32.1 How can I programmatically maximize or minimize a form?
Use the form's WindowState property.
//minimize
this.WindowState = System.Windows.Forms.FormWindowState.Minimized;
.....
//maximize
this.WindowState = System.Windows.Forms.FormWindowState.Maximized;
32.2 How can I display a pop up a confirmation dialog when the user closes the form?
You can listen to the Form's Closing event, where you can display a MessageBox as show below:
[C#]
private void Form1_Closing(object sender, System.ComponentModel.CancelEventArgs e)
{
if (MessageBox.Show("Do you want to close the application?", "Close Application", MessageBoxButtons.YesNo) == DialogResult.No)
e.Cancel = true;
}
[VB.NET]
Private Sub Form1_Closing(ByVal sender As Object, ByVal e As System.ComponentModel.CancelEventArgs)
If MessageBox.Show("Do you want to close the application?","Close Application",MessageBoxButtons.YesNo) = DialogResult.No Then
e.Cancel = True
End If
End Sub
32.3 How can I center my form?
You can set the Form's StartPosition property to CenterScreen to achieve this.
32.4 How do I prevent users from resizing a form?
You can prevent the users from resizing a form by setting the FormBorderStyle to FixedDialog and setting the MaximizeBox property to false.
32.5 How do I programmatically set an image as Form's Icon ?
You could do so as shown in the code below :
[C#]
Form form1 = new Form();
Bitmap bmp = imageList1.Images[index] as Bitmap;
form1.Icon = Icon.FromHandle(bmp.GetHicon());
[VB.NET]
Dim form1 As Form = New Form()
Dim bmp As Bitmap = imageList1.Images(index) as Bitmap
form1.Icon = Icon.FromHandle(bmp.GetHicon())
Please refer to the sample attached here that illustrates this.
32.6 How can I add items to the System Menu of a form.
To do this, you can use use iterop to access the GetSystemMenu and AppendMenu Win32 APIs. You also need to override the form's WndProc method to catch and act on the menu message. This idea was posted in the Microsoft newsgroups by Lion Shi. Here are some sample projects.
32.7 How can I have a form with no title bar, but yet keep the resizing borders?
Set your form's Text and ControlBox properties.
myForm.Text = "";
myForm.ControlBox = false;
32.8 I don't want to have the Close box on my form's title bar. How do I remove this system menu box?
Set the property Form.ControlBox to false.
32.9 How do I change my application's icon?
In the Solution Explorer window, you'll see a file called app.ico in your project. This file contains your application icon. You can change this to a different file in the project properties screen which you see by right-clicking the project node in the Solution Explorer, and selecting Properties..
32.10 How can I tell if a form is closed from the controlbox (system menu) or from a call to Form.Close?
One way to do this is to override the form's WndProc method and check for WM_SYSCOMMAND and SC_CLOSE. Looking for WM_CLOSE in the override is not sufficient as WM_CLOSE is seen in both cases. A sample is available for download (C#, VB).
public const int SC_CLOSE = 0xF060;
public const int WM_SYSCOMMAND = 0x0112;
//_closeClick is a bool member of the form initially set false...
// It can be tested in the Closing event to see how the closing came about.
protected override void WndProc(ref System.Windows.Forms.Message m)
{
if(m.Msg == WM_SYSCOMMAND && (int)m.WParam == SC_CLOSE)
this._closeClick = true;
base.WndProc(ref m);
}
32.11 I have two forms. How can I access a textbox on one form from the other form?
One way to do this is to make the TextBox either a public property or a public field. Then you will be able to access it through the instance of its parent form. So, if TextBox1 is a public member of FormA and myFormA is an instance of FormA, then you can use code such as
[VB.NET]
Dim strValue as String = myFormA.TextBox1.Text
[C#]
string strValue = myFormA.TextBox1.Text;
anywhere myFormA is known. Here is a VB project illustrating this technique.
32.12 How do I create a non-modal top level form that always stays on top of all the app's windows (like the VS.Net find dialog)?
Make your main form the "Owner" of the form in question. Refer to Form.Owner in class reference for more information.
[C#]
findReplaceDialog.Owner = this; // Your main form.
findReplaceDialog.TopLevel = false;
[VB.Net]
findReplaceDialog.Owner = Me ' Your main form.
findReplaceDialog.TopLevel = False
32.13 How can I display a form that is 'TopMost' for only my application, but not other applications?
You can do this by setting the child form's TopMost to False and setting its Owner property to the Main Form.
