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我正在尝试在我已经存在RecyclerView的具有标题但不具有粘性的标题中实现粘性标题。SuperSLiM看起来很有希望，但我无法将该库集成到我现有的代码中。源代码后面的示例运行得很好，我已经尝试适应它并遵循SuperSLiM wiki上的步骤。

我RecyclerView的最初是空的。我遇到的问题是当我第一次将项目添加到我的适配器并调用Adapter.notifyItemChanged()这些项目时。完成此操作后，我会陷入LayoutManager.onItemsUpdated(). 该方法如下所示：

public void onItemsUpdated(RecyclerView recyclerView, int positionStart, int itemCount)
{
    super.onItemsUpdated(recyclerView, positionStart, itemCount);
    View first = this.getChildAt(0);                        // null
    View last = this.getChildAt(this.getChildCount() - 1);  // null
    if(positionStart + itemCount > this.getPosition(first)) // NullPointerException
    {
        if(positionStart <= this.getPosition(last))
        {
            this.requestLayout();
        }

    }
}

在这里，两者都first变成last，null因此 aNullPointerException被抛出在下面的行中。请注意，onItemsUpdated() 在示例 app 中未调用，因此此处不会发生此错误。我不知道为什么；Adapter.notifyItemChanged()在示例应用程序中也调用了。

可能是什么问题？

我的片段类：

请注意，在下面的代码中切换回正常状态RecyclerView.LayoutManager会使一切正常工作。

public class MyFragment extends Fragment
{
    private MyRecyclerView      mRecyclerView;
    private MyAdapter           mAdapter;

//  private RecyclerView.LayoutManager      mLayoutManager; // Normal RecyclerView.LayoutManager working just fine
    private LayoutManager                   mLayoutManager; // SuperSLiM LayoutManager crashing

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState)
    {
        View rootView = inflater.inflate(R.layout.my_fragment, container, false);
        MyActivity myActivity = (MyActivity) rootView.getContext();

        mRecyclerView = (MyRecyclerView) rootView.findViewById(R.id.my_recyclerview);

//      mLayoutManager = new LinearLayoutManager(myActivity); // Normal RecyclerView.LayoutManager
        mLayoutManager = new LayoutManager(myActivity);       // SuperSLiM LayoutManager
        mAdapter = new MyAdapter(myActivity);

        mRecyclerView.setLayoutManager(mLayoutManager);
        mRecyclerView.setAdapter(mAdapter);

        myActivity.onShoppingListCreated();
        return rootView;
    }

    public void onDataSetChanged()
    {
        if (mAdapter == null)
        {
            return;
        }
        mAdapter.notifyDataSetChanged();
    }

    // This is called multiple times after a button press at some point.
    // Thereafter, if it is the SuperSLiM LayoutManager that is in play,
    // the error explained above occurs.
    public void onItemChanged(int position)
    {
        if (mAdapter == null)
        {
            return;
        }
        mAdapter.notifyItemChanged(position);
    }
}

