[Implementing the ASP. Net Control as day15] Compound Control hiding

In the previous article, we used compositecontrol to implement the tbtoolbar control. In this article, we will test the compositecontrol to explain some precautions for using composite controls.

ProgramCodeDownload: ASP. NET Server Control-day15.rar

I. Timing of creating child controls for composite controls

I still remember that when we introduced the compositecontrol class, we mentioned that the compositecontrol class will ensure that when we access the child control, its child control will be created in advance; that is, when we use the CONTROLS attribute to access the child control, the createchildcontrols method will be executed to ensure that the child control is created in advance. Let's take a look at the write method of the CONTROLS attribute of the compositecontrol class to understand the reason. In the access to compositecontrol. when the CONTROLS attribute is set, it will first execute control. the ensurechildcontrols method, while the ensurechildcontrols method determines whether the child control has been created. If not, the createchildcontrols method is executed, this is why compositecontrol has the identification method to ensure that the child control is established in advance.

The compositecontrol. Controls attributes are as follows:

 
Public Overrides Readonly PropertyControlsAsControlcollection
 

Get
 

 
Me. Ensurechildcontrols
 

 
Return Mybase. Controls
 

 
End Get
 

 
EndProperty
 

 

 

The method of control. ensurechildcontrols is as follows:

 
Protected Overridable SubEnsurechildcontrols ()
 

If(Not Me. ChildcontrolscreatedAndalso Not Me. Flags. Item (& h100 ))Then
 

 
Me. Flags.Set(& H100)
 

 
Try 
 

 
Me. Resolveadapter
 

 
If(Not Me. _ AdapterIs Nothing)Then
 

 
Me. _ Adapter. createchildcontrols
 

 
Else
 

Me. Createchildcontrols
 

 
End If
 

 
Me. Childcontrolscreated =True
 

 
Finally
 

 
Me. Flags. Clear (& h100)
 

 
End Try
 

 
End If
 

 
EndSub
 

 

 

Ii. Hidden compound controls

Taking the tbtoolbar control as an example, we have written some test cases to illustrate the problem of composite controls. Before writing a test case, modify the tbtoolbar control, overwrite the loadviewstate and saveviewstate methods, and store the items attribute in viewstate to maintain the state.

''' <Summary>
 

 
''' The viewstate also controls the metadata of the listener.
 

 
''' </Summary>
 

 
''' <Param name = "savedstate"> You must restore the original zookeeper control. </Param>
 

 
Protected Overrides SubLoadviewstate (ByvalSavedstateAs Object)
 

 
If Not(SavedstateIs Nothing)Then
 

 
'Load state from the array of objects that was saved;
 

'Savedviewstate.
 

 
DimMystateAs Object() =Ctype(Savedstate,Object())
 

 
If Not(Mystate (0)Is Nothing)Then
 

 
Mybase. Loadviewstate (mystate (0 ))
 

 
End If
 

If Not(Mystate (1)Is Nothing)Then
 

 
Fitems =Ctype(Mystate (1), tbtoolbaritemcollection)
 

 
End If
 

 
End If
 

 
End Sub
 

 
''' <Summary>
 

 
'''Controls whether or not the listener is saved to viewstate.
 

 
''' </Summary>
 

''' <Returns> contains the objects that control the token currently used when the token expires. </Returns>
 

 
Protected Overrides FunctionSaveviewstate ()As Object
 

 
DimBasestateAs Object=Mybase. Saveviewstate ()
 

 
DimMystate (1)As Object
 

 
Mystate (0) = basestate
 

 
Mystate (1) =Me. Items
 

 
ReturnMystate
 

 
EndFunction
 

 

 

 

 

On the test page, place the test 1, Test 2, and PostBack buttons as follows.

Test 1 button: Add a button directly in the tool column.
Test 2 button: Use findcontrol to get the tool column, and then add a button in the tool column.
"PostBack" button: simply execute PostBack without writing program code.

 

The program code for the three buttons is as follows.

 
Protected SubButton#click (ByvalSenderAs Object,ByvalEAsSystem. eventargs)HandlesButton1.click
 

 
DimOitemAsTbtoolbaritem
 

 
'Add a new worker
 

 
Oitem =NewTbtoolbaritem ()
 

 
Oitem. Text ="New by hour"
 

 
Oitem. Key ="Newbutton"
 

 
Tbtoolbar1.items. Add (oitem)
 

Me. Response. Write ("" Zookeeper 1 "by region")
 

 
End Sub
 

 
Protected SubButton2_click (ByvalSenderAs Object,ByvalEAsSystem. eventargs)HandlesButton2.click
 

 
DimOitemAsTbtoolbaritem
 

 
DimObuttonAsButton
 

 
'Obtain the id = "add" by using the findcontrol statement first.
 

Obutton = tbtoolbar1.findcontrol ("Add")
 

 
'Then add the new worker
 

 
Oitem =NewTbtoolbaritem ()
 

 
Oitem. Text ="New by hour"
 

 
Oitem. Key ="Newbutton"
 

 
Tbtoolbar1.items. Add (oitem)
 

 
Me. Response. Write ("" Zookeeper II "by region")
 

 
End Sub
 

Protected SubButton3_click (ByvalSenderAs Object,ByvalEAsSystem. eventargs)HandlesButton3.click
 

 
'Simple PostBack, no program allowed
 

 
Me. Response. Write ("" PostBack "by category")
 

 
EndSub
 

 

Case 1: Execute the test 1 button and add a button directly in the tool column.

When you press test 1, you can add the new button to the tool column.

 

Case 2: run the test 2 button. Use findcontrol to get the tool column, and then add a button in the tool column.

Re-execute the program. When you press test 2, you will find that the tool column is not included in the new button?

 

Press the "PostBack" button to display the button we just added in the tool column.

Why is this strange phenomenon? In fact, the reason is very simple, because the findcontrol will access the CONTROLS attribute, and the subcontrol has been created. However, if you add a new button with the items Attribute before, it will no longer recreate the subcontrol, as a result, no new button is added immediately. However, the items property will be stored in viewstate, so when you execute the "PostBack" button, the button we just added will appear.

 

Iii. Solution

To solve the problem of "Test 2", you only need to override the render method of the tbtoolbar control, execute the recreatechildcontrols method before render, and forcibly recreate the child control.

 
''' <Summary>
 

 
''' Override the render method.
 

 
''' </Summary>
 

 
Protected Overrides SubRender (ByvalWriterAsSystem. Web. UI. htmltextwriter)
 

Me. Recreatechildcontrols ()
 

 
Mybase. Render (writer)
 

 
EndSub
 

 

 

 

If you run test 2 again, you will find that the execution result is normal.

 

Iv. Conclusion

Execute the recreatechildcontrols method before the render of the Composite Control to force re-build the sub-control, but this will lead to another problem, that is, when you directly access the sub-control to modify the attributes of the sub-control, once the subcontrol is re-built in render, the status of the subcontrol is re-created. Therefore, pay special attention to this situation. In addition, the composite control may repeatedly execute the action of creating sub-control, which is not efficient in execution.

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