RecyclerView实现可拖动滚动条并修改宽度

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本文参考了孤调的文章,链接如下:
https://www.jianshu.com/p/67e1df2b1920
基本实现了拖动的需求,但是还有一个问题就是滚动条的宽度跟需求不符,需要进行修改.但是官方并未提供相应的参数.自己动手丰衣足食,开始撸源码.
打开RecyclerView类,搜索fastScrollEnabled,定位到构造方法中的

mEnableFastScroller = a.getBoolean(R.styleable.RecyclerView_fastScrollEnabled, false);
if (mEnableFastScroller) {
                StateListDrawable verticalThumbDrawable = (StateListDrawable) a
                        .getDrawable(R.styleable.RecyclerView_fastScrollVerticalThumbDrawable);
                Drawable verticalTrackDrawable = a
                        .getDrawable(R.styleable.RecyclerView_fastScrollVerticalTrackDrawable);
                StateListDrawable horizontalThumbDrawable = (StateListDrawable) a
                        .getDrawable(R.styleable.RecyclerView_fastScrollHorizontalThumbDrawable);
                Drawable horizontalTrackDrawable = a
                        .getDrawable(R.styleable.RecyclerView_fastScrollHorizontalTrackDrawable);
                initFastScroller(verticalThumbDrawable, verticalTrackDrawable,
                        horizontalThumbDrawable, horizontalTrackDrawable);
            }

可以看到如果mEnableFastScroller 为true会进入initFastScroller方法,我们在xml文件中设置的thumbDrawable和TrackDrawable被作为参数传入了此方法.点击进入此方法:

void initFastScroller(StateListDrawable verticalThumbDrawable,
            Drawable verticalTrackDrawable, StateListDrawable horizontalThumbDrawable,
            Drawable horizontalTrackDrawable) {
        if (verticalThumbDrawable == null || verticalTrackDrawable == null
                || horizontalThumbDrawable == null || horizontalTrackDrawable == null) {
            throw new IllegalArgumentException(
                "Trying to set fast scroller without both required drawables." + exceptionLabel());
        }

        Resources resources = getContext().getResources();
        new FastScroller(this, verticalThumbDrawable, verticalTrackDrawable,
                horizontalThumbDrawable, horizontalTrackDrawable,
                resources.getDimensionPixelSize(R.dimen.fastscroll_default_thickness),
                resources.getDimensionPixelSize(R.dimen.fastscroll_minimum_range),
                resources.getDimensionPixelOffset(R.dimen.fastscroll_margin));
    }

最后一段(最后5行)代码创建了一个FastScroller,并将ThumbDrawable,TrackDrawable作为参数传入,此外还传入了一些dimens资源,最后点击这个FastScroller类:

FastScroller(RecyclerView recyclerView, StateListDrawable verticalThumbDrawable,
            Drawable verticalTrackDrawable, StateListDrawable horizontalThumbDrawable,
            Drawable horizontalTrackDrawable, int defaultWidth, int scrollbarMinimumRange,
            int margin) {
        mVerticalThumbDrawable = verticalThumbDrawable;
        mVerticalTrackDrawable = verticalTrackDrawable;
        mHorizontalThumbDrawable = horizontalThumbDrawable;
        mHorizontalTrackDrawable = horizontalTrackDrawable;
        mVerticalThumbWidth = Math.max(defaultWidth, verticalThumbDrawable.getIntrinsicWidth());
        mVerticalTrackWidth = Math.max(defaultWidth, verticalTrackDrawable.getIntrinsicWidth());
        mHorizontalThumbHeight = Math
            .max(defaultWidth, horizontalThumbDrawable.getIntrinsicWidth());
        mHorizontalTrackHeight = Math
            .max(defaultWidth, horizontalTrackDrawable.getIntrinsicWidth());
mScrollbarMinimumRange = scrollbarMinimumRange;
        mMargin = margin;
        mVerticalThumbDrawable.setAlpha(SCROLLBAR_FULL_OPAQUE);
        mVerticalTrackDrawable.setAlpha(SCROLLBAR_FULL_OPAQUE);

        mShowHideAnimator.addListener(new AnimatorListener());
        mShowHideAnimator.addUpdateListener(new AnimatorUpdater());

        attachToRecyclerView(recyclerView);
    }

bingo!这正是我们要找的类,如下代码设置了滑块和滑轨的宽度:

mVerticalThumbWidth = Math.max(defaultWidth, verticalThumbDrawable.getIntrinsicWidth());
        mVerticalTrackWidth = Math.max(defaultWidth, verticalTrackDrawable.getIntrinsicWidth());

从上面的代码可以看出,滑动条的宽度采用了defaultWidth和Drawable.getIntrinsicWidth()的最大值,即fastscroll_default_thickness和Drawable宽度的最大值,但因为我的项目中用的是shape, 没有设置宽度,所以只要设置fastscroll_default_thickness即可.
在自己的dimens文件中设置R.dimen.fastscroll_default_thickness这个值,运行,效果如丝般润滑.
最后发个福利~~

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