Question

我有一个项目，我使用水平回收视图，我想要一个元素居中。我的实现有效，但不是在每种情况下都在这里检查这个GIF：

正如您可能注意到的，如果我从左边来，它会正确滚动。如果我来自右边，它会过度滚动，我不知道如何停止或如何解决这个问题。

我在这里将代码条带化为此示例：

public class DemoActivity extends ActionBarActivity implements View.OnClickListener {
    private static final int JUMP_TO_LEFT = MyAdapter.NON_VISIBLE_ITEMS + MyAdapter.VISIBLE_ITEMS - 1;
    private static final int JUMP_TO_RIGHT = MyAdapter.NON_VISIBLE_ITEMS;
    private LinearLayoutManager mLayoutManager;
    private RecyclerView mRecycler;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_demo);
        findViewById(android.R.id.button1).setOnClickListener(this);
        mRecycler = (RecyclerView)findViewById(R.id.recycler);
        MyAdapter mAdapter = new MyAdapter();
        mLayoutManager = new LinearLayoutManager(this, LinearLayoutManager.HORIZONTAL, false);
        mRecycler.setLayoutManager(mLayoutManager);
        mRecycler.setHasFixedSize(true);
        mRecycler.scrollToPosition(MyAdapter.NON_VISIBLE_ITEMS);
        mRecycler.setAdapter(mAdapter);
    }

    @Override
    public void onClick(View v) {
        int pos = mLayoutManager.findFirstVisibleItemPosition();
        int outer = (MyAdapter.VISIBLE_ITEMS - 1) / 2;
        if(pos + outer >= MyAdapter.ITEM_IN_CENTER) {
            mRecycler.smoothScrollToPosition(JUMP_TO_RIGHT);
        } else {
            mRecycler.smoothScrollToPosition(JUMP_TO_LEFT);
        }
    }
}

这是我的适配器：

public class MyAdapter extends RecyclerView.Adapter<MyAdapter.Holder> implements View.OnClickListener {
    public static final int VISIBLE_ITEMS = 7;
    public static final int NON_VISIBLE_ITEMS = 150;
    private static final int TOTAL_ITEMS = VISIBLE_ITEMS + NON_VISIBLE_ITEMS * 2;
    public static final int ITEM_IN_CENTER = (int)Math.ceil(VISIBLE_ITEMS / 2f) + NON_VISIBLE_ITEMS;

    private Calendar mCalendar;

    public MyAdapter() {
        mCalendar = GregorianCalendar.getInstance();
        setHasStableIds(true);
    }

    private int getToday() {
        return (int)TimeUnit.MILLISECONDS.toDays(System.currentTimeMillis());
    }

    @Override
    public int getItemCount() {
        return TOTAL_ITEMS;
    }

    @Override
    public Holder onCreateViewHolder(ViewGroup parent, int viewType) {
        final TextView tv = new TextView(parent.getContext());
        int width = parent.getWidth() / VISIBLE_ITEMS;
        tv.setLayoutParams(new TableRow.LayoutParams(width, ViewGroup.LayoutParams.MATCH_PARENT, 1));
        tv.setGravity(Gravity.CENTER);
        tv.setBackgroundColor(Color.TRANSPARENT);
        DisplayMetrics metrics = tv.getContext().getResources().getDisplayMetrics();
        float padding = TypedValue.applyDimension(TypedValue.COMPLEX_UNIT_DIP, 10, metrics);
        tv.setLineSpacing(padding, 1f);
        tv.setPadding(0, (int)padding, 0, 0);
        tv.setOnClickListener(this);
        return new Holder(tv);
    }

    @Override
    public void onBindViewHolder(Holder holder, int position) {
        int today = getToday();
        mCalendar.setTimeInMillis(System.currentTimeMillis());
        mCalendar.set(Calendar.HOUR_OF_DAY, 12); // set to noon to avoid energy saver time problems
        mCalendar.add(Calendar.DAY_OF_YEAR, position - ITEM_IN_CENTER + 1);
        DateFormat format = new SimpleDateFormat("E\nd");
        String label = format.format(mCalendar.getTime()).replace(".\n", "\n");
        int day = (int)TimeUnit.MILLISECONDS.toDays(mCalendar.getTimeInMillis());
        holder.update(day, today, label);
    }

