NullPointerException 发生在 Android 代码片段中 [英] NullPointerException happens in an Android code snippet
问题描述
这是处理会员注册的代码.
Here's the code which deals with member registration.
public class RegisterActivity extends Activity {
private static final String TAG = RegisterActivity.class.getSimpleName();
private Button btnRegister;
private Button btnLinkToLogin;
private EditText inputFullName;
private EditText inputEmail;
private EditText inputPassword;
private ProgressDialog pDialog;
private SessionManager session;
private SQLiteHandler db;
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_register);
inputFullName = (EditText) findViewById(R.id.name);
inputEmail = (EditText) findViewById(R.id.email);
inputPassword = (EditText) findViewById(R.id.password);
btnRegister = (Button) findViewById(R.id.btnRegister);
btnLinkToLogin = (Button) findViewById(R.id.btnLinkToLoginScreen);
// Progress dialog
pDialog = new ProgressDialog(this);
pDialog.setCancelable(false);
// Session manager
session = new SessionManager(getApplicationContext());
// SQLite database handler
db = new SQLiteHandler(getApplicationContext());
// Check if user is already logged in or not
if (session.isLoggedIn()) {
// User is already logged in. Take him to main activity
Intent intent = new Intent(RegisterActivity.this,
MainActivity.class);
startActivity(intent);
finish();
}
// Register Button Click event
btnRegister.setOnClickListener(new View.OnClickListener() {
public void onClick(View view) {
String name = inputFullName.getText().toString();
String email = inputEmail.getText().toString();
String password = inputPassword.getText().toString();
if (!name.isEmpty() && !email.isEmpty() && !password.isEmpty()) {
registerUser(name, email, password);
} else {
Toast.makeText(getApplicationContext(),
"Please enter your details!", Toast.LENGTH_LONG)
.show();
}
}
});
// Link to Login Screen
btnLinkToLogin.setOnClickListener(new View.OnClickListener() {
public void onClick(View view) {
Intent i = new Intent(getApplicationContext(),
LoginActivity.class);
startActivity(i);
finish();
}
});
}
/**
* Function to store user in MySQL database will post params(tag, name,
* email, password) to register url
* */
private void registerUser(final String name, final String email,
final String password) {
// Tag used to cancel the request
String tag_string_req = "req_register";
pDialog.setMessage("Registering ...");
showDialog();
StringRequest strReq = new StringRequest(Method.POST,
AppConfig.URL_REGISTER, new Response.Listener<String>() {
@Override
public void onResponse(String response) {
Log.d(TAG, "Register Response: " + response.toString());
hideDialog();
try {
JSONObject jObj = new JSONObject(response);
boolean error = jObj.getBoolean("error");
if (!error) {
// User successfully stored in MySQL
// Now store the user in sqlite
String uid = jObj.getString("uid");
JSONObject user = jObj.getJSONObject("user");
String name = user.getString("name");
String email = user.getString("email");
String created_at = user
.getString("created_at");
// Inserting row in users table
db.addUser(name, email, uid, created_at);
// Launch login activity
Intent intent = new Intent(
RegisterActivity.this,
LoginActivity.class);
startActivity(intent);
finish();
} else {
// Error occurred in registration. Get the error
// message
String errorMsg = jObj.getString("error_msg");
Toast.makeText(getApplicationContext(),
errorMsg, Toast.LENGTH_LONG).show();
}
} catch (JSONException e) {
e.printStackTrace();
}
}
}, new Response.ErrorListener() {
@Override
public void onErrorResponse(VolleyError error) {
Log.e(TAG, "Registration Error: " + error.getMessage());
Toast.makeText(getApplicationContext(),
error.getMessage(), Toast.LENGTH_LONG).show();
hideDialog();
}
}) {
@Override
protected Map<String, String> getParams() {
// Posting params to register url
Map<String, String> params = new HashMap<String, String>();
params.put("tag", "register");
params.put("name", name);
params.put("email", email);
params.put("password", password);
return params;
}
};
// Adding request to request queue
AppController.getInstance().addToRequestQueue(strReq, tag_string_req);
}
private void showDialog() {
if (!pDialog.isShowing())
pDialog.show();
}
private void hideDialog() {
if (pDialog.isShowing())
pDialog.dismiss();
}
}
当我运行代码时，它抛出一个NullPointerException，显示以下日志.
When I run the code, it throws a NullPointerException, showing the following logs.
