我很难理解为什么我在RecyclerAdapter类中遇到ClassCastException。我已将其设置为接受两种不同类型的视图，一种用于常规Feed项，另一种用于本机广告。出了什么问题？
在我的主要活动中，我按如下方式调用我的构造函数：
feedItems = new ArrayList<>();
List<Feed> adItems = new ArrayList<>();
recyclerView = (RecyclerView) findViewById(R.id.recycler_view);
marketFeedRecyclerAdapter = new MarketFeedRecyclerAdapter(this, feedItems, new ImageLoader(new FeedItemFileCache(this)), adItems);
我在RecyclerAdapter课程的这一行收到投诉，其中包含以下堆栈跟踪：
bindAdItemView((AdViewHolder) viewHolder);
我的堆栈跟踪：
java.lang.ClassCastException： com.elgami.utility.LoadingRowRecyclerAdapter $ LoadingViewHolder不能 被投射到com.elgami.market.MarketFeedRecyclerAdapter $ AdViewHolder 在com.elgami.market.MarketFeedRecyclerAdapter.onBindViewHolder（MarketFeedRecyclerAdapter.java:80） 在android.support.v7.widget.RecyclerView $ Adapter.onBindViewHolder（RecyclerView.java:5768） 在android.support.v7.widget.RecyclerView $ Adapter.bindViewHolder（RecyclerView.java:5801） 在android.support.v7.widget.RecyclerView $ Recycler.getViewForPosition（RecyclerView.java:5037） 在android.support.v7.widget.RecyclerView $ Recycler.getViewForPosition（RecyclerView.java:4913） 在android.support.v7.widget.LinearLayoutManager $ LayoutState.next（LinearLayoutManager.java:2029） 在android.support.v7.widget.LinearLayoutManager.layoutChunk（LinearLayoutManager.java:1414） 在android.support.v7.widget.LinearLayoutManager.fill（LinearLayoutManager.java:1377） 在android.support.v7.widget.LinearLayoutManager.onLayoutChildren（LinearLayoutManager.java:578） 在android.support.v7.widget.RecyclerView.dispatchLayoutStep2（RecyclerView.java:3260） 在android.support.v7.widget.RecyclerView.dispatchLayout（RecyclerView.java:3069） 在android.support.v7.widget.RecyclerView.onLayout（RecyclerView.java:3518） 在android.view.View.layout（View.java:16636） 在android.view.ViewGroup.layout（ViewGroup.java:5437） 在android.support.v4.widget.SwipeRefreshLayout.onLayout（SwipeRefreshLayout.java:598） 在android.view.View.layout（View.java:16636） 在android.view.ViewGroup.layout（ViewGroup.java:5437） 在android.widget.LinearLayout.setChildFrame（LinearLayout.java:1743） 在android.widget.LinearLayout.layoutVertical（LinearLayout.java:1586） 在android.widget.LinearLayout.onLayout（LinearLayout.java:1495） 在android.view.View.layout（View.java:16636） 在android.view.ViewGroup.layout（ViewGroup.java:5437） 在android.widget.RelativeLayout.onLayout（RelativeLayout.java:1079） 在android.view.View.layout（View.java:16636） 在android.view.ViewGroup.layout（ViewGroup.java:5437） 在android.widget.FrameLayout.layoutChildren（FrameLayout.java:336） 在android.widget.FrameLayout.onLayout（FrameLayout.java:273） 在android.view.View.layout（View.java:16636） 在android.view.ViewGroup.layout（ViewGroup.java:5437） 在android.widget.LinearLayout.setChildFrame（LinearLayout.java:1743） 在android.widget.LinearLayout.layoutVertical（LinearLayout.java:1586） 在android.widget.LinearLayout.onLayout（LinearLayout.java:1495） 在android.view.View.layout（View.java:16636） 在android.view.ViewGroup.layout（ViewGroup.java:5437） 在android.widget.FrameLayout.layoutChildren（FrameLayout.java:336） 在android.widget.FrameLayout.onLayout（FrameLayout.java:273） 在android.view.View.layout（View.java:16636） 在android.view.ViewGroup.layout（ViewGroup.java:5437） 在android.widget.LinearLayout.setChildFrame（LinearLayout.java:1743） 在android.widget.LinearLayout.layoutVertical（LinearLayout.java:1586） 在android.widget.LinearLayout.onLayout（LinearLayout.java:1495） 在android.view.View.layout（View.java:16636） 在android.view.ViewGroup.layout（ViewGroup.java:5437） 在android.widget.FrameLayout.layoutChildren（FrameLayout.java:336） 在android.widget.FrameLayout.onLayout（FrameLayout.java:273） 在com.android.internal.policy.PhoneWindow $ DecorView.onLayout（PhoneWindow.java:2678） 在android.view.View.layout（View.java:16636） 在android.view.ViewGroup.layout（ViewGroup.java:5437） 