如何隐藏自定义ComboBox中的Items属性

Question

我正在创建一个继承自ComboBox的自定义控件。将项添加到ComboBox时，我需要执行自定义操作。无论是C＃还是Vb.NET都没关系，但我不知道该怎么做。

看起来修改所有内容以检测它是不值得的，如下所示：
Event to detect item added to ComboBox

所以也许可以创建我的自定义.Add();方法，但是我需要隐藏Items属性，因此控件不允许两种不同的添加方法，只允许一种方法工作。

我尝试使用this thread中的内容，但我没有设法让它发挥作用。例如，我尝试了重载属性private，但没有改变任何东西，如Vb.NET中的这个例子所示：

Private Overloads ReadOnly Property Items() As ObjectCollection
'...

可以吗？

Answer 1

是和否。

是的，您可以隐藏原始项目集合，并将其替换为 其他内容。

但是，您的新“自定义”商品无法工作;它始终为空 - 至少这是我发现的。也许有人可以详细介绍为什么......？

这就是为什么我用一些相当无用的东西替换它 - 一个赤裸的物体。

可以做的是：您可以在中间人类中公开原始项目，并在自定义ComboBox类中使用它。你可以，例如命名公开的类Items_并创建一个类来替换最终继承级别中的Items。此类需要实现您希望自定义类的使用者拥有的所有方法和属性。

我已命名为自定义项目'项目'，并实现了一个方法和一个属性。 （对于不区分大小写的VB，可能Itemz会更好; - ）

这是最小的中间人：

[ToolboxItem(false)]
public class mimComboBox : ComboBox
{
    public ObjectCollection items_;

    public mimComboBox()
    {
        items_ = Items;
    }

}

这是一个自定义的ComboBox：

public class myComboBox : mimComboBox
{
    public myComboBox()
    {
        Items = new object();               // (1)
        items = new myItems(this);
    }

    new public object Items { get; set; }  // this hides the real Items  (2)
    public myItems items { get; set; }     // this is the custom property

    public class myItems // the custom Items class with all necessary methods etc..
    {
        public myItems( myComboBox parent )
        {
            parentCB = parent;  // reference to the outer class
        }

        private mimComboBox parentCB;  // the man-in-the-middle

        // all your methods..
        new public int Add(object o)  // one example of a custom method
        {
            // add your item-added event here
            return parentCB.items_.Add(o);
        }

        // one of many many properties  to provide..
        public int Count { get { return parentCB.items_.Count; } } 

    }

}

这是一个如何使用ComboBox的例子：

private void button1_Click(object sender, EventArgs e)
{
    myComboBox1.items.Add("uiuiuiiui");
    // myComboBox1.Items.Add("sadsds");  // <== this doesn't compile! (3)
    button1.Text = myComboBox1.items.Count.ToString();
}

这听起来很有意思!!

（也许中产阶级没有必要......？我想了解那个......！）

编辑：我根据Plutonix评论中的链接更改了一些细节。

注意：

• 如上所述，通过收听ComboBox系统消息可以更好地解决原始问题

• 我仍然想知道为什么会这样：

当我更换（1）＆amp; （2）通过

Items = new myItems(this);
new public myItems Items { get; set; } 

然后（3）编译就好了。但是在运行时它会抛出一个空对象引用错误。

这是缺少的Overridable属性的迟来效果吗？ @Jon Skeet来救援！ ; - ）

Answer 2

MyComboBox 充当普通的组合框（通过覆盖Item属性）和扩展事件（ItemAdded，ItemRemoved）

样本使用：

    MyComboBox1.Items.Add("0")
    MyComboBox1.Items.AddRange(New String() {"1", "2", "3", "55"})
    MyComboBox1.Items.Remove("55")
    MyComboBox1.Items.RemoveAt(0)
    Debug.WriteLine(MyComboBox1.Items.IndexOf("2")) '2
    Debug.WriteLine(MyComboBox1.Items.IndexOf("55")) '-1
    MyComboBox1.Items.Clear()

VB.NET代码：

Public Class MyComboBox
Inherits ComboBox

Public Event ItemAdded As EventHandler
'Public Event ItemsAdded As EventHandler
Public Event ItemRemoved As EventHandler
'Public Event ItemInserted(sender As Object, insertedIndex As Integer, e As EventArgs)

Private ItemContainer_ As ItemContainer

Sub New()

    ItemContainer_ = New ItemContainer(Me)

