I have a Window set to the height and width of my monitors:
var r = System.Drawing.Rectangle.Union( System.Windows.Forms.Screen.AllScreens[0].Bounds, System.Windows.Forms.Screen.AllScreens[1].Bounds );
Height = r.Height;
Width = r.Width;
This is all fine until I Lock my computer (WIN+L), when I come back the window has resized itself to be on one monitor only.
What I want to do is prevent the decrease in size, as I'm drawing on a canvas on the second monitor, and when the resize occurs, this is all lost..
Any thoughts on how I can prevent this?
Cheers!
You can use the Unlock/Lock event in .NET. Store your window height, width and position during the lock event and restore it on an Unlock event. Make sure you add "using Microsoft.Win32"
SystemEvents.SessionSwitch += new SessionSwitchEventHandler(SystemEvents_SessionSwitch);
private void SystemEvents_SessionSwitch(object sender, SessionSwitchEventArgs e)
{
if (e.Reason == SessionSwitchReason.SessionUnlock)
{
//Put resize logic here
}
else if (e.Reason == SessionSwitchReason.SessionLock)
{
//Put size store logic here
}
}
Related
Using VS2010 and .NET 4.0 with C# and WinForms:
I always want a Vertical Scrollbar to show for my panel as a disabled scrollbar (when it's not needed, and a enabled one when it can be used.
So it's like a hybrid AutoScroll. I've tried using VScrollBars but I can't figure out where to place them to make this work.
Essentially I've got a user control that acts as a "Document" of controls, its size changes so when using auto-scroll it works perfectly. The scrollbar appears when the usercontrol doesn't fit and the user can move it updown.
It's like a web browser essentially. However, redrawing controls takes a long time (it's forms with many fields and buttons etc within groups in a grid within a panel :P
So anyhow, when autoscroll enables the vertical scrollbar, it takes a while to redraw the window. I'd like to ALWAYS show the vertical scrollbar as indicated above (with the enable/disable functionality).
If anyone has some help, i've read many posts on the subject of autoscroll, but noone has asked what I'm asking and I can't come up with a solution.
C# Version of competent_Tech's answer
using System.Runtime.InteropServices;
public class MyUserControl : UserControl
{
[DllImport("user32.dll")]
[return: MarshalAs(UnmanagedType.Bool)]
private static extern bool ShowScrollBar(IntPtr hWnd, int wBar, bool bShow);
private enum ScrollBarDirection
{
SB_HORZ = 0,
SB_VERT = 1,
SB_CTL = 2,
SB_BOTH = 3
}
public MyUserControl()
{
InitializeComponent();
ShowScrollBar(this.Handle, (int) ScrollBarDirection.SB_VERT, true);
}
}
You can use the auto-scroll functionality of the panel, you just need to send it a windows message to show the vertical scrollbar:
<DllImport("user32.dll")> _
Public Shared Function ShowScrollBar(ByVal hWnd As System.IntPtr, ByVal wBar As Integer, ByVal bShow As Boolean) As Boolean
End Function
Private Const SB_VERT As Integer = 1
Public Sub New()
' This call is required by the designer.
InitializeComponent()
ShowScrollBar(Panel1.Handle, SB_VERT, True)
End Sub
The scrollbar will be displayed and appear as though it can be scrolled, but it won't do anything until it is actually ready to scroll. If you disable it, it won't be automatically re-enabled, so this is probably the best approach.
Also, to improve the performance while resizing, you can call SuspendLayout on the panel before updating and ResumeLayout when done.
What worked for me was overriding the CreateParams call and enabling the WS_VSCROLL style.
public class VerticalFlowPanel : FlowLayoutPanel
{
protected override CreateParams CreateParams
{
get
{
var cp = base.CreateParams;
cp.Style |= 0x00200000; // WS_VSCROLL
return cp;
}
}
}
The AutoScroll logic will now adjust the scrolling bounds without ever hiding the scrollbar.
Here is what solved this for me. My case is that I have a panel sandwiched between another three panels with no degree of liberty in any direction. I needed this panel to be so big that the whole structure would go out of my 1920x1080 screen.
The solution is actually very simple.
For the panel that needs scroll bars set the AutoScroll property to true. Then, add on it another control in the far right far down position (right-bottom position). The control I choose is a label which I made invisible.... And that is all.
Now my panel occupies its restricted area, but I can scroll to the size that I needed and use it for the size I need.
If you only need horizontal scroll bars add the invisible control outside left, for vertical only far down bottom.
The actual size of the panel is the one you restrict it to when display it, but the virtual size is dictated by the invisible control.
This code will draw a disabled vertical scrollbar whenever the built in scrollbar of the Panel is invisible. The codes assumes that
AutoScroll = true;
AutoSize = false;
The following code is speed-optimized. It does as few as possible in OnPaint().
Derive a class from Panel.
Add these member variables:
// NOTE: static variables are not thread safe.
// But as we have only one GUI thread this does not matter.
static IntPtr mh_ScrollTheme = IntPtr.Zero;
static int ms32_ScrollWidth = SystemInformation.VerticalScrollBarWidth;
Win32.RECT mk_ScrollTop;
Win32.RECT mk_ScrollBot; // coordinates of top scrollbar button
Win32.RECT mk_ScrollShaft; // coordinates of bottom scrollbar button
Then override OnSizeChanged:
protected override void OnSizeChanged(EventArgs e)
{
base.OnSizeChanged(e);
Win32.RECT k_ScrollBar = new Win32.RECT(ClientRectangle);
k_ScrollBar.Left = k_ScrollBar.Right - ms32_ScrollWidth;
mk_ScrollTop = new Win32.RECT(k_ScrollBar);
mk_ScrollBot = new Win32.RECT(k_ScrollBar);
mk_ScrollShaft = new Win32.RECT(k_ScrollBar);
int s32_Upper = k_ScrollBar.Top + ms32_ScrollWidth;
int s32_Lower = k_ScrollBar.Bottom - ms32_ScrollWidth;
mk_ScrollTop .Bottom = s32_Upper;
mk_ScrollBot .Top = s32_Lower;
mk_ScrollShaft.Top = s32_Upper;
mk_ScrollShaft.Bottom = s32_Lower;
}
And paint the scrollbar when required:
protected override void OnPaint(PaintEventArgs e)
{
base.OnPaint(e);
if (VScroll)
return; // The 'real' scrollbar is visible
if (mh_ScrollTheme == IntPtr.Zero)
mh_ScrollTheme = Win32.OpenThemeData(Handle, "SCROLLBAR");
if (mh_ScrollTheme == IntPtr.Zero)
return; // The user has disabled themes
// Draw the disabled vertical scrollbar.
IntPtr h_DC = e.Graphics.GetHdc();
// Draw shaft
const int SBP_UPPERTRACKVERT = 7;
const int SCRBS_DISABLED = 4;
Win32.DrawThemeBackground(mh_ScrollTheme, h_DC, SBP_UPPERTRACKVERT, SCRBS_DISABLED, ref mk_ScrollShaft, IntPtr.Zero);
// Draw top button
const int SBP_ARROWBTN = 1;
const int ABS_UPDISABLED = 4;
Win32.DrawThemeBackground(mh_ScrollTheme, h_DC, SBP_ARROWBTN, ABS_UPDISABLED, ref mk_ScrollTop, IntPtr.Zero);
// Draw lower button
const int ABS_DOWNDISABLED = 8;
Win32.DrawThemeBackground(mh_ScrollTheme, h_DC, SBP_ARROWBTN, ABS_DOWNDISABLED, ref mk_ScrollBot, IntPtr.Zero);
e.Graphics.ReleaseHdc(h_DC);
}
For some years, the answer of BradJ and fiat worked for me. Now I needed to show the disabled scrollbar look. But I failed to find the correct way… So here is my workaround.
The code bellow just draw the disabled scrollbar at the position of the real scrollbar.
