Unity3D：在重定孩子时遍历孩子的问题

Question

I'm trying to change all the children of a GameObject to another.

foreach (Transform child in transform) {
child.parent = new_parent.transform;
}

This code detaches the children partially and leaves a few children back in the original parent. I use the below code to perform the above operation.

foreach (Transform child in transform) {
    child.tag = "collected";
}

GameObject[] collected = GameObject.FindGameObjectsWithTag ("collected");
foreach (Transform child in collected.transform) {
    child.transform.parent = new_parent.transform;
}

And this works perfectly. I also used for along with parent.GetChild(i) and similar issue happens. Where am I missing?

Answer 1

As explained in the comments, items are going missing because you're modifying the collection of children at the same time as you're iterating through it with 'foreach.' In general this is a bad idea and you should never modify a collection as you're iterating through it (unless you know exactly what you're doing).

One solution, which you've found, is to make a copy of the collection, iterate through the copy, and then safely remove items from the original collection. Tagging the objects and then calling FindGameObjectsWithTag is unnecessarily inefficient because it searches through every single GameObject, and also error-prone (if you forget to remove the tags you will get weird behaviour). You're better off making a list:

var collected = new List<Transform>();
foreach (var child in transform) {
    collected.Add(child);
}
foreach (Transform child in collected) {
    child.transform.parent = new_parent.transform;
}

Easier still in this case is to use a while loop to remove the last child as long as the parent has any children:

while (transform.childCount > 0) {
    transform.GetChild(transform.childCount - 1).parent = new_parent.transform;
}