我试着理解如何根据对象的某些信息轻松地告诉两个不同的观点...
我的设置是这样的，但我一直在崩溃这个错误：
java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.TextView.setTypeface(android.graphics.Typeface)' on a null object reference
指向这一行：
myViewHolder.commentUsername.setTypeface(boldTypeface);
这是我的适配器：
public class CommentsAdapter extends RecyclerView.Adapter<RecyclerView.ViewHolder> {
private List<DatabaseComment> dbCommentsList;
private DatabaseHelper db;
private Context context;
private Typeface typeFace, italicTypeface, boldTypeface;
public class MyViewHolder extends RecyclerView.ViewHolder implements View.OnClickListener{
public TextView commentUsername, commentUserMsg, commentUserDate, commentUserRemove;
public ImageView emojiIcon;
public MyViewHolder(View view) {
super(view);
commentUsername = (TextView) view.findViewById(R.id.userAdapterUsername);
commentUserMsg = (TextView) view.findViewById(R.id.commentUserMsg);
commentUserDate = (TextView) view.findViewById(R.id.commentUserDate);
commentUserRemove = (TextView) view.findViewById(R.id.commentUserRemove);
emojiIcon = (ImageView) view.findViewById(R.id.emojiIcon);
Log.d(Constants.DEBUG, "IN MY VIEW HOLDER");
view.setOnClickListener(this);
commentUserRemove.setOnClickListener(this);
}
@Override
public void onClick(View v) {
if (mOnEntryClickListener != null) {
Log.d(Constants.DEBUG, "IN On click");
mOnEntryClickListener.onEntryClick(v, getAdapterPosition());
}
}
}
private static OnEntryClickListener mOnEntryClickListener;
public interface OnEntryClickListener {
void onEntryClick(View view, int position);
}
public void setOnEntryClickListener(OnEntryClickListener onEntryClickListener) {
mOnEntryClickListener = onEntryClickListener;
}
public class MyFeatureViewHolder extends RecyclerView.ViewHolder {
public TextView commentCompany, commentCompanyMsg, commentCompanyDate;
public ImageView emojiIcon;
public MyFeatureViewHolder(View view) {
super(view);
commentCompany = (TextView) view.findViewById(R.id.commentCompany);
commentCompanyMsg = (TextView) view.findViewById(R.id.commentCompanyMsg);
commentCompanyDate = (TextView) view.findViewById(R.id.commentCompanyDate);
emojiIcon = (ImageView) view.findViewById(R.id.emojiIcon);
Log.d(Constants.DEBUG, "IN MY VIEW HOLDER");
}
}
public CommentsAdapter(Context mContext, List<DatabaseComment> comments, Typeface myTypeface, Typeface myTypefaceItalic, Typeface myTypefaceBold) {
context = mContext;
db = new DatabaseHelper(context);
dbCommentsList = comments;
typeFace = myTypeface;
italicTypeface = myTypefaceItalic;
boldTypeface = myTypefaceBold;
}
@Override
public RecyclerView.ViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
switch (viewType){
case 0:
return new MyFeatureViewHolder(LayoutInflater.from(parent.getContext())
.inflate(R.layout.comment_business_item, parent, false));
case 1:
return new MyFeatureViewHolder(LayoutInflater.from(parent.getContext())
.inflate(R.layout.comment_user_item, parent, false));
}
return new MyViewHolder(LayoutInflater.from(parent.getContext())
.inflate(R.layout.comment_user_item, parent, false));
}
@Override
public void onBindViewHolder(RecyclerView.ViewHolder holder, int position) {
//int pos = getItemViewType(position);
//is a business comment
if(dbCommentsList.get(position).getIsType() == 0) {
MyFeatureViewHolder featureViewHolder = (MyFeatureViewHolder) holder;
DatabaseComment dbComment = dbCommentsList.get(position);
featureViewHolder.commentCompany.setTypeface(boldTypeface);
featureViewHolder.commentCompanyMsg.setTypeface(typeFace);
featureViewHolder.commentCompanyDate.setTypeface(italicTypeface);
featureViewHolder.commentCompany.setText(dbComment.getUsername());
featureViewHolder.commentCompanyMsg.setText(dbComment.getCommentText());
Calendar date = Calendar.getInstance();
date.setTimeInMillis(dbComment.getCommentDate());
String commentDateTxt = (date.get(Calendar.MONTH) + "." + date.get(Calendar.DAY_OF_MONTH) + "." + date.get(Calendar.YEAR));
featureViewHolder.commentCompanyDate.setText(commentDateTxt);
//anything greater than 0 is a user comment
} else {
//TODO show x button near viewHolder if isChanged is 1
