本篇内容主要讲解“Android中如何通过自定义ViewGroup实现一个弹性滑动效果”，感兴趣的朋友不妨来看看。本文介绍的方法操作简单快捷，实用性强。下面就让小编来带大家学习“Android中如何通过自定义ViewGroup实现一个弹性滑动效果”吧!
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实现原理
onMeasure()中测量所有子View
@Override
protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
// 测量所有子View
int count = getChildCount();
for (int i = 0; i < count; i++) {
View childView = getChildAt(i);
measureChild(childView, widthMeasureSpec, heightMeasureSpec);
}
setMeasuredDimension(widthMeasureSpec, heightMeasureSpec);
}onLayout()中,将所有的子View按照位置依次往下排列
@Override
protected void onLayout(boolean changed, int l, int t, int r, int b) {
// 设置ViewGroup的高度,对所有子View进行排列
int childCount = getChildCount();
MarginLayoutParams params = (MarginLayoutParams) getLayoutParams();
params.height = mScreenHeight * childCount;
for (int i = 0; i < childCount; i++) {
View childView = getChildAt(i);
if (childView.getVisibility() != View.GONE) {
// 给每个ChildView放置在指定位置
childView.layout(l, i * mScreenHeight, r, (i + 1) * mScreenHeight);
}
}
}onTouchEvent()中处理滑动
@Override
public boolean onTouchEvent(MotionEvent event) {
switch (event.getAction()) {
case MotionEvent.ACTION_DOWN:
mLastY = (int) event.getY();
mStart = getScrollY();
return true;
case MotionEvent.ACTION_MOVE:
if (!mScroller.isFinished()) {
// 终止滑动
mScroller.abortAnimation();
}
int offsetY = (int) (mLastY - event.getY());
Log.d(TAG, "onTouchEvent: getScrollY: " + getScrollY());
Log.d(TAG, "onTouchEvent: offsetY " + offsetY);
// 到达顶部,使用offset判断方向
if (getScrollY() + offsetY < 0) { // 当前已经滑动的 Y 位置
offsetY = 0;
}
// 到达底部
if (getScrollY() > getHeight() - mScreenHeight && offsetY > 0) {
offsetY = 0;
}
scrollBy(0, offsetY);
// 滑动完成后,重新设置LastY位置
mLastY = (int) event.getY();
break;
case MotionEvent.ACTION_UP:
mEnd = getScrollY();
int distance = mEnd - mStart;
if (distance > 0) { // 向上滑动
if (distance < mScreenHeight / 3) {
Log.d(TAG, "onTouchEvent: distance < screen/3");
// 回到原来位置
mScroller.startScroll(0, getScrollY(), 0, -distance);
} else {
// 滚到屏幕的剩余位置
mScroller.startScroll(0, getScrollY(), 0, mScreenHeight - distance);
}
} else { // 向下滑动
if (-distance < mScreenHeight / 3) {
mScroller.startScroll(0, getScrollY(), 0, -distance);
} else {
mScroller.startScroll(0, getScrollY(), 0, -mScreenHeight - distance);
}
}
postInvalidate();
}
return super.onTouchEvent(event);
}其中ACTION_UP这段代码是处理弹性滑动的
case MotionEvent.ACTION_UP:
mEnd = getScrollY();
int distance = mEnd - mStart;
if (distance > 0) { // 向上滑动
if (distance < mScreenHeight / 3) {
Log.d(TAG, "onTouchEvent: distance < screen/3");
// 回到原来位置
mScroller.startScroll(0, getScrollY(), 0, -distance);
} else {
// 滚到屏幕的剩余位置
mScroller.startScroll(0, getScrollY(), 0, mScreenHeight - distance);
}
} else { // 向下滑动
if (-distance < mScreenHeight / 3) {
mScroller.startScroll(0, getScrollY(), 0, -distance);
} else {
mScroller.startScroll(0, getScrollY(), 0, -mScreenHeight - distance);
}
}
postInvalidate();完整代码
public class ScrollViewGroup extends ViewGroup {
private static final String TAG = "ScrollView";
private Scroller mScroller;
