Question

我正在创建一个有登录或登录按钮的应用程序，登录按钮工作正常，但是注册按钮给我一个致命的错误，让AVD停止运行应用程序，这是代码注册活动

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

    // Set up the signup form.
    usernameView = (EditText) findViewById(R.id.username);
    passwordView = (EditText) findViewById(R.id.password);
    passwordAgainView = (EditText) findViewById(R.id.passwordAgain);

    // Set up the submit button click handler
    findViewById(R.id.action_button).setOnClickListener(new View.OnClickListener() {
        public void onClick(View view) {

            // Validate the sign up data
            boolean validationError = false;
            StringBuilder validationErrorMessage =
                    new StringBuilder(getResources().getString(R.string.error_intro));
            if (isEmpty(usernameView)) {
                validationError = true;
                validationErrorMessage.append(getResources().getString(R.string.error_blank_username));
            }
            if (isEmpty(passwordView)) {
                if (validationError) {
                    validationErrorMessage.append(getResources().getString(R.string.error_join));
                }
                validationError = true;
                validationErrorMessage.append(getResources().getString(R.string.error_blank_password));
            }
            if (!isMatching(passwordView, passwordAgainView)) {
                if (validationError) {
                    validationErrorMessage.append(getResources().getString(R.string.error_join));
                }
                validationError = true;
                validationErrorMessage.append(getResources().getString(
                        R.string.error_mismatched_passwords));
            }
            validationErrorMessage.append(getResources().getString(R.string.error_end));

            // If there is a validation error, display the error
            if (validationError) {
                Toast.makeText(SignUpActivity.this, validationErrorMessage.toString(), Toast.LENGTH_LONG)
                        .show();
                return;
            }

            // Set up a progress dialog
            final ProgressDialog dlg = new ProgressDialog(SignUpActivity.this);
            dlg.setTitle("Please wait.");
            dlg.setMessage("Signing up.  Please wait.");
            dlg.show();

            // Set up a new Parse user
            ParseUser user = new ParseUser();
            user.setUsername(usernameView.getText().toString());
            user.setPassword(passwordView.getText().toString());
            // Call the Parse signup method
            user.signUpInBackground(new SignUpCallback() {

                @Override
                public void done(ParseException e) {
                    dlg.dismiss();
                    if (e != null) {
                        // Show the error message
                        Toast.makeText(SignUpActivity.this, e.getMessage(), Toast.LENGTH_LONG).show();
                    } else {
                        // Start an intent for the dispatch activity
                        Intent intent = new Intent(SignUpActivity.this, DispatchActivity.class);
                        intent.addFlags(Intent.FLAG_ACTIVITY_CLEAR_TASK | Intent.FLAG_ACTIVITY_NEW_TASK);
                        startActivity(intent);
                    }
                }
            });
        }
    });
}

private boolean isEmpty(EditText etText) {
    if (etText.getText().toString().trim().length() > 0) {
        return false;
    } else {
        return true;
    }
}

private boolean isMatching(EditText etText1, EditText etText2) {
    if (etText1.getText().toString().equals(etText2.getText().toString())) {
        return true;
    } else {
        return false;
    }
}

这是清单

<uses-permission android:name="android.permission.INTERNET" />
<uses-permission android:name="android.permission.ACCESS_NETWORK_STATE" />

<application

    android:allowBackup="true"
    android:icon="@drawable/ic_launcher"
    android:label="@string/app_name"
    android:theme="@style/AppTheme"
    android:name=".ParseStarter">
    <activity
        android:screenOrientation="portrait"
        android:name=".MainActivity"
        android:label="@string/app_name" >

    </activity>

    <activity android:name=".SignUpOrLogInActivity"

        android:label="@string/app_name">
        <intent-filter>
            <action android:name="android.intent.action.MAIN" />

            <category android:name="android.intent.category.LAUNCHER" />
        </intent-filter>
    </activity >
    <activity android:name=".DispatchActivity"/>
    <activity android:name=".LoginActivity" />
    <activity android:name=".SignUpActivity" />


    <meta-data android:name="com.facebook.sdk.ApplicationId" android:value="@string/facebook_app_id"/>


