尝试在Android中为Facebook创建登录按钮时,我收到以下无法解释的错误:
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中的代码如下所示:
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
}
如果您认为这些文件可能是错误的来源,我也可以发布Android清单XML和登录按钮XML。
这是android清单文件:
<?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>
此外,这是我的登录按钮布局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>
此外,这是我的活动主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>
答案 0 :(得分:1)
我认为这一行是问题
setContentView(R.layout.login_button);
避免多次使用setContentView,可以使用片段代替。 如果您不想使用片段,可以尝试以下方法。
mainActivity = getLayoutInflater().inflate(R.layout.activity_main, null);
loginButtonLayout = getLayoutInflater().inflate(R.layout.login_button, null);
首先设置您的活动布局如下:
setContentView(mainActivity);
然后在if语句中使用:
setContentView(loginButtonLayout);
您的代码应如下所示:
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
}
}
}
}