我有一个在房间数据库中存储一些数据的应用程序。一开始，我的适配器是这样的：
public class ViewCourseAdapter extends ListAdapter<Course, ViewCourseAdapter.ViewCourseHolder> {
private int previousPosition = 0;
public ViewCourseAdapter() {
super(DIFF_CALLBACK);
}
private static final DiffUtil.ItemCallback<Course> DIFF_CALLBACK = new DiffUtil.ItemCallback<Course>() {
@Override
public boolean areItemsTheSame(@NonNull Course oldItem, @NonNull Course newItem) {
return oldItem.getId() == newItem.getId();
}
@Override
public boolean areContentsTheSame(@NonNull Course oldItem, @NonNull Course newItem) {
return oldItem.getfName().equals(newItem.getfName());
}
};
@NonNull
@Override
public ViewCourseHolder onCreateViewHolder(@NonNull ViewGroup parent, int viewType) {
View itemView = LayoutInflater.from(parent.getContext())
.inflate(R.layout.view_courses_item, parent, false);
return new ViewCourseHolder(itemView);
}
@Override
public void onBindViewHolder(@NonNull ViewCourseHolder holder, int position) {
Course currentCourse = getItem(position);
String fullName = currentCourse.getfName() + " " + currentCourse.getlName();
SpannableString SfullName = new SpannableString(fullName);
SfullName.setSpan(new UnderlineSpan(), 0, fullName.length(), 0);
holder.text_view_firstName_1.setText(SfullName);
if (position > previousPosition) {
AnimationUtil.animate(holder, true);
} else {
AnimationUtil.animate(holder, false);
}
previousPosition = position;
}
class ViewCourseHolder extends RecyclerView.ViewHolder {
private TextView text_view_firstName_1;
ViewCourseHolder(@NonNull View itemView) {
super(itemView);
text_view_firstName_1 = itemView.findViewById(R.id.text_view_firstName_1);
}
}
@Override
public int getItemCount() {
return super.getItemCount();
}
而且一切都运转良好。现在，我想在recyclerview中展示广告，所以我更改了适配器：
public class ViewCourseAdapter extends RecyclerView.Adapter<RecyclerView.ViewHolder> {
private static final int COURSE_VIEW_TYPE = 0;
private static final int AD_VIEW_TYPE = 1;
private List<Course> data;
private List<Object> ad;
private Context context;
private LayoutInflater layoutInflater;
private int previousPosition = 0;
public ViewCourseAdapter(Context context, List<Object> ad) {
this.data = new ArrayList<>();
this.context = context;
this.layoutInflater = (LayoutInflater) context.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
this.ad = ad;
}
@NonNull
@Override
public RecyclerView.ViewHolder onCreateViewHolder(@NonNull ViewGroup parent, int viewType) {
switch (viewType ) {
case COURSE_VIEW_TYPE:
View courseView = LayoutInflater.from(parent.getContext()).inflate(R.layout.view_courses_item, parent, false);
return new ViewCourseViewHolder(courseView);
case AD_VIEW_TYPE:
default:
View adView = LayoutInflater.from(parent.getContext()).inflate(R.layout.native_ads, parent, false);
return new AdViewHolder(adView);
}
}
@Override
public void onBindViewHolder(@NonNull RecyclerView.ViewHolder holder, int position) {
int viewType = getItemViewType(position);
switch (viewType) {
case COURSE_VIEW_TYPE:
ViewCourseViewHolder holder1 = (ViewCourseViewHolder) holder;
Course currentCourse = (Course) data.get(position);
String fullName = currentCourse.getfName() + " " + currentCourse.getlName();
SpannableString SfullName = new SpannableString(fullName);
SfullName.setSpan(new UnderlineSpan(), 0, fullName.length(), 0);
holder1.text_view_firstName_1.setText(SfullName);
break;
case AD_VIEW_TYPE:
default:
AdViewHolder bannerHolder = (AdViewHolder) holder;
AdView adView = (AdView) ad.get(position);
ViewGroup adCardView = (ViewGroup) bannerHolder.itemView;
if (adCardView.getChildCount() > 0) {
adCardView.removeAllViews();
}
if (adView.getParent() != null) {
((ViewGroup) adView.getParent()).removeView(adView);
}
adCardView.addView(adView);
}
if (position > previousPosition) {
AnimationUtil.animate(holder, true);
} else {
AnimationUtil.animate(holder, false);
}
previousPosition = position;
}
class AdViewHolder extends RecyclerView.ViewHolder {
AdViewHolder(View view) {
super(view);
}
}
@Override
public int getItemViewType(int position) {
return (position % ViewCoursesActivity.ITEMS_PER_AD == 0) ? AD_VIEW_TYPE
: COURSE_VIEW_TYPE;
}
@Override
public int getItemCount() {
return data.size();
}
public void setData(List<Course> newData) {
if (data != null) {
CourseDiffCallback courseDiffCallback = new CourseDiffCallback(data, newData);
DiffUtil.DiffResult diffResult = DiffUtil.calculateDiff(courseDiffCallback);
data.clear();
data.addAll(newData);
diffResult.dispatchUpdatesTo(this);
} else {
data = newData;
}
}
public class ViewCourseViewHolder extends RecyclerView.ViewHolder {
private TextView text_view_firstName_1;
ViewCourseViewHolder(@NonNull View itemView) {
super(itemView);
text_view_firstName_1 = itemView.findViewById(R.id.text_view_firstName_1);
}
}
private class CourseDiffCallback extends DiffUtil.Callback {
private final List<Course> oldItem, newItem;
private CourseDiffCallback(List<Course> oldItem, List<Course> newItem) {
this.oldItem = oldItem;
this.newItem = newItem;
}
@Override
public int getOldListSize() {
return oldItem.size();
}
@Override
public int getNewListSize() {
return newItem.size();
}
@Override
public boolean areItemsTheSame(int oldItemPosition, int newItemPosition) {
return oldItem.get(oldItemPosition).getId() == newItem.get(newItemPosition).getId();
}
@Override
public boolean areContentsTheSame(int oldItemPosition, int newItemPosition) {
return oldItem.get(oldItemPosition).getfName().equals(newItem.get(newItemPosition).getfName());
}
}
我的活动是：
public class ViewCoursesActivity extends AppCompatActivity {
private CourseViewModel courseViewModel;
// A banner ad is placed in every 8th position in the RecyclerView.
