phdesign » programming

WPF RadioButton Binding to IsChecked Property

paul — Thu, 08 Jul 2010 00:08:30 +0000

I wasted a few development hours discovering this strange behaviour when binding to the IsChecked property of a RadioButton in WPF when using MVVM. You can read about the issue on the MSDN forum, but from my experience if you have a two way binding on the is IsChecked property of a RadioButton which is part of a group, then after you set the bound property in code a couple of times, the RadioButton loses it’s binding all together.

Here is my original code that kept losing it’s binding:

There a couple of ways to solve this,

You can subclass the RadioButton
You could use OneWay binding on IsChecked to set the RadioButton state from code, then bind the Command property to a Command when user clicks on the RadioButton.
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My preferred option: (as suggested by karliwatson) use a ListBox for the grouping and bind the ListBoxItem’s IsSelected property to your ViewModel, then bind the RadioButton’s IsChecked property to the list box item’s IsSelected property. Don’t set a group on the RadioButton.

Logging Messages in Dot Net

paul — Thu, 17 Jun 2010 10:39:15 +0000

The .Net Framework provides an easy way to log messages using the System.Diagnostics.Trace class. By using Trace the user can configure where and what to log in the config file.

Below are two simple ways to log a message to a text file.

1. The simplest way if you don’t care about the format of the message is to use a filter on the trace listener in app.config to determine which events to log.

Then you only need to call one of the following methods to log a message with a specific EventType.

System.Diagnostics.Trace.TraceInformation("Information messge");
System.Diagnostics.Trace.TraceError("Error messge");

2. If you want more control over the format of the message you can use a TraceSwitch in app.config:

Then retrieve the TraceSwitch in code as follows:

TraceSwitch logLevel = new TraceSwitch("LogLevel", "The logging level");
Trace.WriteLineIf(logLevel.Level >= level, string.Format("[{0}] [{1}]: {2}", DateTime.Now, level, message));

The examples are for a desktop application, but they would work equally well in a web application by configuring web.config. Note that web applications aren’t compiled with Trace enabled, so you need to enable them in web.config by using the following after the node:

IE Autocomplete Doesn’t Fire onchange Event Handler

paul — Sat, 17 Apr 2010 00:10:24 +0000

While testing an ASP validation control in Internet Explorer I found that the validation wasn’t triggered if I selected an item from the autocomplete list for a text box, this was the same in Safari for Windows, but worked fine in Mozilla Firefox. What?!

Turns out that when selecting an item from the autocomplete list the onchange event handler doesn’t fire, therefore the validation scripts don’t fire. The onblur event does fire however, meaning we can do a check to see if the data has changed and if so, manually fire the onchange event handler.

/*
Author:     Paul Heasley
Date:       15.04.2010
Version:    0.1
Description:
IE and safari do not trigger the onchange events for textboxes when using autocomplete,
so validation events don't trigger. The blur event does trigger however so this script
checks to see if the value has changed (by saving the value on focus) and manually
calling onchange.
*/
function onChangeFix() {
    var previousValue = [];
    // Get all input elements
    var inputs = document.getElementsByTagName('input');

    for (var i = 0; i < inputs.length; i++) {
        var elt = inputs[i];

        // Only update text boxes. Depending on your application you
        // may also need to fix text areas.
        if (elt.type.toLowerCase() == "text")
        {
            // Save old value.
            addEvent(elt, 'focus', function() {
                previousValue[this] = this.value;
            });

            // Compare to old value, do we need to trigger an onchange event?
            addEvent(elt, 'blur', function() {
                if (previousValue[this] != this.value)
                {
                    if (this.onchange)
                        this.onchange();
                }
            });

            // Set old value = new value to stop the blur event triggering
            // another onchange.
            addEvent(elt, 'change', function() {
                previousValue[this] = this.value;
            });
        }
    }
}

Alternatively, you can disable the autocomplete feature by adding the attrribute autocomplete=”off” for either a specific input or for the entire form.

Download the entire code sample including the addEvent() function.

Registering phreplace DLL in Windows Vista

paul — Wed, 17 Mar 2010 10:10:46 +0000

phreplace is a VB6 DLL which is called from a vbscript plugin for PSPad. The script tests to see if the correct version of the DLL is registered on this computer, if not it registers it using regsvr32. This works fine in XP but not Vista where the script will error.

A while ago a user pointed out to me this article on Experts Exchange explaining why administrative rights are required to register a DLL in Windows Vista, in the hopes that we could automate the registration of phreplace in Vista.

Feeling defeated, I decided to explain why I haven’t been able to do this yet.

The fundamental problem is that Vista requires administrative privledges to write to the registry key required to register DLLs:

HKEY_CLASSES_ROOT\

However the user can register DLLs in their own section of the registry:

HKEY_CURRENT_USER\SOFTWARE\Classes\

So all is well right? Well not if you’re using VB6, you see when you run regsvr32, it calls the methods DllRegisterSever and DllUnregisterSever to add / remove entries from the registry, these methods are generated automatically by VB6 to register to HKEY_CLASSES_ROOT, and there is no way to change this.

Well, there is one way. Apparently the vbAdvance addon for VB6 allowed a user to customise DllRegisterServer / DllUnregisterServer, this sounds great, except that it doesn’t work. I tried modifying these methods according to the instruction, but the resulting DLL just wont register. I even tried registering the included example DLL in the download package, but this threw the same error.

I’m certain it must have worked at some stage, they wouldn’t have included an example that didn’t work, so I can’t figure out what’s different. Did it only work in Windows 98 or 2000?

So in summary, for as long as I’m using VB6 I don’t think I can change where phreplace tries to register the DLL, the only other workaround is to use RegOverridePredefKey to tell the registry to redirect any calls to HKEY_CLASSES_ROOT to HKEY_CURRENT_USER\SOFTWARE\Classes, this would work but I don’t think it can be done with vbscript, so I would need to add another executable to phreplace to use in registering / unregistering the DLL from the registry, seems pretty messy.

If you’ve got any tips for me (especially how I can customise DllRegisterServer) feel free to email me. I haven’t setup the facility for leaving comments on this site yet, sorry.

No Validation Messages when Disabling & Enabling ASP.Net Validator in Javascript

paul — Thu, 04 Mar 2010 06:21:31 +0000

Need to validate a form field based on the value of another field in ASP.Net? The .Net Framework provides a javascript function to do just that:

ValidatorEnable(val, enable)

This function takes the validator control (val) and a boolean to determine whether it should be enable or disabled. The problem with this function is that it triggers the validator to validate itself immediately, showing any validation error messages before the user has submitted the form, which may not always be want you want. The alternative is to set the validator’s enabled property to trigger this validator to validate itself when the user submits the form, and by using the Page_IsValid variable you can test whether the user has triggered a validation or not, then use ValidatorEnable function only after the validation has occurred when the user expects to see validation messages.

Consider a scenario where you want the user to enter their address only if they select Australia as the country, you also need to validate the address fields. Two ways to approach this are:

For each address field you need to validate use a CustomValidator control, and in the ClientValidationFunction first check to see if the country is set to Australia and if it’s not then consider any response for this control as valid. The problem with this is you will have to recrete all of the validator functionality in your client validation function, which means more work.
Use standard validator controls for the address fields, and enable or disable them in javascript. The code you call to enable or disable the validators could be a CustomValidation control on the country field, or a standard javascript call when the user selects a country. If the Page_IsValid variable is set to true then assume that the page has just been loaded and no validation has occured, in this case just set the validator controls enabled property so it will be validated (or not) when the user submits the form.
If Page_IsValid is false then assume the user has tried to submit but failed, in this case we expect validation messages to show / hide as the user changes data on the form – this is the normal ASP.Net behaviour.

