Android Recycler 返回零 output 盡管每行都達到了 onBindViewHolder()

Question

我在我的應用程序的“教程”活動中放置了一個 RecyclerView，以列出來自我的應用程序擁有的 Room 數據庫的教程版本。 它托管在一個片段中，但這沒什么影響，因為在將它放在那里之前我遇到了同樣的問題。 RecyclerView 適配器到達 onBindViewHolder() 沒有任何問題，我從用於調試的 Log.w 中獲取日志，其中包含正確的數據。 問題似乎是 Layout 根本沒有膨脹，並且每行應該為 output 的按鈕從未出現。

適配器

public class VersionListAdapter extends RecyclerView.Adapter<VersionListAdapter.VersionViewHolder> {

    private List<Version> mVersionList;
    private final LayoutInflater mInflater;
    private final OnViewClickListener mListener;

    public VersionListAdapter(Context context)
    {
        this.mInflater = LayoutInflater.from(context);
        this.mVersionList = null;
        this.mListener = (OnViewClickListener) context;
    }

    @NonNull
    @Override
    public VersionViewHolder onCreateViewHolder(@NonNull ViewGroup viewGroup, int viewType) {
        View row = mInflater.inflate(R.layout.row_versions_rv, viewGroup, false);
        return new VersionViewHolder(row, mListener);
    }

    @Override
    public void onBindViewHolder(@NonNull VersionViewHolder versionHolder, int rowNumber) {
        versionHolder.thisVersion = mVersionList.get(rowNumber);
        versionHolder.versionButton.setText((mVersionList.get(rowNumber).getText()));
        Log.w("THIS IS A TAG", mVersionList.get(rowNumber).getText()); //correct output
    }

    @Override
    public int getItemCount() {
        if(mVersionList!=null) return mVersionList.size();
        else return 0;
    }

    public void setElementList(List<Version> versions){
        this.mVersionList = versions;
        notifyDataSetChanged();
    }

    public static class VersionViewHolder extends RecyclerView.ViewHolder
            implements View.OnClickListener
    {
        OnViewClickListener listenerForThisRow;
        Version thisVersion;
        Button versionButton;

        public VersionViewHolder(
                @NonNull View viewForThisRow, OnViewClickListener listenerFromActivity)
        {
            super(viewForThisRow);
            this.listenerForThisRow = listenerFromActivity;
            versionButton = viewForThisRow.findViewById(R.id.version_button);
            viewForThisRow.setOnClickListener(this);
        }

        @Override
        public void onClick(View v){
            listenerForThisRow.onViewClick(thisVersion);
        }
    }

    public interface OnViewClickListener{
        void onViewClick(Version version);
    }
}

承載回收站視圖的片段 CLASS

public class VersionRecycler extends Fragment {

    protected RecyclerView mRecycler;
    protected VersionListAdapter mAdapter;

    public VersionRecycler(){
        super(R.layout.fragment_recycler_versions);
    }

    @Override
    public View onCreateView(
            @NotNull LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState
    ) {
        VersionViewModel mVersionViewModel = new VersionViewModel(requireActivity().getApplication());
        long tutorialId = requireArguments().getLong("tutorialId");
        View view = inflater.inflate(R.layout.fragment_recycler_versions, container, false);
        mAdapter = new VersionListAdapter(requireActivity());
        mRecycler = view.findViewById(R.id.versions_rv);
        mRecycler.setLayoutManager(new LinearLayoutManager(view.getContext(), LinearLayoutManager.VERTICAL, false));
        mVersionViewModel.getByTutorialId(tutorialId).observe(requireActivity(), versions->mAdapter.setElementList(versions));
        mRecycler.setAdapter(mAdapter);
        return view;
    }
}

片段是如何嵌入到活動中的

 <LinearLayout
        android:id="@+id/layout_versions_list"
        android:layout_width="match_parent"
        android:layout_height="0dp"
        android:orientation="vertical"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintTop_toTopOf="parent"/>

片段布局

<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".versionrecycler.VersionRecycler">

    <androidx.recyclerview.widget.RecyclerView
        android:id="@+id/versions_rv"
        android:layout_width="match_parent"
        android:layout_height="0dp"
        app:layout_constraintTop_toTopOf="parent"
        tools:listitem="@layout/row_versions_rv"/>

</androidx.constraintlayout.widget.ConstraintLayout>

RECYCLERVIEW ROW 的布局

<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:baselineAligned="false">

    <Button
        android:id="@+id/version_button"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:textSize="40sp"
        app:layout_constraintTop_toTopOf="parent"/>

</androidx.constraintlayout.widget.ConstraintLayout>

Answer 1

您還應該添加 Start 和 Bottom 約束：

<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".versionrecycler.VersionRecycler">

    <androidx.recyclerview.widget.RecyclerView
        android:id="@+id/versions_rv"
        android:layout_width="match_parent"
        android:layout_height="0dp"
        app:layout_constraintTop_toTopOf="parent"

        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintBottom_toBottomOf="parent"

        tools:listitem="@layout/row_versions_rv"/>

</androidx.constraintlayout.widget.ConstraintLayout>

您還可以將 RecyclerView layout_height 更改為 wrap_content 並僅添加 Start 約束