Java 在空引用上由于RecyclerView按钮setOnClickListener导致崩溃

我正在使用解决方案作为指南，将页脚按钮添加到我的RecyclerView中。最后一个ViewHolder项是一个按钮，但当我尝试在按钮上设置onClickListener时，我在适配器类的onBindViewHolder中得到一个空对象引用

我觉得这个问题很简单，我想我只是在调试之后忽略了它

当我设置on-click侦听器时，您能发现是什么导致按钮mAddChordButton为空吗

适配器类

---

我解决了这个问题。我只是在onCreateViewHolder中夸大了错误的布局。在为页脚视图声明了正确的布局ID并在else语句中对其进行膨胀后，它就工作了

正确的代码是：

@Override
    public ChordViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
        Context context = parent.getContext();
        int layoutIdForListItem = R.layout.user_chord_list_item;
        int layoutIdForFooterItem = R.layout.user_chord_add_new; //SOLUTION
        LayoutInflater inflater = LayoutInflater.from(context);
        boolean shouldAttachToParentImmediately = false;

        View listItem;
        ChordViewHolder viewHolder;

        if (viewType == R.layout.user_chord_list_item) {    //inflate normal list item
            listItem = inflater.inflate(layoutIdForListItem, parent, shouldAttachToParentImmediately);
            viewHolder = new ChordViewHolder(listItem);
            viewHolder.viewHolderIndex.setText("Chord " + viewHolderCount);
        }
        else{   //inflate "+ Add new" button for last list item
            listItem = inflater.inflate(layoutIdForFooterItem, parent, shouldAttachToParentImmediately);
            viewHolder = new ChordViewHolder(listItem);
        }

        viewHolderCount++;
        return viewHolder;
    }

---

请添加logcatPost full Logcat。请看一下这个示例，您是否打算在if和else语句中使用ChordViewHolder？换句话说，除了setText之外，if-else的真正用途是什么？在任何布局中都缺少id为button\u add\u new的按钮

05-24 22:31:26.284 3083-7540/com.example.foo E/AndroidRuntime: FATAL EXCEPTION: main
                                                                 Process: com.example.foo, PID: 3083
                                                                 java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.Button.setOnClickListener(android.view.View$OnClickListener)' on a null object reference
                                                                     at com.example.foo.UserChordsAdapter.onBindViewHolder(UserChordsAdapter.java:68)
                                                                     at com.example.foo.UserChordsAdapter.onBindViewHolder(UserChordsAdapter.java:15)
                                                                     at android.support.v7.widget.RecyclerView$Adapter.onBindViewHolder(RecyclerView.java:6067)
                                                                     at android.support.v7.widget.RecyclerView$Adapter.bindViewHolder(RecyclerView.java:6100)
                                                                     at android.support.v7.widget.RecyclerView$Recycler.getViewForPosition(RecyclerView.java:5282)
                                                                     at android.support.v7.widget.RecyclerView$Recycler.getViewForPosition(RecyclerView.java:5158)
                                                                     at android.support.v7.widget.LinearLayoutManager$LayoutState.next(LinearLayoutManager.java:2061)
                                                                     at android.support.v7.widget.LinearLayoutManager.layoutChunk(LinearLayoutManager.java:1445)
                                                                     at android.support.v7.widget.LinearLayoutManager.fill(LinearLayoutManager.java:1408)
                                                                     at android.support.v7.widget.LinearLayoutManager.onLayoutChildren(LinearLayoutManager.java:580)
                                                                     at android.support.v7.widget.RecyclerView.dispatchLayoutStep2(RecyclerView.java:3379)
                                                                     at android.support.v7.widget.RecyclerView.onMeasure(RecyclerView.java:2906)
                                                                     at android.view.View.measure(View.java:19734)
                                                                     at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:6120)
                                                                     at android.widget.LinearLayout.measureChildBeforeLayout(LinearLayout.java:1464)
                                                                     at android.widget.LinearLayout.measureHorizontal(LinearLayout.java:1117)
                                                                     at android.widget.LinearLayout.onMeasure(LinearLayout.java:642)
                                                                     at android.view.View.measure(View.java:19734)
                                                                     at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:6120)
                                                                     at android.widget.LinearLayout.measureChildBeforeLayout(LinearLayout.java:1464)
                                                                     at android.widget.LinearLayout.measureVertical(LinearLayout.java:758)
                                                                     at android.widget.LinearLayout.onMeasure(LinearLayout.java:640)
                                                                     at android.view.View.measure(View.java:19734)
                                                                     at android.widget.LinearLayout.measureHorizontal(LinearLayout.java:1098)
                                                                     at android.widget.LinearLayout.onMeasure(LinearLayout.java:642)
                                                                     at android.view.View.measure(View.java:19734)
                                                                     at android.widget.LinearLayout.measureVertical(LinearLayout.java:911)
                                                                     at android.widget.LinearLayout.onMeasure(LinearLayout.java:640)
                                                                     at android.view.View.measure(View.java:19734)
                                                                     at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:6120)
                                                                     at android.widget.FrameLayout.onMeasure(FrameLayout.java:185)
                                                                     at android.view.View.measure(View.java:19734)
                                                                     at android.view.ViewRootImpl.performMeasure(ViewRootImpl.java:2271)
                                                                     at android.view.ViewRootImpl.measureHierarchy(ViewRootImpl.java:1358)
                                                                     at android.view.ViewRootImpl.performTraversals(ViewRootImpl.java:1607)
                                                                     at android.view.ViewRootImpl.doTraversal(ViewRootImpl.java:1246)
                                                                     at android.view.ViewRootImpl$TraversalRunnable.run(ViewRootImpl.java:6301)
                                                                     at android.view.Choreographer$CallbackRecord.run(Choreographer.java:871)
                                                                     at android.view.Choreographer.doCallbacks(Choreographer.java:683)
                                                                     at android.view.Choreographer.doFrame(Choreographer.java:619)
                                                                     at android.view.Choreographer$FrameDisplayEventReceiver.run(Choreographer.java:857)
                                                                     at android.os.Handler.handleCallback(Handler.java:751)
                                                                     at android.os.Handler.dispatchMessage(Handler.java:95)
                                                                     at android.os.Looper.loop(Looper.java:154)
                                                                     at android.app.ActivityThread.main(ActivityThread.java:6077)
                                                                     at java.lang.reflect.Method.invoke(Native Method)
                                                                     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:865)
                                                                     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:755)

@Override
    public ChordViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
        Context context = parent.getContext();
        int layoutIdForListItem = R.layout.user_chord_list_item;
        int layoutIdForFooterItem = R.layout.user_chord_add_new; //SOLUTION
        LayoutInflater inflater = LayoutInflater.from(context);
        boolean shouldAttachToParentImmediately = false;

        View listItem;
        ChordViewHolder viewHolder;

        if (viewType == R.layout.user_chord_list_item) {    //inflate normal list item
            listItem = inflater.inflate(layoutIdForListItem, parent, shouldAttachToParentImmediately);
            viewHolder = new ChordViewHolder(listItem);
            viewHolder.viewHolderIndex.setText("Chord " + viewHolderCount);
        }
        else{   //inflate "+ Add new" button for last list item
            listItem = inflater.inflate(layoutIdForFooterItem, parent, shouldAttachToParentImmediately);
            viewHolder = new ChordViewHolder(listItem);
        }

        viewHolderCount++;
        return viewHolder;
    }