Android Firebase Facebook登錄上的運行時異常

Question

嘗試在Android中為Facebook創建登錄按鈕時，出現以下無法解釋的錯誤：

java.lang.RuntimeException: Unable to start activity ComponentInfo{cs126.chat/cs126.chay.MainActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.view.View.setOnClickListener(android.view.View$OnClickListener)' on a null object reference

我在Main中的代碼如下所示：

private CallbackManager callbackManager;
private TextView info;
private LoginButton loginButton;
@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    Firebase.setAndroidContext(this);
    if (FirebaseAuth.getInstance().getCurrentUser() == null) {
        FacebookSdk.sdkInitialize(getApplicationContext());          FacebookSdk.setApplicationId(getResources().getString(R.string.facebook_app_id));
        setContentView(R.layout.login_button);
        callbackManager = CallbackManager.Factory.create();
        info = (TextView)findViewById(R.id.info);
        loginButton = (LoginButton)findViewById(R.id.login_button);
        loginButton.registerCallback(callbackManager, new FacebookCallback<LoginResult>() {
            @Override
            public void onSuccess(LoginResult loginResult) {
                // Start app
            }

我也可以發布Android清單XML和登錄按鈕XML，如果你們中的任何人認為這些文件可能是錯誤的根源。

這是android清單文件：

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    package="cs.melochat">

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

    <application
        android:allowBackup="true"
        android:icon="@mipmap/ic_launcher"
        android:label="@string/app_name"
        android:supportsRtl="true"
        android:theme="@style/AppTheme" >
        <activity android:name=".MainActivity" >
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />

                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>

        </activity>
        <activity android:name="com.facebook.FacebookActivity"
            android:theme="@android:style/Theme.Translucent.NoTitleBar"
            android:configChanges="keyboard|keyboardHidden|screenLayout|screenSize|orientation"
            tools:replace="android:theme"
            android:label="@string/app_name" />
        <meta-data
            android:name="com.google.android.gms.version"
            android:value="@integer/google_play_services_version" />
        <meta-data android:name="com.facebook.sdk.ApplicationId"
            android:value="@string/facebook_app_id"/>
    </application>


</manifest>

另外，這是我的登錄按鈕布局XML：

<?xml version="1.0" encoding="utf-8"?>
<!-- sourced from https://code.tutsplus.com/tutorials/quick-tip-add-facebook-login-to-your-android-
app-cms-23837 !-->
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent" android:layout_height="match_parent"
    android:padding="16dp"
    >

    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:id="@+id/info"
        android:layout_alignParentLeft="true"
        android:layout_alignParentTop="true"
        android:textSize="18sp"
        />

    <com.facebook.login.widget.LoginButton
        android:id="@+id/login_button"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_centerInParent="true"
        />

</RelativeLayout>

另外，這是我的活動主要XML：

<?xml version="1.0" encoding="utf-8"?>

<!-- parts of the following code were sourced from this online tutorial:
https://code.tutsplus.com/tutorials/how-to-create-an-android-chat-app-using-firebase-cms-27397 -->

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:id="@+id/activity_main"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:paddingBottom="@dimen/activity_vertical_margin"
    android:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:paddingTop="@dimen/activity_vertical_margin"
    tools:context=".MainActivity">

    <android.support.design.widget.FloatingActionButton
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:clickable="true"
        android:src="@drawable/ic_send_black_24dp"
        android:id="@+id/fab"
        android:tint="@android:color/white"
        android:layout_alignParentBottom="true"
        android:layout_alignParentEnd="true"
        app:fabSize="mini" />

    <android.support.design.widget.TextInputLayout
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_toLeftOf="@id/fab"
        android:layout_alignParentBottom="true"
        android:layout_alignParentStart="true">

        <EditText
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:hint="Input"
            android:id="@+id/input"
            />
    </android.support.design.widget.TextInputLayout>

    <ListView
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:layout_alignParentTop="true"
        android:layout_alignParentStart="true"
        android:layout_above="@id/fab"
        android:dividerHeight="16dp"
        android:divider="@android:color/transparent"
        android:id="@+id/list_of_messages"
        android:layout_marginBottom="16dp"/>
</RelativeLayout>

Answer 1

我認為這是問題所在

  setContentView(R.layout.login_button); 

避免多次使用setContentView，而可以使用片段。 如果您不想處理碎片，可以嘗試跟隨方法。

 mainActivity = getLayoutInflater().inflate(R.layout.activity_main, null);
 loginButtonLayout = getLayoutInflater().inflate(R.layout.login_button, null);

首先像這樣設置活動布局：

setContentView(mainActivity);

然后在您的if語句中使用this：

setContentView(loginButtonLayout);

您的代碼應如下所示：

 protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);

    mainActivity = getLayoutInflater().inflate(R.layout.activity_main, null);
    loginButtonLayout = getLayoutInflater().inflate(R.layout.login_button, null);

    setContentView(mainActivity);
    Firebase.setAndroidContext(this);
    if (FirebaseAuth.getInstance().getCurrentUser() == null) {
        FacebookSdk.sdkInitialize(getApplicationContext());
        FacebookSdk.setApplicationId(getResources().getString(R.string.facebook_app_id));
        setContentView(loginButtonLayout);
        callbackManager = CallbackManager.Factory.create();
        info = (TextView) findViewById(R.id.info);
        loginButton = (LoginButton) findViewById(R.id.login_button);
        loginButton.registerCallback(callbackManager, new FacebookCallback<LoginResult>() {
            @Override
            public void onSuccess(LoginResult loginResult) {
                // Start app
            }
        }
    }
}