THE CODE
using System;
using System.Drawing;
using System.Windows.Forms;
using System.Windows.Forms.VisualStyles;
public class VerticalFlowPanel : FlowLayoutPanel
{
public VerticalFlowPanel()
{
AutoScroll = true;
}
protected override void OnPaint(PaintEventArgs e)
{
base.OnPaint(e);
var width = Width;
var height = Height;
var vsWidth = SystemInformation.VerticalScrollBarWidth;
var vsHeight = SystemInformation.VerticalScrollBarArrowHeight;
var left = width - vsWidth;
var sbUpper = new Rectangle(left, 0, vsWidth, height / 2);
var sbLower = new Rectangle(left, sbUpper.Height, vsWidth, height - sbUpper.Height);
var arUp = new Rectangle(left, 0, vsWidth, vsHeight);
var arDown = new Rectangle(left, height - vsHeight, vsWidth, vsHeight);
ScrollBarRenderer.DrawUpperVerticalTrack(e.Graphics, sbUpper, ScrollBarState.Disabled);
ScrollBarRenderer.DrawLowerVerticalTrack(e.Graphics, sbLower, ScrollBarState.Disabled);
ScrollBarRenderer.DrawArrowButton(e.Graphics, arUp, ScrollBarArrowButtonState.UpDisabled);
ScrollBarRenderer.DrawArrowButton(e.Graphics, arDown, ScrollBarArrowButtonState.DownDisabled);
}
// Necessary to avoid visual artifacts
protected override void OnSizeChanged(EventArgs e)
{
base.OnSizeChanged(e);
var width = Width;
var height = Height;
var vsWidth = SystemInformation.VerticalScrollBarWidth;
var scrollBounds = new Rectangle(width - vsWidth, 0, vsWidth, height);
Invalidate(scrollBounds);
}
}
NOTE
This is not the best solution. But it was easier than migrate my hole solution to WPF…
I want to show my window on top of the TaskBar's clock when the windows starts.
How can I find the bottom right corner location of my desktop?
I use this code that works well in windows forms app but does not work correctly in WPF:
var desktopWorkingArea = System.Windows.Forms.Screen.PrimaryScreen.WorkingArea;
this.Left = desktopWorkingArea.Right - this.Width;
this.Top = desktopWorkingArea.Bottom - this.Height;
This code works for me in WPF both with Display 100% and 125%
private void Window_Loaded(object sender, RoutedEventArgs e)
{
var desktopWorkingArea = System.Windows.SystemParameters.WorkArea;
this.Left = desktopWorkingArea.Right - this.Width;
this.Top = desktopWorkingArea.Bottom - this.Height;
}
In brief I use
System.Windows.SystemParameters.WorkArea
instead of
System.Windows.Forms.Screen.PrimaryScreen.WorkingArea
To access the desktop rectangle, you could use the Screen class - Screen.PrimaryScreen.WorkingArea property is the rectangle of your desktop.
Your WPF window has Top and Left properties as well as Width and Height, so you could set those properties relative to the desktop location.
You can use the window's SizeChanged event instead of Loaded if you want the window to stay in the corner when its size changes. This is especially handy if the window has Window.SizeToContent set to some value other than SizeToContent.Manual; in this case it will adjust to fit the content while staying in the corner.
public MyWindow()
{
SizeChanged += (o, e) =>
{
var r = SystemParameters.WorkArea;
Left = r.Right - ActualWidth;
Top = r.Bottom - ActualHeight;
};
InitializeComponent();
}
Note also that you should subtract ActualWidth and ActualHeight (instead of Width and Height as shown in some other replies) to handle more possible situations, for example switching between SizeToContent modes at runtime.
My code:
MainWindow.WindowStartupLocation = WindowStartupLocation.Manual;
MainWindow.Loaded += (s, a) =>
{
MainWindow.Height = SystemParameters.WorkArea.Height;
MainWindow.Width = SystemParameters.WorkArea.Width;
MainWindow.SetLeft(SystemParameters.WorkArea.Location.X);
MainWindow.SetTop(SystemParameters.WorkArea.Location.Y);
};
I solved this problem with a new window containing a label named MessageDisplay. The code accompanying the window was as follows:
public partial class StatusWindow : Window
{
static StatusWindow display;
public StatusWindow()
{
InitializeComponent();
}
static public void DisplayMessage( Window parent, string message )
{
if ( display != null )
ClearMessage();
display = new StatusWindow();
display.Top = parent.Top + 100;
display.Left = parent.Left + 10;
display.MessageDisplay.Content = message;
display.Show();
}
static public void ClearMessage()
{
display.Close();
display = null;
}
}
For my application, the setting of top and left puts this window below the menu on the main window (passed to DisplayMessage in the first parameter);
This above solutions did not entirely work for my window - it was too low and the bottom part of the window was beneath the taskbar and below the desktop workspace. I needed to set the position after the window content had been rendered:
private void Window_ContentRendered(object sender, EventArgs e)
{
var desktopWorkingArea = System.Windows.SystemParameters.WorkArea;
this.Left = desktopWorkingArea.Right - this.Width - 5;
this.Top = desktopWorkingArea.Bottom - this.Height - 5;
}
Also, part of the frame was out of view, so I had to adjust by 5. Not sure why this is needed in my situation.