在android.view.ViewRootImpl.performLayout（ViewRootImpl.java:2171） 在android.view.ViewRootImpl.performTraversals（ViewRootImpl.java:1931） 在android.view.ViewRootImpl.doTraversal（ViewRootImpl.java:1107） 在android.view.ViewRootImpl $ TraversalRunnable.run（ViewRootImpl.java:6013） 在android.view.Choreographer $ CallbackRecord.run（Choreographer.java:858） 在android.view.Choreographer.doCallbacks（Choreographer.java:670） 在android.view.Choreographer.doFrame（Choreographer.java:606） 在android.view.Choreographer $ FrameDisplayEventReceiver.run（Choreographer.java:844） 在
以下是我的RecyclerAdapter类：
public class MarketFeedRecyclerAdapter extends LoadingRowRecyclerAdapter {
private static final int VIEW_TYPE_MARKET_FEED = 0;
private static final int VIEW_TYPE_AD = 1;
private final Context context;
private final List<Feed> feedItems;
private final ImageLoader feedItemImageLoader;
private FeedItemClickListener feedItemClickListener;
private boolean isLongPressed = false;
public MarketFeedRecyclerAdapter(Context context, List<Feed> feedItems, ImageLoader feedItemImageLoader, List<Feed> adItems) {
this.context = context;
this.feedItems = feedItems;
this.feedItemImageLoader = feedItemImageLoader;
this.feedItems.addAll(adItems);
}
@Override
public RecyclerView.ViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
switch (viewType) {
case VIEW_TYPE_MARKET_FEED:
return new MarketFeedViewHolder(new FeedItemView(context));
case VIEW_TYPE_AD:
return new AdViewHolder(new MarketFeedAdItemView(context));
}
return super.onCreateViewHolder(parent, viewType);
}
// Differentiate between feedItem views and nativeAds
@Override
public int getViewType(int position) {
int viewType = VIEW_TYPE_MARKET_FEED;
if ((position % 25 == 0)) {
viewType = VIEW_TYPE_AD;
}
return viewType;
}
@Override
public void onBindViewHolder(RecyclerView.ViewHolder viewHolder, int position) {
if (getViewType(position) == VIEW_TYPE_MARKET_FEED) {
bindMarketFeedItemView((MarketFeedViewHolder) viewHolder, position - position / 6);
} else {
bindAdItemView((AdViewHolder) viewHolder);
}
}
// For Ad Objects
private void bindAdItemView(AdViewHolder viewHolder) {
showNativeAd(viewHolder);
}
private void bindMarketFeedItemView(MarketFeedViewHolder viewHolder, int position) {
final FeedItemView feedItemView = viewHolder.feedItemView;
final Feed feedDesign = feedItems.get(position);
// TODO we can probably conditionally show or hide these based on the type of feed item, same as in FeedActivitySingle
feedItemView.showOrHideEditButton(false);
feedItemView.showOrHideBuyButton(true);
feedItemView.showOrHideFlipButton(feedDesign.getDesign().getCompressedBackImage() != null);
feedItemView.showOrHidePriceText(true);
// Set the results into TextViews
feedItemView.setProductPriceText(String.valueOf(feedDesign.getDesign().getPrice()));
feedItemView.setDownloadsText(String.valueOf(feedDesign.getDesign().getDownloadCount()));
feedItemView.setLikesText(String.valueOf(feedDesign.getDesign().getLikesCount()));
feedItemView.setUsernameText(feedDesign.getDesign().getAuthor().getUsername());
feedItemView.setTimestampText(feedDesign.getTimestampText());
feedItemView.getSaveImage().setImageResource(feedDesign.isInPersonalGallery() ? R.drawable.ic_action_saved : R.drawable.ic_not_saved);
feedItemView.getLikeImage().setImageResource(feedDesign.isLiked() ? R.drawable.ic_action_like_feed_full : R.drawable.ic_action_like_feed);
feedItemView.getTrashImage().setVisibility(ParseHelper.isCurrentUser(feedDesign.getDesign().getAuthor().getObjectId()) ? View.VISIBLE : View.GONE);
feedItemView.getFeedSocialShareImage().setVisibility(View.VISIBLE);
switch(feedDesign.getDisplayedSide()) {
case FRONT:
feedItemImageLoader.DisplayImage(feedDesign.getDesign().getCompressedImage().getUrl(), feedItemView.getImage(), feedItemView.getProgressBar());
