The specified child already has a parent. You must call removeView() on the child's parent first分析

• 异常

java.lang.IllegalStateException: The specified child already has a parent. You must call removeView() on the child's parent first.
        at android.view.ViewGroup.addViewInner(ViewGroup.java:4465)
        at android.view.ViewGroup.addView(ViewGroup.java:4301)
        at android.view.ViewGroup.addView(ViewGroup.java:4242)
        at android.view.ViewGroup.addView(ViewGroup.java:4215)

• 异常的原因child.getParent()!=null

//ViewGroup中
private void addViewInner(View child, int index, LayoutParams params,
            boolean preventRequestLayout) {
        if (mTransition != null) {
            // Don't prevent other add transitions from completing, but cancel remove
            // transitions to let them complete the process before we add to the container
            mTransition.cancel(LayoutTransition.DISAPPEARING);
        }

        if (child.getParent() != null) {
            throw new IllegalStateException("The specified child already has a parent. " +
                    "You must call removeView() on the child's parent first.");
        }
       //省略代码。。。。
    }

• view.getParent初始化及重置

  • 初始化

    //无法通过View重置child.mParent，只能使用ViewGroup中的removeXXX方法进行重置,下面是View.mParent初始化方法，位于View中
        /*
        * Caller is responsible for calling requestLayout if necessary.
        * (This allows addViewInLayout to not request a new layout.)
        */
        void assignParent(ViewParent parent) {
            if (mParent == null) {
                mParent = parent;
            } else if (parent == null) {
                mParent = null;
            } else {
                throw new RuntimeException("view " + this + " being added, but"
                        + " it already has a parent");
            }
        }
    
    

  • 重置

    //位于ViewGroup中，具体调用逻辑不再展开
    
    // This method also sets the child's mParent to null
        private void removeFromArray(int index) {
            final View[] children = mChildren;
            if (!(mTransitioningViews != null && mTransitioningViews.contains(children[index]))) {
                children[index].mParent = null;
            }
            final int count = mChildrenCount;
            if (index == count - 1) {
                children[--mChildrenCount] = null;
            } else if (index >= 0 && index < count) {
                System.arraycopy(children, index + 1, children, index, count - index - 1);
                children[--mChildrenCount] = null;
            } else {
                throw new IndexOutOfBoundsException();
            }
            if (mLastTouchDownIndex == index) {
                mLastTouchDownTime = 0;
                mLastTouchDownIndex = -1;
            } else if (mLastTouchDownIndex > index) {
                mLastTouchDownIndex--;
            }
        }
    
        // This method also sets the children's mParent to null
        private void removeFromArray(int start, int count) {
            final View[] children = mChildren;
            final int childrenCount = mChildrenCount;
    
            start = Math.max(0, start);
            final int end = Math.min(childrenCount, start + count);
    
            if (start == end) {
                return;
            }
    
            if (end == childrenCount) {
                for (int i = start; i < end; i++) {
                    children[i].mParent = null;
                    children[i] = null;
                }
            } else {
                for (int i = start; i < end; i++) {
                    children[i].mParent = null;
                }
    
                // Since we're looping above, we might as well do the copy, but is arraycopy()
                // faster than the extra 2 bounds checks we would do in the loop?
                System.arraycopy(children, end, children, start, childrenCount - end);
    
                for (int i = childrenCount - (end - start); i < childrenCount; i++) {
                    children[i] = null;
                }
            }
    
            mChildrenCount -= (end - start);
        }
    
    

• 解决方法

  View childView=...;
  ViewGroup parent=....;
  /**
  * 抛出异常的错误代码
  * parent.removeView(child);
  * parent.addView(child);
  **/
   parent.removeView(childView);
   //parent和childView.getParent可能不是同一对象
   if(childView.getParent instanceof ViewGroup){
      ((ViewGroup)child.getParent).removeView(childView);
   }
   parent.addView(childView);