这是 sample code我跟着。

下面的代码是示例代码中onCreateViewHolder的部分:

@Override
public MyAdapter.ViewHolder onCreateViewHolder(ViewGroup parent,
                                               int viewType) {
    // create a new view
    View v = LayoutInflater.from(parent.getContext())
                           .inflate(R.layout.my_text_view, parent, false);
    // set the view's size, margins, paddings and layout parameters
    ...
    ViewHolder vh = new ViewHolder(v);
    return vh;
}

这是 ViewHolder 的一部分:

public static class ViewHolder extends RecyclerView.ViewHolder {
    public TextView mTextView;
    public ViewHolder(TextView v) {
        super(v);
        mTextView = v;
    }
}

很明显，参数TextView v是错误的。

然后我在 onCreateViewHolder 方法中玩了一个小把戏，如下所示:

    ...
    TextView textView = (TextView) v.findViewById(R.id.tv_test);
    ViewHolder vh = new ViewHolder(textView);

但是当我运行应用程序时出现异常。

    java.lang.IllegalStateException: The specified child already has a parent. You must call removeView() on the child's parent first.
        at android.view.ViewGroup.addViewInner(ViewGroup.java:3693)
        at android.view.ViewGroup.addView(ViewGroup.java:3546)
        at android.view.ViewGroup.addView(ViewGroup.java:3491)
        at android.support.v7.widget.RecyclerView$LayoutManager.addView(RecyclerView.java:3533)
        at android.support.v7.widget.RecyclerView$LayoutManager.addView(RecyclerView.java:3558)
        at android.support.v7.widget.LinearLayoutManager.fill(LinearLayoutManager.java:1012)
        at android.support.v7.widget.LinearLayoutManager.onLayoutChildren(LinearLayoutManager.java:524)
        at android.support.v7.widget.RecyclerView.dispatchLayout(RecyclerView.java:1461)
        at android.support.v7.widget.RecyclerView.onLayout(RecyclerView.java:1600)
        at android.view.View.layout(View.java:15273)
        at android.view.ViewGroup.layout(ViewGroup.java:4763)
        at android.widget.RelativeLayout.onLayout(RelativeLayout.java:1069)
        at android.view.View.layout(View.java:15273)
        at android.view.ViewGroup.layout(ViewGroup.java:4763)
        at android.widget.FrameLayout.layoutChildren(FrameLayout.java:457)
        at android.widget.FrameLayout.onLayout(FrameLayout.java:392)
        at android.view.View.layout(View.java:15273)
        at android.view.ViewGroup.layout(ViewGroup.java:4763)
        at com.android.internal.widget.ActionBarOverlayLayout.onLayout(ActionBarOverlayLayout.java:494)
        at android.view.View.layout(View.java:15273)
        at android.view.ViewGroup.layout(ViewGroup.java:4763)
        at android.widget.FrameLayout.layoutChildren(FrameLayout.java:457)
        at android.widget.FrameLayout.onLayout(FrameLayout.java:392)
        at android.view.View.layout(View.java:15273)
        at android.view.ViewGroup.layout(ViewGroup.java:4763)
        at android.view.ViewRootImpl.performLayout(ViewRootImpl.java:2057)
        at android.view.ViewRootImpl.performTraversals(ViewRootImpl.java:1814)
        at android.view.ViewRootImpl.doTraversal(ViewRootImpl.java:1044)
        at android.view.ViewRootImpl$TraversalRunnable.run(ViewRootImpl.java:5749)
        at android.view.Choreographer$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$FrameDisplayEventReceiver.run(Choreographer.java:753)
        at android.os.Handler.handleCallback(Handler.java:738)
        at android.os.Handler.dispatchMessage(Handler.java:95)
        at android.os.Looper.loop(Looper.java:135)
        at android.app.ActivityThread.main(ActivityThread.java:5070)
        at java.lang.reflect.Method.invoke(Native Method)
        at java.lang.reflect.Method.invoke(Method.java:372)
        at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:836)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:631)

但是当我像这样更改 ViewHolder 代码时:

    public ViewHolder(View v) {
        super(v);
        mTextView = (TextView) v;
    }

会好的。

我想知道这个异常是什么意思？ 是什么导致了这个异常？

最佳答案

我偶然发现了同一个样本，很快也感到困惑。传递给 ViewHolder 构造函数的 View 是膨胀的父 View ，其中包含一个列表项的所有 View 。使用这个传递的 View 在其构造函数中初始化 ViewHolder 的所有字段，如下所示:

public class MyViewHolder extends RecyclerView.ViewHolder  {

    public TextView titleWithIcon;
    public TextView teaser;        

    public MyViewHolder(View itemView) {
        super(itemView);
        
        titleWithIcon = (TextView) itemView.findViewById(R.id.title_with_icon);
        teaser = (TextView) itemView.findViewById(R.id.teaser);
    }
}

关于来自 RecyclerView#onCreateViewHolder differents 的 Android ViewHolder 参数，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/25574470/