</application>

这是logCat

Process: com.sebasdeldihotmail.mediocre11, PID: 2020
java.lang.RuntimeException: Unable to start activity ComponentInfo{com.sebasdeldihotmail.mediocre11/com.sebasdeldihotmail.mediocre11.SignUpActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.view.View.setOnClickListener(android.view.View$OnClickListener)' on a null object reference
        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2298)
        at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2360)
        at android.app.ActivityThread.access$800(ActivityThread.java:144)
        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1278)
        at android.os.Handler.dispatchMessage(Handler.java:102)
        at android.os.Looper.loop(Looper.java:135)
        at android.app.ActivityThread.main(ActivityThread.java:5221)
        at java.lang.reflect.Method.invoke(Native Method)
        at java.lang.reflect.Method.invoke(Method.java:372)
        at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:899)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:694)
 Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.view.View.setOnClickListener(android.view.View$OnClickListener)' on a null object reference
        at com.sebasdeldihotmail.mediocre11.SignUpActivity.onCreate(SignUpActivity.java:35)
        at android.app.Activity.performCreate(Activity.java:5933)
        at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1105)
        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2251)

at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2360)

at android.app.ActivityThread.access$800(ActivityThread.java:144)

at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1278)
            at android.os.Handler.dispatchMessage(Handler.java:102)
            at android.os.Looper.loop(Looper.java:135)
            at android.app.ActivityThread.main(ActivityThread.java:5221)
            at java.lang.reflect.Method.invoke(Native Method)
            at java.lang.reflect.Method.invoke(Method.java:372)
            at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:899)
            at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:694)

这是具有调用注册活动按钮的类的代码

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

    // Log in button click handler
    ((Button) findViewById(R.id.login)).setOnClickListener(new View.OnClickListener() {
        public void onClick(View v) {
            // Starts an intent of the log in activity
            startActivity(new Intent(SignUpOrLogInActivity.this, LoginActivity.class));
        }
    });

    // Sign up button click handler
    ((Button) findViewById(R.id.signup)).setOnClickListener(new View.OnClickListener() {
        public void onClick(View v) {
            // Starts an intent for the sign up activity
            startActivity(new Intent(SignUpOrLogInActivity.this, SignUpActivity.class));
        }
    });
}

}

这是注册的布局

   <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="vertical" android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:background="#67AAE4">


    <EditText
        android:id="@+id/username"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:hint="@string/prompt_username"
        android:inputType="textEmailAddress"
        android:maxLines="1"
        android:singleLine="true" />

    <EditText
        android:id="@+id/password"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:hint="@string/prompt_password"
        android:inputType="textPassword"
        android:maxLines="1"
        android:singleLine="true" />

    <EditText
        android:id="@+id/passwordAgain"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:hint="@string/prompt_password_again"
        android:imeActionLabel="@string/action_sign_in_short"
        android:imeOptions="actionUnspecified"
        android:inputType="textPassword"
        android:maxLines="1"
        android:singleLine="true" />



</LinearLayout>

这是注册按钮出现的布局

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:orientation="vertical" android:layout_width="match_parent"
android:layout_height="match_parent"
android:background="#67AAE4">

<Button
    android:id="@+id/signup"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:text="Sign Up"/>

<Button
    android:id="@+id/login"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:text="Login"/>


<com.facebook.widget.LoginButton
    android:id="@+id/authButton"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_gravity="center_horizontal"
    android:layout_marginTop="30dp"
    />

非常感谢您阅读:)。

Answer 1

java.lang.NullPointerException: Attempt to invoke virtual method 'void android.view.View.setOnClickListener(android.view.View$OnClickListener)' on a null object reference

您的signup_activity.xml布局似乎没有ID为action_button的视图，findViewById()返回null。

Answer 2

找不到将onClickListener添加到r.id.action_button的视图，因此发现NullPointerException。

因此，请确保您在当前视图中signup_activity.xml。

更多

要使'onCreate'方法不那么厚实，并且为了避免再次发生这种情况，请考虑在布局文件android:onClick中的按钮上使用signup_activity.xml。

<Button android:id="@+id/action_button" android:onClick="onSignUpClick" ... />

然后在SignUpActivity.java中添加方法：

public void onSignUpClick(View view) { // add code here instead of creating onClickListener in onCreate... }

如何解决java.lang.RuntimeException：无法启动活动？

2 个答案: