在wpf界面上遍历一个控件（在模板里面的时候不能访问的时候，用这个方法很好用

public T FindFirstVisualChild<T>(DependencyObject obj, string childName) where T : DependencyObject
{
for (int i = 0; i < VisualTreeHelper.GetChildrenCount(obj); i++)
{
DependencyObject child = VisualTreeHelper.GetChild(obj, i);
if (child != null&& child is T && child.GetValue(NameProperty).ToString() == childName)
{
return (T)child;
}
else
{
T childOfChild = FindFirstVisualChild<T>(child, childName);
if (childOfChild != null)
{
return childOfChild;
}
}
}
return null;
}