【发布时间】：2015-07-29 10:43:37
【问题描述】：
所以我正在关注这个tutorial，我有一个 RecyclerView 和 GridLayoutManager 实现。GridLayoutManager 有 2 列。我想要两种视图类型，所以我使用了两个 ViewHolders 扩展了 RecyclerView.ViewHolder 并且我覆盖了这个方法：getItemViewType(int position)，但我接受了 Cast Exception。 Logcat 显示如下：
java.lang.ClassCastException：adapter.AdapterListItemHome$CommentViewHolder0 无法转换为 adapter.AdapterListItemHome$CommentViewHolder1 在 adapter.AdapterListItemHome.onBindViewHolder(AdapterListItemHome.java:200) 在 adapter.AdapterListItemHome.onBindViewHolder(AdapterListItemHome.java:25)
但我不会将 CommentViewHolder0 与 CommentViewHolder1 一起使用，例如 Line 问题是这样的：
final CommentViewHolder0 vh0 = (CommentViewHolder0)cvh;
这是来自适配器 (AdapterListItemHome.java) 的代码：
public class AdapterListItemHome extends RecyclerView.Adapter<RecyclerView.ViewHolder> {
ArrayList<GadgetItem> mListItem;
Context mContext;
private int choice;
public static OnItemClickListener listener;// Define listener member variable
public static final int FIRST_ITEM = 0;
public static final int REST_ITEMS = 1;
/**
* Defines the listener interface
*/
public interface OnItemClickListener {
void onItemClick(View itemView, int position);
}
// Define the method that allows the parent activity or fragment to define the listener
public void setOnItemClickListener(OnItemClickListener listener) {
this.listener = listener;
}
/**
* view holder - holds the widgets - classical
*/
public class CommentViewHolder1 extends RecyclerView.ViewHolder {
public ProgressBar pgLoading;
public TextView tv_title;
public ImageView imgView;
//constructor
public CommentViewHolder1(final View itemView) {
super(itemView);
// Find the TextView in the LinearLayout
tv_title = ((TextView) itemView.findViewById(R.id.namgeItem));
pgLoading = (ProgressBar) itemView.findViewById(R.id.pbLoadingImage);
imgView = (ImageView) itemView.findViewById(R.id.imgItem);
itemView.setOnClickListener(new View.OnClickListener(){
@Override
public void onClick(View v) {
// Triggers click upwards to the adapter on click
if (listener != null)
listener.onItemClick(itemView, getPosition());
}
});
}
}
/**
* second viewHolder
*/
public class CommentViewHolder0 extends RecyclerView.ViewHolder {
public ProgressBar pgLoading;
public TextView tv_title;
public ResizableImageView imgView;
public TextView tv_date;
//constructor
public CommentViewHolder0(final View itemView) {
super(itemView);
// Find the TextView in the LinearLayout
tv_title = ((TextView) itemView.findViewById(R.id.namgeItem));
tv_date = ((TextView) itemView.findViewById(R.id.tv_date));
pgLoading = (ProgressBar) itemView.findViewById(R.id.pbLoadingImage);
imgView = (ResizableImageView) itemView.findViewById(R.id.resizable_image);
imgView.setOnClickListener(new View.OnClickListener(){
@Override
public void onClick(View v) {
// Triggers click upwards to the adapter on click
if (listener != null)
listener.onItemClick(imgView, getPosition());
}
});
}
}
/*
* VF: Constructor
*/
public AdapterListItemHome(Context pContext, ArrayList<GadgetItem> pListGadget) {
this.mContext = pContext;
this.mListItem = pListGadget;
}
/**
* Replace the contents of a view (invoked by the layout manager)
* @param viewGroup
* @param ViewType
* @return
*/
@Override
public RecyclerView.ViewHolder onCreateViewHolder(ViewGroup viewGroup, int ViewType){
View v;
//Log.d("bill", "viewtype = " + String.valueOf(ViewType));
switch(ViewType){
case REST_ITEMS:
v = LayoutInflater.from(viewGroup.getContext()).inflate(R.layout.row_item, viewGroup, false);
CommentViewHolder1 cvh1 = new CommentViewHolder1(v);
return cvh1;
case FIRST_ITEM:
v = LayoutInflater.from(viewGroup.getContext()).inflate(R.layout.row_item_home, viewGroup, false);
CommentViewHolder0 cvh0 = new CommentViewHolder0(v);
return cvh0;
default:
v = LayoutInflater.from(viewGroup.getContext()).inflate(R.layout.row_item, viewGroup, false);
CommentViewHolder1 cvh2 = new CommentViewHolder1(v);
return cvh2;
}
}
@Override
public void onBindViewHolder(RecyclerView.ViewHolder cvh, int position) {
Transformation transformation;
GadgetItem item;
switch ( cvh.getItemViewType () ){
case REST_ITEMS:
final CommentViewHolder1 vh1 = (CommentViewHolder1)cvh;