private int mScreenHeight; // 窗口高度
private int mLastY;
private int mStart;
private int mEnd;
public ScrollViewGroup(Context context) {
this(context, null);
}
public ScrollViewGroup(Context context, AttributeSet attrs) {
this(context, attrs, 0);
}
public ScrollViewGroup(Context context, AttributeSet attrs, int defStyleAttr) {
super(context, attrs, defStyleAttr);
mScroller = new Scroller(context);
// 获取屏幕高度
WindowManager windowManager = (WindowManager) context.getSystemService(Context.WINDOW_SERVICE);
DisplayMetrics metrics = new DisplayMetrics();
windowManager.getDefaultDisplay().getMetrics(metrics);
mScreenHeight = metrics.heightPixels;
Log.d(TAG, "ScrollViewGroup: ScreenHeight " + mScreenHeight);
}
@Override
protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
// 测量所有子View
int count = getChildCount();
for (int i = 0; i < count; i++) {
View childView = getChildAt(i);
measureChild(childView, widthMeasureSpec, heightMeasureSpec);
}
setMeasuredDimension(widthMeasureSpec, heightMeasureSpec);
}
@Override
protected void onLayout(boolean changed, int l, int t, int r, int b) {
// 设置ViewGroup的高度,对所有子View进行排列
int childCount = getChildCount();
MarginLayoutParams params = (MarginLayoutParams) getLayoutParams();
params.height = mScreenHeight * childCount;
for (int i = 0; i < childCount; i++) {
View childView = getChildAt(i);
if (childView.getVisibility() != View.GONE) {
// 给每个ChildView放置在指定位置
childView.layout(l, i * mScreenHeight, r, (i + 1) * mScreenHeight);
}
}
}
@Override
public boolean onTouchEvent(MotionEvent event) {
switch (event.getAction()) {
case MotionEvent.ACTION_DOWN:
mLastY = (int) event.getY();
mStart = getScrollY();
return true;
case MotionEvent.ACTION_MOVE:
if (!mScroller.isFinished()) {
// 终止滑动
mScroller.abortAnimation();
}
int offsetY = (int) (mLastY - event.getY());
Log.d(TAG, "onTouchEvent: getScrollY: " + getScrollY());
Log.d(TAG, "onTouchEvent: offsetY " + offsetY);
// 到达顶部,使用offset判断方向
if (getScrollY() + offsetY < 0) { // 当前已经滑动的 Y 位置
offsetY = 0;
}
// 到达底部
if (getScrollY() > getHeight() - mScreenHeight && offsetY > 0) {
offsetY = 0;
}
scrollBy(0, offsetY);
// 滑动完成后,重新设置LastY位置
mLastY = (int) event.getY();
break;
case MotionEvent.ACTION_UP:
mEnd = getScrollY();
int distance = mEnd - mStart;
if (distance > 0) { // 向上滑动
if (distance < mScreenHeight / 3) {
Log.d(TAG, "onTouchEvent: distance < screen/3");
// 回到原来位置
mScroller.startScroll(0, getScrollY(), 0, -distance);
} else {
// 滚到屏幕的剩余位置
mScroller.startScroll(0, getScrollY(), 0, mScreenHeight - distance);
}
} else { // 向下滑动
if (-distance < mScreenHeight / 3) {
mScroller.startScroll(0, getScrollY(), 0, -distance);
} else {
mScroller.startScroll(0, getScrollY(), 0, -mScreenHeight - distance);
}
}
postInvalidate();
}
return super.onTouchEvent(event);
}
@Override
public void computeScroll() {
if (mScroller.computeScrollOffset()) {
scrollTo(mScroller.getCurrX(), mScroller.getCurrY());
postInvalidate();
}
}
}到此，相信大家对“Android中如何通过自定义ViewGroup实现一个弹性滑动效果”有了更深的了解，不妨来实际操作一番吧！这里是创新互联网站，更多相关内容可以进入相关频道进行查询，关注我们，继续学习！
