RecyclerView不显示任何CardView项目 [英] RecyclerView Not Displaying Any CardView Items

问题描述

我已经从ListView切换到RecyclerView，并没有看到我的移动设备上显示的任何项目。

我知道一个事实，它不必做与 getItemCount（）方法，因为我已经硬编码了一个数字返回来测试它。

这是我的初始化，我用Firebase来获取新的数据：

$ @ $ $ $ $ b $保护无效的onCreate（Bundle savedInstanceState）{
super.onCreate（savedInstanceState）;
Firebase.setAndroidContext（this）;
setContentView（R.layout.activity_discussion）;
toolbar =（Toolbar）findViewById（R.id.tool_bar）;
setSupportActionBar（toolbar）;
setTitle（R.string.discussion_title_text）;

mDateFormat = new SimpleDateFormat（MM-dd-yyyy）;
mDate = new Date（）;
mCurrentDateString = mDateFormat.format（mDate）;

mBaseRef =新的Firebase（FIREBASE_URL）;
mPollsRef = mBaseRef.child（POLLS_LABEL）;
mUpdateRef = mPollsRef.child（mCurrentDateString）.child（String.valueOf（mPollIndex + 1））;
mCommentsRef = mUpdateRef.child（COMMENTS_LABEL）;

mPollImage =（ImageView）findViewById（R.id.comments_image）;
mPollCommentQuestion =（TextView）findViewById（R.id.poll_comment_question）;

mUserComment =（EditText）findViewById（R.id.user_comment）;
mUserAvatar =（ImageView）findViewById（R.id.profile_image_avatar）;
mPollCommentsList =（RecyclerView）findViewById（R.id.poll_comments_list）;
LinearLayoutManager llm = new LinearLayoutManager（this）;
llm.setOrientation（LinearLayoutManager.VERTICAL）;
mPollCommentsList.setLayoutManager（llm）;
mCommentArrayList = new ArrayList< Comments>（）;
mCommentIDArrayList = new ArrayList< String>（）;
mPollCommentsList.setAdapter（mCommentAdapter）;
getWindow（）。setSoftInputMode（WindowManager.LayoutParams.SOFT_INPUT_STATE_HIDDEN）;

Intent intent = getIntent（）;
String pollID = intent.getStringExtra（POLL_ID）;
mPollIndex = intent.getIntExtra（POLL_INDEX，0）;

$ b mUpdateRef.addListenerForSingleValueEvent（new ValueEventListener（）{
@Override
public void onDataChange（DataSnapshot dataSnapshot）{$ b $ setImage（dataSnapshot）;
setQuestion（dataSnapshot）;
createInitialCommentIDArray（dataSnapshot）;
mNumberOfCommentsAtPoll =（int）dataSnapshot.child（COMMENTS_LABEL）.getChildrenCount（）;
for（int i = 0; i< mNumberOfCommentsAtPoll; i ++）{
String commentID =（String）dataSnapshot.child（COMMENTS_LABEL）.child（mCommentIDArrayList.get（i））。child（COMMENT）。getValue（）;
Log.v （COMMENT_ID，评论ID是+ commentID）;
String userID =（String）dataSnapshot.child（COMMENTS_LABEL）.child（mCommentIDArrayList.get（i））。child（USER_ID）。getValue （）;
Log.v（USER_ID，用户ID是+ userID）;
mCommentArrayList.add（0，new Comments（mUserA vatar，userID，commentID））;
mCommentAdapter.notifyDataSetChanged（）;
}

}

@Override
public void onCancelled（FirebaseError firebaseError）{

}
} ）;
mCommentAdapter = new MyAdapter（mCommentArrayList）;

// TODO：将唯一注释ID存储在数组中

// TODO：了解如何以编程方式将图像添加到AWS，然后将URL存储在Firebase中
ImageView fab =（ImageView）findViewById（R.id.add_comment）;
fab.setOnClickListener（new View.OnClickListener（）{
@Override
public void onClick（View view）{
HashMap< String，Object> commentMap = new HashMap< String，对象>（）;
commentMap.put（USER_ID，mBaseRef.getAuth（）。getUid（））;
commentMap.put（COMMENT，mUserComment.getText（）。toString（）） ;
mUpdateRef.child（COMMENTS_LABEL）.push（）。updateChildren（commentMap）;
hideKeyboard（view）;
mUserComment.setText（）;
Toast.makeText getApplicationContext（），R.string.comment_added，Toast.LENGTH_LONG）.show（）;
}
}）;