Here’s an example:

// The ClientValidationFunction of a custom validator for country
function validateCountry(source, args) {
    // We we haven't submitted the form yet
    if (Page_IsValid) {
        // Turn the postcode validator on / off, but don't validate
        requiredFieldValidatorPostcode.enabled = enable;
    } else {
        // Turn the postcode validator on / off, and immediately validate
        ValidatorEnable(requiredFieldValidatorPostcode, enable);
    }

    // Validate country is not empty
    args.IsValid = (args.Value.length > 0);
}

Don’t forget to include server side code to mimic this enabling / disabling of validators. To do this override the Validate() function, enable or disable validators depending on the country selected and call the base.Validate() function.

public override void Validate()
{
    // Check if we need to validate the postcode.
    bool requireAddress = (dropDownListCountry.Text == "Australia");
    requiredFieldValidatorPostcode.Enabled = requireAddress;

    // Call the normal validation methods.
    base.Validate();
}

protected void customValidatorCountry_ServerValidate(object source, ServerValidateEventArgs args)
{
    // Implement the server side custom validation for country.
    args.IsValid = (args.Value.Length > 0);
}

Microsoft Certified Professional Training Kit 70-536 Errata

paul — Sun, 10 Jan 2010 22:37:19 +0000

I’m currently studying for the Microsoft® .NET Framework 2.0—Application Development Foundation (70-536) exam, using the Microsoft Press Training Kit and I am appalled at the number of errors, both editorial and technical, in this book. There are whole paragraphs that have been taken out of one chapter and used as a place holder in another chapter then never changed, at one stage I was very confused when the book was talking about two different classes that seemed to do the same thing, only to find that they were the same class, it’s name had just be written wrong in places, arrggg.

The problem I find is when I’m not sure about something in the book, I don’t know whether my understanding is wrong or the book is wrong, so I went hunting for a list of known errors and sure enough, Microsoft already know about them, in fact there are so many they created 4 knowledge base pages for them! When combining these in a Word document it ended up being 90+ pages, that’s really bad.

If you have this book or think about getting it, here are the official list of updates from Microsoft:

MCTS Self-Paced Training Kit (Exam 70-536): Microsoft® .NET Framework 2.0—Application Development Foundation comments and corrections Part 1

MCTS Self-Paced Training Kit (Exam 70-536): Microsoft® .NET Framework 2.0—Application Development Foundation Comments and Corrections Part 2

MCTS Self-Paced Training Kit (Exam 70-536): Microsoft® .NET Framework 2.0—Application Development Foundation Comments and Corrections Part 3

MCTS Self-Paced Training Kit (Exam 70-536): Microsoft® .NET Framework 2.0—Application Development Foundation Comments and Corrections Part 4

Perhaps it’s time to reprint the book?

Create a PDF using the .Net ReportViewer control

paul — Tue, 24 Nov 2009 23:48:48 +0000

Need to generate a pdf programmatically in dot net? You could purchase an HTML to PDF converter and worry about getting the page to format nicely for paper, or you could use the freely available ReportViewer control from Microsoft.

Microsoft offers SQL Server Reporting Services (SSRS) with SQL Server 2005 and later editions to generate and publish reports using the Report Definition Language (RDL), as an alternative to Crystal Reports. SSRS requires a Report Server to publish reports to so they can be useful, however they also offer a ASP.Net or Windows Forms component called the ReportViewer which we can use in our code without the need for any SQL database to generate reports, and these reports can be saved as Excel files, PDF’s or images.

The ReportViewer uses a modified version of RDL called RDLC, which does not save any information about the data source along with the report, which makes it perfect for generating reports from objects that aren’t a database. For instance, I recently needed to generate PDF letters with custom information in them, so this solution proved perfect.

