如何登录facebook android sdk 3.15.0

我正在尝试facebook sdk 3.15.0。我只想登录facebook。我读文件。当我运行我的项目时，我就崩溃了。但我不明白我的错误在哪里。请帮帮我

错误：

 07-09 22:47:28.472: E/AndroidRuntime(1404):    at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2230)
07-09 22:52:23.411: E/AndroidRuntime(1578): FATAL EXCEPTION: main
07-09 22:52:23.411: E/AndroidRuntime(1578): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.fbapps/com.example.fbapps.MainActivity}: java.lang.NullPointerException: Argument 'applicationId' cannot be null
07-09 22:52:23.411: E/AndroidRuntime(1578):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2180)
07-09 22:52:23.411: E/AndroidRuntime(1578):     at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2230)
07-09 22:52:23.411: E/AndroidRuntime(1578):     at android.app.ActivityThread.access$600(ActivityThread.java:141)
07-09 22:52:23.411: E/AndroidRuntime(1578):     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1234)
07-09 22:52:23.411: E/AndroidRuntime(1578): Caused by: java.lang.NullPointerException: Argument 'applicationId' cannot be null

主要活动：

public class MainActivity extends Activity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        // start Facebook Login
        Session.openActiveSession(this, true, new Session.StatusCallback() {

            // callback when session changes state
            @Override
            public void call(Session session, SessionState state,
                    Exception exception) {

                if (session.isOpened()) {

                    Request.newMeRequest(session,
                            new Request.GraphUserCallback() {

                                // callback after Graph API response with user
                                // object
                                @Override
                                public void onCompleted(GraphUser user,
                                        Response response) {

                                    if (user != null) {
                                        TextView welcome = (TextView) findViewById(R.id.welcome);
                                        welcome.setText("Hello "
                                                + user.getName() + "!");
                                    }

                                }
                            }).executeAsync();
                }

            }
        });

    }

    @Override
    public void onActivityResult(int requestCode, int resultCode, Intent data) {
        super.onActivityResult(requestCode, resultCode, data);
        Session.getActiveSession().onActivityResult(this, requestCode,
                resultCode, data);
    }

AndroidManifest：

我将此代码添加到AndroidManifest中

 <uses-permission android:name="android.permission.INTERNET"/> 
 <meta-data android:value="@string/app_id" android:name="com.facebook.sdk.ApplicationId"/>
  <activity android:label="@string/app_id" android:name="com.facebook.LoginActivity"></activity>

---

几天前我遇到了这个错误。我怀疑在您的案例中，问题出在AndroidManifest文件中

活动标记和元数据标记应位于

标记下，权限应位于

标记下

<manifest... >
    <application>
        <meta-data android:value="@string/app_id" android:name="com.facebook.sdk.ApplicationId"/>
        <activity android:label="@string/app_id" android:name="com.facebook.LoginActivity"></activity>
    </application>
    <uses-permission android:name="android.permission.INTERNET"/> 
</manifest>