$ / code $ / $ p

这是我的适配器：

  public class MyAdapter extends RecyclerView.Adapter< MyAdapter.ViewHolder> {
 
 private ArrayList< Comments> mDataSet; 
 
 //提供对每个数据项的视图的引用
 //复杂数据项可能需要每个项目多个视图，
 //您提供对所有数据项的访问视图持有者中的数据项的视图
 public class ViewHolder extends RecyclerView.ViewHolder {
 //在这种情况下，每个数据项只是一个字符串
 protected ImageView userAvatar; 
保护TextView userID; 
保护TextView userComment; 
 
 public ViewHolder（View v）{
 super（v）; 
 userAvatar =（ImageView）findViewById（R.id.profile_image_avatar）; 
 userID =（TextView）findViewById（R.id.user_ID）; 
 userComment =（TextView）findViewById（R.id.user_comment）; 
 
 
 
提供一个合适的构造函数（取决于数据集的类型）
 public MyAdapter（ArrayList< Comments> myDataset）{
 mDataSet = myDataset; 
} 
 
 //创建新视图（由布局管理器调用）
 @Override $ b $ public MyAdapter.ViewHolder onCreateViewHolder（ViewGroup parent，
 int viewType ）{
 //创建一个新视图
 View v = LayoutInflater.from（parent.getContext（））
 .inflate（R.layout.individual_comment，parent，false）; 
 //设置视图的大小，边距，填充和布局参数
 ViewHolder x = new ViewHolder（v）; 
 
 return x; 
} 
 
 //替换一个视图的内容（由布局管理器调用）
 $ b $ @覆盖
 public void onBindViewHolder（ViewHolder holder，int位置）{
 holder.userComment.setText（mCommentArrayList.get（position）.getUserComment（））; 
 holder.userID.setText（mCommentArrayList.get（position）.getUserID（））; 
 
 
 //返回数据集的大小（由布局管理器调用）
 @Override 
 public int getItemCount（）{
 return mNumberOfCommentsAtPoll ; 
 
 
 $ / code $ / pre 
 
解决方案
 Make确定你在 RecyclerAdapter 上设置了 LayoutManager 。最常见的方法是：
 $ b $ m $ c $ mCommentAdapter.setLayoutManager（LinearLayoutManager（this））;  
 
I have switched from ListView to RecyclerView and am not seeing any items displayed on my mobile device.

I know for a fact that it doesn't have to do with the getItemCount() method as I have hardcoded a number to that return to test it.

Here is my initialization, I used Firebase to pull new data:
 @Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    Firebase.setAndroidContext(this);
    setContentView(R.layout.activity_discussion);
    toolbar = (Toolbar) findViewById(R.id.tool_bar);
    setSupportActionBar(toolbar);
    setTitle(R.string.discussion_title_text);

    mDateFormat = new SimpleDateFormat("MM-dd-yyyy");
    mDate = new Date();
    mCurrentDateString = mDateFormat.format(mDate);

    mBaseRef = new Firebase(FIREBASE_URL);
    mPollsRef = mBaseRef.child(POLLS_LABEL);
    mUpdateRef = mPollsRef.child(mCurrentDateString).child(String.valueOf(mPollIndex + 1));
    mCommentsRef = mUpdateRef.child(COMMENTS_LABEL);

    mPollImage = (ImageView) findViewById(R.id.comments_image);
    mPollCommentQuestion = (TextView) findViewById(R.id.poll_comment_question);

    mUserComment = (EditText) findViewById(R.id.user_comment);
    mUserAvatar = (ImageView) findViewById(R.id.profile_image_avatar);
    mPollCommentsList = (RecyclerView) findViewById(R.id.poll_comments_list);
    LinearLayoutManager llm = new LinearLayoutManager(this);
    llm.setOrientation(LinearLayoutManager.VERTICAL);
    mPollCommentsList.setLayoutManager(llm);
    mCommentArrayList = new ArrayList<Comments>();
    mCommentIDArrayList = new ArrayList<String>();
    mPollCommentsList.setAdapter(mCommentAdapter);
    getWindow().setSoftInputMode(WindowManager.LayoutParams.SOFT_INPUT_STATE_HIDDEN);