MyViewHolder myViewHolder = (MyViewHolder) holder;
if(dbCommentsList.get(position).getIsChanged() == 1) {
myViewHolder.commentUserRemove.setVisibility(View.VISIBLE);
} else {
myViewHolder.commentUserRemove.setVisibility(View.GONE);
}
DatabaseComment dbComment = dbCommentsList.get(position);
myViewHolder.commentUsername.setTypeface(boldTypeface);
myViewHolder.commentUserMsg.setTypeface(typeFace);
myViewHolder.commentUserDate.setTypeface(italicTypeface);
myViewHolder.commentUsername.setText(dbComment.getUsername());
myViewHolder.commentUserMsg.setText(dbComment.getCommentText());
Calendar date = Calendar.getInstance();
date.setTimeInMillis(dbComment.getCommentDate());
String commentDateTxt = (date.get(Calendar.MONTH) + "." + date.get(Calendar.DAY_OF_MONTH) + "." + date.get(Calendar.YEAR));
myViewHolder.commentUserDate.setText(commentDateTxt);
int[] commentsImageList = new int[]{R.drawable.ic_announcement_black_18dp, R.drawable.ic_announcement_black_18dp, R.drawable.ic_announcement_black_18dp, R.drawable.ic_explore_black_18dp};
myViewHolder.emojiIcon.setImageResource(commentsImageList[dbComment.getIsType()]);
}
//grab more comments
if(position > (dbCommentsList.size() - 3) && (dbCommentsList.size() % 20) == 0) {
grabMoreComments();
}
}
private void grabMoreComments() {
//TODO
//GRABAPI - OFFSET dbCommentsList.SIZE - IN LIMIT OF 20
}
@Override
public int getItemCount() {
return dbCommentsList.size();
}
@Override
public int getItemViewType(int position) {
if(dbCommentsList.get(position).getIsType() == 0) {
return 0;
}
return 1;
}
}
这是我设置适配器的类：
private void setupAdapter() {
commentsAdapter = new CommentsAdapter(this, dbCommentsList, TypeFaceProvider.getTypeFace(this, 0),
TypeFaceProvider.getTypeFace(this, 1), TypeFaceProvider.getTypeFace(this, 2));
RecyclerView.LayoutManager mLayoutManager = new LinearLayoutManager(getApplicationContext());
commentsRecyclerView.setLayoutManager(mLayoutManager);
commentsRecyclerView.setItemAnimator(new DefaultItemAnimator());
//TODO CHECK THAT CLICKING ON COMMENT BY BUSINESS NOTHING HAPPENS
commentsAdapter.setOnEntryClickListener(new CommentsAdapter.OnEntryClickListener() {
@Override
public void onEntryClick(View view, int position) {
DatabaseComment comment = dbCommentsList.get(position);
TextView deleteBtn = (TextView) view.findViewById(R.id.commentUserRemove);
if(view == deleteBtn) {
//used to remove the comment from db and the list
db.removeSingleComment(comment);
dbCommentsList.remove(position);
commentsAdapter.notifyDataSetChanged();
} else {
Toast.makeText(getApplicationContext(), comment.getUsername() + " is selected!", Toast.LENGTH_SHORT).show();
takeToUserProfile(dbCommentsList.get(position));
}
}
});
commentsRecyclerView.setAdapter(commentsAdapter);
commentsAdapter.notifyDataSetChanged();
}
所以在适配器中getItemViewType没有正确完成...如果注释isType为0表示一个视图而其他任何东西显示另一个视图怎么说？
答案 0 :(得分：3)
首先，您需要覆盖适配器的getItemViewType，如下所示:(我假设您可以将viewholders与对象的getType()方法匹配。）
@Override
public int getItemViewType(int position) {
return items.get(position).getType();
}
在您的onCreateViewHolder方法切换类型中，返回相关的视图。
@Override
public RecyclerView.ViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
View view = null;
switch (viewType) {
case ITEM_TYPE_A:
view = mInflater.inflate(R.layout.your_row_a, parent, false);
return new ATypeViewHolder(view);
case ITEM_TYPE_B:
view = mInflater.inflate(R.layout.your_row_b, parent, false);
return new BTypeViewHolder(view);
}
}
使用适配器的onBindViewHolder方法。
@Override
public void onBindViewHolder(RecyclerView.ViewHolder holder, int position) {
Item item = items.get(position);
if(item != null){
initializeViews(item, holder, position);
}
}
最后，在您的initializeViews方法中，根据您的项目类型投射您的观看者并使用它：
private void initializeViews(final Item item, final RecyclerView.ViewHolder viewHolder, final int position) {
swtich(item.gettype())
{
case ITEM_TYPE_A:
ATypeViewHolder holder = (ATYpeViewHolder)viewHolder;
// init your views
case ITEM_TYPE_B:
BTypeViewHolder holder = (BTypeViewHolder)viewHolder;
// init your views.
}
}
不是：您的观看者必须扩展RecyclerView.ViewHolder
我希望这对你有帮助。祝你好运。
答案 1 :(得分：1)
根据错误，它看起来像布局文件中缺少id为R.id.userAdapterUsername的视图comment_user_item.xml