Question: EnsureChildControls Method in CompositeControl

古城微笑少年丶 2021-11-10 00:50 125阅读 0赞

来源：[http://www.imcoder.org/custom-control/189732.htm][http_www.imcoder.org_custom-control_189732.htm]

I don't get it... what's the objective of EnsureChildControls method in a CompositeControl class properties? There's no difference if I use it or not!

Public Property Required() As Boolean  
        Get  
            EnsureChildControls()  
            Return \_Required  
        End Get  
        Set(ByVal value As Boolean)  
            EnsureChildControls()  
            \_Required = value  
        End Set  
    End Property

there's no difference using

Public Property Required() As Boolean  
        Get  
            Return \_Required  
        End Get  
        Set(ByVal value As Boolean)  
            \_Required = value  
        End Set  
    End Property

Let me cite you from \[1, p.924\]

*"In ASP.NET 1.x, the process for creating a composite control was subtly different. No CompositeControl  class existed, so you had to derive from the WebControl class yourself. However, there are only two differences between CompositeControl and WebControl. First, CompositeControl implements INamingContainer so all the child controls are uniquely scoped and their IDs won’t conflict with page controls or other instances of your composite control. Second, CompositeControl calls the EnsureChildControls() method automatically when you access the Controls collection, which makes sure child controls are created before you try to manipulate them."*  
  
So, apprently there is no difference  
  
\[1\]  
Matthew MacDonald and Mario Szpuszta  
Pro ASP.NET 2.0 in [C\#][C] 2005

EnsureChildControls makes sure child controls are created prior to accessing them.  For example, if you had a property such as the following…

Public Class MySampleControl

Inherits System.Web.UI.WebControls.CompositeControl

' This sample is only meant to show why EnsureChildControls can be necessary.

Protected WithEvents FirstNameTextBox As System.Web.UI.WebControls.TextBox

Public Property FirstName() As String

Get

' Will call CreateChildControls if needed

EnsureChildControls()

Return FirstNameTextBox.Text

End Get

Set(ByVal value As String)

' Will call CreateChildControls if needed

EnsureChildControls()

FirstNameTextBox.Text = value

End Set

End Property

Protected Overrides Sub CreateChildControls()

MyBase.CreateChildControls()

FirstNameTextBox = New System.Web.UI.WebControls.TextBox

FirstNameTextBox.ID = "FirstNameTextBox"

Controls.Add(FirstNameTextBox)

End Sub

End Class

' Some page/user control class...

Public Sub CreateSampleControl()

Dim ctl As New MySampleControl()

' EnsureChildControls makes sure the property will

' not fail when accessed before default call to CreateChildControls

ctl.FirstName = "Brian"

Controls.Add(ctl)

End Sub

Yet Microsoft's own post on the topic indicates that if you are using the new CompositeControl in ASP.NET 2.0 you no longer have to explicitly call EnsureChildControls():

The **CompositeControl** class is new in ASP.NET 2.0. If you created [custom controls][] in ASP.NET version 1.0 or 1.1, you had to implement the INamingContainer interface to create a new naming scope for child controls. In addition, you had to override the Controls property and invoke the EnsureChildControls method. In ASP.NET 2.0, these and other steps are performed by the **CompositeControl** class.

转载于:https://www.cnblogs.com/kangshifu/archive/2008/08/26/1276494.html

[http_www.imcoder.org_custom-control_189732.htm]: http://www.imcoder.org/custom-control/189732.htm
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[custom controls]: http://www.imcoder.org/custom-control/