[C#]
Form1 f = new Form1();
f.TopMost = false;
f.Owner = this;
f.Show();
[VB.NET]
dim f as New Form1()
f.TopMost = False
f.Owner = Me
f.Show()
32.14 How do I automatically resize the Form when the screen resolution changes between design-time and runtime?
The framework automatically resizes the form if the current Font size during runtime is different from the font size in design-time. It however doesn't auto size when the resolution changes. But it should be easy for you to accomplish. You could derive a custom Form, provide a "ScreenResolutionBase" property that could return the current screen resolution (Screen.PrimarScreen.Bounds will give you this). This value will get serialized in code during design time. Then during runtime in the Form's OnLoad you could check for the current screen resolution and resize the Form appropriately.
32.15 How can I ensure that my form will always be on the desktop?
To set or control the location of the form using desktop coordinates, you can use the SetDeskTopLocation property. You can do this by setting the child form's TopMost to False and setting its Owner property to the Main Form.
[C#]
this.SetDesktopLocation(1,1);
[VB.NET]
Me.SetDesktopLocation(1,1)
32.16 How can I restrict or control the size of my form?
You can restrict the size of a form by setting it's MaximumSize and MinimumSize properties. This will help you control the maximum and minimum size the form can be resized to. Also note that WindowState property of the form plays a part in how the form can be resized.
[C#]
//Minimum width = 300, Minimum height= 300
this.MinimumSize = new Size(300, 300);
//Maximum width = 800, Maximum height= unlimited
this.MaximumSize = new Size(800, int.MaxValue);
[VB.NET]
'Minimum width = 300, Minimum height= 300
Me.MinimumSize = New Size(300, 300)
'Maximum width = 800, Maximum height= unlimited
Me.MaximumSize = New Size(800, Integer.MaxValue)
32.17 How can I prevent a form from being shown in the taskbar?
You need to set the form's ShowInTaskbar property to False to prevent it from being displayed in the Windows taskbar.
[C#]
this.ShowInTaskbar = false;
[VB.NET]
Me.ShowInTaskbar = False
32.18 How do I prevent a user from moving a form at run time?
The following code snippet (posted in the Windows Forms FAQ forums) shows how you can prevent a user from moving a form at run time:
[C#]
protected override void WndProc(ref Message m)
{
const int WM_NCLBUTTONDOWN = 161;
const int WM_SYSCOMMAND = 274;
const int HTCAPTION = 2;
const int SC_MOVE = 61456;
if((m.Msg == WM_SYSCOMMAND) && (m.WParam.ToInt32() == SC_MOVE))
{
return;
}
if((m.Msg == WM_NCLBUTTONDOWN) && (m.WParam.ToInt32() == HTCAPTION))
{
return;
}
base.WndProc (ref m);
}
[VB.NET]
Protected Overrides Sub WndProc(ByRef m As Message)
const Integer WM_NCLBUTTONDOWN = 161
const Integer WM_SYSCOMMAND = 274
const Integer HTCAPTION = 2
const Integer SC_MOVE = 61456
If (m.Msg = WM_SYSCOMMAND) &&(m.WParam.ToInt32() = SC_MOVE) Then
Return
End If
If (m.Msg = WM_NCLBUTTONDOWN) &&(m.WParam.ToInt32() = HTCAPTION) Then
Return
End If
MyBase.WndProc( m)
End Sub
32.19 How can I create a non rectangular form?
This MSDN article titled Shaped Windows Forms and Controls in Visual Studio .NET shows how you can create non rectangular forms.
32.20 How can I make my form cover the whole screen including the TaskBar?
The following code snippet demonstrates how you can make your form cover the whole screen including the Windows Taskbar.
[C#]
// Prevent form from being resized.
this.FormBorderStyle = FormBorderStyle.FixedSingle;
// Get the screen bounds
Rectangle formrect = Screen.GetBounds(this);
// Set the form's location and size
this.Location = formrect.Location;
this.Size = formrect.Size;
[VB.NET]
' Prevent form from being resized.