I’m going to demonstrate how to pass parameters to an ASP.Net page and return a PDF with that information in it, this could just as easily be done in a Windows Forms project. I’m using Visual Studio 2005, in my preferred language of c#.

Start by creating a new Web Site in Visual Studio. We are going to use a collection of custom business objects as the data source for our report, so add a new class to our project and call it Person.cs. Copy the following code into your Person.cs file.

using System;
using System.Collections.Generic;

/// 
/// The business object we want to use in our report.
/// 
public class Person
{
    /// 
    /// Some fields to hold information about this person.
    /// 
    private string _title;
    private string _firstName;
    private string _lastName;

    /// 
    /// The person properties are only able to be set at instantiation.
    /// After the object is created the properties are read only.
    /// 
    public string Title
    {
        get { return _title; }
    }

    public string FirstName
    {
        get { return _firstName; }
    }

    public string LastName
    {
        get { return _lastName; }
    }

    /// 
    /// The person constructor.
    /// 
    /// The person's title
    /// Their first name
    /// Their last name
    public Person(string title, string firstName, string lastname)
    {
        _title = title;
        _firstName = firstName;
        _lastName = lastname;
    }
}

/// 
/// Creates a data source for our report.
/// 
public class PersonDataSource
{
    /// 
    /// This method creates a new person object and adds them to a new collection that
    /// can be used as a data source for the report.
    /// 
    /// A collection of person objects.
    public static List GetPerson(string title, string firstName, string lastName)
    {
        List people = new List();
        people.Add(new Person(title, firstName, lastName));
        return people;
    }
}

Now that we have our business object we can create the report. Click add item on the project and select Report. Call this item Report.rdlc.

In the left hand toolbar you should see Website Data Sources (if not select Data > Show Data Sources from the file menu) and in the data sources you should see our Person object. You can now build a report using the fields from our person object and the tools in the toobox. For simplicity just drag some Textboxes onto the report from the toolbox and enter any static text in them that you want, then drag on the Person’s title, firstName and lastName and arrange them appropriately.

Finally we need to write the code which will create the person data source and generate the report. Before we do this we need a reference to the ReportViewer control, right click on the project and Add Reference, in the .Net tab, select Microsoft.ReportViewer.WebForms.Now copy the following code into the Default.aspx source.

<%@ Page Language="C#" AutoEventWireup="true"  CodeFile="Default.aspx.cs" Inherits="_Default" %>



	Untitled Page


	
	
	
	Mr

	
	John

	
	Smith

And copy the following into the Code View of Default.aspx (Default.aspx.cs).

using System;
using System.Web;
using Microsoft.Reporting.WebForms;
using System.IO;
using System.Text;
using System.Collections.Generic;
public partial class _Default : System.Web.UI.Page
{
	protected void Page_Load(object sender, EventArgs e)
	{
		if (Page.IsPostBack)
		{
			LocalReport report = new LocalReport();
			string reportName = "CompletionCertificate";
			string deviceInfo =
				"" +
				"  EMF" +
				"  8.5in" +
				"  11in" +
				"  0.25in" +
				"  0.25in" +
				"  0.25in" +
				"  0.25in" +
				"";
			Warning[] warnings;
			string[] streamids;
			string mimeType;
			string encoding;
			string extension;

			report.ReportPath = "Report.rdlc";
			report.DataSources.Add(new ReportDataSource("Person", PersonDataSource.GetPerson(txtTitle.Text, txtFirstName.Text, txtLastName.Text)));
			byte[] bytes = report.Render("PDF", deviceInfo, out mimeType, out encoding, out extension, out streamids, out warnings);

			Response.Clear();
			Response.ContentType = mimeType;
			Response.AddHeader("Content-Disposition", "attachment; filename=" + reportName + "." + extension);
			Response.OutputStream.Write(bytes, 0, bytes.Length);
			Response.End();
		}
	}
}

Now run your project, enter some person data into the form and click submit. Open the PDF file and verify that the report is addressed to your person.