我使用支持包中的RecyclerView遇到了一个非常奇怪的问题。
我RecyclerView内有ViewPager。 ViewPager显示RecyclerView时，应用程序崩溃并显示以下堆栈跟踪：
java.lang.NullPointerException
at android.support.v7.widget.RecyclerView.clearOldPositions(RecyclerView.java:2378)
at android.support.v7.widget.RecyclerView.dispatchLayout(RecyclerView.java:1968)
at android.support.v7.widget.RecyclerView.onLayout(RecyclerView.java:2237)
at android.view.View.layout(View.java:14817)
at android.view.ViewGroup.layout(ViewGroup.java:4631)
at android.widget.LinearLayout.setChildFrame(LinearLayout.java:1671)
at android.widget.LinearLayout.layoutVertical(LinearLayout.java:1525)
at android.widget.LinearLayout.onLayout(LinearLayout.java:1434)
at android.view.View.layout(View.java:14817)
at android.view.ViewGroup.layout(ViewGroup.java:4631)
at android.widget.FrameLayout.layoutChildren(FrameLayout.java:453)
at android.widget.FrameLayout.onLayout(FrameLayout.java:388)
at android.widget.ScrollView.onLayout(ScrollView.java:1468)
at android.view.View.layout(View.java:14817)
at android.view.ViewGroup.layout(ViewGroup.java:4631)
at android.widget.LinearLayout.setChildFrame(LinearLayout.java:1671)
at android.widget.LinearLayout.layoutVertical(LinearLayout.java:1525)
at android.widget.LinearLayout.onLayout(LinearLayout.java:1434)
at android.view.View.layout(View.java:14817)
at android.view.ViewGroup.layout(ViewGroup.java:4631)
at android.widget.FrameLayout.layoutChildren(FrameLayout.java:453)
at android.widget.FrameLayout.onLayout(FrameLayout.java:388)
at android.view.View.layout(View.java:14817)
at android.view.ViewGroup.layout(ViewGroup.java:4631)
at android.support.v4.view.ViewPager.onLayout(ViewPager.java:1594)
at android.view.View.layout(View.java:14817)
at android.view.ViewGroup.layout(ViewGroup.java:4631)
at android.widget.LinearLayout.setChildFrame(LinearLayout.java:1671)
at android.widget.LinearLayout.layoutVertical(LinearLayout.java:1525)
at android.widget.LinearLayout.onLayout(LinearLayout.java:1434)
at android.view.View.layout(View.java:14817)
at android.view.ViewGroup.layout(ViewGroup.java:4631)
at android.widget.RelativeLayout.onLayout(RelativeLayout.java:1055)
at android.view.View.layout(View.java:14817)
at android.view.ViewGroup.layout(ViewGroup.java:4631)
at android.widget.RelativeLayout.onLayout(RelativeLayout.java:1055)
at android.view.View.layout(View.java:14817)
at android.view.ViewGroup.layout(ViewGroup.java:4631)
at android.support.v4.widget.DrawerLayout.onLayout(DrawerLayout.java:890)
at android.view.View.layout(View.java:14817)
at android.view.ViewGroup.layout(ViewGroup.java:4631)
at android.widget.FrameLayout.layoutChildren(FrameLayout.java:453)
at android.widget.FrameLayout.onLayout(FrameLayout.java:388)
at android.view.View.layout(View.java:14817)
at android.view.ViewGroup.layout(ViewGroup.java:4631)
at android.view.ViewRootImpl.performLayout(ViewRootImpl.java:1987)
at android.view.ViewRootImpl.performTraversals(ViewRootImpl.java:1744)
at android.view.ViewRootImpl.doTraversal(ViewRootImpl.java:1000)
at android.view.ViewRootImpl$TraversalRunnable.run(ViewRootImpl.java:5670)
at android.view.Choreographer$CallbackRecord.run(Choreographer.java:761)
at android.view.Choreographer.doCallbacks(Choreographer.java:574)
at android.view.Choreographer.doFrame(Choreographer.java:544)
at android.view.Choreographer$FrameDisplayEventReceiver.run(Choreographer.java:747)
at android.os.Handler.handleCallback(Handler.java:733)
at android.os.Handler.dispatchMessage(Handler.java:95)
at android.os.Looper.loop(Looper.java:136)
at android.app.ActivityThread.main(ActivityThread.java:5017)
at java.lang.reflect.Method.invokeNative(Native Method)
at java.lang.reflect.Method.invoke(Method.java:515)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:779)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:595)
at dalvik.system.NativeStart.main(Native Method)
我在互联网上找不到任何有关此内容的消息来源，所以如果有人在此之前遇到此问题，我们将不胜感激。
一些背景知识：
我正在build.gradle中导入RecyclerView，如下所示：
compile 'com.android.support:recyclerview-v7:+'
我正在将Adapter和LayoutManager设置为RecyclerView构造函数中的RecyclerView，如下所示：
public CategoryParallaxView(Context context)
{
super(context);
init();
}
public CategoryParallaxView(Context context, AttributeSet attrs)
{
super(context, attrs);
init();
}
public CategoryParallaxView(Context context, AttributeSet attrs, int defStyle)
{
super(context, attrs, defStyle);
init();
}
private void init()
{
mLayoutManager = new CategoryParallaxLayoutManager();
setLayoutManager(mLayoutManager);
mCategoryList = new ArrayList<CartCategory>();
mAdapter = new CategoryParallaxAdapter();
setAdapter(mAdapter);
}
当显示RecyclerView时，数据源（mCategoryList）的大小为0，但列表本身不为空。
RecyclerView嵌套在LinearLayout内（它本身嵌套在ScrollView中），并且在宽度和高度上定义了MATCH_PARENT。从一些调试来看，似乎RecyclerView计算的宽度和高度是正确的。
不确定这是否相关，但在我的实现中，Adapter，ViewHolder和LayoutManager子类都是my RecyclerView子类的私有内部类。
答案 0 :(得分：0)
问题是RecyclerView在LayoutManager中RecyclerView显示ViewPager时，正在清除我在init方法中设置的LayoutManager。
我通过在RecyclerView变得可见后立即分配{{1}}来修复此问题。感觉有点hacky，但我找不到任何其他工作。如果有人能找到更好的解决方案，请发帖。