Me.FormBorderStyle = FormBorderStyle.FixedSingle
' Get the screen bounds
Dim formrect As Rectangle = Screen.GetBounds(Me)
' Set the form's location and size
Me.Location = formrect.Location
Me.Size = formrect.Size
32.21 How can I move a Borderless form?
This code snippet shows how you can move a borderless form.
[C#]
public const int WM_NCLBUTTONDOWN = 0xA1;
public const int HTCAPTION = 0x2;
[DllImport("User32.dll")]
public static extern bool ReleaseCapture();
[DllImport("User32.dll")]
public static extern int SendMessage(IntPtr hWnd, int Msg, int wParam, int lParam);
private void Form1_MouseDown(object sender, System.Windows.Forms.MouseEventArgs e)
{
if (e.Button == MouseButtons.Left)
{
ReleaseCapture();
SendMessage(Handle, WM_NCLBUTTONDOWN, HTCAPTION, 0);
}
}
32.22 How do I force a Windows Form application to exit?
Your main form is an object of type System.Windows.Forms.Form. Use its Close method to exit the application. If you wish to Exit from a Form's constructor, this will not work. A workaround is to set a boolean flag that you can later check in the Form's Load method to call Close if required.
Another way is to use the Application.Exit() method.
32.23 How do I set the default button for a form?
Set the form's AcceptButton property. You can do this either through the designer, or through code such as
Form1.AcceptButton = button1;
32.24 How do I get an HWND for a form?
See the Control.Handle property which returns the HWND. Be careful if you pass this handle to some Win32 API as Windows Forms controls do their own handle management so they may recreate the handle which would leave this HWND dangling.
(from sburke_online@microsoft..nospam..com on microsoft.public.dotnet.framework.windowsforms)
32.25 How can I detect if the user clicks into another window from my modal dialog?
Use the Form.Deactivate event:
this.Deactivate += new EventHandle(OnDeactivate);
//...
private void OnDeactivate(object s, EventArgs e)
{
this.Close();
}
(from sburke_online@microsoft..nospam..com on microsoft.public.dotnet.framework.windowsforms)
32.26 How do I create a form with no border?
Use the Form.FormBorderStyle property to control a form's border.
public void InitMyForm()
{
// Adds a label to the form.
Label label1 = new Label();
label1.Location = new System.Drawing.Point(80,80);
label1.Name = "label1";
label1.Size = new System.Drawing.Size(132,80);
label1.Text = "Start Position Information";
this.Controls.Add(label1);
// Changes the border to Fixed3D.
FormBorderStyle = FormBorderStyle.Fixed3D;
// Displays the border information.
label1.Text = "The border is " + FormBorderStyle;
}
(From the .NET Framework SDK documentation)
32.27 How do I prevent a Form from closing when the user clicks on the close button on the form's system menu?
Handle the form's Closing event.
private void Form1_Closing(object sender, System.ComponentModel.CancelEventArgs e)
{
if( NotOkToClose() )
e.Cancel = true; //don't close
}
32.28 How do I display a splash screen type form, one with only client area (no border or titlebar)?
You can download a working project that uses this code.
public void CreateMyBorderlessWindow()
{
this.FormBorderStyle = FormBorderStyle.None;
this.MaximizeBox = false;
this.MinimizeBox = false;
this.StartPosition = FormStartPosition.CenterScreen;
this.ControlBox = false;
}
32.29 How do I get the window handle (HWND) of my form or control?
Use the Control.Handle property.
32.30 How can I make sure I don't open a second instance modeless dialog that is already opened from my main form?
One way to do this is to maintain a list of opened modeless dialogs, and check this list before you open a new one to see if one is already present.
If you open all these modeless dialog's from the same 'main' form, then you can use the OwnedForms property of that main form to maintain this list of opened dialogs. Below are some code snippets that suggest how you must go about this. Note that your dialog forms need to be able to turn off the ownership. This is done below by adding an Owner field to the dialog form.
//sample code that either opens a new dialog or displays an already opened dialog
private void button1_Click(object sender, System.EventArgs e)
{
foreach ( Form f in this.OwnedForms )
{
if (f is Form2)
{
f.Show();
f.Focus();
return;
}
}
//need a new one
Form2 f2 = new Form2();
this.AddOwnedForm(f2);
f2.Owner = this;
f2.Show();
}
//code for form2
public class Form2 : System.Windows.Forms.Form
{
private System.Windows.Forms.Label label1;
public Form Owner;
.......
