场景
项目中要求横向滚动，可自动滚动，可左右滑动。
横向自动滚动.gif
代码
AutoPollRecyclerView.java
import android.content.Context;
import android.support.annotation.Nullable;
import android.support.v7.widget.RecyclerView;
import android.util.AttributeSet;
import android.view.MotionEvent;
import android.view.animation.LinearInterpolator;
import java.lang.ref.WeakReference;
public class AutoPollRecyclerView extends RecyclerView {
private static final long TIME_AUTO_POLL = 2000;
AutoPollTask autoPollTask;
private boolean running; //标示是否正在自动轮询
private boolean canRun;//标示是否可以自动轮询,可在不需要的是否置false
public AutoPollRecyclerView(Context context, @Nullable AttributeSet attrs) {
super(context, attrs);
autoPollTask = new AutoPollTask(this);
}
static class AutoPollTask implements Runnable {
private final WeakReference<AutoPollRecyclerView> mReference;
//使用弱引用持有外部类引用->防止内存泄漏
public AutoPollTask(AutoPollRecyclerView reference) {
this.mReference = new WeakReference<AutoPollRecyclerView>(reference);
}
@Override
public void run() {
AutoPollRecyclerView recyclerView = mReference.get();
if (recyclerView != null && recyclerView.running && recyclerView.canRun) {
recyclerView.smoothScrollBy(550, 0, new LinearInterpolator());
recyclerView.postDelayed(recyclerView.autoPollTask, recyclerView.TIME_AUTO_POLL);
}
}
}
//开启:如果正在运行,先停止->再开启
public void start() {
if (running)
stop();
canRun = true;
running = true;
postDelayed(autoPollTask, TIME_AUTO_POLL);
}
public void stop() {
running = false;
removeCallbacks(autoPollTask);
}
@Override
public boolean onTouchEvent(MotionEvent e) {
switch (e.getAction()) {
case MotionEvent.ACTION_DOWN:
if (running)
stop();
break;
case MotionEvent.ACTION_UP:
case MotionEvent.ACTION_CANCEL:
case MotionEvent.ACTION_OUTSIDE:
if (canRun)
start();
break;
}
return super.onTouchEvent(e);
}
}
调用
mRecycleview.start()
viewpager效果
GallerySnapHelper.java
import android.graphics.PointF;
import android.support.v7.widget.LinearLayoutManager;
import android.support.v7.widget.LinearSmoothScroller;
import android.support.v7.widget.OrientationHelper;
import android.support.v7.widget.RecyclerView;
import android.support.v7.widget.SnapHelper;
import android.util.DisplayMetrics;
import android.view.View;
import android.support.annotation.NonNull;
import android.support.annotation.Nullable;
public class GallerySnapHelper extends SnapHelper {
private static final float INVALID_DISTANCE = 1f;
private static final float MILLISECONDS_PER_INCH = 40f;
private OrientationHelper mHorizontalHelper;
private RecyclerView mRecyclerView;
@Override
public void attachToRecyclerView(@Nullable RecyclerView recyclerView) throws IllegalStateException {
mRecyclerView = recyclerView;
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;
}
return out;
}
private int distanceToStart(View targetView, OrientationHelper helper) {
return helper.getDecoratedStart(targetView) - helper.getStartAfterPadding();
}
@Nullable
protected LinearSmoothScroller createSnapScroller(final RecyclerView.LayoutManager layoutManager) {
if (!(layoutManager instanceof RecyclerView.SmoothScroller.ScrollVectorProvider)) {
return null;
}
return new LinearSmoothScroller(mRecyclerView.getContext()) {
@Override
protected void onTargetFound(View targetView, RecyclerView.State state, Action action) {
int[] snapDistances = calculateDistanceToFinalSnap(mRecyclerView.getLayoutManager(), targetView);
final int dx = snapDistances[0];
final int dy = snapDistances[1];
final int time = calculateTimeForDeceleration(Math.max(Math.abs(dx), Math.abs(dy)));
if (time > 0) {
action.update(dx, dy, time, mDecelerateInterpolator);
}
}
@Override
protected float calculateSpeedPerPixel(DisplayMetrics displayMetrics) {
return MILLISECONDS_PER_INCH / displayMetrics.densityDpi;
}
};
}
@Override
public int findTargetSnapPosition(RecyclerView.LayoutManager layoutManager, int velocityX, int velocityY) {
if (!(layoutManager instanceof RecyclerView.SmoothScroller.ScrollVectorProvider)) {
return RecyclerView.NO_POSITION;
}
final int itemCount = layoutManager.getItemCount();
if (itemCount == 0) {
return RecyclerView.NO_POSITION;
}
final View currentView = findSnapView(layoutManager);
if (currentView == null) {
return RecyclerView.NO_POSITION;
}
final int currentPosition = layoutManager.getPosition(currentView);
if (currentPosition == RecyclerView.NO_POSITION) {
return RecyclerView.NO_POSITION;
}
RecyclerView.SmoothScroller.ScrollVectorProvider vectorProvider =
(RecyclerView.SmoothScroller.ScrollVectorProvider) layoutManager;
// deltaJumps sign comes from the velocity which may not match the order of children in
// the LayoutManager. To overcome this, we ask for a vector from the LayoutManager to
// get the direction.
