a.度娘一下什么都知道了,整理这些东西有什么用?还费时费力的! 如何才能完全掌握一个知识?当你能把它讲清楚的时候,你才算掌握了他,所以这也是我整理这些知识点最大的原因。
想完全把mScrollX和mScrollY,scrollTo()和scrollBy(),smoothScrollTo和smoothScrollBy弄明白并不容易,但查阅他们的源代码基本就能明白个大概,这篇文章就是从源码分析他们究竟有什么作用和区别,读懂了基本就会用!
我的CSDN主页:http://blog.csdn.net/xiangyong1521 文章地址:http://blog.csdn.net/xiangyong1521/article/details/77826942
/**
* The offset, in pixels, by which the content of this view is scrolled
* horizontally.
* {@hide}
*/
@ViewDebug.ExportedProperty(category = "scrolling")
protected int mScrollX;
/**
* The offset, in pixels, by which the content of this view is scrolled
* vertically.
* {@hide}
*/
@ViewDebug.ExportedProperty(category = "scrolling")
protected int mScrollY;
/**
* Return the scrolled left position of this view. This is the left edge of
* the displayed part of your view. You do not need to draw any pixels
* farther left, since those are outside of the frame of your view on
* screen.
*
* @return The left edge of the displayed part of your view, in pixels.
*/
public final int getScrollX() {
return mScrollX;
}
/**
* Return the scrolled top position of this view. This is the top edge of
* the displayed part of your view. You do not need to draw any pixels above
* it, since those are outside of the frame of your view on screen.
*
* @return The top edge of the displayed part of your view, in pixels.
*/
public final int getScrollY() {
return mScrollY;
}
直接翻译就可以得知
mScrollX:表示离视图起始位置的x水平方向的偏移量
mScrollY:表示离视图起始位置的y垂直方向的偏移量
通过getScrollX() 和getScrollY()方法获这兄弟俩。 注意:mScrollX和mScrollY指的并不是坐标,而是偏移量。
<span style="font-family:SimSun;font-size:14px;"> /**
* Set the scrolled position of your view. This will cause a call to
* {@link #onScrollChanged(int, int, int, int)} and the view will be
* invalidated.
* @param x the x position to scroll to
* @param y the y position to scroll to
*/
public void scrollTo(int x, int y) {
if (mScrollX != x || mScrollY != y) {
int oldX = mScrollX;
int oldY = mScrollY;
mScrollX = x;
mScrollY = y;
invalidateParentCaches();
onScrollChanged(mScrollX, mScrollY, oldX, oldY);
if (!awakenScrollBars()) {
postInvalidateOnAnimation();
}
}
}
/**
* Move the scrolled position of your view. This will cause a call to
* {@link #onScrollChanged(int, int, int, int)} and the view will be
* invalidated.
* @param x the amount of pixels to scroll by horizontally
* @param y the amount of pixels to scroll by vertically
*/
public void scrollBy(int x, int y) {
scrollTo(mScrollX + x, mScrollY + y);
}</span>
源码可以看出,scrollTo 和 scrollBy区别,其实2者的效果是一样的,只是过程不同而已。
scrollTo(int x,int y):
如果偏移位置发生了改变,就会给mScrollX和mScrollY赋新值,改变当前位置。 注意:x,y代表的不是坐标点,而是偏移量。 例如: 我要移动view到坐标点(100,100),那么我的偏移量就是(0,,0) - (100,100) = (-100 ,-100) ,我就要执行view.scrollTo(-100,-100),达到这个效果。
scrollBy(int x,int y):
从源码中看出,它实际上是调用了scrollTo(mScrollX + x, mScrollY + y); mScrollX + x和mScrollY + y,即表示在原先偏移的基础上在发生偏移,通俗的说就是相对我们当前位置偏移。 根据父类VIEW里面移动,如果移动到了超出的地方,就不会显示。
ScrollView.smoothScrollBy和smoothScrollTo的源码
/**
* Like {@link View#scrollBy}, but scroll smoothly instead of immediately.
