Use the OnReadyStateChange Property in Visual Basic and Visual C/C++
The onreadystatechange property and event notification was intended primarily for use by scripting clients (VBScript, Jscript). It can, however, also be used in Win32 applications.This topic discusses the implementation details necessary to use onreadystatechange notification in applications written using Microsoft Visual Basic and Microsoft Visual C/C++.Background Information for OnReadyStateChange events
The onreadystatechange callback function was not implemented as a COM automation event in the IXMLHTTPRequest and IServerXMLHTTPRequest components. This is because these components are heavily used in scripting environments, many of which do not support COM events. The onreadystatechange callback function was intended to be easy to use when working with scripting clients such as VBScript and JScript.Because the onreadystatechange property was not implemented through COM-based automation events, using this callback functionality in Visual Basic and Visual C/C++ applications can be awkward for developers using those tools. Several options for implementing onreadystatechange, however, allow you to choose a way to work around this awkwardness.Using OnReadyStateChange in Visual Basic applications
In Visual Basic, you can use any of the following approaches to design applications that support onreadystatechange events. Use a timer control to poll the readyState property. When the data is ready, turn the timer off.
Use a DomDocument object to load the XML and handle the state using the WithEvents keyword.
Note If you are using the IXMLHTTPRequest and IServerXMLHTTPRequest components is to first post your XML data to a Web server, this option will not work for you.
Create a wrapper class and create a procedure to handle the event within the class module. Set the procedure to be the default, and bind the class to the onreadystatechange event to either the IXMLHTTPRequest or IServerXMLHTTPRequest component, depending on which component you are using with your application.
The following sample application demonstrates each of these three approaches.To demonstrate OnReadyStateChange in a Visual Basic application Open Microsoft® Visual Basic® 6.0. In the New Project dialog box, double-click Standard EXE.
On the Project menu, click References.
In the Available References list, select Microsoft XML,v4.0, and then click OK.
Add four command buttons to Form1 and set the caption of each button as follows: Control Caption
Command1 Fail
Command2 Polling using Timer
Command3 Using Class Wrapper
Command4 Using DOMDocument
Add a timer control to Form1.
Copy and paste the following code into Form1.
Option ExplicitPublic XMLHttpRequest As MSXML2.XMLHTTP40
Public WithEvents XMLDom As MSXML2.DOMDocument40Private Function FunctionReadyStateChange()
Debug.Print XMLHttpRequest.readyState
End FunctionPrivate Sub Command1_Click()
FailedOnReadyState
End SubPrivate Sub Command2_Click()
TimerResolution
End SubPrivate Sub Command3_Click()
ClassResolution
End SubPrivate Sub Command4_Click()
DOMResolution
End SubPrivate Sub FailedOnReadyState()
On Error GoTo FailedState
If Not XMLHttpRequest Is Nothing Then Set XMLHttpRequest = Nothing
Set XMLHttpRequest = New MSXML2.XMLHTTP40
' Assign the wrapper class object to onreadystatechange.
XMLHttpRequest.OnReadyStateChange = FunctionReadyStateChange ' Get some stuff asynchronously.
XMLHttpRequest.open "GET", "http://localhost/test.xml", True
XMLHttpRequest.send
Exit SubFailedState:
MsgBox Err.Number & ": " & Err.DescriptionEnd SubPrivate Sub TimerResolution()
If Not XMLHttpRequest Is Nothing Then Set XMLHttpRequest = Nothing
Timer1.Interval = 1
Set XMLHttpRequest = New MSXML2.XMLHTTP40
' Get some stuff asynchronously.
XMLHttpRequest.open "GET", "http://localhost/test.xml", True
XMLHttpRequest.send
End SubPrivate Sub ClassResolution()
If Not XMLHttpRequest Is Nothing Then Set XMLHttpRequest = Nothing
Dim MyOnReadyStateWrapper As MyReadyStateHandler
Set XMLHttpRequest = New MSXML2.XMLHTTP40 ' Create an instance of the wrapper class.
Set MyOnReadyStateWrapper = New MyReadyStateHandler ' Assign the wrapper class object to onreadystatechange.
XMLHttpRequest.OnReadyStateChange = MyOnReadyStateWrapper ' Get some stuff asynchronously.
XMLHttpRequest.open "GET", "http://localhost/test.xml", True
XMLHttpRequest.sendEnd SubPrivate Sub DOMResolution()
If Not XMLHttpRequest Is Nothing Then Set XMLHttpRequest = Nothing
If Not XMLDom Is Nothing Then Set XMLDom = Nothing
Set XMLDom = New MSXML2.DOMDocument40
XMLDom.async = True
XMLDom.Load "http://localhost/test.xml"
End SubPrivate Sub Timer1_Timer()
Debug.Print XMLHttpRequest.readyState
If XMLHttpRequest.readyState = 4 Then
MsgBox "Done"
Timer1.Interval = 0
End If
End SubPrivate Sub XMLDom_onreadystatechange()
Debug.Print XMLDom.readyState
If XMLDom.readyState = 4 Then
MsgBox "Done"
End If
End Sub
From the Project menu, click Add Class Module.