    Intent intent = getIntent();
    String pollID = intent.getStringExtra("POLL_ID");
    mPollIndex = intent.getIntExtra("POLL_INDEX", 0);


    mUpdateRef.addListenerForSingleValueEvent(new ValueEventListener() {
        @Override
        public void onDataChange(DataSnapshot dataSnapshot) {
            setImage(dataSnapshot);
            setQuestion(dataSnapshot);
            createInitialCommentIDArray(dataSnapshot);
            mNumberOfCommentsAtPoll = (int) dataSnapshot.child(COMMENTS_LABEL).getChildrenCount();
            for (int i = 0; i < mNumberOfCommentsAtPoll; i++) {
                String commentID = (String) dataSnapshot.child(COMMENTS_LABEL).child(mCommentIDArrayList.get(i)).child("COMMENT").getValue();
                Log.v("COMMENT_ID", "The comment ID is " + commentID);
                String userID = (String) dataSnapshot.child(COMMENTS_LABEL).child(mCommentIDArrayList.get(i)).child("USER_ID").getValue();
                Log.v("USER_ID", "The user ID is " + userID);
                mCommentArrayList.add(0, new Comments(mUserAvatar, userID, commentID));
                mCommentAdapter.notifyDataSetChanged();
            }

        }

        @Override
        public void onCancelled(FirebaseError firebaseError) {

        }
    });
    mCommentAdapter = new MyAdapter(mCommentArrayList);

    //TODO: Store unique comment ID's in an array

    //TODO: Figure out how to programatically add images to AWS and then store URL in Firebase
    ImageView fab = (ImageView) findViewById(R.id.add_comment);
    fab.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View view) {
            HashMap<String, Object> commentMap = new HashMap<String, Object>();
            commentMap.put("USER_ID", mBaseRef.getAuth().getUid());
            commentMap.put("COMMENT", mUserComment.getText().toString());
            mUpdateRef.child(COMMENTS_LABEL).push().updateChildren(commentMap);
            hideKeyboard(view);
            mUserComment.setText("");
            Toast.makeText(getApplicationContext(), R.string.comment_added, Toast.LENGTH_LONG).show();
        }
    });
}
Here is my adapter:
public class MyAdapter extends RecyclerView.Adapter<MyAdapter.ViewHolder> {

    private ArrayList<Comments> mDataSet;

    // Provide a reference to the views for each data item
    // Complex data items may need more than one view per item, and
    // you provide access to all the views for a data item in a view holder
    public class ViewHolder extends RecyclerView.ViewHolder {
        // each data item is just a string in this case
        protected ImageView userAvatar;
        protected TextView userID;
        protected TextView userComment;

        public ViewHolder(View v) {
            super(v);
            userAvatar = (ImageView) findViewById(R.id.profile_image_avatar);
            userID = (TextView) findViewById(R.id.user_ID);
            userComment = (TextView) findViewById(R.id.user_comment);
        }
    }

    // Provide a suitable constructor (depends on the kind of dataset)
    public MyAdapter(ArrayList<Comments> myDataset) {
        mDataSet = myDataset;
    }

    // Create new views (invoked by the layout manager)
    @Override
    public MyAdapter.ViewHolder onCreateViewHolder(ViewGroup parent,
                                                   int viewType) {
        // create a new view
        View v = LayoutInflater.from(parent.getContext())
                .inflate(R.layout.individual_comment, parent, false);
        // set the view's size, margins, paddings and layout parameters
        ViewHolder x = new ViewHolder(v);

        return x;
    }

    // Replace the contents of a view (invoked by the layout manager)

    @Override
    public void onBindViewHolder(ViewHolder holder, int position) {
        holder.userComment.setText(mCommentArrayList.get(position).getUserComment());
        holder.userID.setText(mCommentArrayList.get(position).getUserID());
    }

    // Return the size of your dataset (invoked by the layout manager)
    @Override
    public int getItemCount() {
        return mNumberOfCommentsAtPoll;
    }
}

解决方案
Make sure you set a LayoutManager on your RecyclerAdapter.  The most common way would be:

mCommentAdapter.setLayoutManager(new LinearLayoutManager(this));

                        
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