以编程方式添加控件时占位符未实例化
我有一个 ASPX 页面，其中声明了占位符控件。
在代码隐藏中，我创建了一个 UserControl 并将其添加到占位符中。
protected void Page_Load(object sender, EventArgs e)
{
UserControl uc = new ChartUserControl();
myForm.Controls.Add(uc);
}
UserControl 反过来有一个占位符，但是在 Page_Load （对于 UserControl）中，当我这样做时：
protected void Page_Load(object sender, EventArgs e)
{
WebControl x = new WebControl();
userControlPlaceholder.Controls.Add(x);
}
它给了我无处不在的“对象引用未设置为对象的实例”异常。
我尝试通过调用构造函数来强制实例化，但这给我带来了其他麻烦。 任何帮助，将不胜感激。
I have a an ASPX Page with a Placeholder control declared.
In the Codebehind I create a UserControl I have and add it to the Placeholder.
protected void Page_Load(object sender, EventArgs e)
{
UserControl uc = new ChartUserControl();
myForm.Controls.Add(uc);
}
The UserControl in turn has a Placeholder, but in the Page_Load (for the UserControl) when I do:
protected void Page_Load(object sender, EventArgs e)
{
WebControl x = new WebControl();
userControlPlaceholder.Controls.Add(x);
}
It gives me the ubiquitous "Object reference not set to an instance of an object" exception.
I've tried forcing instantiation by calling a constructor, but that has gotten me into other trouble. Any help would be appreciated.
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评论（2）
我自己就花了4个小时。
问题是，您正在创建用户控件，
但必须使用 LoadControl：
显然，LoadControl 会初始化用户控件，以便其占位符（我假设它包含的其他控件）在您使用时不会为空他们。
I just spent 4 hours on this myself.
The problem is that you're creating the user controls with
but you have to use LoadControl:
Apparently, LoadControl initializes the user control so that its PlaceHolders (and I would assume, other controls it contains), won't be null when you use them.
不要在 Page_Load 中添加控件，而是重写 CreateChildControls 方法并将其添加到那里。
Instead of adding the control in the Page_Load, Override the CreateChildControls method and add it there.