layout_margintop 百分比_layout marginleft_layout marginend用法(6)

再看一下PercentLayoutInfo.fillLayoutParams()的实现，该方法是通过百分比设置View的尺寸:

        /**
         * Fills {@code ViewGroup.LayoutParams} dimensions based on percentage values.
         */
        public void fillLayoutParams(ViewGroup.LayoutParams params, int widthHint,
                int heightHint) {
            // mPreservedParams来记录原始的宽高值
            // Preserve the original layout params, so we can restore them after the measure step.
            mPreservedParams.width = params.width;
            mPreservedParams.height = params.height;

            // We assume that width/height set to 0 means that value was unset. This might not
            // necessarily be true, as the user might explicitly set it to 0. However, we use this
            // information only for the aspect ratio. If the user set the aspect ratio attribute,
            // it means they accept or soon discover that it will be disregarded.
            final boolean widthNotSet =
                    (mPreservedParams.mIsWidthComputedFromAspectRatio
                            || mPreservedParams.width == 0) && (widthPercent < 0);
            final boolean heightNotSet =
                    (mPreservedParams.mIsHeightComputedFromAspectRatio
                            || mPreservedParams.height == 0) && (heightPercent < 0);

            // 如果指定了百分比属性，就用宽高值和百分比去算出具体的宽高
            if (widthPercent >= 0) {
                params.width = (int) (widthHint * widthPercent);
            }

            if (heightPercent >= 0) {
                params.height = (int) (heightHint * heightPercent);
            }
            // 如果指定了宽高的比例值，就用比例值去算出宽高，从这里能看出`aspectRatio`的优先级比百分比要高。他可以覆盖百分比之前设置的值。
            if (aspectRatio >= 0) {
                if (widthNotSet) {
                    params.width = (int) (params.height * aspectRatio);
                    // Keep track that we've filled the width based on the height and aspect ratio.
                    mPreservedParams.mIsWidthComputedFromAspectRatio = true;
                }
                if (heightNotSet) {
                    params.height = (int) (params.width / aspectRatio);
                    // Keep track that we've filled the height based on the width and aspect ratio.
                    mPreservedParams.mIsHeightComputedFromAspectRatio = true;
                }
            }

            if (Log.isLoggable(TAG, Log.DEBUG)) {
                Log.d(TAG, "after fillLayoutParams: (" + params.width + ", " + params.height + ")");
            }
        }

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