#Klaus78 's answer is correct. But since this is first thing google pops up and if working in environments where screen resolution can change often such that your app runs on virtual desktops or virtual servers and you still need it to update its placement when the screen resolution changes I have found linking to the SystemEvents.DisplaySettingsChanged event to be beneficial. Here is an example using rx and you can put this in your constructor for your view.
Observable
.FromEventPattern<EventHandler, EventArgs>(_ => SystemEvents.DisplaySettingsChanged += _, _ => SystemEvents.DisplaySettingsChanged -= _)
.Select(_ => SystemParameters.WorkArea)
.Do(_ =>
{
Left = _.Right - Width;
Top = _.Bottom - Height;
})
.Subscribe();
Clicking the middle mouse button (aka: mouse wheel) and then moving the mouse down slightly lets users scroll in IE, and most Windows apps. This behavior appears to be missing in WPF controls by default? Is there a setting, a workaround, or something obvious that I'm missing?
I have found how to achieve this using 3 mouse events (MouseDown, MouseUp, MouseMove). Their handlers are attached to the ScrollViewer element in the xaml below:
<Grid>
<ScrollViewer MouseDown="ScrollViewer_MouseDown" MouseUp="ScrollViewer_MouseUp" MouseMove="ScrollViewer_MouseMove">
<StackPanel x:Name="dynamicLongStackPanel">
</StackPanel>
</ScrollViewer>
<Canvas x:Name="topLayer" IsHitTestVisible="False" />
</Grid>
It would be better to write a behaviour instead of events in code-behind, but not everyone has the necessary library, and also I don't know how to connect it with the Canvas.
The event handlers:
private bool isMoving = false; //False - ignore mouse movements and don't scroll
private bool isDeferredMovingStarted = false; //True - Mouse down -> Mouse up without moving -> Move; False - Mouse down -> Move
private Point? startPosition = null;
private double slowdown = 200; //The number 200 is found from experiments, it should be corrected
private void ScrollViewer_MouseDown(object sender, MouseButtonEventArgs e)
{
if (this.isMoving == true) //Moving with a released wheel and pressing a button
this.CancelScrolling();
else if (e.ChangedButton == MouseButton.Middle && e.ButtonState == MouseButtonState.Pressed)
{
if (this.isMoving == false) //Pressing a wheel the first time
{
this.isMoving = true;
this.startPosition = e.GetPosition(sender as IInputElement);
this.isDeferredMovingStarted = true; //the default value is true until the opposite value is set
this.AddScrollSign(e.GetPosition(this.topLayer).X, e.GetPosition(this.topLayer).Y);
}
}
}
private void ScrollViewer_MouseUp(object sender, MouseButtonEventArgs e)
{
if (e.ChangedButton == MouseButton.Middle && e.ButtonState == MouseButtonState.Released && this.isDeferredMovingStarted != true)
this.CancelScrolling();
}
private void CancelScrolling()
{
this.isMoving = false;
this.startPosition = null;
this.isDeferredMovingStarted = false;
this.RemoveScrollSign();
}
private void ScrollViewer_MouseMove(object sender, MouseEventArgs e)
{
var sv = sender as ScrollViewer;
if (this.isMoving && sv != null)
{
this.isDeferredMovingStarted = false; //standard scrolling (Mouse down -> Move)
var currentPosition = e.GetPosition(sv);
var offset = currentPosition - startPosition.Value;
offset.Y /= slowdown;
offset.X /= slowdown;
//if(Math.Abs(offset.Y) > 25.0/slowdown) //Some kind of a dead space, uncomment if it is neccessary
sv.ScrollToVerticalOffset(sv.VerticalOffset + offset.Y);
sv.ScrollToHorizontalOffset(sv.HorizontalOffset + offset.X);
}
}
If to remove the method calls AddScrollSign and RemoveScrollSign this example will work. But I have extended it with 2 methods which set scroll icon:
private void AddScrollSign(double x, double y)
{
int size = 50;
var img = new BitmapImage(new Uri(#"d:\middle_button_scroll.png"));
var adorner = new Image() { Source = img, Width = size, Height = size };
//var adorner = new Ellipse { Stroke = Brushes.Red, StrokeThickness = 2.0, Width = 20, Height = 20 };
this.topLayer.Children.Add(adorner);
Canvas.SetLeft(adorner, x - size / 2);
Canvas.SetTop(adorner, y - size / 2);
}
private void RemoveScrollSign()
{
this.topLayer.Children.Clear();
}
Example of icons:
And one last remark: there are some problems with the way Press -> Immediately Release -> Move. It is supposed to cancel scrolling if a user clicks the mouse left button, or any key of keyboard, or the application looses focus. There are many events and I don't have time to handle them all.