.......
private void Form2_Closing(object sender, System.ComponentModel.CancelEventArgs e)
{
Owner.RemoveOwnedForm(this);
}
}
32.31 Is there a way to halt a screen from painting until all the controls on the form are initialized?
Shawn Burke responded to this question in a posting on microsoft.public.dotnet.framework.windowsforms newsgroup. There is not currently a way to do this built into the framework, but WM_SETREDRAW will do what you're looking for. It can't be called recursively, so here's code for a property you can add to your form to handle it. A VB sample is also available.
int paintFrozen;
private const int WM_SETREDRAW = 0xB;
[DllImport("User32")]
private static extern bool SendMessage(IntPtr hWnd, int msg, int wParam, int lParam);
private bool FreezePainting
{
get { return paintFrozen > 0; }
set {
if (value && IsHandleCreated && this.Visible)
{
if (0 == paintFrozen++)
{
SendMessage(Handle, WM_SETREDRAW, 0, 0);
}
}
if (!value)
{
if (paintFrozen == 0)
{
return;
}
if (0 == --paintFrozen)
{
SendMessage(Handle, WM_SETREDRAW, 1, 0);
Invalidate(true);
}
}
}
}
32.32 How do I return values from a form?
Add public properties to your form. Then these properties can be accessed by any object that creates an instance of your form.
32.33 How can I easily manage whether controls on my form are readonly or not?
One way is to place all the controls into a single GroupBox and then use the GroupBox.Enabled property to manage whether the controls are editable or not.
32.34 The controls that I've try to add to my form at runtime don't show up. What's wrong?
Make sure you implemented and executed code similar to the InitializeComponent method that VS adds to your Windows Forms project for controls added during design time. Recall that InitializeComponent() is called from your Forms constructor to create the controls, size, position and show the controls, and finally add the controls to the form's Controls collection. So, your code at runtime should also implement these same steps. In particular, don't forget the this.Controls.AddRange call that adds your new controls to the form's Controls collection.
32.35 Setting Form.Visible to false does not make my main form start up invisibly. How can I make my main form start up invisibly?
This problem is discussed in an article in the .NET docs. Search for "Setting a Form to Be Invisible at Its Inception". The idea is to startup the application in a different module than your main form. Then the application and main form can have indiependent lifetimes. Sample code is given in the referenced article.
32.36 How to make a form transparent?
The opacity property enables you to specify a level of transparency for the form and its controls. See the .NET documentation for Form.Opacity for differences between Opacity and TransparencyKey properties.
Opacity only works with Windows 2000 and later.
32.37 How can I create an instance of a Form class just from knowing its name in a string?
You can use the System.Reflection.Assembly.CreateInstance method to create a form from its name. Below is a code snippet. The name in the textbox has to be the full name including its namespace. So if there is a class named Form2 in namespace MyCompanyName, then the textbox would contain MyCompanyName.Form2. This snippet also assumes that the class is defined in the current executing assembly. If not, you would have to create an instance of the assembly that contains the class instead of calling the static method GetExecutingAssembly. As noted on this board, using reflection in this manner might affect performance.
You can download working samples (VB.NET, C#).
[C#]
try
{
Assembly tempAssembly = Assembly.GetExecutingAssembly();
// if class is located in another DLL or EXE, use something like
// Assembly tempAssembly = Assembly.LoadFrom("myDLL.DLL");
// or
// Assembly tempAssembly = Assembly.LoadFrom("myEXE.exe");
Form frm1 = (Form) tempAssembly.CreateInstance(textBox1.Text);// as Form;
frm1.Show();
}
catch(Exception ex)
{
MessageBox.Show("Error creating: "+ textBox1.Text);
}
[VB.NET]
textBox1.Text = "MyNameSpace.Form2"
......
Try
Dim tempAssembly As System.Reflection.Assembly = System.Reflection.Assembly.GetExecutingAssembly()
' if class is located in another DLL or EXE, use something like
' tempAssembly = Assembly.LoadFrom("myDLL.DLL")
' or
' tempAssembly = Assembly.LoadFrom("myEXE.exe")
Dim frm1 As Form = CType(tempAssembly.CreateInstance(textBox1.Text), Form) ' as Form;
frm1.Show()
Catch ex As Exception
MessageBox.Show("Error creating: " + ex.ToString())
End Try
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