PointF vectorForEnd = vectorProvider.computeScrollVectorForPosition(itemCount - 1);
if (vectorForEnd == null) {
// cannot get a vector for the given position.
return RecyclerView.NO_POSITION;
}
//在松手之后,列表最多只能滚多一屏的item数
int deltaThreshold = layoutManager.getWidth() / getHorizontalHelper(layoutManager).getDecoratedMeasurement(currentView);
int hDeltaJump;
if (layoutManager.canScrollHorizontally()) {
hDeltaJump = estimateNextPositionDiffForFling(layoutManager,
getHorizontalHelper(layoutManager), velocityX, 0);
if (hDeltaJump > deltaThreshold) {
hDeltaJump = deltaThreshold;
}
if (hDeltaJump < -deltaThreshold) {
hDeltaJump = -deltaThreshold;
}
if (vectorForEnd.x < 0) {
hDeltaJump = -hDeltaJump;
}
} else {
hDeltaJump = 0;
}
if (hDeltaJump == 0) {
return RecyclerView.NO_POSITION;
}
int targetPos = currentPosition + hDeltaJump;
if (targetPos < 0) {
targetPos = 0;
}
if (targetPos >= itemCount) {
targetPos = itemCount - 1;
}
return targetPos;
}
@Override
public View findSnapView(RecyclerView.LayoutManager layoutManager) {
return findStartView(layoutManager, getHorizontalHelper(layoutManager));
}
private View findStartView(RecyclerView.LayoutManager layoutManager, OrientationHelper helper) {
if (layoutManager instanceof LinearLayoutManager) {
int firstChildPosition = ((LinearLayoutManager) layoutManager).findFirstVisibleItemPosition();
if (firstChildPosition == RecyclerView.NO_POSITION) {
return null;
}
if (((LinearLayoutManager) layoutManager).findLastCompletelyVisibleItemPosition() == layoutManager.getItemCount() - 1) {
return null;
}
View firstChildView = layoutManager.findViewByPosition(firstChildPosition);
if (helper.getDecoratedEnd(firstChildView) >= helper.getDecoratedMeasurement(firstChildView) / 2 && helper.getDecoratedEnd(firstChildView) > 0) {
return firstChildView;
} else {
return layoutManager.findViewByPosition(firstChildPosition + 1);
}
} else {
return null;
}
}
private int estimateNextPositionDiffForFling(RecyclerView.LayoutManager layoutManager,
OrientationHelper helper, int velocityX, int velocityY) {
int[] distances = calculateScrollDistance(velocityX, velocityY);
float distancePerChild = computeDistancePerChild(layoutManager, helper);
if (distancePerChild <= 0) {
return 0;
}
int distance = distances[0];
if (distance > 0) {
return (int) Math.floor(distance / distancePerChild);
} else {
return (int) Math.ceil(distance / distancePerChild);
}
}
private float computeDistancePerChild(RecyclerView.LayoutManager layoutManager,
OrientationHelper helper) {
View minPosView = null;
View maxPosView = null;
int minPos = Integer.MAX_VALUE;
int maxPos = Integer.MIN_VALUE;
int childCount = layoutManager.getChildCount();
if (childCount == 0) {
return INVALID_DISTANCE;
}
for (int i = 0; i < childCount; i++) {
View child = layoutManager.getChildAt(i);
final int pos = layoutManager.getPosition(child);
if (pos == RecyclerView.NO_POSITION) {
continue;
}
if (pos < minPos) {
minPos = pos;
minPosView = child;
}
if (pos > maxPos) {
maxPos = pos;
maxPosView = child;
}
}
if (minPosView == null || maxPosView == null) {
return INVALID_DISTANCE;
}
int start = Math.min(helper.getDecoratedStart(minPosView),
helper.getDecoratedStart(maxPosView));
int end = Math.max(helper.getDecoratedEnd(minPosView),
helper.getDecoratedEnd(maxPosView));
int distance = end - start;
if (distance == 0) {
return INVALID_DISTANCE;
}
return 1f * distance / ((maxPos - minPos) + 1);
}
private OrientationHelper getHorizontalHelper(RecyclerView.LayoutManager layoutManager) {
if (mHorizontalHelper == null) {
mHorizontalHelper = OrientationHelper.createHorizontalHelper(layoutManager);
}
return mHorizontalHelper;
}
}
调用
mGallerySnapHelper.attachToRecyclerView(mRecycleView)
总结
- 自动滚动主要是：开一个定时任务Runnable，
recyclerView.smoothScrollBy(550, 0, new LinearInterpolator()); - 类似viewpager效果 主要是：
SnapHelper
参考链接:
image
