如何在水平RecyclerView中捕捉到LinearSnapHelper的特定位置? [英] How to snap to particular position of LinearSnapHelper in horizontal RecyclerView?
本文介绍了如何在水平RecyclerView中捕捉到LinearSnapHelper的特定位置?的处理方法，对大家解决问题具有一定的参考价值，需要的朋友们下面随着小编来一起学习吧！
问题描述
如何在水平RecyclerView中捕捉到LinearSnapHelper()的特定位置? RecyclerView有一个功能scrolltoposition，可滚动到该位置，但不会在此snaphelper的中心位置保持不变.
我正在寻找下图所示的内容.因此，当我设置到特定位置时，它将保持居中.我没有找到与 SnapHelper 的选择位置相关的任何内容
我找到此 ，但这对我没有帮助. 任何帮助将不胜感激.
解决方案
如果我理解您的问题，则您正在寻找一种跳到某个位置并将该位置居于RecyclerView中心的方法.
也许您已经尝试过RecyclerView.scrollToPosition()，但是并不能捕捉到视图.您可能还尝试过RecyclerView.smoothScrollToPosition()，并且效果更好，但是如果您有很多项目并且滚动很长的距离，则可能希望避免所有移动.
scrollToPosition()不起作用的原因是，它不会触发使用滚动侦听器检测何时捕捉的LinearSnapHelper.由于smoothScrollToPosition()确实触发了LinearSnapHelper，因此我们将使用scrollToPosition()将我们带到目标视图的区域，然后使用smoothScrollToPosition()将视图居中，如下所示:
private RecyclerView mRecycler;
private void newScrollTo(final int pos) {
RecyclerView.ViewHolder vh = mRecycler.findViewHolderForLayoutPosition(pos);
if (vh != null) {
// Target view is available, so just scroll to it.
mRecycler.smoothScrollToPosition(pos);
} else {
// Target view is not available. Scroll to it.
mRecycler.addOnScrollListener(new RecyclerView.OnScrollListener() {
// From the documentation:
// This callback will also be called if visible item range changes after a layout
// calculation. In that case, dx and dy will be 0.This callback will also be called
// if visible item range changes after a layout calculation. In that case,
// dx and dy will be 0.
@Override
public void onScrolled(RecyclerView recyclerView, int dx, int dy) {
super.onScrolled(recyclerView, dx, dy);
mRecycler.removeOnScrollListener(this);
if (dx == 0) {
newScrollTo(pos);
}
}
});
mRecycler.scrollToPosition(pos);
}
}
示例应用
MainActivity.java
public class MainActivity extends AppCompatActivity {
private final LinearLayoutManager mLayoutManager = new LinearLayoutManager(this, LinearLayoutManager.HORIZONTAL, false);
private final List<String> mItems = new ArrayList<>();
private RecyclerView mRecycler;
private final int mItemCount = 2000;
private final Handler mHandler = new Handler();
private final LinearSnapHelper mLinearSnapHelper = new LinearSnapHelper();
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
for (int i = 0; i < mItemCount; i++) {
mItems.add(i + "");
}
mRecycler = findViewById(R.id.recyclerView);
final RecyclerViewAdapter adapter = new RecyclerViewAdapter(null);
adapter.setItems(mItems);
mRecycler.setLayoutManager(mLayoutManager);
mRecycler.setAdapter(adapter);
mLinearSnapHelper.attachToRecyclerView(mRecycler);
newScrollTo(1);
// fireScrollTo();
}
private int maxScrolls = mItemCount;
private void fireScrollTo() {
if (--maxScrolls > 0) {
int pos = (int) (Math.random() * mItemCount);
newScrollTo(pos);
mHandler.postDelayed(new Runnable() {
@Override
public void run() {
fireScrollTo();
}
}, 2000);
}
}
private void newScrollTo(final int pos) {
mRecycler.smoothScrollToPosition(pos);
RecyclerView.ViewHolder vh = mRecycler.findViewHolderForLayoutPosition(pos);
if (vh != null) {
// Target view is available, so just scroll to it.
mRecycler.smoothScrollToPosition(pos);
} else {
// Target view is not available. Scroll to it.
mRecycler.addOnScrollListener(new RecyclerView.OnScrollListener() {
// From the documentation:
// This callback will also be called if visible item range changes after a layout
// calculation. In that case, dx and dy will be 0.This callback will also be called
// if visible item range changes after a layout calculation. In that case,
// dx and dy will be 0.
