渲染问题：java.lang.NullPointerException 在 android.support。v7.widget.RecyclerView 在 Android Studio 1.1.0

Question

我最近将 android sdk 更新为 api 22 和 android studio 1.1.0。之后，我在 RecyclerView 上遇到渲染问题。这是我得到的

  java.lang.NullPointerException
at android.support.v7.widget.RecyclerView.computeVerticalScrollRange(RecyclerView.java:1216)
at android.view.View.onDrawScrollBars(View.java:12943)
at android.view.View.draw(View.java:15237)
at android.support.v7.widget.RecyclerView.draw(RecyclerView.java:2440)
at android.view.View.draw(View.java:15140)
at android.view.ViewGroup.drawChild_Original(ViewGroup.java:3405)
at android.view.ViewGroup_Delegate.drawChild(ViewGroup_Delegate.java:53)
at android.view.ViewGroup.drawChild(ViewGroup.java:3405)
at android.view.ViewGroup.dispatchDraw(ViewGroup.java:3198)
at android.view.View.draw(View.java:15138)
at android.view.ViewGroup.drawChild_Original(ViewGroup.java:3405)
at android.view.ViewGroup_Delegate.drawChild(ViewGroup_Delegate.java:53)
at android.view.ViewGroup.drawChild(ViewGroup.java:3405)
at android.view.ViewGroup.dispatchDraw(ViewGroup.java:3198)
at android.view.View.draw(View.java:15234)
at android.view.View.draw(View.java:15140)
at android.view.ViewGroup.drawChild_Original(ViewGroup.java:3405)
at android.view.ViewGroup_Delegate.drawChild(ViewGroup_Delegate.java:53)
at android.view.ViewGroup.drawChild(ViewGroup.java:3405)
at android.support.v4.widget.DrawerLayout.drawChild(DrawerLayout.java:1086)
at android.view.ViewGroup.dispatchDraw(ViewGroup.java:3198)
at android.view.View.draw(View.java:15138)
at android.view.ViewGroup.drawChild_Original(ViewGroup.java:3405)
at android.view.ViewGroup_Delegate.drawChild(ViewGroup_Delegate.java:53)
at android.view.ViewGroup.drawChild(ViewGroup.java:3405)
at android.view.ViewGroup.dispatchDraw(ViewGroup.java:3198)
at android.view.View.draw(View.java:15138)
at android.view.ViewGroup.drawChild_Original(ViewGroup.java:3405)
at android.view.ViewGroup_Delegate.drawChild(ViewGroup_Delegate.java:53)
at android.view.ViewGroup.drawChild(ViewGroup.java:3405)
at android.view.ViewGroup.dispatchDraw(ViewGroup.java:3198)
at android.view.View.draw(View.java:15234)
at android.view.View.draw(View.java:15140)
at android.view.ViewGroup.drawChild_Original(ViewGroup.java:3405)
at android.view.ViewGroup_Delegate.drawChild(ViewGroup_Delegate.java:53)
at android.view.ViewGroup.drawChild(ViewGroup.java:3405)
at android.view.ViewGroup.dispatchDraw(ViewGroup.java:3198)
at android.view.View.draw(View.java:15234)

I am getting this exception on xml preview/design, so I am not able to view the xml design.

项目运行良好，没有任何异常。这是我的小部件

 <android.support.v7.widget.RecyclerView
            android:id="@+id/my_recycler_view"
            android:layout_width="match_parent"
            android:layout_height="0dp"
            android:layout_weight="8"
            android:layout_gravity="center"
            android:gravity="center"
            android:scrollbars="vertical"
            android:fadeScrollbars="false"
            />

这是我的代码

    recyclerView= (RecyclerView) findViewById(R.id.my_recycler_view);
    layoutManager=new GridLayoutManager(this,2);
    recyclerView.setLayoutManager(layoutManager);
    recyclerView.setHasFixedSize(true);
    recyclerView.setItemAnimator(new DefaultItemAnimator());

如何解决这个问题？

Answer 1

您只是忘记设置 LayoutManager: https://developer.android.com/reference/android/support/v7/widget/RecyclerView.html#setLayoutManager(android.support.v7.widget.RecyclerView.LayoutManager)

Answer 2

我也遇到过同样的错误。 RecyclerView 的第 1216 行是：

return mLayout.canScrollVertically() ? mLayout.computeVerticalScrollRange(mState) : 0;

mLayout 当时为 null 是问题所在，我不确定为什么它为 null，但看来您必须在 setContentView() 或 inflate() 之后立即在 RecyclerView 上调用 setLayoutManager() .在我尝试访问 RecyclerView 并调用其 setLayoutManager() 之前，我的代码是运行一个后台线程。一旦我更改为以下内容，它就可以工作

即

this.setContentView(R.layout.schedule);
rv = (RecyclerView) this.findViewById(R.id.schedule_listview);
rv.setLayoutManager(new LinearLayoutManager(this));

我还是不太明白为什么要那样做

Answer 3

当我从 RecyclerView 的 xml 文件中取出这一行时，我的问题就解决了：

android:scrollbars="vertical"

我正在使用以下依赖项：

dependencies {
    compile fileTree(dir: 'libs', include: ['*.jar'])
    compile 'com.android.support:appcompat-v7:22.0.0'
    compile 'com.android.support:recyclerview-v7:22.0.0'
    compile 'com.android.support:cardview-v7:22.0.0'
}

编辑：此解决方案的评论员指出了此问题的根源 - 要解决此问题，您只需确保在显示带有滚动条的 RecyclerView 之前设置 RecyclerView 的 LayoutManager 属性设置。

Answer 4

为了防止人们仍然疑惑，您应该通过 SDK 管理器更新到 API 22 的最新 SDK 平台，并通过 SDK 管理器更新支持存储库来更新到最新的回收站视图，并在您的 build.gradle 文件中使用最新版本 (22.0.0)

Answer 5

您无需删除任何行，只需将以下行添加到您的代码中：

recyclerView.setLayoutManager(new LinearLayoutManager(recyclerView.getContext()));

这样RecyclerView的Vertical scrolling就没有问题了

希望对您有所帮助！

Answer 6

我刚刚删除了属性 android:scrollbars="vertical" 一切都会好的

渲染问题：java.lang.NullPointerException 在 android.support。v7.widget.RecyclerView 在 Android Studio 1.1.0

Rendering Problems: java.lang.NullPointerException at android.support.v7.widget.RecyclerView in Android Studio 1.1.0

android

android-studio

android-recyclerview