layout_margintop 百分比_layout marginleft_layout marginend用法(10)

调用了PercentLayoutInfo.restoreMarginLayoutParams()方法，我们看下它的源码:

/**
         * Restores original dimensions and margins after they were changed for percentage based
         * values. Calling this method only makes sense if you previously called
         * {@link PercentLayoutHelper.PercentLayoutInfo#fillMarginLayoutParams}.
         */
        public void restoreMarginLayoutParams(ViewGroup.MarginLayoutParams params) {
            restoreLayoutParams(params);
            // mPreservedParams的值在之前ad
            params.leftMargin = mPreservedParams.leftMargin;
            params.topMargin = mPreservedParams.topMargin;
            params.rightMargin = mPreservedParams.rightMargin;
            params.bottomMargin = mPreservedParams.bottomMargin;
            MarginLayoutParamsCompat.setMarginStart(params,
                    MarginLayoutParamsCompat.getMarginStart(mPreservedParams));
            MarginLayoutParamsCompat.setMarginEnd(params,
                    MarginLayoutParamsCompat.getMarginEnd(mPreservedParams));
        }

意思是说，再他们被以百分比为基础的数据更改之后恢复成原始的尺寸和margin。

然后继续看一下restoreLayoutParams():

/**
         * Restores original dimensions after they were changed for percentage based values. Calling
         * this method only makes sense if you previously called
         * {@link PercentLayoutHelper.PercentLayoutInfo#fillLayoutParams}.
         */
        public void restoreLayoutParams(ViewGroup.LayoutParams params) {
            if (!mPreservedParams.mIsWidthComputedFromAspectRatio) {
                // Only restore the width if we didn't compute it based on the height and
                // aspect ratio in the fill pass.
                params.width = mPreservedParams.width;
            }
            if (!mPreservedParams.mIsHeightComputedFromAspectRatio) {
                // Only restore the height if we didn't compute it based on the width and
                // aspect ratio in the fill pass.
                params.height = mPreservedParams.height;
            }

            // Reset the tracking flags.
            mPreservedParams.mIsWidthComputedFromAspectRatio = false;
            mPreservedParams.mIsHeightComputedFromAspectRatio = false;
        }

好了到这里也分析完了onLayout的方法，大意就是在onMeasure之前先将原始的宽高和margin都备份一下，然后在onMeasure中根据百分比去设置对应的宽高和margin，等到设置完之后在onLayout方法中再去将这些值恢复到之前备份的起始数据。说实话我没看明白为什么要这样做？

通过上面的代码分析我们知道对布局影响力的优先顺序: app:layout_aspectRatio > app:layout_heightPercent > android:layout_height如果我们同时都设置这三个参数值的话，最终会用app:layout_aspectRatio的值。

遗留问题:

为什么在onLayout方法中去恢复数据，这有什么作用？

看代码在处理如果指定的百分比过小但又指定wrap_content时，会重新根据wrap_content去重新计算的逻辑没有错，但是为什么我在上面测试的时候确没效果？

有知道上面这两个问题的告诉我一下。

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