@Override
public void onScrolled(RecyclerView recyclerView, int dx, int dy) {
super.onScrolled(recyclerView, dx, dy);
mRecycler.removeOnScrollListener(this);
if (dx == 0) {
newScrollTo(pos);
}
}
});
mRecycler.scrollToPosition(pos);
}
}
}
activity_main.xml
<android.support.constraint.ConstraintLayout
android:layout_width="match_parent"
android:layout_height="match_parent">
<View
android:layout_width="3px"
android:layout_height="match_parent"
android:background="@android:color/holo_red_light"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toTopOf="parent" />
<android.support.v7.widget.RecyclerView
android:id="@+id/recyclerView"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:clipToPadding="false"
android:paddingStart="660px"
android:paddingEnd="660px"/>
</android.support.constraint.ConstraintLayout>
RecyclerViewAdapter.java
class RecyclerViewAdapter extends RecyclerView.Adapter<RecyclerView.ViewHolder> {
private List<String> mItems;
RecyclerViewAdapter(List<String> items) {
mItems = items;
}
@Override
public @NonNull
RecyclerView.ViewHolder onCreateViewHolder(@NonNull ViewGroup parent, int viewType) {
View view = LayoutInflater.from(parent.getContext()).inflate(android.R.layout.simple_list_item_1, parent, false);
view.getLayoutParams().width = 220;
view.getLayoutParams().height = 220;
// view.setPadding(220 * 3, 0, 220 * 3, 0);
((TextView) view).setGravity(Gravity.CENTER);
return new ItemViewHolder(view);
}
@Override
public void onBindViewHolder(@NonNull RecyclerView.ViewHolder holder, int position) {
ItemViewHolder vh = (ItemViewHolder) holder;
String itemText = mItems.get(position);
vh.mItemTextView.setText(itemText);
int bgColor = (position % 2 == 0)
? android.R.color.holo_blue_light
: android.R.color.holo_green_light;
holder.itemView.setBackgroundColor(
holder.itemView.getContext().getResources().getColor(bgColor));
}
@Override
public int getItemCount() {
return (mItems == null) ? 0 : mItems.size();
}
@Override
public int getItemViewType(int position) {
return TYPE_ITEM;
}
static class ItemViewHolder extends RecyclerView.ViewHolder {
private TextView mItemTextView;
ItemViewHolder(View item) {
super(item);
mItemTextView = item.findViewById(android.R.id.text1);
}
}
public void setItems(List<String> items) {
mItems = items;
}
@SuppressWarnings("unused")
private final static String TAG = "RecyclerViewAdapter";
private final static int TYPE_ITEM = 1;
}
How can I snap to particular position for LinearSnapHelper() in horizontal RecyclerView? There is a function scrolltoposition for RecyclerView which scroll to that position but did not keep it in center for this snaphelper.
I am looking for something like below image. So when I set to particular position, it will keep it in center. I dont find anything related to select position for SnapHelper
i find this , but this doesn't help me. Any help would be appreciated.
解决方案
If I understand your question, you are looking for a way to jump to a position and have that position centered in the RecyclerView.
Maybe you have tried RecyclerView.scrollToPosition() but that doesn't snap to the view. You may also have tried RecyclerView.smoothScrollToPosition() and that works better but you may want to avoid all the movement if you have a lot of items and are scrolling a long way.
The reason that scrollToPosition() doesn't work is that it doesn't trigger the LinearSnapHelper which uses a scroll listener to detect when to snap. Since smoothScrollToPosition() does trigger the LinearSnapHelper, we will use scrollToPosition() to get us in the area of the target view then use smoothScrollToPosition() to get the view centered as follows:
private RecyclerView mRecycler;
private void newScrollTo(final int pos) {
RecyclerView.ViewHolder vh = mRecycler.findViewHolderForLayoutPosition(pos);
if (vh != null) {
// Target view is available, so just scroll to it.
mRecycler.smoothScrollToPosition(pos);
} else {
// Target view is not available. Scroll to it.
mRecycler.addOnScrollListener(new RecyclerView.OnScrollListener() {
// From the documentation:
// This callback will also be called if visible item range changes after a layout
// calculation. In that case, dx and dy will be 0.This callback will also be called
// if visible item range changes after a layout calculation. In that case,
// dx and dy will be 0.
