android - 测量 ViewPager

Question

我有一个自定义 ViewGroup，它有一个子 ViewPager。 ViewPager 由 PagerAdapter 提供，该 LinearLayout 向 ViewPager 提供 LayoutParams 的 WRAP_CONTENT 高度和宽度。

View 显示正确，但是当在 ViewPager 上调用 child.measure() 方法时，它不会返回 LinearLayout 的实际尺寸，但似乎会填满所有剩余空间。

任何想法为什么会发生这种情况以及如何修改它？

Answer 1

我对接受的答案不太满意(也不对评论中的 pre-inflate-all-views 解决方案)，所以我整理了一个 ViewPager ，它的高度从第一个开始可用的 child 。它通过进行第二次测量来做到这一点，允许您窃取第一个 child 的高度。

更好的解决方案是在 android.support.v4.view 包中创建一个新类，该类实现更好的 onMeasure 版本(可以访问包- populate())

等可见方法

不过，就目前而言，下面的解决方案很适合我。

public class HeightWrappingViewPager extends ViewPager {

    public HeightWrappingViewPager(Context context) {
        super(context);
    }

    public HeightWrappingViewPager(Context context, AttributeSet attrs) {
        super(context, attrs);
    }

    @Override
    protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
        super.onMeasure(widthMeasureSpec, heightMeasureSpec);

        boolean wrapHeight = MeasureSpec.getMode(heightMeasureSpec) 
                == MeasureSpec.AT_MOST;

        if(wrapHeight) {
            /**
             * The first super.onMeasure call made the pager take up all the 
             * available height. Since we really wanted to wrap it, we need 
             * to remeasure it. Luckily, after that call the first child is 
             * now available. So, we take the height from it. 
             */

            int width = getMeasuredWidth(), height = getMeasuredHeight();

            // Use the previously measured width but simplify the calculations
            widthMeasureSpec = MeasureSpec.makeMeasureSpec(width, MeasureSpec.EXACTLY);

            /* If the pager actually has any children, take the first child's 
             * height and call that our own */ 
            if(getChildCount() > 0) {
                View firstChild = getChildAt(0);

                /* The child was previously measured with exactly the full height.
                 * Allow it to wrap this time around. */
                firstChild.measure(widthMeasureSpec, 
                        MeasureSpec.makeMeasureSpec(height, MeasureSpec.AT_MOST));

                height = firstChild.getMeasuredHeight();
            }

            heightMeasureSpec = MeasureSpec.makeMeasureSpec(height, MeasureSpec.EXACTLY);

            super.onMeasure(widthMeasureSpec, heightMeasureSpec);
        }
    }
}