ASP.NET PDF Viewer using C#, VB/NET

You can create new server controls for ASP.NET on two conceptual levels: user controls and custom (web) server controls. User controls are similar to web forms: they are a collection of server control and/or HTML markup, which is named (declared) and then used via reference. They can also expose public properties that can be set to control various aspects of the user control. In this chapter we consider only user controls. User controls are contained in .ascx files. You can create a new user control in Visual Studio by selecting the Web User Control template from the New/File menu option. The new user control is empty except for a Control directive that acts similarly to the Page directive of a web form. You can add any additional markup as needed. As an example, consider a user control that repeats a given text fragment a specified number of times. Our user control (RepeatText.ascx in Listing 14-10) contains a single control, a placeholder label. The code-behind file is located in RepeatText.ascx.fs, shown in Listing 14-11. Listing 14-10. RepeatText.ascx: A Simple User Control Implemented in F# <%@ Control Language="F#" AutoEventWireup="true" CodeFile="RepeatText.ascx.fs" Inherits="MyUserControl.RepeatText" %> <asp:Label ID="Place" runat="server"/> Listing 14-11. RepeatText.ascx.fs: The Implementation of an ASP.NET User Control #light namespace MyUserControl open System open System.Web.UI.WebControls type RepeatText() = inherit System.Web.UI.UserControl() /// This is the internal state and parameters of the control let mutable text = "" let mutable count = 0 /// This internal control is initialized by ASP.NET [<DefaultValue>] val mutable Place : Label

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It waits until after this trigger fires to get the block in current mode, because the trigger can modify the :NEW values So Oracle can t modify the block until after this trigger executes, and the trigger could take a very long time to execute Since only one session at a time can hold a block in current mode, Oracle needs to limit the time we have it in that mode After this trigger fired, Oracle retrieved the block in current mode and noticed that the column used to find this row, X, had been modified Since X was used to locate this record and X was modified, the database decided to restart our query Notice that the update of X from 1 to 2 did not put this row out of scope; we ll still be updating it with this UPDATE statement.

Rather, it is the fact that X was used to locate the row, and the consistent read value of X (1 in this case) differs from the current mode read of X (2) Now, upon restart, the trigger sees the value of X=2 (following modification by the other session) as the :OLD value and X=3 as the :NEW value So, this shows that these restarts happen It takes a trigger to see them in action; otherwise, they are generally undetectable That does not mean you can t see other symptoms such as a large UPDATE statement rolling back work after updating many rows and then discovering a row that causes it to restart just that it is hard to definitively say, This symptom is caused by a restart An interesting observation is that triggers themselves may cause restarts to occur even when the statement itself doesn t warrant them.

/// These properties allow the state to be used from the page member self.Text with get() = text and set(v) = text <- v member self.RepeatCount with get() = count and set(v) = count <- v /// This event is automatically wired up through the use of the /// AutoEventWireup ASP.NET directive (true by default) member self.Page_Load (sender: obj, e: EventArgs) = let acc = new Text.StringBuilder() for i in 1..count do acc.Append(self.Text) |> ignore self.Place.Text <- acc.ToString() The state and parameters of the control are ultimately held in the variables text and count. Note how we defined public properties (Text and RepeatCount) that will be available when we use the control from a page. All we need to use this user control from a page is to register it using the Register directive, giving a tag prefix and a tag name by which we can refer to it. For example, the code in Listing 14-12 results in an HTML label element containing the text Monkey! 10 times. Listing 14-12. TestRepeat.aspx: Using the Control from Listing 14-4 <%@ Page AutoEventWireup="true" %> <%@ Register Src="RepeatText.ascx" TagName="Repeater" TagPrefix="text" %> <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"> <html xmlns="http://www.w3.org/1999/xhtml"> <head runat="server"> <title>My User Control Test</title> </head> <body> <form runat="server"> <text:Repeater id="chart" runat="server" RepeatCount="10" Text="Monkey!" /> </form> </body> </html> You can find more details on implementing user controls in the books on ASP.NET referenced at http://www.expert-fsharp.com/Topics/WebProgramming.