@Override
public void onScrolled(RecyclerView recyclerView, int dx, int dy) {
super.onScrolled(recyclerView, dx, dy);
mRecycler.removeOnScrollListener(this);
if (dx == 0) {
newScrollTo(pos);
}
}
});
mRecycler.scrollToPosition(pos);
}
}
Sample app
MainActivity.java
public class MainActivity extends AppCompatActivity {
private final LinearLayoutManager mLayoutManager = new LinearLayoutManager(this, LinearLayoutManager.HORIZONTAL, false);
private final List<String> mItems = new ArrayList<>();
private RecyclerView mRecycler;
private final int mItemCount = 2000;
private final Handler mHandler = new Handler();
private final LinearSnapHelper mLinearSnapHelper = new LinearSnapHelper();
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
for (int i = 0; i < mItemCount; i++) {
mItems.add(i + "");
}
mRecycler = findViewById(R.id.recyclerView);
final RecyclerViewAdapter adapter = new RecyclerViewAdapter(null);
adapter.setItems(mItems);
mRecycler.setLayoutManager(mLayoutManager);
mRecycler.setAdapter(adapter);
mLinearSnapHelper.attachToRecyclerView(mRecycler);
newScrollTo(1);
// fireScrollTo();
}
private int maxScrolls = mItemCount;
private void fireScrollTo() {
if (--maxScrolls > 0) {
int pos = (int) (Math.random() * mItemCount);
newScrollTo(pos);
mHandler.postDelayed(new Runnable() {
@Override
public void run() {
fireScrollTo();
}
}, 2000);
}
}
private void newScrollTo(final int pos) {
mRecycler.smoothScrollToPosition(pos);
RecyclerView.ViewHolder vh = mRecycler.findViewHolderForLayoutPosition(pos);
if (vh != null) {
// Target view is available, so just scroll to it.
mRecycler.smoothScrollToPosition(pos);
} else {
// Target view is not available. Scroll to it.
mRecycler.addOnScrollListener(new RecyclerView.OnScrollListener() {
// From the documentation:
// This callback will also be called if visible item range changes after a layout
// calculation. In that case, dx and dy will be 0.This callback will also be called
// if visible item range changes after a layout calculation. In that case,
// dx and dy will be 0.
@Override
public void onScrolled(RecyclerView recyclerView, int dx, int dy) {
super.onScrolled(recyclerView, dx, dy);
mRecycler.removeOnScrollListener(this);
if (dx == 0) {
newScrollTo(pos);
}
}
});
mRecycler.scrollToPosition(pos);
}
}
}
activity_main.xml
<android.support.constraint.ConstraintLayout
android:layout_width="match_parent"
android:layout_height="match_parent">
<View
android:layout_width="3px"
android:layout_height="match_parent"
android:background="@android:color/holo_red_light"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toTopOf="parent" />
<android.support.v7.widget.RecyclerView
android:id="@+id/recyclerView"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:clipToPadding="false"
android:paddingStart="660px"
android:paddingEnd="660px"/>
</android.support.constraint.ConstraintLayout>
RecyclerViewAdapter.java
class RecyclerViewAdapter extends RecyclerView.Adapter<RecyclerView.ViewHolder> {
private List<String> mItems;
RecyclerViewAdapter(List<String> items) {
mItems = items;
}
@Override
public @NonNull
RecyclerView.ViewHolder onCreateViewHolder(@NonNull ViewGroup parent, int viewType) {
View view = LayoutInflater.from(parent.getContext()).inflate(android.R.layout.simple_list_item_1, parent, false);
view.getLayoutParams().width = 220;
view.getLayoutParams().height = 220;
// view.setPadding(220 * 3, 0, 220 * 3, 0);
((TextView) view).setGravity(Gravity.CENTER);
return new ItemViewHolder(view);
}
@Override
public void onBindViewHolder(@NonNull RecyclerView.ViewHolder holder, int position) {
ItemViewHolder vh = (ItemViewHolder) holder;
String itemText = mItems.get(position);
vh.mItemTextView.setText(itemText);
int bgColor = (position % 2 == 0)
? android.R.color.holo_blue_light
: android.R.color.holo_green_light;
holder.itemView.setBackgroundColor(
holder.itemView.getContext().getResources().getColor(bgColor));
}
@Override
public int getItemCount() {
return (mItems == null) ? 0 : mItems.size();
}
@Override
public int getItemViewType(int position) {
return TYPE_ITEM;
}
static class ItemViewHolder extends RecyclerView.ViewHolder {
private TextView mItemTextView;
ItemViewHolder(View item) {
super(item);
mItemTextView = item.findViewById(android.R.id.text1);
}
}
public void setItems(List<String> items) {
mItems = items;
}
@SuppressWarnings("unused")
private final static String TAG = "RecyclerViewAdapter";
private final static int TYPE_ITEM = 1;
}
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