HorizontalScrollView重新layout之后自动滑动初始位置问题解决

最新推荐文章于 2022-10-14 17:22:04 发布

hbRyando

最新推荐文章于 2022-10-14 17:22:04 发布

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分类专栏：安卓文章标签： Android ScrollView

本文链接：https://blog.youkuaiyun.com/yaosizy/article/details/74211195

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本文探讨了HorizontalScrollView在重新layout时自动滑动的问题，并详细分析了其内部机制，包括焦点处理逻辑。最后提供了解决方案，即通过覆写onLayout方法避免自动滚动。

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HorizontalScrollView在重新layout时，有时候会自动滑动到其他位置，这是由于他的后代view获取到焦点导致的，来让我们从代码层面看清这个问题：

 @Override
    protected void onLayout(boolean changed, int l, int t, int r, int b) {
        int childWidth = 0;
        int childMargins = 0;

        if (getChildCount() > 0) {
            childWidth = getChildAt(0).getMeasuredWidth();
            LayoutParams childParams = (LayoutParams) getChildAt(0).getLayoutParams();
            childMargins = childParams.leftMargin + childParams.rightMargin;
        }

        final int available = r - l - getPaddingLeftWithForeground() -
                getPaddingRightWithForeground() - childMargins;

        final boolean forceLeftGravity = (childWidth > available);

        layoutChildren(l, t, r, b, forceLeftGravity);

        mIsLayoutDirty = false;
        // Give a child focus if it needs it
        //就是在这一行，scrollView自动滑动到那个有焦点的view的位置
        if (mChildToScrollTo != null && isViewDescendantOf(mChildToScrollTo, this)) {
            scrollToChild(mChildToScrollTo);
        }
        mChildToScrollTo = null;

        if (!isLaidOut()) {
            final int scrollRange = Math.max(0,
                    childWidth - (r - l - mPaddingLeft - mPaddingRight));
            if (mSavedState != null) {
                mScrollX = isLayoutRtl()
                        ? scrollRange - mSavedState.scrollOffsetFromStart
                        : mSavedState.scrollOffsetFromStart;
                mSavedState = null;
            } else {
                if (isLayoutRtl()) {
                    mScrollX = scrollRange - mScrollX;
                } // mScrollX default value is "0" for LTR
            }
            // Don't forget to clamp
            if (mScrollX > scrollRange) {
                mScrollX = scrollRange;
            } else if (mScrollX < 0) {
                mScrollX = 0;
            }
        }

        // Calling this with the present values causes it to re-claim them
        scrollTo(mScrollX, mScrollY);
    }

而mChildToScrollTo这个view是在requestChildFocus中赋值的，

  @Override
    public void requestChildFocus(View child, View focused) {
        if (!mIsLayoutDirty) {
            scrollToChild(focused);
        } else {
            // The child may not be laid out yet, we can't compute the scroll yet
            mChildToScrollTo = focused;
        }
        super.requestChildFocus(child, focused);
    }

解决办法：

覆写父类方法onLayout，就可以解决这个问题

  @Override
    protected void onLayout(boolean changed, int l, int t, int r, int b) {
        final int tempScrollX = getScrollX();
        super.onLayout(changed, l, t, r, b);
        final int scrollX = getScrollX();

       
            if (tempScrollX != scrollX) {
                this.scrollTo(tempScrollX, 0);
            }
        
    }