Java 粘性标头回收视图不与ArrayList一起使用<；ItemObject>；为什么会这样？

我想用粘性标题创建recycleview，我可以用标题创建recycleview，它工作得很好，但是当我试图使它们粘性时，我的应用程序崩溃了。我尝试了它的代码，但是当我尝试使用

ArrayList

时，我的应用程序崩溃了

这是我的日志

2019-07-13 15:34:53.144 22566-22566/com.elytelabs.stickyrecyclerview E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.elytelabs.stickyrecyclerview, PID: 22566
java.lang.NullPointerException: Attempt to invoke virtual method 'boolean java.lang.Object.equals(java.lang.Object)' on a null object reference
    at com.elytelabs.stickyrecyclerview.RecyclerSectionItemDecoration.onDrawOver(RecyclerSectionItemDecoration.java:55)
    at androidx.recyclerview.widget.RecyclerView.draw(RecyclerView.java:4223)
    at android.view.View.updateDisplayListIfDirty(View.java:18168)
    at android.view.View.draw(View.java:18946)
    at android.view.ViewGroup.drawChild(ViewGroup.java:4240)
    at android.view.ViewGroup.dispatchDraw(ViewGroup.java:4024)
    at android.view.View.updateDisplayListIfDirty(View.java:18159)
    at android.view.View.draw(View.java:18946)
    at android.view.ViewGroup.drawChild(ViewGroup.java:4240)
    at android.view.ViewGroup.dispatchDraw(ViewGroup.java:4024)
    at android.view.View.updateDisplayListIfDirty(View.java:18159)
    at android.view.View.draw(View.java:18946)
    at android.view.ViewGroup.drawChild(ViewGroup.java:4240)
    at android.view.ViewGroup.dispatchDraw(ViewGroup.java:4024)
    at android.view.View.updateDisplayListIfDirty(View.java:18159)
    at android.view.View.draw(View.java:18946)
    at android.view.ViewGroup.drawChild(ViewGroup.java:4240)
    at android.view.ViewGroup.dispatchDraw(ViewGroup.java:4024)
    at android.view.View.updateDisplayListIfDirty(View.java:18159)
    at android.view.View.draw(View.java:18946)
    at android.view.ViewGroup.drawChild(ViewGroup.java:4240)
    at android.view.ViewGroup.dispatchDraw(ViewGroup.java:4024)
    at android.view.View.updateDisplayListIfDirty(View.java:18159)
    at android.view.View.draw(View.java:18946)
    at android.view.ViewGroup.drawChild(ViewGroup.java:4240)
    at android.view.ViewGroup.dispatchDraw(ViewGroup.java:4024)
    at android.view.View.draw(View.java:19221)
    at com.android.internal.policy.DecorView.draw(DecorView.java:791)
    at android.view.View.updateDisplayListIfDirty(View.java:18168)
    at android.view.ThreadedRenderer.updateViewTreeDisplayList(ThreadedRenderer.java:685)
    at android.view.ThreadedRenderer.updateRootDisplayList(ThreadedRenderer.java:691)
    at android.view.ThreadedRenderer.draw(ThreadedRenderer.java:799)
    at android.view.ViewRootImpl.draw(ViewRootImpl.java:3051)
    at android.view.ViewRootImpl.performDraw(ViewRootImpl.java:2846)
    at android.view.ViewRootImpl.performTraversals(ViewRootImpl.java:2399)
    at android.view.ViewRootImpl.doTraversal(ViewRootImpl.java:1432)
    at android.view.ViewRootImpl$TraversalRunnable.run(ViewRootImpl.java:6861)
    at android.view.Choreographer$CallbackRecord.run(Choreographer.java:1026)
    at android.view.Choreographer.doCallbacks(Choreographer.java:838)
    at android.view.Choreographer.doFrame(Choreographer.java:769)
    at android.view.Choreographer$FrameDisplayEventReceiver.run(Choreographer.java:1012)
    at android.os.Handler.handleCallback(Handler.java:790)
    at android.os.Handler.dispatchMessage(Handler.java:99)
    at android.os.Looper.loop(Looper.java:171)
    at android.app.ActivityThread.main(ActivityThread.java:6651)
    at java.lang.reflect.Method.invoke(Native Method)
    at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:547)
    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:824)
2019-07-13 15:34:53.200 22566-22566/com.elytelabs.stickyrecyclerview I/Process: Sending signal. PID: 22566 SIG: 9

