问题
Any idea how to create a page indicator for recyclerview list ?
回答1:
You can add an indicator by using RecyclerView.ItemDecoration.
Just draw some lines or circles at the bottom and use layoutManager.findFirstVisibleItemPosition() to get the current active item. Since pagers tend to fill the whole width this is an accruate way of getting the displayed item. This also allows us to calculate the scrolling distance by comparing the childs left edge to the parents.
Below you find a sample decoration that draws some lines and animates between them
public class LinePagerIndicatorDecoration extends RecyclerView.ItemDecoration {
private int colorActive = 0xFFFFFFFF;
private int colorInactive = 0x66FFFFFF;
private static final float DP = Resources.getSystem().getDisplayMetrics().density;
/**
* Height of the space the indicator takes up at the bottom of the view.
*/
private final int mIndicatorHeight = (int) (DP * 16);
/**
* Indicator stroke width.
*/
private final float mIndicatorStrokeWidth = DP * 2;
/**
* Indicator width.
*/
private final float mIndicatorItemLength = DP * 16;
/**
* Padding between indicators.
*/
private final float mIndicatorItemPadding = DP * 4;
/**
* Some more natural animation interpolation
*/
private final Interpolator mInterpolator = new AccelerateDecelerateInterpolator();
private final Paint mPaint = new Paint();
public LinePagerIndicatorDecoration() {
mPaint.setStrokeCap(Paint.Cap.ROUND);
mPaint.setStrokeWidth(mIndicatorStrokeWidth);
mPaint.setStyle(Paint.Style.STROKE);
mPaint.setAntiAlias(true);
}
@Override
public void onDrawOver(Canvas c, RecyclerView parent, RecyclerView.State state) {
super.onDrawOver(c, parent, state);
int itemCount = parent.getAdapter().getItemCount();
// center horizontally, calculate width and subtract half from center
float totalLength = mIndicatorItemLength * itemCount;
float paddingBetweenItems = Math.max(0, itemCount - 1) * mIndicatorItemPadding;
float indicatorTotalWidth = totalLength + paddingBetweenItems;
float indicatorStartX = (parent.getWidth() - indicatorTotalWidth) / 2F;
// center vertically in the allotted space
float indicatorPosY = parent.getHeight() - mIndicatorHeight / 2F;
drawInactiveIndicators(c, indicatorStartX, indicatorPosY, itemCount);
// find active page (which should be highlighted)
LinearLayoutManager layoutManager = (LinearLayoutManager) parent.getLayoutManager();
int activePosition = layoutManager.findFirstVisibleItemPosition();
if (activePosition == RecyclerView.NO_POSITION) {
return;
}
// find offset of active page (if the user is scrolling)
final View activeChild = layoutManager.findViewByPosition(activePosition);
int left = activeChild.getLeft();
int width = activeChild.getWidth();
// on swipe the active item will be positioned from [-width, 0]
// interpolate offset for smooth animation
float progress = mInterpolator.getInterpolation(left * -1 / (float) width);
drawHighlights(c, indicatorStartX, indicatorPosY, activePosition, progress, itemCount);
}
private void drawInactiveIndicators(Canvas c, float indicatorStartX, float indicatorPosY, int itemCount) {
mPaint.setColor(colorInactive);
// width of item indicator including padding
final float itemWidth = mIndicatorItemLength + mIndicatorItemPadding;
float start = indicatorStartX;
for (int i = 0; i < itemCount; i++) {
// draw the line for every item
c.drawLine(start, indicatorPosY, start + mIndicatorItemLength, indicatorPosY, mPaint);
start += itemWidth;
}
}
private void drawHighlights(Canvas c, float indicatorStartX, float indicatorPosY,
int highlightPosition, float progress, int itemCount) {
mPaint.setColor(colorActive);
// width of item indicator including padding
final float itemWidth = mIndicatorItemLength + mIndicatorItemPadding;
if (progress == 0F) {
// no swipe, draw a normal indicator
float highlightStart = indicatorStartX + itemWidth * highlightPosition;
c.drawLine(highlightStart, indicatorPosY,
highlightStart + mIndicatorItemLength, indicatorPosY, mPaint);
} else {
float highlightStart = indicatorStartX + itemWidth * highlightPosition;
// calculate partial highlight
float partialLength = mIndicatorItemLength * progress;
// draw the cut off highlight
c.drawLine(highlightStart + partialLength, indicatorPosY,
highlightStart + mIndicatorItemLength, indicatorPosY, mPaint);
// draw the highlight overlapping to the next item as well
if (highlightPosition < itemCount - 1) {
highlightStart += itemWidth;
c.drawLine(highlightStart, indicatorPosY,
highlightStart + partialLength, indicatorPosY, mPaint);
}
}
}
@Override
public void getItemOffsets(Rect outRect, View view, RecyclerView parent, RecyclerView.State state) {
super.getItemOffsets(outRect, view, parent, state);
outRect.bottom = mIndicatorHeight;
}
}
Which will give you a result like the following
There is also a blog post that goes more into detail about how the decoration works here and the full source code is available at GitHub
回答2:
I have changed the code for circles. Removed the the code to draw line and the same is replaced with draw circle methods. Please find below the complete class:
public class CirclePagerIndicatorDecoration extends RecyclerView.ItemDecoration {
private int colorActive = 0xDE000000;
private int colorInactive = 0x33000000;
private static final float DP = Resources.getSystem().getDisplayMetrics().density;
/**
* Height of the space the indicator takes up at the bottom of the view.