*
* @param dx the number of pixels to scroll by on the X axis
* @param dy the number of pixels to scroll by on the Y axis
*/
public final void smoothScrollBy(int dx, int dy) {
if (getChildCount() == 0) {
// Nothing to do.
return;
}
long duration = AnimationUtils.currentAnimationTimeMillis() - mLastScroll;
if (duration > ANIMATED_SCROLL_GAP) {
final int height = getHeight() - mPaddingBottom - mPaddingTop; //获取部件高度
final int bottom = getChildAt(0).getHeight(); //获取当前能看到的item高度
final int maxY = Math.max(0, bottom - height);
final int scrollY = mScrollY;
dy = Math.max(0, Math.min(scrollY + dy, maxY)) - scrollY;
mScroller.startScroll(mScrollX, scrollY, 0, dy);
postInvalidateOnAnimation();
} else {
if (!mScroller.isFinished()) {
mScroller.abortAnimation();
if (mFlingStrictSpan != null) {
mFlingStrictSpan.finish();
mFlingStrictSpan = null;
}
}
scrollBy(dx, dy);
}
mLastScroll = AnimationUtils.currentAnimationTimeMillis();
}
/**
* Like {@link #scrollTo}, but scroll smoothly instead of immediately.
*
* @param x the position where to scroll on the X axis
* @param y the position where to scroll on the Y axis
*/
public final void smoothScrollTo(int x, int y) {
smoothScrollBy(x - mScrollX, y - mScrollY);
}
源码可以看出,是ScrollBy和ScrollTo增加滚动动画的升级方案;
moothScrollBy(int dx, int dy) :
dy = Math.max(0, Math.min(scrollY + dy, maxY)) - scrollY;为方法的核心,比较绕,大致为计算当前滑动状态下可划动距离;
if(duration > ANIMATEDSCROLLGAP) 这句是判断当前是否在滚动,当还在滚动状态下,执行mScroller.startScroll(mScrollX, scrollY, 0, dy);当不在滚动,就立马打断。
smoothScrollTo(int x, int y):
从源码中看出,它实际上是调用了smoothScrollBy(x - mScrollX, y - mScrollY);方法 根据x,y的值来计算剩余可滚动的位移量;
最后讲讲view和viewgroup这俩,完全吃透有点难,通俗讲,Android的UI界面都是由View和ViewGroup及其派生类组合而成的,View是所有UI组件的基类,而ViewGroup是容纳这些组件的容器; View类是ViewGroup的父类,ViewGroup具有View的所有特性,ViewGroup主要用来充当View的容器,将其中的View作为自己孩子,并对其进行管理,当然孩子也可以是ViewGroup类型。
View派生出的直接子类有:AnalogClock,ImageView,KeyboardView, ProgressBar,SurfaceView,TextView,ViewGroup,ViewStub
View派生出的间接子类有:AbsListView,AbsSeekBar, AbsSpinner, AbsoluteLayout, AdapterView,AdapterViewAnimator, AdapterViewFlipper, AppWidgetHostView, AutoCompleteTextView,Button,CalendarView, CheckBox, CheckedTextView, Chronometer, CompoundButton
ViewGroup派生出的直接子类有:AbsoluteLayout,AdapterView,FragmentBreadCrumbs,FrameLayout,LinearLayout,RelativeLayout,SlidingDrawer;
ViewGroup派生出的间接子类有:AbsListView,AbsSpinner, AdapterViewAnimator, AdapterViewFlipper, AppWidgetHostView, CalendarView, DatePicker, DialerFilter, ExpandableListView, Gallery, GestureOverlayView,GridView,HorizontalScrollView, ImageSwitcher,ListView,
当然,随着Android版本不断地更新,这些派生出来的子类也是在不段增加的!
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