最近做項(xiàng)目遇到一個tab切換的選項(xiàng)的需求類似輪播圖损姜，用的是viewpager來做的据悔，遇到的問題是每個item的高度不一樣剿吻，所以在切換時需要每次去重新計算viewpager的高度箱玷，所以自定義了一個viewpager重寫onMeasure方法：

public void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
        if(this.mCurrentView == null) {
            super.onMeasure(widthMeasureSpec, heightMeasureSpec);
        } else {
            int height = 0;
            this.mCurrentView.measure(widthMeasureSpec, MeasureSpec.makeMeasureSpec(0, 0));
            int h = this.mCurrentView.getMeasuredHeight();
            if(h > height) {
                height = h;
            }

            heightMeasureSpec = MeasureSpec.makeMeasureSpec(height, 1073741824);
            super.onMeasure(widthMeasureSpec, heightMeasureSpec);
        }
    }

然后在setPrimaryItem中重新設(shè)置viewpager高度

 @Override
 public void setPrimaryItem(ViewGroup container, int position, Object object) {
       super.setPrimaryItem(container, position, object);
       View view= (View) object;
       ((CustomPager) container).measureCurrentView(view);
 }

但是在實(shí)際使用中發(fā)現(xiàn)setPrimaryItem會連續(xù)不斷的調(diào)用吮龄，最后研究后發(fā)現(xiàn)viewpager的onMeasure方法中會調(diào)用populate方法拷窜，而populate方法會調(diào)用setPrimaryItem方法开皿，所以才會導(dǎo)致死循環(huán)，結(jié)果就是setPrimaryItem方法無限調(diào)用:

@Override
protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
     //省略部分源碼
    populate(); 
}

void populate(int newCurrentItem) {
     //省略部分源碼
    mAdapter.setPrimaryItem(this, mCurItem, curItem != null ? curItem.object : null);
}

解決方法是重新自定義一個pageradapter篮昧，在里面記錄當(dāng)前的位置赋荆，位置變化時才會調(diào)用重新設(shè)置viewpager高度的方法：

public abstract class BasePagerAdapter extends PagerAdapter {
    private int lastPosition = -1;

    @Override
    public void setPrimaryItem(ViewGroup container, int position, Object object) {
        super.setPrimaryItem(container, position, object);
        if (lastPosition != position && object instanceof DatePickerView && container instanceof CustomPager) {
            lastPosition = position;
            View view = (View) object;
            ((CustomPager) container).measureCurrentView(view);
        }
    }
}