Question

作品：

<FlatList
  data={['0', '1', '2', '3', '4']}
  renderItem={({ item }) => (
    <Button title={item} />
  )}
/>

不起作用（没有渲染）：

<FlatList
  data={[...Array(5).keys()].map(String)}
  renderItem={({ item }) => (
    <Button title={item} />
  )}
/>

可能是什么原因？

Answer 1

它实际上有效，请查看下面的演示

https://snack.expo.io/H1elODwPb

代码

public class TaskProvider extends ContentProvider {

    private static final String TAG = "TaskProvider";
    private static final int TASKS=100;
    private static final int TASK_ID=101;
    private static final UriMatcher URI_MATCHER=new UriMatcher(UriMatcher.NO_MATCH);

    static {
        URI_MATCHER.addURI(TaskContract.CONTENT_AUTHORITY,TaskContract.PATH_TASKS,TASKS);
        URI_MATCHER.addURI(TaskContract.CONTENT_AUTHORITY,TaskContract.PATH_TASKS+"/#",TASK_ID);
    }

    private TaskDBHelper taskDBHelper;

    @Override
    public boolean onCreate() {

        taskDBHelper=new TaskDBHelper(getContext());
        return true;
    }

    @Nullable
    @Override
    public Cursor query(@NonNull Uri uri, @Nullable String[] projection, @Nullable String selection, @Nullable String[] selectionArgs, @Nullable String sortOrder) {
       SQLiteDatabase sqLiteDatabase=taskDBHelper.getReadableDatabase();
        Cursor cursor;

        int match=URI_MATCHER.match(uri);
        switch (match){
            case TASKS:
                cursor=sqLiteDatabase.query(TaskContract.TaskEntry.TABLE_NAME,projection,selection,
                        selectionArgs,null,null,sortOrder);
                break;
            case TASK_ID:
                selection= TaskContract.TaskEntry._ID+"=?";
                selectionArgs=new String[]{String.valueOf(ContentUris.parseId(uri))};
                cursor=sqLiteDatabase.query(TaskContract.TaskEntry.TABLE_NAME,projection,selection,
                        selectionArgs,null,null,sortOrder);
                break;
            default:
                throw new IllegalArgumentException("Cannot query Unknown Uri "+uri);
        }
        cursor.setNotificationUri(getContext().getContentResolver(),uri);
        return cursor;
    }

    @Nullable
    @Override
    public String getType(@NonNull Uri uri) {
        final int match = URI_MATCHER.match(uri);
        switch (match) {
            case TASKS:
                return TaskContract.TaskEntry.CONTENT_LIST_TYPE;
            case TASK_ID:
                return TaskContract.TaskEntry.CONTENT_ITEM_TYPE;
            default:
                throw new IllegalStateException("Unknown URI " + uri + " with match " + match);
        }
    }

    @Nullable
    @Override
    public Uri insert(@NonNull Uri uri, @Nullable ContentValues values) {
        final int match=URI_MATCHER.match(uri);
        switch (match){
            case TASKS:
                return insertTask(uri,values);
            default:
                throw new IllegalArgumentException("Insertion is not supported for "+uri);

        }
    }

    private Uri insertTask(Uri uri, ContentValues values) {
        String name=values.getAsString(TaskContract.TaskEntry.NAME);
        if(name==null){
            throw new IllegalArgumentException("Task Name is required");
        }

       /* String duedate=values.getAsString(TaskContract.TaskEntry.DUEDATE);
        if(duedate==null){
            throw new IllegalArgumentException("DUEDATE is required");
        }

        String duetime=values.getAsString(TaskContract.TaskEntry.DUETIME);
        if(duetime==null){
            throw new IllegalArgumentException("DUETIME is required");
        }*/

        SQLiteDatabase sqLiteDatabase=taskDBHelper.getWritableDatabase();
        long id=sqLiteDatabase.insert(TaskContract.TaskEntry.TABLE_NAME,
                null,values);
        if(id==-1){
            return null;
        }
        getContext().getContentResolver().notifyChange(uri,null);
        return ContentUris.withAppendedId(uri,id);
    }

    @Override
    public int delete(@NonNull Uri uri, @Nullable String selection, @Nullable String[] selectionArgs) {
        SQLiteDatabase database = taskDBHelper.getWritableDatabase();

        // Track the number of rows that were deleted
        int rowsDeleted;

        final int match = URI_MATCHER.match(uri);
        switch (match) {
            case TASKS:
                // Delete all rows that match the selection and selection args
                rowsDeleted = database.delete(TaskContract.TaskEntry.TABLE_NAME, selection, selectionArgs);
                break;
            case TASK_ID:
                // Delete a single row given by the ID in the URI
                selection = TaskContract.TaskEntry._ID + "=?";
                selectionArgs = new String[] { String.valueOf(ContentUris.parseId(uri)) };
                rowsDeleted = database.delete(TaskContract.TaskEntry.TABLE_NAME, selection, selectionArgs);
                break;
            default:
                throw new IllegalArgumentException("Deletion is not supported for " + uri);
        }

        // If 1 or more rows were deleted, then notify all listeners that the data at the
        // given URI has changed
        if (rowsDeleted != 0) {
            getContext().getContentResolver().notifyChange(uri, null);
        }

        // Return the number of rows deleted
        return rowsDeleted;
    }

    @Override
    public int update(@NonNull Uri uri, @Nullable ContentValues values, @Nullable String selection, @Nullable String[] selectionArgs) {
        final int match=URI_MATCHER.match(uri);
        switch (match){
            case TASKS:
                return updateTask(uri,values,selection,selectionArgs);

            case TASK_ID:
                selection = TaskContract.TaskEntry._ID + "=?";
                selectionArgs = new String[] { String.valueOf(ContentUris.parseId(uri)) };
                return updateTask(uri, values, selection, selectionArgs);
            default:
                throw new IllegalArgumentException("Update is not supported for " + uri);

        }

    }

    private int updateTask(Uri uri, ContentValues values, String selection, String[] selectionArgs) {
        if (values.containsKey(TaskContract.TaskEntry.NAME)) {
            String name = values.getAsString(TaskContract.TaskEntry.NAME);
            if (name == null) {
                throw new IllegalArgumentException("Task requires a name");
            }
        }

        if (values.containsKey(TaskContract.TaskEntry.DUEDATE)) {
            String duedate = values.getAsString(TaskContract.TaskEntry.DUEDATE);
            if (duedate == null) {
                throw new IllegalArgumentException("Task requires a duedate");
            }
        }

        if (values.containsKey(TaskContract.TaskEntry.DUETIME)) {
            String duetime = values.getAsString(TaskContract.TaskEntry.DUETIME);
            if (duetime == null) {
                throw new IllegalArgumentException("Task requires a duetime");
            }
        }


        // If there are no values to update, then don't try to update the database
        if (values.size() == 0) {
            return 0;
        }

        // Otherwise, get writeable database to update the data
        SQLiteDatabase database = taskDBHelper.getWritableDatabase();

        // Perform the update on the database and get the number of rows affected
        int rowsUpdated = database.update(TaskContract.TaskEntry.TABLE_NAME, values, selection, selectionArgs);

        // If 1 or more rows were updated, then notify all listeners that the data at the
        // given URI has changed
        if (rowsUpdated != 0) {
            getContext().getContentResolver().notifyChange(uri, null);
        }

        // Return the number of rows updated
        return rowsUpdated;

    }
}

React Native FlatList不使用构造数据

1 个答案: