java - 我如何知道是什么引发了异常？

Question

首先我想说，我通常知道如何找到异常。但我遇到了一种情况，stackstrace 不显示我的任何类，而只显示库类。

我尝试调试代码但没有成功。

这是堆栈跟踪

E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.app.ys571.realdeal, PID: 11175
java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.Class java.lang.Object.getClass()' on a null object reference
    at android.support.v4.app.BackStackRecord.doAddOp(BackStackRecord.java:396)
    at android.support.v4.app.BackStackRecord.add(BackStackRecord.java:391)
    at android.support.v4.app.FragmentPagerAdapter.instantiateItem(FragmentPagerAdapter.java:107)
    at android.support.v4.view.ViewPager.addNewItem(ViewPager.java:1010)
    at android.support.v4.view.ViewPager.populate(ViewPager.java:1224)
    at android.support.v4.view.ViewPager.populate(ViewPager.java:1092)
    at android.support.v4.view.ViewPager.onMeasure(ViewPager.java:1622)
    at android.view.View.measure(View.java:23169)
    at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:6749)
    at android.widget.LinearLayout.measureChildBeforeLayout(LinearLayout.java:1535)
    at android.widget.LinearLayout.measureVertical(LinearLayout.java:825)
    at android.widget.LinearLayout.onMeasure(LinearLayout.java:704)
    at android.view.View.measure(View.java:23169)
    at android.support.v4.widget.DrawerLayout.onMeasure(DrawerLayout.java:1119)
    at android.view.View.measure(View.java:23169)
    at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:6749)
    at android.widget.FrameLayout.onMeasure(FrameLayout.java:185)
    at android.support.v7.widget.ContentFrameLayout.onMeasure(ContentFrameLayout.java:143)
    at android.view.View.measure(View.java:23169)
    at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:6749)
    at android.widget.LinearLayout.measureChildBeforeLayout(LinearLayout.java:1535)
    at android.widget.LinearLayout.measureVertical(LinearLayout.java:825)
    at android.widget.LinearLayout.onMeasure(LinearLayout.java:704)
    at android.view.View.measure(View.java:23169)
    at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:6749)
    at android.widget.FrameLayout.onMeasure(FrameLayout.java:185)
    at android.view.View.measure(View.java:23169)
    at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:6749)
    at android.widget.LinearLayout.measureChildBeforeLayout(LinearLayout.java:1535)
    at android.widget.LinearLayout.measureVertical(LinearLayout.java:825)
    at android.widget.LinearLayout.onMeasure(LinearLayout.java:704)
    at android.view.View.measure(View.java:23169)
    at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:6749)
    at android.widget.FrameLayout.onMeasure(FrameLayout.java:185)
    at com.android.internal.policy.DecorView.onMeasure(DecorView.java:716)
    at android.view.View.measure(View.java:23169)
    at android.view.ViewRootImpl.performMeasure(ViewRootImpl.java:2718)
    at android.view.ViewRootImpl.measureHierarchy(ViewRootImpl.java:1572)
    at android.view.ViewRootImpl.performTraversals(ViewRootImpl.java:1855)
    at android.view.ViewRootImpl.doTraversal(ViewRootImpl.java:1460)
    at android.view.ViewRootImpl$TraversalRunnable.run(ViewRootImpl.java:7183)
    at android.view.Choreographer$CallbackRecord.run(Choreographer.java:949)
    at android.view.Choreographer.doCallbacks(Choreographer.java:761)
    at android.view.Choreographer.doFrame(Choreographer.java:696)
    at android.view.Choreographer$FrameDisplayEventReceiver.run(Choreographer.java:935)
    at android.os.Handler.handleCallback(Handler.java:873)
    at android.os.Handler.dispatchMessage(Handler.java:99)
    at android.os.Looper.loop(Looper.java:193)
    at android.app.ActivityThread.main(ActivityThread.java:6669)
    at java.lang.reflect.Method.invoke(Native Method)
    at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:493)
    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:858)

这是当我尝试使用抽屉导航从主要 Activity 移动到另一个 Activity 时的堆栈跟踪。它可能在新 Activity onResume 之后终止。我无法确切知道从何而来。

谢谢!

Answer 1

看起来这与ViewPager有关。我假设在您的新 Activity 中您有一个 ViewPager 并且我猜测它没有正确实例化。查看this question这似乎有同样的问题并提供了一些解决方案。