But standard way Press -> Move -> Release works without problems.
vorrtex posted a nice solution, please upvote him!
I do have some suggestions for his solution though, that are too lengthy to fit them all in comments, that's why I post a separate answer and direct it to him!
You mention problems with Press->Release->Move. You should use MouseCapturing to get the MouseEvents even when the Mouse is not over the ScrollViewer anymore. I have not tested it, but I guess your solution also fails in Press->Move->Move outside of ScrollViewer->Release, Mousecapturing will take care of that too.
Also you mention using a Behavior. I'd rather suggest an attached behavior that doesn't need extra dependencies.
You should definately not use an extra Canvas but do this in an Adorner.
The ScrollViewer itsself hosts a ScrollContentPresenter that defines an AdornerLayer. You should insert the Adorner there. This removes the need for any further dependency and also keeps the attached behavior as simple as IsMiddleScrollable="true".
I'm creating a custom drawn window by specifying border style NONE and custom processing of WM_NCHITTEST. I've defined some area as 'my window caption' and returning HTCAPTION result for WM_NCHITTEST in this area. When window is in normal state the behavior is expected by me. The window can be moved by dragging 'my window caption' and can be maximized by double clicking on it.
The problem is with the behavior of my window in maximized state. I still returning HTCAPTION result for WM_NCHITTEST in area of 'my window caption' and window can be restored to original size by double clicking on it again, but it's also still can be moved and this isn't what I want. What should I do to fix such behavior?
Fix:
protected override void WndProc(ref Message m)
{
if(m.Msg == WM_NCHITTEST)
{
Point pos = new Point(m.LParam.ToInt32() & 0xffff, m.LParam.ToInt32() >> 16);
pos = this.PointToClient(pos);
if(HitTestForNC(ref m, pos))
{
if(WindowState != FormWindowState.Maximized || m.Result != (IntPtr)HitTestValues.HTCAPTION)
{
return;
}
}
}
else if(m.Msg == WM_GETMINMAXINFO)
{
base.WndProc(ref m);
MinMaxInfo mmi = (MinMaxInfo)Marshal.PtrToStructure(m.LParam, typeof(MinMaxInfo));
mmi.ptMaxPosition = Screen.FromControl(this).WorkingArea.Location;
mmi.ptMaxSize = Screen.FromControl(this).WorkingArea.Size;
Marshal.StructureToPtr(mmi, m.LParam, false);
return;
}
base.WndProc(ref m);
}
protected override void OnMouseDoubleClick(MouseEventArgs e)
{
if(e.Button == MouseButtons.Left)
{
Message m = new Message();
if(HitTestForNC(ref m, e.Location))
{
if(m.Result == (IntPtr)HitTestValues.HTCAPTION && WindowState == FormWindowState.Maximized)
{
WindowState = FormWindowState.Normal;
return;
}
}
}
base.OnMouseDoubleClick(e);
}
HitTestForNC method is responsible for evaluation of hit test result on my custom drawn form. The implementation may look ugly, but it's pretty simple.
This is the code I use to prevent the window from being draggable when maximized.
// Indicates the form caption
Const HT_CAPTION As Integer = &H2
// Windows Message Non Client Button Down
Const WM_NCLBUTTONDOWN As Integer = &HA1
//Routine to implement the 'Drag Window' functionality.