public static final int ITEMS_PER_AD = 8;
private static final String AD_UNIT_ID = "ca-app-pub-3940256099942544/6300978111";
// The RecyclerView that holds and displays banner ads and menu items.
private RecyclerView recyclerView;
// List of banner ads and MenuItems that populate the RecyclerView.
private List<Object> data = new ArrayList<>();
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_view_courses);
recyclerView = findViewById(R.id.recycler_view_3);
recyclerView.setHasFixedSize(true);
recyclerView.setLayoutManager(new LinearLayoutManager(this));
addBannerAds();
loadBannerAds();
final ViewCourseAdapter adapter = new ViewCourseAdapter(this, data);
recyclerView.setAdapter(adapter);
courseViewModel = ViewModelProviders.of(this).get(CourseViewModel.class);
courseViewModel.setIdForCourse(0);
//courseViewModel.getCourseByStudentId().observe(this, adapter::submitList);
courseViewModel.getCourseByStudentId().observe(this, adapter::setData);
}
@Override
protected void onResume() {
for (Object item : data) {
if (item instanceof AdView) {
AdView adView = (AdView) item;
adView.resume();
}
}
super.onResume();
}
@Override
protected void onPause() {
for (Object item : data) {
if (item instanceof AdView) {
AdView adView = (AdView) item;
adView.pause();
}
}
super.onPause();
}
@Override
protected void onDestroy() {
for (Object item : data) {
if (item instanceof AdView) {
AdView adView = (AdView) item;
adView.destroy();
}
}
super.onDestroy();
}
/**
* Adds banner ads to the items list.
*/
private void addBannerAds() {
// Loop through the items array and place a new banner ad in every ith position in
// the items List.
for (int i = 0; i <= data.size(); i += ITEMS_PER_AD) {
final AdView adView = new AdView(ViewCoursesActivity.this);
adView.setAdSize(AdSize.SMART_BANNER);
adView.setAdUnitId(AD_UNIT_ID);
data.add(i, adView);
}
}
/**
* Sets up and loads the banner ads.
*/
private void loadBannerAds() {
// Load the first banner ad in the items list (subsequent ads will be loaded automatically
// in sequence).
loadBannerAd(0);
}
/**
* Loads the banner ads in the items list.
*/
private void loadBannerAd(final int index) {
if (index >= data.size()) {
return;
}
Object item = data.get(index);
if (!(item instanceof AdView)) {
throw new ClassCastException("Expected item at index " + index + " to be a banner ad"
+ " ad.");
}
final AdView adView = (AdView) item;
// Set an AdListener on the AdView to wait for the previous banner ad
// to finish loading before loading the next ad in the items list.
adView.setAdListener(new AdListener() {
@Override
public void onAdLoaded() {
super.onAdLoaded();
// The previous banner ad loaded successfully, call this method again to
// load the next ad in the items list.
loadBannerAd(index + ITEMS_PER_AD);
}
@Override
public void onAdFailedToLoad(int errorCode) {
// The previous banner ad failed to load. Call this method again to load
// the next ad in the items list.
Log.e("ViewCoursesActivity", "The previous banner ad failed to load. Attempting to"
+ " load the next banner ad in the items list.");
loadBannerAd(index + ITEMS_PER_AD);
}
});
// Load the banner ad.
adView.loadAd(new AdRequest.Builder().build());
}
此后，我有两个问题：1.在第一位置显示的是广告，而不是我的数据库中的第一项，而第一项无处。如果我检查数据库中的第一项，则不会出现在recyclerview中。2.如果我要滚动项目，则应用程序崩溃，错误是“ java.lang.IndexOutOfBoundsException：索引：8，大小：1”。我究竟做错了什么？请帮我。谢谢！
我的一个问题解决了，而且我不敢相信我花了这么长时间才弄清楚……正如Sanjay Kumar所说，列表广告只有一项，因此ad.get（position）给出IndexOutOfBoundsException错误。解决方法非常简单。在适配器中，我替换为：
基本而言，RecyclerView用于向用户显示List。用它来指导您的实施。