Change the name of the new class module from "Class1" to "MyReadyStateHandler"
Paste the following code into the class module:
Option ExplicitSub OnReadyStateChange()
Debug.Print Form1.XMLHttpRequest.readyState
If Form1.XMLHttpRequest.readyState = 4 Then
MsgBox "Done"
End If
End Sub
In the sample code added in the previous step, highlight the procedure name "OnReadyStateChange" by selecting it in the Code window.
From the Tools menu, click Procedure Attributes.
In the Procedure Attributes dialog, the Name combo box should show "OnReadyStateChange." Click Advanced.
In Procedure ID, select "(Default)" from the available options.
Click OK.
Save the class module (MyReadyStateHandler.cls) to file.
Open Notepad and paste the following XML into it
<?xml version="1.0"?>
<Root>
<Testing>This is to test the onreadystatechange event on the XMLHTTPRequest or DOMDocument</Testing>
<Testing>This is due to the event not being declared in the type library</Testing>
</Root>
Save the file as test.xml to your IIS localhost directory. For example, this folder might be C:\Inetpub\wwwroot for a typical default installation of IIS with Windows 2000.
In Visual Basic, from the Run menu, click Start to run the application.
Try the following command options to observe the different approaches to using the onreadystatechange event within Visual Basic.
To force a ready state failure, click Fail.
To view the polling resolution, click Polling using Timer.
To view the wrapper class solution, click Using Class Wrapper.
To view the DOMDocument approach, click Using DomDocument.
For each of the code paths in the previous step, you can place brake-points at various places to step through the code.
Res
For step 19a, the following error message should appear indicating the failure:424: Object required
For steps 19b, 19c and 19d, return values for onreadystatechange should appear in the Immediate window while the document loads. When the document completes loading, a message box saying "Done" should then appear.Using OnReadyStateChange in Visual C/C++ applciations
In C++, use connection points to trap all XMLDOMDocument events. The DISPID of the connection point container is DIID_XMLDOMDocumentEvents. The DISPID for the connection point to trap the readystatechange event is DISPID_XMLDOMEVENT_ONREADYSTATECHANGE.For a C/C++ example, see onreadystatechange Event.
The onreadystatechange property and event notification was intended primarily for use by scripting clients (VBScript, Jscript). It can, however, also be used in Win32 applications.This topic discusses the implementation details necessary to use onreadystatechange notification in applications written using Microsoft Visual Basic and Microsoft Visual C/C++.Background Information for OnReadyStateChange events
The onreadystatechange callback function was not implemented as a COM automation event in the IXMLHTTPRequest and IServerXMLHTTPRequest components. This is because these components are heavily used in scripting environments, many of which do not support COM events. The onreadystatechange callback function was intended to be easy to use when working with scripting clients such as VBScript and JScript.Because the onreadystatechange property was not implemented through COM-based automation events, using this callback functionality in Visual Basic and Visual C/C++ applications can be awkward for developers using those tools. Several options for implementing onreadystatechange, however, allow you to choose a way to work around this awkwardness.Using OnReadyStateChange in Visual Basic applications
In Visual Basic, you can use any of the following approaches to design applications that support onreadystatechange events. Use a timer control to poll the readyState property. When the data is ready, turn the timer off.
Use a DomDocument object to load the XML and handle the state using the WithEvents keyword.
Note If you are using the IXMLHTTPRequest and IServerXMLHTTPRequest components is to first post your XML data to a Web server, this option will not work for you.
Create a wrapper class and create a procedure to handle the event within the class module. Set the procedure to be the default, and bind the class to the onreadystatechange event to either the IXMLHTTPRequest or IServerXMLHTTPRequest component, depending on which component you are using with your application.
The following sample application demonstrates each of these three approaches.To demonstrate OnReadyStateChange in a Visual Basic application Open Microsoft® Visual Basic® 6.0. In the New Project dialog box, double-click Standard EXE.
On the Project menu, click References.
In the Available References list, select Microsoft XML,v4.0, and then click OK.
Add four command buttons to Form1 and set the caption of each button as follows: Control Caption
Command1 Fail
Command2 Polling using Timer
Command3 Using Class Wrapper
Command4 Using DOMDocument
Add a timer control to Form1.
Copy and paste the following code into Form1.
