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8: Control Events and Event Handlers
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</div> </form> </body> </html>
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Before entering the C# section, you might want to quickly review how C# uses arrays in the section on arrays in 3 The purpose of using an array is to simulate dealing with data stored in a database Beginning in 12 you will learn how to enter and extract data from a table in a database Here you will get a feel of it by extracting and displaying data from an array
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C# CmdSortaspxcs
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using System; using SystemWebUIWebControls; public partial class DoCommand : SystemWebUIPage { private string cmdArg; private string[] testList; private const int ARRAYSIZE=10; protected void CommandClick(object sender, CommandEventArgs e) { testList = new string[ARRAYSIZE]; testList[0] = "Mouse"; testList[1] = "Monitor"; testList[2] = "Keyboard"; testList[3] = "Processor"; testList[4] = "Webcam"; testList[5] = "Scanner"; cmdArg = eCommandArgumentToString(); switch (cmdArg) { case "Sort": ArraySort(testList); outList(); break; case "Reverse": ArrayReverse(testList); outList(); break; case "Clear" : TextBox1Text = cmdArg+"\n\n"; break;
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ASPNET 35: A Beginner s Guide
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} } private void outList() { for (int goodie = 0; goodie < ARRAYSIZE;goodie++ ) { if (testList[goodie] != null) { TextBox1Text += testList[goodie] + "\n"; } } TextBox1Text += "\n"; } }
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Figure 8-7 shows how the data from the array are sorted in one order (for example, ascending) or its reverse in a TextBox control Both operations are handled in the same C# event handler method
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Sorted and reversed array data displayed using Command properties
8: Control Events and Event Handlers
Clicking the Clear button removes everything in the TextBox control except the word Clear The string Clear is the assigned value of the CommandArgument property in a Button control tag as shown in the following code snippet:
<asp:Button ID="Button3" OnCommand="CommandClick" CommandName="Erase" CommandArgument="Clear" runat="server" Text="Clear" />
Even though the assignment appears to be a string, it still must be converted to a string in the C# portion of the application The following line makes that conversion:
cmdArg = eCommandArgumentToString();
Once that is done, you have successfully transferred the value of the CommandArgument from the ASPNET Web form to a C# string variable Instead of using a simple string like Clear, you can also enter a more detailed command using Structured Query Language (SQL) such as the following:
CommandArgument="INSERT ENames (eName,eMail) Values (@eName, @eMail)";
By assigning different SQL statements to the web controls, you will be able to store query and nonquery SQL commands as values with the CommandArgument property in Button web controls (s 11 and 12 explain using SQL commands and working with data in database tables)
Summary
In s 5 and 6, the review of Web forms and web controls introduced events associated with the forms and controls This chapter sought to isolate certain events and to look more closely at events and handling them For the most part, the use of events and a control is a one-to-one operation Each event has a unique event handler, and all C# code handles the event with a single method In this chapter you saw that not only can events come from unexpected places, but also that a single event handler can deal with more than a single control TextBox controls can use Change events, and the Init event has similar properties and consequences as the Load events found in different controls Further, using Button web controls and command events, you can use a single event handler to filter out the actions required for several different buttons By assigning values to both CommandName and CommandArgument properties and using the C# CommandEventArgs object as a parameter in the event handler method, you can pass command values the ASPNET Button controls to C#
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Validation Controls
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ASPNET 35: A Beginner s Guide
Key Skills & Concepts
Where to validate Types of validation: RequiredFieldValidator, RangeValidator, RegularExpressionValidator, CompareValidator, CustomValidator Summarizing errors with ValidationSummary control
n your mind s eye, imagine people all over the world entering data into your ASPNET creation I like to think of someone in Timbuktu happily typing into a TextBox control If the Timbuktu user does not enter the data correctly, he gets a reminder either that something is missing (like the @ sign from an e-mail address) or that he must fill in a certain box (a last name, for example) With this image in mind, I now go about creating a UI with validation that helps the user fill in everything correctly In ASPNET, several controls are available to make it easy to add any and all the validation that you need Remember, that guy in Timbuktu is depending on you
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