Private Sub frm_Drag(ByVal sender As Object, ByVal e As System.Windows.Forms.MouseEventArgs) _
Handles Me.MouseDown
//Do not move the form if it is maximized.
If Not Me.WindowState = FormWindowState.Maximized Then
If e.Button = Windows.Forms.MouseButtons.Left Then
sender.Capture = False
Me.WndProc(Message.Create(Me.Handle, WM_NCLBUTTONDOWN, _
CType(HT_CAPTION, IntPtr), IntPtr.Zero))
End If
End If
End Sub
What you describe is a bit weird - the maximized window can't usually be moved. In particular it occupies the whole desktop area, and AFAIK the system doesn't 'drag' it when its caption (i.e. - the area for which hit test was HT_CAPTION) is dragged.
Can you please specify more info:
How many desktops do you have (is it a multi-monitor system)?
Do you respond on WM_GETMINMAXINFO to prevent your window from occupying the whole desktop area?
BTW I can imagine a workaround: when your window is maximized - don't return HT_CAPTION on hit test. Instead you may return HT_CLIENT, this will prevent your window from dragging.
However you'll have to manually implement "restoring" of your window when double-clicked. You should then respond on WM_LBUTTONDBLCLK and restore your position manually.
From Windows 7 the expected and correct behaviour is that maximized windows that are dragged should be draggable. Try it with Notepad or any other windows app:- Windows that are docked or maximized will automatically revert to the "restore" size and be draggable.
For a System.Windows.Forms.TextBox with Multiline=True, I'd like to only show the scrollbars when the text doesn't fit.
This is a readonly textbox used only for display. It's a TextBox so that users can copy the text out. Is there anything built-in to support auto show of scrollbars? If not, should I be using a different control? Or do I need to hook TextChanged and manually check for overflow (if so, how to tell if the text fits?)
Not having any luck with various combinations of WordWrap and Scrollbars settings. I'd like to have no scrollbars initially and have each appear dynamically only if the text doesn't fit in the given direction.
#nobugz, thanks, that works when WordWrap is disabled. I'd prefer not to disable wordwrap, but it's the lesser of two evils.
#André Neves, good point, and I would go that way if it was user-editable. I agree that consistency is the cardinal rule for UI intuitiveness.
I came across this question when I wanted to solve the same problem.
The easiest way to do it is to change to System.Windows.Forms.RichTextBox. The ScrollBars property in this case can be left to the default value of RichTextBoxScrollBars.Both, which indicates "Display both a horizontal and a vertical scroll bar when needed." It would be nice if this functionality were provided on TextBox.
Add a new class to your project and paste the code shown below. Compile. Drop the new control from the top of the toolbox onto your form. It's not quite perfect but ought to work for you.
using System;
using System.Drawing;
using System.Windows.Forms;
public class MyTextBox : TextBox {
private bool mScrollbars;
public MyTextBox() {
this.Multiline = true;
this.ReadOnly = true;
}
private void checkForScrollbars() {
bool scroll = false;
int cnt = this.Lines.Length;
if (cnt > 1) {
int pos0 = this.GetPositionFromCharIndex(this.GetFirstCharIndexFromLine(0)).Y;
if (pos0 >= 32768) pos0 -= 65536;
int pos1 = this.GetPositionFromCharIndex(this.GetFirstCharIndexFromLine(1)).Y;
if (pos1 >= 32768) pos1 -= 65536;
int h = pos1 - pos0;
scroll = cnt * h > (this.ClientSize.Height - 6); // 6 = padding
}
if (scroll != mScrollbars) {
mScrollbars = scroll;
this.ScrollBars = scroll ? ScrollBars.Vertical : ScrollBars.None;
}
}
protected override void OnTextChanged(EventArgs e) {
checkForScrollbars();
base.OnTextChanged(e);
}
protected override void OnClientSizeChanged(EventArgs e) {
checkForScrollbars();
base.OnClientSizeChanged(e);
}
}
I also made some experiments, and found that the vertical bar will always show if you enable it, and the horizontal bar always shows as long as it's enabled and WordWrap == false.
I think you're not going to get exactly what you want here. However, I believe that users would like better Windows' default behavior than the one you're trying to force. If I were using your app, I probably would be bothered if my textbox real-estate suddenly shrinked just because it needs to accomodate an unexpected scrollbar because I gave it too much text!