*/
private final int mIndicatorHeight = (int) (DP * 16);
/**
* Indicator stroke width.
*/
private final float mIndicatorStrokeWidth = DP * 4;
/**
* Indicator width.
*/
private final float mIndicatorItemLength = DP * 4;
/**
* Padding between indicators.
*/
private final float mIndicatorItemPadding = DP * 8;
/**
* Some more natural animation interpolation
*/
private final Interpolator mInterpolator = new AccelerateDecelerateInterpolator();
private final Paint mPaint = new Paint();
public CirclePagerIndicatorDecoration() {
mPaint.setStrokeWidth(mIndicatorStrokeWidth);
mPaint.setStyle(Paint.Style.STROKE);
mPaint.setAntiAlias(true);
}
@Override
public void onDrawOver(Canvas c, RecyclerView parent, RecyclerView.State state) {
super.onDrawOver(c, parent, state);
int itemCount = parent.getAdapter().getItemCount();
// center horizontally, calculate width and subtract half from center
float totalLength = mIndicatorItemLength * itemCount;
float paddingBetweenItems = Math.max(0, itemCount - 1) * mIndicatorItemPadding;
float indicatorTotalWidth = totalLength + paddingBetweenItems;
float indicatorStartX = (parent.getWidth() - indicatorTotalWidth) / 2F;
// center vertically in the allotted space
float indicatorPosY = parent.getHeight() - mIndicatorHeight / 2F;
drawInactiveIndicators(c, indicatorStartX, indicatorPosY, itemCount);
// find active page (which should be highlighted)
LinearLayoutManager layoutManager = (LinearLayoutManager) parent.getLayoutManager();
int activePosition = layoutManager.findFirstVisibleItemPosition();
if (activePosition == RecyclerView.NO_POSITION) {
return;
}
// find offset of active page (if the user is scrolling)
final View activeChild = layoutManager.findViewByPosition(activePosition);
int left = activeChild.getLeft();
int width = activeChild.getWidth();
int right = activeChild.getRight();
// on swipe the active item will be positioned from [-width, 0]
// interpolate offset for smooth animation
float progress = mInterpolator.getInterpolation(left * -1 / (float) width);
drawHighlights(c, indicatorStartX, indicatorPosY, activePosition, progress);
}
private void drawInactiveIndicators(Canvas c, float indicatorStartX, float indicatorPosY, int itemCount) {
mPaint.setColor(colorInactive);
// width of item indicator including padding
final float itemWidth = mIndicatorItemLength + mIndicatorItemPadding;
float start = indicatorStartX;
for (int i = 0; i < itemCount; i++) {
c.drawCircle(start, indicatorPosY, mIndicatorItemLength / 2F, mPaint);
start += itemWidth;
}
}
private void drawHighlights(Canvas c, float indicatorStartX, float indicatorPosY,
int highlightPosition, float progress) {
mPaint.setColor(colorActive);
// width of item indicator including padding
final float itemWidth = mIndicatorItemLength + mIndicatorItemPadding;
if (progress == 0F) {
// no swipe, draw a normal indicator
float highlightStart = indicatorStartX + itemWidth * highlightPosition;
c.drawCircle(highlightStart, indicatorPosY, mIndicatorItemLength / 2F, mPaint);
} else {
float highlightStart = indicatorStartX + itemWidth * highlightPosition;
// calculate partial highlight
float partialLength = mIndicatorItemLength * progress + mIndicatorItemPadding*progress;
c.drawCircle(highlightStart + partialLength, indicatorPosY, mIndicatorItemLength / 2F, mPaint);
}
}
@Override
public void getItemOffsets(Rect outRect, View view, RecyclerView parent, RecyclerView.State state) {
super.getItemOffsets(outRect, view, parent, state);
outRect.bottom = mIndicatorHeight;
}
}
Many Thanks, LB Gupta Happy Coding !!!!!