    AddHandler ItemContainer_.ItemAdded, AddressOf ItemContainer_ItemAdded
    'AddHandler ItemContainer_.ItemsAdded, AddressOf ItemContainer_ItemsAdded
    AddHandler ItemContainer_.ItemRemoved, AddressOf ItemContainer_ItemRemoved
    'AddHandler ItemContainer_.ItemInserted, AddressOf ItemContainer_ItemInserted

End Sub

Private Sub ItemContainer_ItemAdded(sender As Object, e As EventArgs)
    RaiseEvent ItemAdded(Me, e)
End Sub
'Private Sub ItemContainer_ItemsAdded(sender As Object, e As EventArgs)
'    RaiseEvent ItemsAdded(Me, e)
'End Sub
Private Sub ItemContainer_ItemRemoved(sender As Object, e As EventArgs)
    RaiseEvent ItemRemoved(Me, e)
End Sub
'Private Sub ItemContainer_ItemInserted(sender As Object, insertedIndex As Integer, e As EventArgs)
'    RaiseEvent ItemInserted(Me, insertedIndex, e)
'End Sub

Public Shadows ReadOnly Property Items As ItemContainer
    Get
        Return ItemContainer_
    End Get
End Property
Public Shadows ReadOnly Property Items(index As Integer) As Object
    Get
        Return ItemContainer_.Item(index)
    End Get
End Property


Public Class ItemContainer
    Inherits System.Windows.Forms.ComboBox.ObjectCollection

    Public Event ItemAdded As EventHandler
    'Public Event ItemsAdded As EventHandler
    Public Event ItemRemoved As EventHandler
    'Public Event ItemInserted(sender As Object, insertedIndex As Integer, e As EventArgs)


    Private owner_ As ComboBox

    Sub New(owner As ComboBox)
        MyBase.New(owner)
        owner_ = owner
    End Sub


    Public Overloads Sub Add(item As Object)
        owner_.Items.Add(item)
        RaiseEvent ItemAdded(Me, New EventArgs)
    End Sub

    Public Overloads Sub AddRange(item() As Object)
        owner_.Items.AddRange(item)
        'RaiseEvent ItemsAdded(Me, New EventArgs)
        RaiseEvent ItemAdded(Me, New EventArgs)
    End Sub

    Public Overloads Sub Insert(index As Integer, item As Object)
        owner_.Items.Insert(index, item)
        'RaiseEvent ItemInserted(Me, index, New EventArgs)
        RaiseEvent ItemAdded(Me, New EventArgs)
    End Sub



    Public Overloads Sub Remove(item As Object)
        owner_.Items.Remove(item)
        RaiseEvent ItemRemoved(Me, New EventArgs)
    End Sub

    Public Overloads Sub RemoveAt(index As Integer)
        owner_.Items.RemoveAt(index)
        RaiseEvent ItemRemoved(Me, New EventArgs)
    End Sub
    Public Overloads Sub Clear()
        owner_.Items.Clear()
        RaiseEvent ItemRemoved(Me, New EventArgs)
    End Sub



    Public Overloads Function IndexOf(value As Object) As Integer
        Return owner_.Items.IndexOf(value)
    End Function

    Public Overloads Function Contains(value As Object) As Boolean
        Return owner_.Items.Contains(value)
    End Function

    Public Overloads Function GetHashCode() As Integer
        Return owner_.Items.GetHashCode
    End Function

    Public Overloads Function ToString() As String
        Return owner_.Items.ToString
    End Function

    Public Overloads Function GetEnumerator() As System.Collections.IEnumerator
        Return owner_.Items.GetEnumerator
    End Function

    Public Overloads Function Equals(obj As Object) As Boolean
        Return owner_.Items.Equals(obj)
    End Function
    Public Overloads Function Equals(objA As Object, objB As Object) As Boolean
        Return Object.Equals(objA, objB)
    End Function

    Public Overloads Sub CopyTo(Destination() As Object, arrayIndex As Integer)
        owner_.Items.CopyTo(Destination, arrayIndex)
    End Sub



    Public Overloads ReadOnly Property Count As Integer
        Get
            Return owner_.Items.Count
        End Get
    End Property

    Public Overloads ReadOnly Property IsReadOnly As Boolean
        Get
            Return owner_.Items.IsReadOnly
        End Get
    End Property

    Public Overloads ReadOnly Property Item(index As Integer) As Object
        Get
            Return owner_.Items.Item(index)
        End Get
    End Property


