How To Manage State Between DHTML Page Designer Pages (190886)

SUMMARY

DHTML Applications, like other Internet applications, are stateless. For example, if you navigate from Page1.HTM to Page2.HTM in your DHTML Application, you can no longer access information stored in Page1.HTM. A separate instance of your Visual Basic code behind the DHTML Application is created for each page. The instance is destroyed when you navigate away from a given page. In some cases, you may need to save some "state" information that can be accessed by multiple pages.

To save state information in a DHTML application, you use the GetProperty and PutProperty functions to store and retrieve data.

MORE INFORMATION

The GetProperty and PutProperty functions are part of the modDHTML module that is added to your project when you create a new project using the DHTML Application template. These functions are implemented in Visual Basic using the client side cookies and are simpler to use then coding cookies directly.

You store state information using the PutProperty function and retrieve the information using the GetProperty function. Here are the declarations of these functions:

   Public Sub PutProperty(objDocument As HTMLDocument,
                          strName As String,
                          vntValue As Variant,
                          Optional Expires As Date)

   Public Function GetProperty(objDocument As HTMLDocument,
                               strName As String) As Variant

Following are some important things to remember while using these functions:

Pass BaseWindow.Document for objDocument.
Pass a unique key name in strName that identifies your property.
Pass the property value in vntValue. Use the same key to retrieve the value.
vntValue is a variant, but only string values should be stored because the values are stored in cookies. Do not pass object references.
The date and time passed in Expires should be in GMT.
Remember to stay within the cookie limits of the Browser. The cookie spec lists the following limits:
- 20 cookies per server or domain
- 4 KB per cookie
- 300 total cookies

Example

For example, suppose you want to build a simple application that will store and retrieve data across page boundaries. The application will consist of two pages: one to store values, and one to retrieve them.

The first page in the application contains a text field into which the end user can enter a value, and a button that stores the value to the cookie. The code for the button, called StoreButton1, would look like this:

   Private Function StoreButton1_onclick() As Boolean
       PutProperty BaseWindow.Document, "Property1", TextField1.Value
   End Function

The second page in the same application contains a button that, when clicked, retrieves the property from the cookie. The code for that button, called GetButton1, would look like this:

   Private Function GetButton1_onclick() As Boolean
      MyValue.innerText = "The value of the property is " & _
          GetProperty(BaseWindow.Document, "Property1")
   End Function

This function uses the innerText property of Dynamic HTML to replace the contents of a DIV tag, called "MyValue," with a sentence that contains the retrieved property.