PercentAspectRatioMeasure.java

package com.sxjs.common.widget.percentlayout;

import android.support.annotation.Nullable;
import android.view.View;
import android.view.ViewGroup;

/**
 * @author：admin on 2017/3/27 16:34.
 */

public class PercentAspectRatioMeasure {
    /**
     * Holder for width and height measure specs.
     */
    public static class Spec {
        public int width;
        public int height;
    }

    /**
     * Updates the given measure spec with respect to the aspect ratio.
     *
     * <p>Note: Measure spec is not changed if the aspect ratio is not greater than zero or if
     * layoutParams is null.
     *
     * <p>Measure spec of the layout dimension (width or height) specified as "0dp" is updated
     * to match the measure spec of the other dimension adjusted by the aspect ratio. Exactly one
     * layout dimension should be specified as "0dp".
     *
     * <p>Padding is taken into account so that the aspect ratio refers to the content without
     * padding: {@code aspectRatio == (viewWidth - widthPadding) / (viewHeight - heightPadding)}
     *
     * <p>Updated measure spec respects the parent's constraints. I.e. measure spec is not changed
     * if the parent has specified mode {@code EXACTLY}, and it doesn't exceed measure size if parent
     * has specified mode {@code AT_MOST}.
     *
     * @param spec in/out measure spec to be updated
     * @param aspectRatio desired aspect ratio
     * @param layoutParams view's layout params
     * @param widthPadding view's left + right padding
     * @param heightPadding view's top + bottom padding
     */
    public static void updateMeasureSpec(
            Spec spec,
            float aspectRatio,
            @Nullable ViewGroup.LayoutParams layoutParams,
            int widthPadding,
            int heightPadding) {
        if (aspectRatio <= 0 || layoutParams == null) {
            return;
        }
        if (shouldAdjust(layoutParams.height)) {
            int widthSpecSize = View.MeasureSpec.getSize(spec.width);
            int desiredHeight = (int) ((widthSpecSize - widthPadding) / aspectRatio + heightPadding);
            int resolvedHeight = View.resolveSize(desiredHeight, spec.height);
            spec.height = View.MeasureSpec.makeMeasureSpec(resolvedHeight, View.MeasureSpec.EXACTLY);
        } else if (shouldAdjust(layoutParams.width)) {
            int heightSpecSize = View.MeasureSpec.getSize(spec.height);
            int desiredWidth = (int) ((heightSpecSize - heightPadding) * aspectRatio + widthPadding);
            int resolvedWidth = View.resolveSize(desiredWidth, spec.width);
            spec.width = View.MeasureSpec.makeMeasureSpec(resolvedWidth, View.MeasureSpec.EXACTLY);
        }
    }

    private static boolean shouldAdjust(int layoutDimension) {
        // Note: wrap_content is supported for backwards compatibility, but should not be used.
        return layoutDimension == 0 || layoutDimension == ViewGroup.LayoutParams.WRAP_CONTENT;
    }
}