End Class

结束班

C＃代码：

    using System;
using System.Collections;
using System.Collections.Generic;
using System.Data;
using System.Diagnostics;
public class MyComboBox : System.Windows.Forms.ComboBox
{

    public event EventHandler ItemAdded;
    //public event EventHandler ItemsAdded;
    public event EventHandler ItemRemoved;
    public event ItemInsertedEventHandler ItemInserted;
    public delegate void ItemInsertedEventHandler(object sender, int insertedIndex, EventArgs e);


    private ItemContainer ItemContainer_;

    public MyComboBox()
    {
        ItemContainer_ = new ItemContainer(this);

        ItemContainer_.ItemAdded += ItemContainer_ItemAdded;
        //ItemContainer_.ItemsAdded += ItemContainer_ItemsAdded;
        ItemContainer_.ItemRemoved += ItemContainer_ItemRemoved;
        ItemContainer_.ItemInserted += ItemContainer_ItemInserted;

    }

    private void ItemContainer_ItemAdded(object sender, EventArgs e)
    {
        if (ItemAdded != null)
        {
            ItemAdded(this, e);
        }
    }
    /*private void ItemContainer_ItemsAdded(object sender, EventArgs e)
    {
        if (ItemsAdded != null)
        {
            ItemsAdded(this, e);
        }
    }*/
    private void ItemContainer_ItemRemoved(object sender, EventArgs e)
    {
        if (ItemRemoved != null)
        {
            ItemRemoved(this, e);
        }
    }
    private void ItemContainer_ItemInserted(object sender, int insertedIndex, EventArgs e)
    {
        if (ItemInserted != null)
        {
            ItemInserted(this, insertedIndex, e);
        }
    }

    public new ItemContainer Items
    {
        get { return ItemContainer_; }
    }


    public class ItemContainer : System.Windows.Forms.ComboBox.ObjectCollection
    {

        public event EventHandler ItemAdded;
        //public event EventHandler ItemsAdded;
        public event EventHandler ItemRemoved;
        public event ItemInsertedEventHandler ItemInserted;
        public delegate void ItemInsertedEventHandler(object sender, int insertedIndex, EventArgs e);



        private System.Windows.Forms.ComboBox owner_;
        public ItemContainer(System.Windows.Forms.ComboBox owner)
            : base(owner)
        {
            owner_ = owner;
        }


        public new void Add(object item)
        {
            owner_.Items.Add(item);
            if (ItemAdded != null)
            {
                ItemAdded(this, new EventArgs());
            }
        }

        public new void AddRange(object[] item)
        {
            owner_.Items.AddRange(item);
            /*if (ItemsAdded != null)
            {
                ItemsAdded(this, new EventArgs());
            }*/

            if (ItemAdded != null)
            {
                ItemAdded(this, new EventArgs());
            }
        }

        public new void Insert(int index, object item)
        {
            owner_.Items.Insert(index, item);
            if (ItemInserted != null)
            {
                ItemInserted(this, index, new EventArgs());
            }
        }



        public new void Remove(object item)
        {
            owner_.Items.Remove(item);
            if (ItemRemoved != null)
            {
                ItemRemoved(this, new EventArgs());
            }
        }

        public new void RemoveAt(int index)
        {
            owner_.Items.RemoveAt(index);
            if (ItemRemoved != null)
            {
                ItemRemoved(this, new EventArgs());
            }
        }
        public new void Clear()
        {
            owner_.Items.Clear();
            if (ItemRemoved != null)
            {
                ItemRemoved(this, new EventArgs());
            }
        }



        public new int IndexOf(object value)
        {
            return owner_.Items.IndexOf(value);
        }

        public new bool Contains(object value)
        {
            return owner_.Items.Contains(value);
        }

        public new int GetHashCode()
        {
            return owner_.Items.GetHashCode();
        }

        public new string ToString()
        {
            return owner_.Items.ToString();
        }

        public new System.Collections.IEnumerator GetEnumerator()
        {
            return owner_.Items.GetEnumerator();
        }

        public new bool Equals(object obj)
        {
            return owner_.Items.Equals(obj);
        }
        public new bool Equals(object objA, object objB)
        {
            return object.Equals(objA, objB);
        }

        public new void CopyTo(object[] Destination, int arrayIndex)
        {
            owner_.Items.CopyTo(Destination, arrayIndex);
        }


        public new int Count
        {
            get { return owner_.Items.Count; }
        }

        public new object this[int index]
        {
            get { return owner_.Items[index]; }
        }

        public new bool IsReadOnly
        {
            get { return owner_.Items.IsReadOnly; }
        }

    }

}