崩溃时的堆栈跟踪：

java.lang.NullPointerException: Attempt to invoke virtual method 'android.view.ViewGroup$LayoutParams android.view.View.getLayoutParams()' on a null object reference
            at android.support.v7.widget.RecyclerView$LayoutManager.getPosition(RecyclerView.java:6097)
            at com.tonicartos.superslim.LayoutManager.onItemsUpdated(LayoutManager.java:542)
            at android.support.v7.widget.RecyclerView$5.dispatchUpdate(RecyclerView.java:665)
            at android.support.v7.widget.RecyclerView$5.onDispatchSecondPass(RecyclerView.java:675)
            at android.support.v7.widget.AdapterHelper.consumeUpdatesInOnePass(AdapterHelper.java:547)
            at android.support.v7.widget.RecyclerView.processAdapterUpdatesAndSetAnimationFlags(RecyclerView.java:2530)
            at android.support.v7.widget.RecyclerView.onMeasure(RecyclerView.java:2318)
            at android.view.View.measure(View.java:17547)
            at android.widget.LinearLayout.measureVertical(LinearLayout.java:875)
            at android.widget.LinearLayout.onMeasure(LinearLayout.java:613)
            at android.view.View.measure(View.java:17547)
            at android.support.v4.view.ViewPager.onMeasure(ViewPager.java:1488)
            at android.view.View.measure(View.java:17547)
            at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5535)
            at android.widget.LinearLayout.measureChildBeforeLayout(LinearLayout.java:1436)
            at android.widget.LinearLayout.measureVertical(LinearLayout.java:722)
            at android.widget.LinearLayout.onMeasure(LinearLayout.java:613)
            at android.view.View.measure(View.java:17547)
            at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5535)
            at android.widget.FrameLayout.onMeasure(FrameLayout.java:436)
            at android.view.View.measure(View.java:17547)
            at android.widget.RelativeLayout.measureChildHorizontal(RelativeLayout.java:727)
            at android.widget.RelativeLayout.onMeasure(RelativeLayout.java:463)
            at android.view.View.measure(View.java:17547)
            at android.support.v4.widget.DrawerLayout.onMeasure(DrawerLayout.java:868)
            at android.view.View.measure(View.java:17547)
            at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5535)
            at android.widget.FrameLayout.onMeasure(FrameLayout.java:436)
            at android.support.v7.internal.widget.ContentFrameLayout.onMeasure(ContentFrameLayout.java:124)
            at android.view.View.measure(View.java:17547)
            at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5535)
            at android.widget.LinearLayout.measureChildBeforeLayout(LinearLayout.java:1436)
            at android.widget.LinearLayout.measureVertical(LinearLayout.java:722)
            at android.widget.LinearLayout.onMeasure(LinearLayout.java:613)
            at android.view.View.measure(View.java:17547)
            at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5535)
            at android.widget.FrameLayout.onMeasure(FrameLayout.java:436)
            at android.view.View.measure(View.java:17547)
            at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5535)
            at android.widget.LinearLayout.measureChildBeforeLayout(LinearLayout.java:1436)
            at android.widget.LinearLayout.measureVertical(LinearLayout.java:722)
            at android.widget.LinearLayout.onMeasure(LinearLayout.java:613)
            at android.view.View.measure(View.java:17547)
            at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5535)
            at android.widget.FrameLayout.onMeasure(FrameLayout.java:436)
            at com.android.internal.policy.impl.PhoneWindow$DecorView.onMeasure(PhoneWindow.java:2615)
            at android.view.View.measure(View.java:17547)
            at android.view.ViewRootImpl.performMeasure(ViewRootImpl.java:2015)
            at android.view.ViewRootImpl.measureHierarchy(ViewRootImpl.java:1173)
            at android.view.ViewRootImpl.performTraversals(ViewRootImpl.java:1379)
            at android.view.ViewRootImpl.doTraversal(ViewRootImpl.java:1061)
            at android.view.ViewRootImpl$TraversalRunnable.run(ViewRootImpl.java:5885)
            at android.view.Choreographer$CallbackRecord.run(Choreographer.java:767)
            at android.view.Choreographer.doCallbacks(Choreographer.java:580)
            at android.view.Choreographer.doFrame(Choreographer.java:550)
            at android.view.Choreographer$FrameDisplayEventRe
4

2 回答 2

0

I had to do something similar these days, I used this library: https://github.com/timehop/sticky-headers-recyclerview

Its pretty easy if you are used to RecyclerViews adapters.

于 2015-10-06T20:13:45.283 回答
0

将此行添加到onBindViewHolder方法的末尾：

 //configuring sticky headers
    final LayoutManager.LayoutParams lp = LayoutManager.LayoutParams.from(holder.itemView.getLayoutParams());
    lp.setSlm(LinearSLM.ID);
    lp.setFirstPosition(getHeaderPosition(position));
    holder.itemView.setLayoutParams(lp);

getHeaderPosition方法返回每个项目的标题位置

于 2016-12-03T10:48:16.093 回答