Option ExplicitPublic XMLHttpRequest As MSXML2.XMLHTTP40
Public WithEvents XMLDom As MSXML2.DOMDocument40Private Function FunctionReadyStateChange()
Debug.Print XMLHttpRequest.readyState
End FunctionPrivate Sub Command1_Click()
FailedOnReadyState
End SubPrivate Sub Command2_Click()
TimerResolution
End SubPrivate Sub Command3_Click()
ClassResolution
End SubPrivate Sub Command4_Click()
DOMResolution
End SubPrivate Sub FailedOnReadyState()
On Error GoTo FailedState
If Not XMLHttpRequest Is Nothing Then Set XMLHttpRequest = Nothing
Set XMLHttpRequest = New MSXML2.XMLHTTP40
' Assign the wrapper class object to onreadystatechange.
XMLHttpRequest.OnReadyStateChange = FunctionReadyStateChange ' Get some stuff asynchronously.
XMLHttpRequest.open "GET", "http://localhost/test.xml", True
XMLHttpRequest.send
Exit SubFailedState:
MsgBox Err.Number & ": " & Err.DescriptionEnd SubPrivate Sub TimerResolution()
If Not XMLHttpRequest Is Nothing Then Set XMLHttpRequest = Nothing
Timer1.Interval = 1
Set XMLHttpRequest = New MSXML2.XMLHTTP40
' Get some stuff asynchronously.
XMLHttpRequest.open "GET", "http://localhost/test.xml", True
XMLHttpRequest.send
End SubPrivate Sub ClassResolution()
If Not XMLHttpRequest Is Nothing Then Set XMLHttpRequest = Nothing
Dim MyOnReadyStateWrapper As MyReadyStateHandler
Set XMLHttpRequest = New MSXML2.XMLHTTP40 ' Create an instance of the wrapper class.
Set MyOnReadyStateWrapper = New MyReadyStateHandler ' Assign the wrapper class object to onreadystatechange.
XMLHttpRequest.OnReadyStateChange = MyOnReadyStateWrapper ' Get some stuff asynchronously.
XMLHttpRequest.open "GET", "http://localhost/test.xml", True
XMLHttpRequest.sendEnd SubPrivate Sub DOMResolution()
If Not XMLHttpRequest Is Nothing Then Set XMLHttpRequest = Nothing
If Not XMLDom Is Nothing Then Set XMLDom = Nothing
Set XMLDom = New MSXML2.DOMDocument40
XMLDom.async = True
XMLDom.Load "http://localhost/test.xml"
End SubPrivate Sub Timer1_Timer()
Debug.Print XMLHttpRequest.readyState
If XMLHttpRequest.readyState = 4 Then
MsgBox "Done"
Timer1.Interval = 0
End If
End SubPrivate Sub XMLDom_onreadystatechange()
Debug.Print XMLDom.readyState
If XMLDom.readyState = 4 Then
MsgBox "Done"
End If
End Sub
From the Project menu, click Add Class Module.
Change the name of the new class module from "Class1" to "MyReadyStateHandler"
Paste the following code into the class module:
Option ExplicitSub OnReadyStateChange()
Debug.Print Form1.XMLHttpRequest.readyState
If Form1.XMLHttpRequest.readyState = 4 Then
MsgBox "Done"
End If
End Sub
In the sample code added in the previous step, highlight the procedure name "OnReadyStateChange" by selecting it in the Code window.
From the Tools menu, click Procedure Attributes.
In the Procedure Attributes dialog, the Name combo box should show "OnReadyStateChange." Click Advanced.
In Procedure ID, select "(Default)" from the available options.
Click OK.
Save the class module (MyReadyStateHandler.cls) to file.
Open Notepad and paste the following XML into it
<?xml version="1.0"?>
<Root>
<Testing>This is to test the onreadystatechange event on the XMLHTTPRequest or DOMDocument</Testing>
<Testing>This is due to the event not being declared in the type library</Testing>
</Root>
Save the file as test.xml to your IIS localhost directory. For example, this folder might be C:\Inetpub\wwwroot for a typical default installation of IIS with Windows 2000.
In Visual Basic, from the Run menu, click Start to run the application.
Try the following command options to observe the different approaches to using the onreadystatechange event within Visual Basic.
To force a ready state failure, click Fail.
To view the polling resolution, click Polling using Timer.
To view the wrapper class solution, click Using Class Wrapper.
To view the DOMDocument approach, click Using DomDocument.
For each of the code paths in the previous step, you can place brake-points at various places to step through the code.
Res
For step 19a, the following error message should appear indicating the failure:424: Object required
For steps 19b, 19c and 19d, return values for onreadystatechange should appear in the Immediate window while the document loads. When the document completes loading, a message box saying "Done" should then appear.Using OnReadyStateChange in Visual C/C++ applciations
In C++, use connection points to trap all XMLDOMDocument events. The DISPID of the connection point container is DIID_XMLDOMDocumentEvents. The DISPID for the connection point to trap the readystatechange event is DISPID_XMLDOMEVENT_ONREADYSTATECHANGE.For a C/C++ example, see onreadystatechange Event.
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