break;
case BACK:
feedItemImageLoader.DisplayImage(feedDesign.getDesign().getCompressedBackImage().getUrl(), feedItemView.getImage(), feedItemView.getProgressBar());
break;
}
if(feedDesign.getDesign().getAuthor().getProfilePicture() != null) {
feedItemImageLoader.DisplayImage(feedDesign.getDesign().getAuthor().getProfilePicture().getUrl(), feedItemView.getProfilePicture(), null); // TODO should this use profilePictureFileCache?
} else {
viewHolder.feedItemView.getProfilePicture().setImageResource(R.drawable.ic_anonymous);
}
SetCommentViews(feedItemView, feedDesign.getComments());
SetClickListeners(feedItemView, feedDesign, position);
}
@Override
protected int getContentDataSize() {
return feedItems.size();
}
class MarketFeedViewHolder extends RecyclerView.ViewHolder {
FeedItemView feedItemView;
public MarketFeedViewHolder(FeedItemView view) {
super(view);
this.feedItemView = view;
}
}
class AdViewHolder extends RecyclerView.ViewHolder {
MarketFeedAdItemView adItemView;
public AdViewHolder(MarketFeedAdItemView view) {
super(view);
this.adItemView = view;
}
}
private NativeAd nativeAd;
private AdChoicesView adChoicesView;
private void showNativeAd(AdViewHolder viewHolder){
AdSettings.addTestDevice("a6ffb7bec7af13f768f033dbfea042df");
nativeAd = new NativeAd(context, "846223392142435_1025413774223395");
nativeAd.setAdListener(new AdListener() {
@Override
public void onError(Ad ad, AdError adError) {
}
@Override
public void onAdLoaded(Ad ad) {
final MarketFeedAdItemView adItemView = viewHolder.adItemView;
// Setting the Text
adItemView.nativeAdSocialContext.setText(nativeAd.getAdSocialContext());
adItemView.nativeAdCallToAction.setText(nativeAd.getAdCallToAction());
adItemView.nativeAdTitle.setText(nativeAd.getAdTitle());
adItemView.nativeAdBody.setText(nativeAd.getAdBody());
// Downloading and setting the ad icon
NativeAd.Image adIcon = nativeAd.getAdIcon();
NativeAd.downloadAndDisplayImage(adIcon, adItemView.nativeAdIcon);
// Download and setting the cover image
/*NativeAd.Image adCoverImage = nativeAd.getAdCoverImage();*/
adItemView.nativeAdMedia.setNativeAd(nativeAd);
// Add adChoices icon
if (adChoicesView == null) {
adChoicesView = new AdChoicesView(context, nativeAd, true);
adItemView.addView(adChoicesView, 0);
}
nativeAd.registerViewForInteraction(adItemView);
}
@Override
public void onAdClicked(Ad ad) {
}
});
nativeAd.loadAd();
}
}
我的RecyclerAdapter扩展了以下类，这有助于加载更多的feedItems：
public abstract class LoadingRowRecyclerAdapter extends RecyclerView.Adapter<RecyclerView.ViewHolder> {
public static final int ROW_VIEW_TYPE_LOADING = 72398; // obscure number
private boolean mContainsLoadingRow;
protected abstract int getContentDataSize();
protected abstract int getViewType(int position);
@Override
public RecyclerView.ViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
switch (viewType) {
case ROW_VIEW_TYPE_LOADING:
return new LoadingViewHolder(LayoutInflater.from(parent.getContext()).inflate(R.layout.loading_row, parent, false));
}
throw new IllegalArgumentException("viewType is not ROW_VIEW_TYPE_LOADING. You must handle all other values of viewType (defined by getViewType) before calling super.");
}
@Override
public void onBindViewHolder(RecyclerView.ViewHolder holder, int position) {
// empty
}
@Override
public final int getItemCount() {
return mContainsLoadingRow ? (getContentDataSize() + 1) : getContentDataSize();
}
@Override
public int getItemViewType(int position) {
return (position == getContentDataSize()) ? ROW_VIEW_TYPE_LOADING : getViewType(position);
}
/**
* Sets a boolean which is used by getItemCount and in turn getItemViewType to determine which view type the row should be (loading view vs. other view).
