IOException", "Error while registering user");
            }
            return response;
        }
        @Override
        protected void onProgressUpdate(Object... values) {
            super.onProgressUpdate(values);
        }
        @Override
        protected void onPostExecute(Object result) {
            responseJson = Utils.readResponse((HttpResponse)result);
            try {
                startLogin(context);
                mCallback.done();
            } catch (JSONException e) {
                Log.e("Json Exception", "Error in reading json response while registering User");
            }
        }


    }

【讨论】：