It is often useful to know how an ASP.NET Web page was invoked: whether by an original request (an HTTP GET), a postback (an HTTP POST), a cross-page post from another page (an HTTP POST), or a transfer from another page using the Transfer method or using a callback from the browser. The Page class exposes a set of properties that you can use to determine how a page was invoked.
To determine how an ASP.NET Web page was invoked
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Examine the values of the following Page class properties, and then refer the table to determine how the page was invoked:
The following table lists ways in which a page can be invoked and the corresponding Page property values.
| Invocation method | Property values |
| Original request | -
IsPostBack is set to false. -
PreviousPage is set to null (Nothing in Visual Basic). -
IsCallback is set to false.
|
| Postback | -
IsPostBack is set to true. -
PreviousPage is set to null (Nothing in Visual Basic). -
IsCallback is set to false.
|
| Cross-page posting | -
IsPostBack is set to false. -
PreviousPage references the source page. -
IsCrossPagePostBack is set to true. -
IsCallback is set to false.
|
| Server transfer | -
IsPostBack is set to false. -
PreviousPage references the source page. -
IsCrossPagePostBack that is referenced in the PreviousPage is set to false. -
IsCallback is set to false.
|
| Callback | -
IsPostBack is set to false. -
PreviousPage is set to null (Nothing in Visual Basic). -
IsCallback is set to true.
|
.gif) Note |
|---|
| Be sure you test the IsCrossPagePostBack property of the page that is referenced in PreviousPage. The IsCrossPagePostBack property of the current page always returns false. |
See Also