item = mListItem.get(position);
vh1.tv_title.setText(item.gadget_title);
vh1.pgLoading.setVisibility(View.VISIBLE);
vh1.imgView.setImageDrawable(null);
/**
* clicking on the image view
*/
transformation = new Transformation() {
@Override
public Bitmap transform(Bitmap source) {
int targetWidth = vh1.imgView.getWidth();
double aspectRatio = (double) source.getHeight() / (double) source.getWidth();
int targetHeight = (int) (targetWidth * aspectRatio);
// Bitmap result = Bitmap.createScaledBitmap(source,
// targetWidth,
// targetHeight, false);
Bitmap result = scaleAndCropImage(source, 300);
if (result != source) {
// Same bitmap is returned if sizes are the same
source.recycle();
}
return result;
}
@Override
public String key() {
return "transformation" + " desiredWidth";
}
};
Picasso.with(mContext).load(item.gadget_image).into(vh1.imgView, new Callback() {
@Override
public void onError() {
}
@Override
public void onSuccess() {
vh1.pgLoading.setVisibility(View.GONE);
}
});
case FIRST_ITEM:
final CommentViewHolder0 vh0 = (CommentViewHolder0)cvh;
item = mListItem.get(position);
vh0.tv_title.setText(item.gadget_title);
vh0.pgLoading.setVisibility(View.VISIBLE);
vh0.imgView.setImageDrawable(null);
vh0.tv_date.setText(item.gadget_pubDate);
/**
* clicking on the image view
*/
transformation = new Transformation() {
@Override
public Bitmap transform(Bitmap source) {
int targetWidth = vh0.imgView.getWidth();
double aspectRatio = (double) source.getHeight() / (double) source.getWidth();
int targetHeight = (int) (targetWidth * aspectRatio);
// Bitmap result = Bitmap.createScaledBitmap(source,
// targetWidth,
// targetHeight, false);
Bitmap result = scaleAndCropImage(source, 300);
if (result != source) {
// Same bitmap is returned if sizes are the same
source.recycle();
}
return result;
}
@Override
public String key() {
return "transformation" + " desiredWidth";
}
};
Picasso.with(mContext).load(item.gadget_image).into(vh0.imgView, new Callback() {
@Override
public void onError() {
}
@Override
public void onSuccess() {
vh0.pgLoading.setVisibility(View.GONE);
}
});
}
}
// Return the size of dataset (invoked by the layout manager)
@Override
public int getItemCount() {
return mListItem.size();
}
/* (non-Javadoc)
* VF: creating a item to show
*/
Bitmap scaleAndCropImage(Bitmap image, int height) {
float ratio = (float) (height) / (float) image.getHeight();
int width = (int) ((float) image.getWidth() * ratio);
return ScalingUtilities.createScaledBitmap(image, width, height, ScalingUtilities.ScalingLogic.CROP);
}
@Override
public int getItemViewType(int position) {
int viewType;
if (position == 1)
viewType = FIRST_ITEM;
else
viewType = REST_ITEMS;
return viewType;
}
}
这就是 RecyclerView 正在实施的 Fragment
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup parent , Bundle savedInstanceState) {
if(parent == null)
return null;
if(v != null)
return v;
//initialize the view v
v = inflater.inflate(R.layout.fragment_list_item_home, parent , false);
//initialization Recycler view
mRecyclerView = (RecyclerView) v.findViewById(R.id.listItem_home);
mRecyclerView.setHasFixedSize(true);
mLayoutManager = new GridLayoutManager(getActivity(),2);
mRecyclerView.addItemDecoration(new DividerItemDecoration(4,2));
mRecyclerView.getItemAnimator().setMoveDuration(5000);
mRecyclerView.setLayoutManager(mLayoutManager);
if(mAdapter == null) {
//setting the adapter
mAdapter = new AdapterListItemHome(getActivity(),mList);
mRecyclerView.setAdapter(mAdapter);
v.setFocusableInTouchMode(true); //focusing when touching
v.requestFocus(); //To force focus to a specific view
mAdapter.setOnItemClickListener(new AdapterListItemHome.OnItemClickListener() {
@Override
public void onItemClick(View view, int position) {
onListViewItemClick(position);
}
});
}
我一直在到处寻找，实现的方法都是一样的，我不知道问题出在哪里。感谢您的帮助
【问题讨论】：
-
你找出问题所在了吗？我在我们的一个项目中遇到了同样的问题。具有讽刺意味的是，我几乎遵循了几周前在另一个项目中首次实施的相同实施，在其中我没有遇到任何问题。
-
@Andrew 是的，我解决了这个问题，我会在下面发布答案
-
也解决了我的问题。显然，我使用的是 onCreateViewHolder(ViewGroup viewGroup, int position)，其中 position 作为第二个参数，而不是 viewType。不知道它在另一个应用程序上的运行情况如何。
标签： android classcastexception android-viewholder android-recyclerview