这是代码

主要活动

mRecyclerView = findViewById(R.id.recyclerview);
    mRecyclerView.setLayoutManager(new LinearLayoutManager(this));
    adapter = new Adapter(this, getData());
    mRecyclerView.setAdapter(adapter);

    RecyclerSectionItemDecoration sectionItemDecoration =
            new RecyclerSectionItemDecoration(getResources().getDimensionPixelSize(R.dimen.header),
                    true,
                    getSectionCallback(getData()));
    mRecyclerView.addItemDecoration(sectionItemDecoration);

}

public ArrayList<ItemObject> getData() {
    ArrayList<ItemObject> list = new ArrayList <ItemObject>();
    list.add(new ItemObject("Header 1",true));
    list.add(new ItemObject("Example Text 1","Something Here 1"));
    list.add(new ItemObject("Example Text 2","Something Here 2 "));
    list.add(new ItemObject("Example Text 3","Something Here 3"));

    list.add(new ItemObject("Header 2",true));
    list.add(new ItemObject("Example Text 1","Something Here 1"));
    list.add(new ItemObject("Example Text 2","Something Here 2 "));
    list.add(new ItemObject("Example Text 3","Something Here 3"));

    list.add(new ItemObject("Header 3",true));
    list.add(new ItemObject("Example Text 1","Something Here 1"));
    list.add(new ItemObject("Example Text 2","Something Here 2 "));
    list.add(new ItemObject("Example Text 3","Something Here 3"));
    return list;
}

private RecyclerSectionItemDecoration.SectionCallback getSectionCallback(final List<ItemObject> list) {
    return new RecyclerSectionItemDecoration.SectionCallback() {
        @Override
        public boolean isSection(int position) {
            return list.get(position).isHeader();
        }

        @Override
        public String getSectionHeader(int position) {
            return list.get(position).getHeaderTitle();
        }

    };
}

---

}

在RecyclerSectionItemDecoration中编辑代码

 if (headerView == null) {
    headerView = inflateHeaderView(parent);
    header = (TextView) headerView.findViewById(R.id.tv_header);
    fixLayoutSize(headerView, parent);
}

到

---

如果不工作，请检查Canvas c，我跟踪它，但从未获得任何参考。

问题出在

onDrawOver

方法中，我们可以将其与此代码隔离：

    CharSequence previousHeader = "";
    for (int i = 0; i < parent.getChildCount(); i++) {
        View child = parent.getChildAt(i);
        final int position = parent.getChildAdapterPosition(child);

        CharSequence title = sectionCallback.getSectionHeader(position);
        header.setText(title);
        if (!previousHeader.equals(title) || sectionCallback.isSection(position)) {
            drawHeader(c, child, headerView);
            previousHeader = title;
        }
    }

换句话说，

sectionCallback.getSectionHeader（位置）

必须在某个点返回

null

那么解决方案是什么呢

视情况而定

• 如果“节头”为

  null

  是不正确的，请找出原因并修复它

• 如果它是正确的（或者如果你无论如何都要处理它！），那么一个最小的改变就是改变

          previousHeader = title;
  

  到

---

如果（someObject==null）

将永远不会引发异常

if（someObject.something==null）

如果

someObject

为null，则可能引发异常，但这是不同的。你的假设是错误的。是的，你是对的！，但是没有必要检查是否使用if.maybe Exception throw Canvas c null object@ZoeThe如果（！previousHeader.equals（title）| | sectionCallback.isSection（position））{drawHeader（c，child，headerView）；previousHeader=title；}在（！previousHeader.equals（title）| sectionCallback.isSection（position））中没有异常，仅在@John此处出现异常drawHeader（c、child、headerView）

    headerView = inflateHeaderView(parent);
    header = (TextView) headerView.findViewById(R.id.tv_header);
    fixLayoutSize(headerView, parent);

    CharSequence previousHeader = "";
    for (int i = 0; i < parent.getChildCount(); i++) {
        View child = parent.getChildAt(i);
        final int position = parent.getChildAdapterPosition(child);

        CharSequence title = sectionCallback.getSectionHeader(position);
        header.setText(title);
        if (!previousHeader.equals(title) || sectionCallback.isSection(position)) {
            drawHeader(c, child, headerView);
            previousHeader = title;
        }
    }

        previousHeader = title;

        previousHeader = title;

        previousHeader = (title == null) ? "" : title;