    @Override
    public long getItemId(int position) {
        mCalendar.setTimeInMillis(System.currentTimeMillis());
        mCalendar.set(Calendar.HOUR_OF_DAY, 12); // set to noon to avoid energy saver time problems
        mCalendar.add(Calendar.DAY_OF_YEAR, position - ITEM_IN_CENTER + 1);
        DateFormat format = new SimpleDateFormat("dMMyyyy");
        return Long.parseLong(format.format(mCalendar.getTime()));
    }

    @Override
    public void onClick(View v) {
        String day = ((TextView)v).getText().toString().replace("\n", " ");
        Toast.makeText(v.getContext(), "You clicked on " + day, Toast.LENGTH_SHORT).show();
    }

    public class Holder extends RecyclerView.ViewHolder {
        private final Typeface font;

        private Holder(TextView v) {
            super(v);
            if(Build.VERSION.SDK_INT >= Build.VERSION_CODES.ICE_CREAM_SANDWICH) {
                font = Typeface.create("sans-serif-light", Typeface.NORMAL);
            } else {
                font = null;
            }
        }

        public void update(int day, int today, String label) {
            TextView tv = (TextView)itemView;
            tv.setText(label);

            if(day == today) {
                tv.setTextSize(18);
                tv.setTypeface(null, Typeface.BOLD);
            } else {
                tv.setTextSize(16);
                tv.setTypeface(font, Typeface.NORMAL);
            }

            tv.setBackgroundColor(0xff8dc380);
        }
    }
}

你看到了原因吗？为了使您更简单，我还将此代码放在GitHub上。 https://github.com/rekire/RecylcerViewBug

Answer 1

我找到了一个令人惊讶的简单解决方法：

@Override
public void onClick(View v) {
    int pos = mLayoutManager.findFirstVisibleItemPosition();
    int outer = (MyAdapter.VISIBLE_ITEMS + 1) / 2;
    int delta = pos + outer - ForecastAdapter.ITEM_IN_CENTER;
    //Log.d("Scroll", "delta=" + delta);
    View firstChild = mForecast.getChildAt(0);
    if(firstChild != null) {
        mForecast.smoothScrollBy(firstChild.getWidth() * -delta, 0);
    }
}

在这里，我计算自己跳跃的宽度，这正是我想要的。

Answer 2

如果LinearLayoutManager具有垂直方向，您可以创建自己的SmoothScroller并覆盖calculateDyToMakeVisible（）方法，您可以在其中设置所需的视图位置。例如，要在smoothScroll（）之后使目标视图始终出现在RecyclerView的顶部，请写下：

class CustomLinearSmoothScroller extends LinearSmoothScroller {

    public CustomLinearSmoothScroller(Context context) {
        super(context);
    }

    @Override
    public int calculateDyToMakeVisible(View view, int snapPreference) {
        final RecyclerView.LayoutManager layoutManager = getLayoutManager();
        if (!layoutManager.canScrollVertically()) {
            return 0;
        }
        final RecyclerView.LayoutParams params = (RecyclerView.LayoutParams)view.getLayoutParams();
        final int top = layoutManager.getDecoratedTop(view) - params.topMargin;
        final int bottom = layoutManager.getDecoratedBottom(view) + params.bottomMargin;
        final int viewHeight = bottom - top;
        final int start = layoutManager.getPaddingTop();
        final int end = start + viewHeight;
        return calculateDtToFit(top, bottom, start, end, snapPreference);
    }

“top”和“bottom” - 目标视图的范围

“start”和“end” - 在smoothScroll期间应放置视图的点

Answer 3

要支持平滑滚动，您必须覆盖   smoothScrollToPosition（RecyclerView，State，int）并创建一个   RecyclerView.SmoothScroller。

RecyclerView.LayoutManager负责   用于创建实际的滚动动作。如果要提供自定义   平滑滚动逻辑，覆盖smoothScrollToPosition（RecyclerView，   在LayoutManager中使用State，int。

https://developer.android.com/reference/android/support/v7/widget/RecyclerView.html#smoothScrollToPosition(int)

在您的情况下，使用smoothScrollBy可能是一种解决方法（不需要此覆盖）。

Answer 4

这对我有用：

itemsView.smoothScrollBy(-recyclerView.computeHorizontalScrollOffset(), 0)

RecyclerView无法按预期滚动

4 个答案: