Windows Forms Tips
FAQ Home
1.
How do I write a screen saver?
2. How do I determine the screen resolution?
3. How do I determine the working area of a screen without the systemtray area?
4. How do I position my form to the bottom right of the screen
when it opens up the first time above the system tray?
5. How do I change my screen's resolution programatically?
6. Is there an easy way to Create/Delete/Move files in the
Windows File System?
7. Can working on WinForms and .Net in general get exciting?
8. I have a long loop. How can I make my application continue
to process events while it is executing this loop?
9. How can I display HTML in a Form?
10. The MessageBox always appears in the center of the
screen. How can I change it's location?
11. If I have a button with &Next as the text, the
N-accelerator key does not appear until I press Alt. Why?
12. How can I add a custom verb to the file and folder
context menus in the explorer shell?
13. How do I create windows shortcuts on my desktop
programatically in .Net?
14. What mechanisms does .Net provide to convert one type to
another?
15. Its possible that some of my class members will not be
initialized when one of my virtual members gets called even before the
constructor. How can I avoid this?
16. In a Hashtable, why doesn't setting the value for an
existing key to be null remove the key from the Hashtable?
17. Why would I be getting a NullReferenceException in
Windows Forms with no application code in the call stack?
18. What are the implications of using the Timer class in
System.Timers as opposed to the Timer class in System.Windows.Forms?
19. When I try to catch the Resize event to handle sizing of
MDI children, the event is called even before my form's constructor can
create the children throwing an exception. How do I avoid this?
20. How can I tell if the user has changed some system
preference such as the locale or display settings?
21. How do I change a directory name?
22. How do I beep the computer's speaker in a Windows Form
application?
23. How do I use the system clipboard?
24. How do I add an application to the Window's Tray?
25. How can I use XP Themes with Windows Forms?
26. How do I use Windows Forms Controls in Internet Explorer?
27. Are event handlers required to have this signature void
MyEventHandler(object sender, EventArgs e)?
28. What is the purpose of the [STA Thread] attribute for the
Main method of a C# program?
29. I get a message 'DragDrop registration' failed. Why?
1 How do I write a screen saver?
Check out this sample on
gotnetdot.com.
2 How do I determine the screen resolution?
Use the System.Windows.Forms.Screen.PrimaryScreen.Bounds property.
3 How do I determine the working area of a screen
without the systemtray area?
The Screen.GetWorkingArea(control) will provide you the working area of a
screen without the system tray area.
4 How do I position my form to the bottom right of the
screen when it opens up the first time above the system tray?
Do as follows in your Form's constructor after setting the StartPosition to
Manual:
[C#]
this.SetBounds(Screen.GetWorkingArea(this).Width-this.Width
,Screen.GetWorkingArea(this).Height-this.Height , this.Width,
this.Height);
[VB.Net]
Me.SetBounds(Screen.GetWorkingArea(Me).Width-Me.Width
,Screen.GetWorkingArea(Me).Height-Me.Height , Me.Width,
Me.Height)
5 How do I change my screen's resolution programatically?
You can do so by calling the native ChangeDisplaySetting api.
This website at www.omniscium.com provides you an article on how to do it:
http://www.omniscium.com/index.asp?page=DotNetScreenResolution
6 Is there an easy way to Create/Delete/Move files in
the Windows File System?
Use File.Create, Delete and Move static methods.
7 Can working on WinForms and .Net in general get
exciting?
Yes, only if you work at Syncfusion,
Inc.
8 I have a long loop. How can I make my application
continue to process events while it is executing this loop?
Call the static Application.DoEvents() method in your loop.
9 How can I display HTML in a Form?
You can add a web browser to a form in a straight forward manner.
1) Right-click your toolbox and select Customize Toolbox. Then add the Com
Component 'Microsoft Web Browser'.
2) Drag the just added Explorer tool and drop it on your form to position it
where you want it.
3) Set the inital display page using code such as:
public Form1()
{
//
// Required for Windows Form Designer support
//
InitializeComponent();
object a = 0;
object b = 0;
object c = 0;
object d = 0;
axWebBrowser1.Navigate("www.syncfusion.com", ref a, ref b, ref c,
ref d);
//
// TODO: Add any constructor code after InitializeComponent call
//
}
10 The MessageBox always appears in the center of the
screen. How can I change it's location?
Its looks like you cannot change this behavior of MessageBox. One solution
is to derive your own MessageForm class from Form to display your message.
Then call its ShowDialog method to show it after you set its Size, Location
and StartPosition properties. (If you don't set the StartPosition , then the
Location is ignored.) One of the values for StartPosition is CenterParent
which would center your new MessageForm.
11 If I have a button with &Next as the text, the
N-accelerator key does not appear until I press Alt. Why?
This behavior has nothing to do with .Net and is expected Windows behavior
beginning with Win2000. Windows will only show accelerator keys after the
alt is pressed. There is a control panel setting that you can use to change
this behavior. Look on the Effects tab under Control Panel|Display to see a
checkbox labeled "Hide keyboard navigation indicators until I use the Alt
key".
12 How can I add a custom verb to the file and folder
context menus in the explorer shell?
The article at www.vbaccelerator.com shows you how it is done in .net:
Associating Applications with Any File or Folder
13 How do I create windows shortcuts on my desktop
programatically in .Net?
The following article explains how shortcuts can be created programatically:
Creating and Modifying Shortcuts
14 What mechanisms does .Net provide to convert one
type to another?
Type conversion is usually possible in one of the following ways:
1) Using explicit methods in source type like:
public class SizeF
{
...
public Size ToSize();
}
There is usually a corresponding explicit or implicit operator that does the
same conversion. The operators are however not available in VB.Net.
2) Using FromXXX static methods exposed in the destination type:
class Image
{
...
public static Image FromStream(Stream);
}
3) Using implicit or explicit operators defined in the source or
destination type. This will allow you to perform implicit or explicit casts
from the source type to the destination type.
SizeF sizeF = size; //
Possible because type Size has an implicit type conversion operator that
converts a Size to SizeF
PointF pointF = (PointF)sizeF; // Possible because type SizeF has an
explict type conversion operator that converts a SizeF to PointF.
There is usually a corresponding ToXXX method that does the same conversion.
You can use either this or the ToXXX methods in C#.
4) Using TypeConverters. Some types come with TypeConverters that allow
you to convert to or convert from another type. This conversion is usually
not documented and can be discovered only by writing some test code.
For example, the System.Drawing.Icon type's TypeConverter converts the Icon
into a byte[]. You can use this functionality in your code as follows:
TypeConverter tc =
TypeDescriptor.GetConverter(typeof(System.Drawing.Icon));
byte[] blob = tc.ConvertTo(myIcon, typeof(byte[]));
It's usually time consuming to figure out whether a TypeConverter's
ConvertTo or ConvertFrom method can perform the necessary conversion.
The attached TypeConverterLookup tool lets you figure that out easily on any
type declared in any assembly available in the GAC or available in the same
directory as the tool's exe. If you have types in custom assemblies, then
just copy over that assembly to the same directory as the tool, you can then
specify the type in the tool.
15 Its possible that some of my class members will not
be initialized when one of my virtual members gets called even before the
constructor. How can I avoid this?
If possible, initialize them in-line:
public class MyClass
{
public ArrayList myArrayList = new ArrayList();
public MyClass(){}
public override void MyOverride()
{
// When this gets called by the base class construcotr,
myArrayList will be initialized.
}
}
16 In a Hashtable, why doesn't setting the value for an
existing key to be null remove the key from the Hashtable?
This is by design. You have to use Remove to actually remove the Key/Value
pair from the Hashtable.
17 Why would I be getting a NullReferenceException in
Windows Forms with no application code in the call stack?
The CLR is catching an Access Violation that's being thrown from unmanaged
code, and that is propogating up as a NullReferenceException. I've seen this
happen with certain common control library windows types if an application
such as spy++ is running, and I see this is the TreeView control that is
having troubles with a mouse down. Have you done any modification to the
control through P/Invoke methods?
(from sburke_online@microsoft..nospam..com on
microsoft.public.dotnet.framework.windowsforms)
18 What are the implications of using the Timer class
in System.Timers as opposed to the Timer class in System.Windows.Forms?
Be careful when useing the Timer from System.Timers from within a
Windows.Form application. Most methods in Windows Forms are not thread safe
and can produce indeterminate results when called from another thread. In
this case, System.Timers.Timer is much higher resolution and less affected
by how busy your application is (since it doesn't use the message pump) but
it's Tick event is fired from another thread. In order to be sure this works
correctly, you'll have to write the proper Control.Invoke code to marshal
over to the thread the control was created on (the main thread) before you
call methods on the control. So, in cases where you don't need
super-high-resolution and regular events to be fired, you're much better off
using System.Windows.Forms.Timer. It's messsage pump is based (WM_TIMER) and
will fire on the UI thread.
(from sburke_online@microsoft..nospam..com on
microsoft.public.dotnet.framework.windowsforms)
19 When I try to catch the Resize event to handle
sizing of MDI children, the event is called even before my form's
constructor can create the children throwing an exception. How do I avoid
this?
The Resize event is getting raised before the constructor completes because
the form is being resized in the constructor. If you are using VS.NET to
create your project, then in your constructor there is a call to
InitializeComponent. In this method there is code to resize the form. You
could instantiate your child form in your constructor *before*
InitializeComponent is called, then when the form gets resized for the first
time you already have an instance of your child form.
(broderonline@microsoft.com_(Brian_Roder))
20 How can I tell if the user has changed some system
preference such as the locale or display settings?
Use the static events in the SystemEvents class found in the Microsoft.Win32
namespace. There are many events in this class. Here are a couple:
SystemEvents.DisplaySettingsChanged
+= new System.EventHandler(displaySettingsChanged);
SystemEvents.UserPreferenceChanged +=
new
UserPreferenceChangedEventHandler(userPreferencesChanged);
.............
.............
private void displaySettingsChanged(object sender, EventArgs e)
{
MessageBox.Show(e.ToString());
}
private void userPreferencesChanged(object sender,
UserPreferenceChangedEventArgs e)
{
switch(e.Category)
{
case UserPreferenceCategory.Locale:
MessageBox.Show("Changed locale");
break;
default:
MessageBox.Show(e.Category.ToString());
break;
}
}
21 How do I change a directory name?
Use the static move member of the Directory class.
Directory.Move(oldPathString,
newPathString);
22 How do I beep the computer's speaker in a Windows
Form application?
There is no Windows Form function to beep your computer's speaker. But you
can just invoke the Win32 API MessageBeep.
using
System.Runtime.InteropServices;
...
[DllImport("user32.dll")]
public static extern int MessageBeep(uint n);
private void button2_Click(object sender, System.EventArgs e)
{
MessageBeep(0x0);
}
Another method (suggested by msauper@sauper.com on
microsoft.public.dotnet.framework.windowsforms)
Reference the VB.NET runtime support and just use the Beep() method.
The method is in:
Microsoft.Visual Basic.NET Runtime
The method is:
Microsoft.VisualBasic.Interaction.Beep();
23 How do I use the system clipboard?
The SetDataObject and GetDataObject methods in the Clipboard class found in
the System.Windows.Forms namespace allows you to access the clipboard. Here
is some code.
string text = "Some text for
the clipboard";
Clipboard.SetDataObject(text); //clipboard now has "Some text for the
clipboard"
text = ""; //zap text so it can be reset...
IDataObject data = Clipboard.GetDataObject();
if(data.GetDataPresent(DataFormats.Text))
{
text = (String)data.GetData(DataFormats.Text);
//text is now back to "Some text for the clipboard"
}
24 How do I add an application to the Window's Tray?
In design mode, you drop a NotifyIcon object on your form. You can then drop
a ContextMenu on your form and add this menu to the NotifyIcon's ContextMenu
property. This menu will be seen when the user rightclicks the try icon. You
can add a handler for the NotifyIcon's Click event to catch the action of a
user clicking the icon.
