C＃弱引用在表单中使用它时会有误解释吗？ [英] C# weakreference misinterpretation while using it for forms?

问题描述

亲爱的专家

看起来我不明白 WeakReference 。我的目标是通过WeakReference观察表单的生命周期。



在我的MainForm中，我使用弱引用创建Formtest：

Dear experts
It looks like I don't get the point on WeakReference. My goal is to let "observe" lifetime of a form by WeakReference.

In my MainForm I create a Formtest using a weak reference:

    public partial class FormMain : Form
    {
        private WeakReference weakRefFormTest= null;

        private void buttonNewForm_Click(object sender, EventArgs e)
        {
            if (weakRefFormTest == null)
            {
		// Create WeakReference and the form
                weakRefFormTest = new WeakReference(new FormTest());
                ((Form)weakRefFormTest.Target).Show();
            }
            else
            {
		// Check form alive  *1)
                Form formTest = (Form)weakRefFormTest.Target;
                if (formTest != null)
                {
                    formTest.Visible = !formTest.Visible;
                }
            }
        }
	...
	......
    }

* 1）我希望在关闭testForm后，（Form）weakRefFormTest.Target 将为null。但它不是这样的，它会给我一个有效的形式。关闭formTest后， weakRefFormTest.IsAlive 也返回true。然后使用代码中的表单抛出一个 System.ObjectDisposedException



你能指出我做的事吗不明白，我哪里错了？





注意：我知道我可以订阅Form.Closed-Event，但是我不喜欢这种方法。



非常感谢您提前。



我尝试了什么：



请参阅问题中的代码段。

*1) Here I expect, that (Form)weakRefFormTest.Target will be null after closing the testForm. But it is not like this, it will give me always a "valid" form. Also weakRefFormTest.IsAlive returns true after closing formTest. And using then the form in the code throws an System.ObjectDisposedException

Can you point me out what I do not understand, where I'm wrong?


N.B: I'm aware I could subscribe for Form.Closed-Event, but I don't like this approach.

Thank you very much in advance.

What I have tried:

See code snippet in the question.

推荐答案

查看文档：WeakReference.Target Property（System） [ ^ ]

并且它声明：

Look at the documentation: WeakReference.Target Property (System)[^]
And it states that:

Property Value
Type: System.Object
null if the object referenced by the current WeakReference object has been garbage collected; otherwise, a reference to the object referenced by the current WeakReference object.

仅仅因为它已关闭，并不意味着它已被垃圾收集器释放 - 请记住，垃圾收集器只会被踢进内存不足时执行，或者在对象上调用Dispose 。关闭表单既不会执行这些操作，也不会在用户填写完表单后按下确定后访问表单的内容：

Just because it is closed, does not mean that it has been deallocated by the Garbage Collector - remember that the garbage collector is only ever kicked into action when memory runs low, or Dispose is called on an object. Closing a form does neither of those things, or you would not be able to access the content of a form once the user had finished filling it in and pressed "OK":

frmLogin f = new frmLogin();
if (f.ShowDialog() == DialogResult.OK)
   {
   string username = f.UserName;
   ...
   }

如果您想知道表格何时关闭，您需要使用该事件，而不是弱参考。



：doh：我需要更多的咖啡因... [/ edit]

If you want to know when a form is closed, you need to use the event, not a weak reference.

[edit]:doh: I need more caffeine...[/edit]

这篇关于C＃弱引用在表单中使用它时会有误解释吗？的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！