Android RecyclerView 未按预期滚动
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原文地址: http://stackoverflow.com/questions/25684167/
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StackOverFlow
RecyclerView does not scroll as expected
提问by rekire
I have a project where I use a horizontal recycler view and I want to center one element. My implementation works, but not in every case check this GIF here:
我有一个项目，我使用水平回收器视图，我想将一个元素居中。我的实现有效，但并非在所有情况下都可以在此处检查此 GIF：
As you may note it scrolls correctly if I come from the left. If I come from the right it overscrolls a lot and I have no idea how to stop nor how to fix that.
正如您可能注意到的那样，如果我来自左侧，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。
I striped my code to this example here:
我将我的代码条带化到此示例中：
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);
}
}
}
And here is my adapter:
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);
}
}
}
Do you see a reason for that? To make it simpler for you I also put this code on GitHub. https://github.com/rekire/RecylcerViewBug
你看有什么原因吗？为了让您更简单，我还将此代码放在 GitHub 上。https://github.com/rekire/RecylcerViewBug
采纳答案by rekire
I found a surprising simple workaround:
我发现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);
}
}
Here I calculate the width to jump myself, that does exactly what I want.
在这里，我计算自己跳跃的宽度，这正是我想要的。
回答by forcelain
In case of LinearLayoutManager with vertical orientation you can create own SmoothScroller and override calculateDyToMakeVisible() method where you can set desired view position. For example, to make the target view always to be appeared at the top side of RecyclerView after smoothScroll() write this:
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，要使目标视图在 smoothScroll() 之后始终出现在 RecyclerView 的顶部，请编写以下内容：
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" and "bottom" - bounds of the target view
"top" 和 "bottom" - 目标视图的边界
"start" and "end" - points between which the view should be placed during smoothScroll
"start" 和 "end" - 在 smoothScroll 期间应放置视图的点
回答by Ixx
This worked for me:
这对我有用：
itemsView.smoothScrollBy(-recyclerView.computeHorizontalScrollOffset(), 0)
回答by stankocken
To support smooth scrolling, you must override smoothScrollToPosition(RecyclerView, State, int) and create a RecyclerView.SmoothScroller.
RecyclerView.LayoutManager is responsible for creating the actual scroll action. If you want to provide a custom smooth scroll logic, override smoothScrollToPosition(RecyclerView, State, int) in your LayoutManager.
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 负责创建实际的滚动动作。如果要提供自定义平滑滚动逻辑，请在 LayoutManager 中覆盖 smoothScrollToPosition(RecyclerView, State, int)。
In your case, use smoothScrollBy could be a workaround (doesn't need this override).
在您的情况下，使用 smoothScrollBy 可能是一种解决方法（不需要此覆盖）。
