android - 检查 (ParseUser.getCurrentUser() != null) 时出现 NullPointerException

Question

我是 Parse.com 的新手，目前正在 Android 中使用 Parse 构建我的第一个项目。我正在尝试复制“Anywall”教程 ( https://www.parse.com/tutorials/anywall-android ) 中显示的登录工作流程，但我绝对无法让它正常工作。

每当我尝试启动应用程序时，它都会给我一个 NullPointerException，我试图在 DispatchActivity 中检查 (ParseUser.getCurrentUser() != null)(代码如下所示):

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

        // Check if there is current user info
        if (ParseUser.getCurrentUser() != null) {
            // Start an intent for the logged in activity
            startActivity(new Intent(this, MainActivity.class));
        } else {
            // Start and intent for the logged out activity
            startActivity(new Intent(this, WelcomeActivity.class));
        }

    }

LogCat 中的堆栈跟踪如下:

07-13 00:34:54.925    6268-6268/com.appzylabs.pratik.groupreceipts W/dalvikvm﹕ threadid=1: thread exiting with uncaught exception (group=0xa6142908)
07-13 00:34:54.925    6268-6268/com.appzylabs.pratik.groupreceipts E/AndroidRuntime﹕ FATAL EXCEPTION: main
    java.lang.RuntimeException: Unable to start activity ComponentInfo{com.appzylabs.pratik.groupreceipts/com.appzylabs.pratik.groupreceipts.DispatchActivity}: java.lang.NullPointerException
            at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2180)
            at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2230)
            at android.app.ActivityThread.access$600(ActivityThread.java:141)
            at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1234)
            at android.os.Handler.dispatchMessage(Handler.java:99)
            at android.os.Looper.loop(Looper.java:137)
            at android.app.ActivityThread.main(ActivityThread.java:5041)
            at java.lang.reflect.Method.invokeNative(Native Method)
            at java.lang.reflect.Method.invoke(Method.java:511)
            at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:793)
            at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:560)
            at dalvik.system.NativeStart.main(Native Method)
     Caused by: java.lang.NullPointerException
            at com.parse.Parse.getParseDir(Parse.java:304)
            at com.parse.ParseObject.getFromDisk(ParseObject.java:667)
            at com.parse.ParseUser$10.then(ParseUser.java:1056)
            at com.parse.ParseUser$10.then(ParseUser.java:1003)
            at bolts.Task$14.run(Task.java:796)
            at bolts.BoltsExecutors$ImmediateExecutor.execute(BoltsExecutors.java:105)
            at bolts.Task.completeAfterTask(Task.java:787)
            at bolts.Task.continueWithTask(Task.java:599)
            at bolts.Task.continueWithTask(Task.java:610)
            at com.parse.ParseUser.getCurrentUserAsync(ParseUser.java:1003)
            at com.parse.ParseUser.access$800(ParseUser.java:26)
            at com.parse.ParseUser$9.then(ParseUser.java:996)
            at com.parse.ParseUser$9.then(ParseUser.java:993)
            at com.parse.TaskQueue.enqueue(TaskQueue.java:61)
            at com.parse.ParseUser.getCurrentUserAsync(ParseUser.java:993)
            at com.parse.ParseUser.getCurrentUser(ParseUser.java:979)
            at com.parse.ParseUser.getCurrentUser(ParseUser.java:966)
            at com.appzylabs.pratik.groupreceipts.DispatchActivity.onCreate(DispatchActivity.java:26)
            at android.app.Activity.performCreate(Activity.java:5104)
            at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1080)
            at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2144)
            at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2230)
            at android.app.ActivityThread.access$600(ActivityThread.java:141)
            at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1234)
            at android.os.Handler.dispatchMessage(Handler.java:99)
            at android.os.Looper.loop(Looper.java:137)
            at android.app.ActivityThread.main(ActivityThread.java:5041)
            at java.lang.reflect.Method.invokeNative(Native Method)
            at java.lang.reflect.Method.invoke(Method.java:511)
            at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:793)
            at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:560)
            at dalvik.system.NativeStart.main(Native Method)

有消息告诉我“ParseUser”没有正确初始化或实例化，但我的应用程序类中已经有以下代码:

public Application() {
    }

    @Override
    public void onCreate() {
        super.onCreate();

        Parse.enableLocalDatastore(this);
        Parse.initialize(this, "XXXX", "YYYY");

   }
}

我在这里做错了什么？我就是想不通。有什么帮助吗？

Answer 1

嗯，我刚刚意识到这个问题。我在一个单独的应用程序类中调用 Parse.initialize() ，如下所示:

public class Application extends android.app.Application {
...
Parse.initialize(this, "XXXX", "YYYY");
...
}

但是，我没有将该类添加到 AndroidManifest.xml 中，因此代码永远不会被执行，Parse 永远不会被初始化，并且 ParseUser 抛出 NullPointerException。一旦我将其添加到我的 list 中，如下所示，它就起作用了:

<application
        android:name="com.appzylabs.pratik.groupreceipts.Application"

抱歉!我希望这对面临同样问题的其他人有用。