回答3:
I have copied the same answer which is given by David Medenjak , but to make the circles below the recyclerview . I have updated few lines of code in the above answer , please have a look and use accordingly .
/**
* Created by shobhan on 4/10/17.
*/
public class CirclePagerIndicatorDecoration extends RecyclerView.ItemDecoration {
private int colorActive = 0x727272;
private int colorInactive = 0xF44336;
private static final float DP = Resources.getSystem().getDisplayMetrics().density;
/**
* Height of the space the indicator takes up at the bottom of the view.
*/
private final int mIndicatorHeight = (int) (DP * 16);
/**
* Indicator stroke width.
*/
private final float mIndicatorStrokeWidth = DP * 2;
/**
* Indicator width.
*/
private final float mIndicatorItemLength = DP * 16;
/**
* Padding between indicators.
*/
private final float mIndicatorItemPadding = DP * 4;
/**
* Some more natural animation interpolation
*/
private final Interpolator mInterpolator = new AccelerateDecelerateInterpolator();
private final Paint mPaint = new Paint();
public CirclePagerIndicatorDecoration() {
mPaint.setStrokeCap(Paint.Cap.ROUND);
mPaint.setStrokeWidth(mIndicatorStrokeWidth);
mPaint.setStyle(Paint.Style.FILL);
mPaint.setAntiAlias(true);
}
@Override
public void onDrawOver(Canvas c, RecyclerView parent, RecyclerView.State state) {
super.onDrawOver(c, parent, state);
int itemCount = parent.getAdapter().getItemCount();
// center horizontally, calculate width and subtract half from center
float totalLength = mIndicatorItemLength * itemCount;
float paddingBetweenItems = Math.max(0, itemCount - 1) * mIndicatorItemPadding;
float indicatorTotalWidth = totalLength + paddingBetweenItems;
float indicatorStartX = (parent.getWidth() - indicatorTotalWidth) / 2F;
// center vertically in the allotted space
float indicatorPosY = parent.getHeight() - mIndicatorHeight / 2F;
drawInactiveIndicators(c, indicatorStartX, indicatorPosY, itemCount);
// find active page (which should be highlighted)
LinearLayoutManager layoutManager = (LinearLayoutManager) parent.getLayoutManager();
int activePosition = layoutManager.findFirstVisibleItemPosition();
if (activePosition == RecyclerView.NO_POSITION) {
return;
}
// find offset of active page (if the user is scrolling)
final View activeChild = layoutManager.findViewByPosition(activePosition);
int left = activeChild.getLeft();
int width = activeChild.getWidth();
// on swipe the active item will be positioned from [-width, 0]
// interpolate offset for smooth animation
float progress = mInterpolator.getInterpolation(left * -1 / (float) width);
drawHighlights(c, indicatorStartX, indicatorPosY, activePosition, progress, itemCount);
}
private void drawInactiveIndicators(Canvas c, float indicatorStartX, float indicatorPosY, int itemCount) {
mPaint.setColor(Color.GRAY);
// width of item indicator including padding
final float itemWidth = mIndicatorItemLength + mIndicatorItemPadding;
float start = indicatorStartX;
for (int i = 0; i < itemCount; i++) {
// draw the line for every item
c.drawCircle(start + mIndicatorItemLength,indicatorPosY,itemWidth/6,mPaint);
// c.drawLine(start, indicatorPosY, start + mIndicatorItemLength, indicatorPosY, mPaint);
start += itemWidth;
}
}
private void drawHighlights(Canvas c, float indicatorStartX, float indicatorPosY,
int highlightPosition, float progress, int itemCount) {
mPaint.setColor(Color.RED);
// width of item indicator including padding
final float itemWidth = mIndicatorItemLength + mIndicatorItemPadding;
if (progress == 0F) {
// no swipe, draw a normal indicator
float highlightStart = indicatorStartX + itemWidth * highlightPosition;
/* c.drawLine(highlightStart, indicatorPosY,
highlightStart + mIndicatorItemLength, indicatorPosY, mPaint);
*/
