AndroidRecyclerView什么也沒顯示-有解無憂

我創建了一個應用程式，它在 Fragment 中有一個 RecyclerView 來顯示資料庫中的資料。幾周前，我用 RecyclerView 和 android 支持包創建了另一個應用程式，一切都很好。現在，使用 androidx，視圖不顯示任何內容。這是我的 RecyclerViewAdapter 類：

public class HistoryRecyclerViewAdapter extends RecyclerView.Adapter<HistoryRecyclerViewAdapter.ViewHolder> {
    private static final String TAG = "HistoryRecyclerView";

    private List<HistoryType> mHistory;

    HistoryRecyclerViewAdapter(List<HistoryType> history){
        mHistory = history;
    }

    @Override
    public ViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
        Context context = parent.getContext();
        LayoutInflater inflater = LayoutInflater.from(context);

        View historyView = inflater.inflate(R.layout.history_list_item,parent,false);

        ViewHolder viewHolder = new ViewHolder(historyView);
        return viewHolder;
    }

    @Override
    public void onBindViewHolder(@NonNull ViewHolder holder, int position) {
        HistoryType history = mHistory.get(position);

        SimpleDateFormat formatter;
        Calendar calendar;


        TextView nameText = holder.mNameText;
        nameText.setText(history.getName());

        TextView durationText = holder.mDurationText;
        formatter = new SimpleDateFormat("HH:mm:ss");
        calendar = Calendar.getInstance();
        calendar.setTimeInMillis(history.getDuration());
        String durationString = formatter.format(calendar.getTime());
        durationText.setText(durationString);

        TextView distanceText = holder.mDistanceText;
        distanceText.setText(String.format("%.2f km",history.getDistance()));

        TextView totalAirTimeText = holder.mTotalAirTimeText;
        formatter = new SimpleDateFormat("mm:ss.SS");
        calendar = Calendar.getInstance();
        calendar.setTimeInMillis(history.getTotalAirTime());
        String totalAirTimeString = formatter.format(calendar.getTime());
        totalAirTimeText.setText(totalAirTimeString);

        TextView dateText= holder.mDateText;
        formatter = new SimpleDateFormat("dd MMMM yyyy");
        String dateString = formatter.format(history.getDate());
        dateText.setText(dateString);
    }

    @Override
    public int getItemCount() {
        return mHistory.size();
    }


    public class ViewHolder extends RecyclerView.ViewHolder{

        public TextView mNameText;
        public TextView mDurationText;
        public TextView mDistanceText;
        public TextView mTotalAirTimeText;
        public TextView mDateText;

        public ViewHolder(View itemView) {
            super(itemView);

            mNameText = (TextView) itemView.findViewById(R.id.history_name);
            mDurationText = (TextView) itemView.findViewById(R.id.history_duration);
            mDistanceText = (TextView) itemView.findViewById(R.id.history_distance);
            mTotalAirTimeText = (TextView) itemView.findViewById(R.id.history_airtime);
            mDateText = (TextView) itemView.findViewById(R.id.history_date);

        }
    }

這里是呼叫配接器的片段（ArrayList 有一項）：

public class HistoryFragment extends Fragment {

    private ArrayList<HistoryType> mHistoryList = new ArrayList<>();
    private RecyclerView mRecyclerView;
    private HistoryRecyclerViewAdapter mHistoryAdapter;
    private SQLiteOpenHelper mSqliteOpenHelper;
    @Nullable
    @Override
    public View onCreateView(@NonNull LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {
        View view = inflater.inflate(R.layout.fragment_history, container, false);

        mRecyclerView = (RecyclerView) view.findViewById(R.id.history_recycler);

        return view;
    }

    @Override
    public void onViewCreated(@NonNull View view, @Nullable Bundle savedInstanceState) {
        super.onViewCreated(view, savedInstanceState);
        mHistoryAdapter = new HistoryRecyclerViewAdapter(mHistoryList);

        mRecyclerView.setLayoutManager(new LinearLayoutManager(view.getContext()));
        mRecyclerView.setAdapter(mHistoryAdapter);

        mSqliteOpenHelper = new SQLiteOpenHelper(getActivity());
        mHistoryList = mSqliteOpenHelper.getHistory();

        for (HistoryType dataSet: mHistoryList) {
            mHistoryAdapter.notifyItemInserted(mHistoryList.indexOf(dataSet));
        }

    }

fragment_history.xml

<?xml version="1.0" encoding="utf-8"?>
<androidx.recyclerview.widget.RecyclerView
    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:id="@ id/history_recycler"
    android:layout_marginLeft="@dimen/text_margin"
    android:layout_marginRight="@dimen/text_margin"
    app:layoutManager="androidx.recyclerview.widget.LinearLayoutManager"/>

history_list_item.xml

<?xml version="1.0" encoding="utf-8"?>

<androidx.constraintlayout.widget.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    xmlns:app="http://schemas.android.com/apk/res-auto">

