为什么 listbox1.Items.Add 使用我的对象的 Equals 方法?

问题描述

我正在检查 Windows 窗体 ListBoxCollection 添加方法，在分析过程中，我发现方法add"调用了基础对象中的 Equals 方法为什么这个方法做这个动作?

i'm scrutinizing Windows Forms ListBoxCollection Add Method, during the analyzing i found that the method "add" calls Equals method in base Object why this method do this action ?

我使用了调用堆栈"并且找到了这个答案:

I Have used "Call Stack" and I have Find This Answer :

我们调用 :System.Windows.Forms.ListBox.ObjectCollection.Add(object item)

We Call :System.Windows.Forms.ListBox.ObjectCollection.Add(object item)

它会调用:System.Windows.Forms.ListBox.ObjectCollection.AddInternal(object item)

and it will Call : System.Windows.Forms.ListBox.ObjectCollection.AddInternal(object item)

它会调用:System.Windows.Forms.ListBox.NativeAdd(object item)

and it will Call : System.Windows.Forms.ListBox.NativeAdd(object item)

它会调用:System.Windows.Forms.ListControl.GetItemText(object item)

and it will call : System.Windows.Forms.ListControl.GetItemText(object item)

它会调用:System.Windows.Forms.Formatter.FormatObject(object value, System.Type targetType, System.ComponentModel.TypeConverter sourceConverter, System.ComponentModel.TypeConverter targetConverter, string formatString, System.IFormatProvider formatInfo, object formattedNullValue, 对象 dataSourceNullValue)

and it will call : System.Windows.Forms.Formatter.FormatObject(object value, System.Type targetType, System.ComponentModel.TypeConverter sourceConverter, System.ComponentModel.TypeConverter targetConverter, string formatString, System.IFormatProvider formatInfo, object formattedNullValue, object dataSourceNullValue)

它会调用 :System.Windows.Forms.Formatter.IsNullData(object value, object dataSourceNullValue)

and it will call :System.Windows.Forms.Formatter.IsNullData(object value, object dataSourceNullValue)

最后它会调用:object.Equals(object objA, object objB)

and Finally it will call : object.Equals(object objA, object objB)

which This Method Make My Equal Method too run :

which This Method Make My Equal Method too Run :

WindowsFormsApplication1.Student.Equals(object obj)

WindowsFormsApplication1.Student.Equals(object obj)

并且将发送到我的 Equals 方法(作为 obj)的最后一个参数是 DBNULL 对象！什么是 DBNULL?

and The Last Parameter which Will be Send to My Equals Method (as obj) is a DBNULL Object ! what is a DBNULL ?

推荐答案

因为它需要能够知道什么项目正在触发事件.如果对象是完全相同的对象，选择、编辑、删除就会变得困难和混乱.

Because it needs to be able to know what item is firing events. If the objects are the exact same object, selection, editing, deletion becomes difficult and confusing.

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