c.drawCircle(highlightStart,indicatorPosY,itemWidth/6,mPaint);
} else {
float highlightStart = indicatorStartX + itemWidth * highlightPosition;
// calculate partial highlight
float partialLength = mIndicatorItemLength * progress;
c.drawCircle(highlightStart + mIndicatorItemLength,indicatorPosY,itemWidth/6,mPaint);
// draw the cut off highlight
/* c.drawLine(highlightStart + partialLength, indicatorPosY,
highlightStart + mIndicatorItemLength, indicatorPosY, mPaint);
*/
// draw the highlight overlapping to the next item as well
/* if (highlightPosition < itemCount - 1) {
highlightStart += itemWidth;
*//*c.drawLine(highlightStart, indicatorPosY,
highlightStart + partialLength, indicatorPosY, mPaint);*//*
c.drawCircle(highlightStart ,indicatorPosY,itemWidth/4,mPaint);
}*/
}
}
@Override
public void getItemOffsets(Rect outRect, View view, RecyclerView parent, RecyclerView.State state) {
super.getItemOffsets(outRect, view, parent, state);
outRect.bottom = mIndicatorHeight;
}
}
And Apply it to the recyclerview as follows
//for horizontal scroll for recycler view
LinearLayoutManager linearLayoutManager
= new LinearLayoutManager(context, LinearLayoutManager.HORIZONTAL, false);
recyclerview.setLayoutManager(linearLayoutManager);
recyclerview.addItemDecoration(new CirclePagerIndicatorDecoration());
回答4:
in case of anyone need, I wrote my own library for this (after a lot of searching): RecyclerView indicator. Here's how you do it:
<com.kingfisher.easyviewindicator.RecyclerViewIndicator
android:id="@+id/circleIndicator"
android:layout_width="match_parent"
android:layout_height="20dp"
app:avi_animation_enable="true"
app:avi_drawable="@drawable/blue_radius"
app:avi_drawable_unselected="@drawable/gray_radius"
app:avi_height="10dp"
app:avi_margin="10dp"
app:avi_width="10dp"
app:layout_constraintTop_toBottomOf="@+id/recyclerView">
</com.kingfisher.easyviewindicator.RecyclerViewIndicator>
// In code:
recyclerView.setAdapter(new TestAdapter());
recyclerViewIndicator.setRecyclerView(recyclerView);
回答5:
Nowadays you could use ViewPager2.
It basically wraps a RecyclerView (so you will be using a RecyclerView.Adapter) but it allows the attachment of a TabLayout with the help of a TabLayoutMediator.
The TabLayout can then be styled to act like a dot page indicator. See for example How do you create an Android View Pager with a dots indicator?
回答6:
First you have to create another RecyclerView for the circles and put this code in the OnScrollListener of the first RecyclerView.
int[] firstVisibleItemPositions = new int[appList.size()];
int[] lastVisibleItemPositions = new int[appList.size()];
int position = ((StaggeredGridLayoutManager) listView.getLayoutManager()).findFirstVisibleItemPositions(firstVisibleItemPositions)[0];
View currentView = circlesList.getChildAt(position);
int lastPosition = ((StaggeredGridLayoutManager) listView.getLayoutManager()).findLastVisibleItemPositions(lastVisibleItemPositions)[0];
View lastView = circlesList.getChildAt(lastPosition);
ImageView circle;
if (dx>0) {
if (currentView != null && lastPosition != position) {
circle = (ImageView) currentView.findViewById(R.id.img);
circle.setImageResource(R.drawable.empty_circle);
}
if (lastView != null && lastPosition != position) {
circle = (ImageView) lastView.findViewById(R.id.img);
circle.setImageResource(R.drawable.selected_circle);
}
}else if (dx<0){
if (currentView != null && lastPosition != position) {
circle = (ImageView) currentView.findViewById(R.id.img);
circle.setImageResource(R.drawable.selected_circle);
}
if (lastView != null && lastPosition != position) {
circle = (ImageView) lastView.findViewById(R.id.img);
circle.setImageResource(R.drawable.empty_circle);
}
}
来源：https://stackoverflow.com/questions/33841363/how-to-make-a-page-indicator-for-horizontal-recyclerview