Perhaps it would be a good idea just to let your application follow Windows' look and feel.
There's an extremely subtle bug in nobugz's solution that results in a heap corruption, but only if you're using AppendText() to update the TextBox.
Setting the ScrollBars property from OnTextChanged will cause the Win32 window (handle) to be destroyed and recreated. But OnTextChanged is called from the bowels of the Win32 edit control (EditML_InsertText), which immediately thereafter expects the internal state of that Win32 edit control to be unchanged. Unfortunately, since the window is recreated, that internal state has been freed by the OS, resulting in an access violation.
So the moral of the story is: don't use AppendText() if you're going to use nobugz's solution.
I had some success with the code below.
public partial class MyTextBox : TextBox
{
private bool mShowScrollBar = false;
public MyTextBox()
{
InitializeComponent();
checkForScrollbars();
}
private void checkForScrollbars()
{
bool showScrollBar = false;
int padding = (this.BorderStyle == BorderStyle.Fixed3D) ? 14 : 10;
using (Graphics g = this.CreateGraphics())
{
// Calcualte the size of the text area.
SizeF textArea = g.MeasureString(this.Text,
this.Font,
this.Bounds.Width - padding);
if (this.Text.EndsWith(Environment.NewLine))
{
// Include the height of a trailing new line in the height calculation
textArea.Height += g.MeasureString("A", this.Font).Height;
}
// Show the vertical ScrollBar if the text area
// is taller than the control.
showScrollBar = (Math.Ceiling(textArea.Height) >= (this.Bounds.Height - padding));
if (showScrollBar != mShowScrollBar)
{
mShowScrollBar = showScrollBar;
this.ScrollBars = showScrollBar ? ScrollBars.Vertical : ScrollBars.None;
}
}
}
protected override void OnTextChanged(EventArgs e)
{
checkForScrollbars();
base.OnTextChanged(e);
}
protected override void OnResize(EventArgs e)
{
checkForScrollbars();
base.OnResize(e);
}
}
What Aidan describes is almost exactly the UI scenario I am facing. As the text box is read only, I don't need it to respond to TextChanged. And I'd prefer the auto-scroll recalculation to be delayed so it's not firing dozens of times per second while a window is being resized.
For most UIs, text boxes with both vertical and horizontal scroll bars are, well, evil, so I'm only interested in vertical scroll bars here.
I also found that MeasureString produced a height that was actually bigger than what was required. Using the text box's PreferredHeight with no border as the line height gives a better result.
The following seems to work pretty well, with or without a border, and it works with WordWrap on.
Simply call AutoScrollVertically() when you need it, and optionally specify recalculateOnResize.
public class TextBoxAutoScroll : TextBox
{
public void AutoScrollVertically(bool recalculateOnResize = false)
{
SuspendLayout();
if (recalculateOnResize)
{
Resize -= OnResize;
Resize += OnResize;
}
float linesHeight = 0;
var borderStyle = BorderStyle;
BorderStyle = BorderStyle.None;
int textHeight = PreferredHeight;
try
{
using (var graphics = CreateGraphics())
{
foreach (var text in Lines)
{
var textArea = graphics.MeasureString(text, Font);
if (textArea.Width < Width)
linesHeight += textHeight;
else
{
var numLines = (float)Math.Ceiling(textArea.Width / Width);
linesHeight += textHeight * numLines;
}
}
}
if (linesHeight > Height)
ScrollBars = ScrollBars.Vertical;
else
ScrollBars = ScrollBars.None;
}
catch (Exception ex)
{
System.Diagnostics.Debug.WriteLine(ex);
}
finally
{
BorderStyle = borderStyle;
ResumeLayout();
}
}
private void OnResize(object sender, EventArgs e)
{
m_timerResize.Stop();
m_timerResize.Tick -= OnDelayedResize;
m_timerResize.Tick += OnDelayedResize;
m_timerResize.Interval = 475;
m_timerResize.Start();
}
Timer m_timerResize = new Timer();
private void OnDelayedResize(object sender, EventArgs e)
{
m_timerResize.Stop();
Resize -= OnResize;
AutoScrollVertically();
Resize += OnResize;
}
}