* Should only be called when there is more results to load in an upcoming api request (determined by calling fragment).
*/
public void toggleLoadingRowOn() {
mContainsLoadingRow = true;
}
/**
* Checks to see if a loading row exists by checking an instance boolean and removes the row / clears the boolean.
* This helps to 'replace' a loading row with a different row.
*/
public void toggleLoadingRowOff() {
if (mContainsLoadingRow) {
mContainsLoadingRow = false;
// removes the loading row explicitly instead of allowing it to be 'pushed' down when new user suggestion rows are added.
// this is only required to maintain consistency with the rest of the app.
int position = getContentDataSize();
if (position >= 0) {
notifyItemRemoved(position);
}
}
}
protected class LoadingViewHolder extends RecyclerView.ViewHolder {
public LoadingViewHolder(View v) {
super(v);
}
}
}
最后，确定加载更多项目的阈值的类：
public abstract class EndlessRecyclerOnScrollListener extends RecyclerView.OnScrollListener {
private static final int VISIBLE_THRESHOLD = 5; // The minimum amount of items to have below your current scroll position before loading more
private LinearLayoutManager mLinearLayoutManager;
public abstract void onLoadMore();
public EndlessRecyclerOnScrollListener(LinearLayoutManager linearLayoutManager) {
this.mLinearLayoutManager = linearLayoutManager;
}
@Override
public void onScrolled(RecyclerView recyclerView, int dx, int dy) {
super.onScrolled(recyclerView, dx, dy);
int totalItemCount = mLinearLayoutManager.getItemCount();
int firstVisibleItem = mLinearLayoutManager.findFirstVisibleItemPosition();
int visibleItemCount = recyclerView.getChildCount();
int lastItemVisible = firstVisibleItem + visibleItemCount;
// once the last visible item is within VISIBLE_THRESHOLD from the bottom, we want to load more
if ((totalItemCount - lastItemVisible) <= VISIBLE_THRESHOLD) {
onLoadMore();
}
}
}
答案 0 :(得分：2)
您的代码中存在问题：
@Override
public void onBindViewHolder(RecyclerView.ViewHolder viewHolder, int position) {
if (getViewType(position) == VIEW_TYPE_MARKET_FEED) {
bindMarketFeedItemView((MarketFeedViewHolder) viewHolder, position - position / 6);
} else {
bindAdItemView((AdViewHolder) viewHolder);
}
}
您正在检查当前行viewType（这很好），但您实际上可以有3种可能的viewType： market ， ad 和 loading 。
所以当这个
@Override
public int getItemViewType(int position) {
return (position == getContentDataSize()) ? ROW_VIEW_TYPE_LOADING : getViewType(position);
}
返回 ROW_VIEW_TYPE_LOADING 您将LoadingViewHolder投射到AdViewHolder。
这导致ClassCastException。
要解决此问题，只需将onBindViewHolder方法更改为包含所有三种可能的视图类型，或使用else if代替else。
希望这有帮助