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package com.mindorks.snaphelperexample.ui.common;
import android.support.annotation.NonNull;
import android.support.annotation.Nullable;
import android.support.v7.widget.LinearLayoutManager;
import android.support.v7.widget.LinearSnapHelper;
import android.support.v7.widget.OrientationHelper;
import android.support.v7.widget.RecyclerView;
import android.view.View;
/**
* Created by amitshekhar on 15/01/17.
*/
public class StartSnapHelper extends LinearSnapHelper {
private OrientationHelper mVerticalHelper, mHorizontalHelper;
public StartSnapHelper() {
}
@Override
public void attachToRecyclerView(@Nullable RecyclerView recyclerView)
throws IllegalStateException {
super.attachToRecyclerView(recyclerView);
}
@Override
public int[] calculateDistanceToFinalSnap(@NonNull RecyclerView.LayoutManager layoutManager,
@NonNull View targetView) {
int[] out = new int[2];
if (layoutManager.canScrollHorizontally()) {
out[0] = distanceToStart(targetView, getHorizontalHelper(layoutManager));
} else {
out[0] = 0;
}
if (layoutManager.canScrollVertically()) {
out[1] = distanceToStart(targetView, getVerticalHelper(layoutManager));
} else {
out[1] = 0;
}
return out;
}
@Override
public View findSnapView(RecyclerView.LayoutManager layoutManager) {
if (layoutManager instanceof LinearLayoutManager) {
if (layoutManager.canScrollHorizontally()) {
return getStartView(layoutManager, getHorizontalHelper(layoutManager));
} else {
return getStartView(layoutManager, getVerticalHelper(layoutManager));
}
}
return super.findSnapView(layoutManager);
}
private int distanceToStart(View targetView, OrientationHelper helper) {
return helper.getDecoratedStart(targetView) - helper.getStartAfterPadding();
}
private View getStartView(RecyclerView.LayoutManager layoutManager,
OrientationHelper helper) {
if (layoutManager instanceof LinearLayoutManager) {
int firstChild = ((LinearLayoutManager) layoutManager).findFirstVisibleItemPosition();
boolean isLastItem = ((LinearLayoutManager) layoutManager)
.findLastCompletelyVisibleItemPosition()
== layoutManager.getItemCount() - 1;
if (firstChild == RecyclerView.NO_POSITION || isLastItem) {
return null;
}
View child = layoutManager.findViewByPosition(firstChild);
if (helper.getDecoratedEnd(child) >= helper.getDecoratedMeasurement(child) / 2
&& helper.getDecoratedEnd(child) > 0) {
return child;
} else {
if (((LinearLayoutManager) layoutManager).findLastCompletelyVisibleItemPosition()
== layoutManager.getItemCount() - 1) {
return null;
} else {
return layoutManager.findViewByPosition(firstChild + 1);
}
}
}
return super.findSnapView(layoutManager);
}
private OrientationHelper getVerticalHelper(RecyclerView.LayoutManager layoutManager) {
if (mVerticalHelper == null) {
mVerticalHelper = OrientationHelper.createVerticalHelper(layoutManager);
}
return mVerticalHelper;
}
private OrientationHelper getHorizontalHelper(RecyclerView.LayoutManager layoutManager) {
if (mHorizontalHelper == null) {
mHorizontalHelper = OrientationHelper.createHorizontalHelper(layoutManager);
}
return mHorizontalHelper;
}
}
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