layout_margintop 百分比_layout marginleft_layout marginend用法(4)

源码不长，主要是三个部分:

重写onMeasure，根据百分比转换成对应的尺寸

重写onLayout

自定义LayoutParams，在FrameLayout.LayoutParams的基础上多实现了一个接口。包含了PercentLayoutHelper.PercentLayoutInfo属性，而文档中对PercentLayoutInfo的介绍是Container for information about percentage dimensions and margins. It acts as an extension for LayoutParams.

我们也先一步步的来分析，首先看下mHelper.adjustChildren(widthMeasureSpec, heightMeasureSpec);:

/**
     * Iterates over children and changes their width and height to one calculated from percentage
     * values.
     * @param widthMeasureSpec Width MeasureSpec of the parent ViewGroup.
     * @param heightMeasureSpec Height MeasureSpec of the parent ViewGroup.
     */
public void adjustChildren(int widthMeasureSpec, int heightMeasureSpec) {
        if (Log.isLoggable(TAG, Log.DEBUG)) {
            Log.d(TAG, "adjustChildren: " + mHost + " widthMeasureSpec: "
                    + View.MeasureSpec.toString(widthMeasureSpec) + " heightMeasureSpec: "
                    + View.MeasureSpec.toString(heightMeasureSpec));
        }

        int widthHint = View.MeasureSpec.getSize(widthMeasureSpec);
        int heightHint = View.MeasureSpec.getSize(heightMeasureSpec);
        // mHost是由构造函数传递过来的，就是PercentFrameLayout自身。
        for (int i = 0, N = mHost.getChildCount(); i < N; i++) {
            View view = mHost.getChildAt(i);
            ViewGroup.LayoutParams params = view.getLayoutParams();
            if (Log.isLoggable(TAG, Log.DEBUG)) {
                Log.d(TAG, "should adjust " + view + " " + params);
            }
            if (params instanceof PercentLayoutParams) {
                // 通过PercentLayoutParams. getPercentLayoutInfo()方法得到PercentLayoutInfo，至于PercentLayoutInfo类在上面也说过了。
                PercentLayoutInfo info =
                        ((PercentLayoutParams) params).getPercentLayoutInfo();
                if (Log.isLoggable(TAG, Log.DEBUG)) {
                    Log.d(TAG, "using " + info);
                }
                if (info != null) {
                    if (params instanceof ViewGroup.MarginLayoutParams) {
                        // PercentFrameLayout.LayoutParams继承自FrameLayout.LayoutParams，而FrameLayout.LayoutParams又继承自ViewGroup.MarginLayoutParams
                        info.fillMarginLayoutParams(view, (ViewGroup.MarginLayoutParams) params,
                                widthHint, heightHint);
                    } else {
                        info.fillLayoutParams(params, widthHint, heightHint);
                    }
                }
            }
        }
    }

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