From code, you create an instance of NotifyIcon, set properties, hook any
handlers you want, and then make it visible. Here are some VB snippets.
Private Sub Form1_Load(ByVal
sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
Dim trayItem As NotifyIcon = New NotifyIcon()
trayItem.Icon = SystemIcons.Question
trayItem.Visible = True
AddHandler trayItem.Click, New EventHandler(AddressOf
HandleTrayClick)
End Sub
Private Sub HandleTrayClick(ByVal sender As Object, ByVal e As
EventArgs)
MessageBox.Show("Tray item clicked")
End Sub
25 How can I use XP Themes with Windows Forms?
Follow these steps to introduce Windows XP visual styles into your Windows
application.
1. Create a new Windows Application and add some controls to the default
form.
2. For every control you place on the form that has a FlatStyle property,
set the property to System.
3. Compile your application.
4. Build a manifest file in the application directory. NOTE: This manifest
file must be located in the same directory as the executable. Open Notepad
and place the code shown below in the file.
.NET control deployment tool
type="win32"
name="Microsoft.Windows.Common-Controls"
version="6.0.0.0"
processorArchitecture="X86"
publicKeyToken="6595b64144ccf1df"
language="*"
/>
Save the file in the application directory with the name of the application
and an extension of exe.manifest. For instance, if your application name is
"MyApp", you will name the manifest file as MyApp.exe.manifest.
5. When your
application runs, Windows XP looks at the application manifest which tells
the operating system to use common controls library version 6.0.
This process is discussed and a sample given in an article by the David C.
Brown on the Windows Forms team at
gotnetdot.com.
26 How do I use Windows Forms Controls in Internet
Explorer?
Erick Ellis steps you through creating a Windows Form and then adding an
object tag to an HTML page in his article Using Windows Forms Controls in IE
on
gotnetdot.com.
27 Are event handlers required to have this signature
void MyEventHandler(object sender, EventArgs e)?
No. The .NET architecture certainly allows you to define your delegate
signatures any way you like. Microsoft chose to used this fixed signature
for its handlers because:
1) Ease of calling and defining (simplicity). The more parameters we had,
the more a user has to type to create a handler for them. Think about when
you need to override a function with a whole bunch of arguments. It's a pain
to type out all those parameters when you may not be interested in handling
them.
2) Reusability. By keeping the signatures consistent, we increased the
likelyhood that we wouldn't need yet another class of handlers for a given
type of event -- reuse is good since it keeps namespaces smaller, has need
for less documentation, etc.
3) Modifiable values. Many of our *EventArg classes have data in them that
can be specified or modified by the event handlers. For example. the
KeyEventArgs class has a read/write Handled property that can be set to
"true" by handler function if the key should not be passed to the default
handler and processing stopped. You can't do this with normal params (unless
they're passed byref which just adds a little more complexity.
4) Extensibility. Having a base class allows us to add functionality (we
don't have plans for this, but if push came to shove it's an option) without
breaking people. Hypothetically, say users were screaming for the new size
in the Resize event, which is currently just a plain EventHandler. Well, we
could derive a ResizeEventArgs from EventArgs and pass that into the
existing handler without breaking anybody's code. Folks that cared about it
could check the type, do a cast, and get the extended info.
(from sburke_online@microsoft..nospam..com on
microsoft.public.dotnet.framework.windowsforms)
28 What is the purpose of the [STA Thread] attribute
for the Main method of a C# program?
That marks the thread as being "Single Thread Apartment" which means any
multiple threaded calls need to be marshaled over to that thread before they
are called. That's there because Windows Forms uses some OLE calls
(Clipboard for example), which must be made from the thread that initialized
OLE.
(from sburke_online@microsoft..nospam..com on
microsoft.public.dotnet.framework.windowsforms)
29 I get a message 'DragDrop registration' failed. Why?
Try placing the attribute [STA Thread] on your Main method. OLE D&D requires
single threaded apartments.
[STAThread]
static void Main()
{
Application.Run(new Form1());
}
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