    //Name
    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:id="@ id/history_name"
        android:layout_margin="@dimen/text_margin"
        android:text="activity name"
        app:layout_constraintLeft_toLeftOf="parent"
        app:layout_constraintTop_toTopOf="parent"
        android:textSize="@dimen/big_text_size"
        android:textStyle="bold"
        />

    //Duration
    <ImageView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:id="@ id/history_duration_icon"
        android:layout_marginTop="@dimen/text_margin"
        android:layout_marginRight="@dimen/icon_margin"
        android:layout_marginLeft="@dimen/text_margin"
        app:layout_constraintTop_toBottomOf="@id/history_name"
        app:layout_constraintLeft_toLeftOf="parent"
        android:background="@drawable/timer_24" />

    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:id="@ id/history_duration"
        android:text="01.01.2021"
        android:layout_margin="@dimen/text_margin"
        app:layout_constraintTop_toBottomOf="@id/history_name"
        app:layout_constraintLeft_toRightOf="@id/history_duration_icon"
        android:textSize="@dimen/medium_text_size"/>

    //Distance
    <ImageView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:id="@ id/history_distance_icon"
        android:layout_marginTop="@dimen/text_margin"
        android:layout_marginLeft="@dimen/text_margin"
        android:layout_marginRight="@dimen/icon_margin"
        app:layout_constraintTop_toBottomOf="@id/history_name"
        app:layout_constraintLeft_toRightOf="@id/history_duration"
        android:background="@drawable/arrow_right_alt_24"/>

    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:id="@ id/history_distance"
        android:text="1h 35min"
        android:layout_marginTop="@dimen/text_margin"
        android:layout_marginLeft="@dimen/icon_margin"
        app:layout_constraintTop_toBottomOf="@id/history_name"
        app:layout_constraintLeft_toRightOf="@id/history_distance_icon"
        android:textSize="@dimen/medium_text_size"/>

    //Total Airtime
    <ImageView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:id="@ id/history_airtime_icon"
        android:layout_marginTop="@dimen/text_margin"
        android:layout_marginLeft="@dimen/text_margin"
        android:layout_marginRight="@dimen/icon_margin"
        app:layout_constraintTop_toBottomOf="@id/history_name"
        app:layout_constraintLeft_toRightOf="@id/history_distance"
        android:background="@drawable/keyboard_arrow_up_24"/>

    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:id="@ id/history_airtime"
        android:text="1h 35min"
        android:layout_marginTop="@dimen/text_margin"
        android:layout_marginLeft="@dimen/icon_margin"
        app:layout_constraintTop_toBottomOf="@id/history_name"
        app:layout_constraintLeft_toRightOf="@id/history_airtime_icon"
        android:textSize="@dimen/medium_text_size"/>

    //Date
    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:id="@ id/history_date"
        android:text="01.01.2021"
        android:layout_margin="@dimen/text_margin"
        app:layout_constraintTop_toBottomOf="@id/history_duration_icon"
        app:layout_constraintLeft_toLeftOf="parent"
        android:textSize="@dimen/small_text_size" />


</androidx.constraintlayout.widget.ConstraintLayout>

有人幫我嗎？非常感謝

uj5u.com熱心網友回復：

據我所知，您的參考資料有問題。首先，您使用 ArrayList 的空實體宣告您的配接器，這沒問題。配接器現在已與此 ArrayList 連接。但是隨后您將串列重新分配給另一個實體，即從

mSqliteOpenHelper.getHistory()

如果比較這兩個實體，您會發現它們并不相同。您應該做的是使用“addAll()”將“mSqliteOpenHelper.getHistory()”的結果添加到已與配接器連接的串列（您已經定義的空ArrayList）。

編輯：只是為了讓自己更清楚：一開始你宣告并初始化你的串列

private ArrayList<HistoryType> mHistoryList = new ArrayList<>();

我們稱這個實體為Instance#1。您將 Instance#1 設定為配接器的資料源。配接器現在有一個空的資料源。

之后，您重新分配此串列

        mHistoryList = mSqliteOpenHelper.getHistory();

這是一個不同的 ArrayList 實體，我們稱之為 Instance#2。盡管 mHistoryList 變數保存了這個實體，但配接器仍然與 Instance#1 鏈接，只是您不再參考它。因此，配接器與空的 ArrayList（Instance#1）鏈接，而不是與有資料的 ArrayList（Instance#2）鏈接。不要重新分配變數，使其成為最終的。ArrayList 是可變的，因此您可以向其中添加資料。因此，將資料添加到其中并通知配接器它已更改。

如果您有任何問題，請告訴我

轉載請註明出處，本文鏈接：https://www.uj5u.com/qianduan/403265.html

標籤：

上一篇：如何使用fn_map將陣列C中的每一行映射到陣列B中的對應行

下一篇：img不顯示在Android上