layer-list被拉伸问题

在 layer-list 中的自定义 shape设定的大小无效

最近在做自定义 shape 效果时发现,自定义shape的大小在layer-list中无效了，较小的shape被拉伸至最大shape的大小了。(API23+没有此问题)
把自定义的 shape 单独拿出来用却没有问题,唯独放在 LayerDrawable 出现问题.

code

原本想实现一个圆环中包含一个实心圆的 drawable, 写出来类似下面的代码,在 IDE 预览时也没啥问题,到了真机就有问题了.
shape_layer.xml

<?xml version="1.0" encoding="utf-8"?>
<layer-list xmlns:android="http://schemas.android.com/apk/res/android">

    <item android:gravity="center">
        <shape
            android:innerRadius="15px"
            android:shape="ring"
            android:thickness="10px"
            android:useLevel="false">
            <size
                android:width="50px"
                android:height="50px" />

            <solid android:color="@color/colorAccent" />
        </shape>
    </item>

    <item android:gravity="center">
        <shape android:shape="oval">
            <size
                android:width="20px"
                android:height="20px" />

            <solid android:color="@color/colorPrimary" />
        </shape>
    </item>

</layer-list>

shape_layer_fixed. xml
后面将这2层的顺序换了下,但是实心和环之间的空白还是没有,所以给设置了位置来限定大小.

<?xml version="1.0" encoding="utf-8"?>
<layer-list xmlns:android="http://schemas.android.com/apk/res/android">

    <item android:gravity="center">
        <shape
            android:innerRadius="15px"
            android:shape="ring"
            android:thickness="10px"
            android:useLevel="false">
            <size
                android:width="50px"
                android:height="50px" />

            <solid android:color="@color/colorAccent" />
        </shape>
    </item>

    // 这里通过计算设置了其4个方向的 inset 值来保证不会覆盖上层的环
    <item
        android:bottom="20px"
        android:gravity="center"
        android:left="20px"
        android:right="20px"
        android:top="20px">
        <shape android:shape="oval">
            <size
                android:width="20px"
                android:height="20px" />

            <solid android:color="@color/colorPrimary" />
        </shape>
    </item>

</layer-list>

Anroid L MR1 以前 预览布局效果

问题跟踪：

LayerDrawable#onBoundsChange

    // API22以前 在Bound更新时直接把所有的子Drawable的bound设置成LayerDrawable的bound了
    @Override
    protected void onBoundsChange(Rect bounds) {
        int padL = 0;
        int padT = 0;
        int padR = 0;
        int padB = 0;

        final boolean nest = mLayerState.mPaddingMode == PADDING_MODE_NEST;
        final ChildDrawable[] array = mLayerState.mChildren;
        final int N = mLayerState.mNum;
        for (int i = 0; i < N; i++) {
            final ChildDrawable r = array[i];
            r.mDrawable.setBounds(bounds.left + r.mInsetL + padL, bounds.top + r.mInsetT + padT,
                    bounds.right - r.mInsetR - padR, bounds.bottom - r.mInsetB - padB);

            if (nest) {
                padL += mPaddingL[i];
                padR += mPaddingR[i];
                padT += mPaddingT[i];
                padB += mPaddingB[i];
            }
        }
    }

LayerDrawable#onBoundsChange

// API 23+ 不会直接使用容器的bound，而是通过相对位置得到
 private void updateLayerBoundsInternal(Rect bounds) {
        int paddingL = 0;
        int paddingT = 0;
        int paddingR = 0;
        int paddingB = 0;

        final Rect outRect = mTmpOutRect;
        final int layoutDirection = getLayoutDirection();
        final boolean isLayoutRtl = layoutDirection == LayoutDirection.RTL;
        final boolean isPaddingNested = mLayerState.mPaddingMode == PADDING_MODE_NEST;
        final ChildDrawable[] array = mLayerState.mChildren;

        for (int i = 0, count = mLayerState.mNum; i < count; i++) {
            final ChildDrawable r = array[i];
            final Drawable d = r.mDrawable;
            if (d == null) {
                continue;
            }

            final int insetT = r.mInsetT;
            final int insetB = r.mInsetB;

            // Resolve insets for RTL. Relative insets override absolute
            // insets.
            final int insetRtlL = isLayoutRtl ? r.mInsetE : r.mInsetS;
            final int insetRtlR = isLayoutRtl ? r.mInsetS : r.mInsetE;
            final int insetL = insetRtlL == INSET_UNDEFINED ? r.mInsetL : insetRtlL;
            final int insetR = insetRtlR == INSET_UNDEFINED ? r.mInsetR : insetRtlR;

            // Establish containing region based on aggregate padding and
            // requested insets for the current layer.
            final Rect container = mTmpContainer;
            container.set(bounds.left + insetL + paddingL, bounds.top + insetT + paddingT,
                    bounds.right - insetR - paddingR, bounds.bottom - insetB - paddingB);

            // Compute a reasonable default gravity based on the intrinsic and
            // explicit dimensions, if specified.
            final int intrinsicW = d.getIntrinsicWidth();
            final int intrinsicH = d.getIntrinsicHeight();
            final int layerW = r.mWidth;
            final int layerH = r.mHeight;
            final int gravity = resolveGravity(r.mGravity, layerW, layerH, intrinsicW, intrinsicH);

            // Explicit dimensions override intrinsic dimensions.
            final int resolvedW = layerW < 0 ? intrinsicW : layerW;
            final int resolvedH = layerH < 0 ? intrinsicH : layerH;
            Gravity.apply(gravity, resolvedW, resolvedH, container, outRect, layoutDirection);
            d.setBounds(outRect);

            if (isPaddingNested) {
                paddingL += mPaddingL[i];
                paddingR += mPaddingR[i];
                paddingT += mPaddingT[i];
                paddingB += mPaddingB[i];
            }
        }
    }

解决方案：

旧版本不支持gravity 属性
可以设置inset left,top,right,bottom 来指定偏移位置，从而得到层叠效果的Drawable