无法转换类型为“System.Windows.Forms.Form”的对象输入“Project.Form1”

发布于 2024-11-03 12:37:33 字数 608 浏览 1 评论 0原文

我有一个 UserControl，它使用我的表单上可用的一些公共属性，位于此 UserControl 的 Paint 事件的顶部，我引用控件的 Parent 并将其转换为我的表单的类型。

var _parent = (Form1)Parent;

但是，此代码可以工作，在“设计”视图中，会引发错误，并且我在 UserControl 处看到的只是一个白框，显示本文标题中的错误。堆栈跟踪直接指向这行代码。

现在，我已经通过用户控件中的属性重新路由此转换来修复此错误，

    public Form1 ControlParent
    {
        get
        {
            if (Parent != null)
            {
                return (Form1)Parent;
            }
            return null;
        }
    }

这对于破坏设计视图的东西来说有点太多了..还有其他想法吗？

原文

I have a UserControl that uses some of the public properties that I have available on my Form, at the top of the Paint event for this UserControl, I reference the Parent of the control and cast it to the type of my Form.

var _parent = (Form1)Parent;

This code works however, in the Design view, an error is thrown and all I see in place of the UserControl is a white box displaying the error in the title of this post. The stacktrace leads directly to this line of code.

Right now, I have fixed this error by re-routing this cast through a Property in my UserControl

    public Form1 ControlParent
    {
        get
        {
            if (Parent != null)
            {
                return (Form1)Parent;
            }
            return null;
        }
    }

This is kind of a little much for something that just breaks the Design view.. any other ideas?

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野心澎湃 2024-11-10 12:37:33

根据代码，您的子 Control 实例似乎已经可以处理 ControlParent 为 null 的情况。因此，最简单的修复方法就是执行以下操作

public Form1 ControlParent
{
    get
    {
        return Parent as Form1;
    }
}

。注意：一般来说，依赖于特定类型的 Control 的 Parent 是一个坏主意。它可以防止它被重新托管在其他控件中，并且可能会破坏经常捏造类型以提供良好设计体验的设计人员。如果您必须依赖像 Parent 这样的特定类型的值，请确保有一个后备计划，该计划不会在面对不同类型时崩溃。

Based on the code it looks like your child Control instance can already deal with ControlParent being null. Hence the simplest fix would be to just do the following

public Form1 ControlParent
{
    get
    {
        return Parent as Form1;
    }
}

Note: In general it's a bad idea to depend on the Parent of a Control being of a specific type. It prevents it from being re-hosted in other controls and can break designers which often fudge types around in order to provide a nice design experience. If you must depend on a value like Parent being of a specific type make sure to have a fall back plan which doesn't crash in the face of a different type.

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