07-03 16:13:33.061 24078-24078/com.marshall.gruppo E/AndroidRuntime:致命例外:主进程:com.marshall.gruppo，PID:24078java.lang.NullPointerException在 com.marshall.gruppo.ui.RegisterActivity.registerUser(RegisterActivity.java:184)在 com.marshall.gruppo.ui.RegisterActivity.access$300(RegisterActivity.java:31)在 com.marshall.gruppo.ui.RegisterActivity$1.onClick(RegisterActivity.java:80)在 android.view.View.performClick(View.java:4633)在 android.view.View$PerformClick.run(View.java:19270)在 android.os.Handler.handleCallback(Handler.java:733)在 android.os.Handler.dispatchMessage(Handler.java:95)在 android.os.Looper.loop(Looper.java:146)在 android.app.ActivityThread.main(ActivityThread.java:5602)在 java.lang.reflect.Method.invokeNative(Native Method)在 java.lang.reflect.Method.invoke(Method.java:515)在 com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1283)在 com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1099)在 dalvik.system.NativeStart.main(Native Method)
07-03 16:13:33.061 24078-24078/com.marshall.gruppo E/AndroidRuntime﹕ FATAL EXCEPTION: main Process: com.marshall.gruppo, PID: 24078 java.lang.NullPointerException at com.marshall.gruppo.ui.RegisterActivity.registerUser(RegisterActivity.java:184) at com.marshall.gruppo.ui.RegisterActivity.access$300(RegisterActivity.java:31) at com.marshall.gruppo.ui.RegisterActivity$1.onClick(RegisterActivity.java:80) at android.view.View.performClick(View.java:4633) at android.view.View$PerformClick.run(View.java:19270) at android.os.Handler.handleCallback(Handler.java:733) at android.os.Handler.dispatchMessage(Handler.java:95) at android.os.Looper.loop(Looper.java:146) at android.app.ActivityThread.main(ActivityThread.java:5602) at java.lang.reflect.Method.invokeNative(Native Method) at java.lang.reflect.Method.invoke(Method.java:515) at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1283) at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1099) at dalvik.system.NativeStart.main(Native Method)
根据日志，似乎有问题的片段是:
According to the log, the snippet that seems to have the problem is:
AppController.getInstance().addToRequestQueue(strReq, tag_string_req);
AppController.getInstance().addToRequestQueue(strReq, tag_string_req);
这是 registerUser 方法的最后一行.
Which is the last line of the registerUser method.
你认为问题是什么?如果您需要进一步了解此代码的任何信息，请告诉我.
What do you think the problem is? If there is any information that you should know further about this code, please let me know.
AppController 类如下.
public class AppController extends Application {
public static final String TAG = AppController.class.getSimpleName();
private RequestQueue mRequestQueue;
private static AppController mInstance;
@Override
public void onCreate() {
super.onCreate();
mInstance = this;
}
public static synchronized AppController getInstance() {
return mInstance;
}
public RequestQueue getRequestQueue() {
if (mRequestQueue == null) {
mRequestQueue = Volley.newRequestQueue(getApplicationContext());
}
return mRequestQueue;
}
public <T> void addToRequestQueue(Request<T> req, String tag) {
req.setTag(TextUtils.isEmpty(tag) ? TAG : tag);
getRequestQueue().add(req);
}
public <T> void addToRequestQueue(Request<T> req) {
req.setTag(TAG);
getRequestQueue().add(req);
}
public void cancelPendingRequests(Object tag) {
if (mRequestQueue != null) {
mRequestQueue.cancelAll(tag);
}
}
}
Manifest.xml:
Manifest.xml:
<uses-permission android:name="android.permission.INTERNET" />
<application
android:allowBackup="true"
android:icon="@mipmap/ic_launcher"
android:label="@string/app_name"
android:theme="@style/AppTheme" >
<activity
android:name=".ui.LoginActivity"
android:label="@string/app_name"
android:launchMode="singleTop"
android:windowSoftInputMode="adjustPan" >
<intent-filter>
<action android:name="android.intent.action.MAIN" />
<category android:name="android.intent.category.LAUNCHER" />
</intent-filter>
</activity>
<activity
android:name=".ui.RegisterActivity"
android:label="@string/app_name"
android:launchMode="singleTop"
android:windowSoftInputMode="adjustPan" />
<activity
android:name=".ui.MainActivity"
android:label="@string/app_name"
android:launchMode="singleTop" />
</application>
推荐答案
问题是您没有将应用程序的子类声明到 AndroidManifest.将 android:name="path.to.AppController" 添加到 Application 标记，否则您的 Application 子类不会被实例化并且 mInstance 保持未初始化(默认为 null).这解释了 NPE
the problem is you didn't declare your Subclass of Application to the AndroidManifest. Add android:name="path.to.AppController" to the Application tag, otherwise your subclass of Application is not instantiated and mInstance remains not initialized (null by default). And that explains the NPE
<application
android:name="path.to.AppController"
android:allowBackup="true"
android:icon="@mipmap/ic_launcher"
android:label="@string/app_name"
android:theme="@style/AppTheme" >
这篇关于NullPointerException 发生在 Android 代码片段中的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！
