I made a subclass for TextBox and tested the following method in a separate test project.
internal static int NumberOfPhysicalLinesInTextBox(TextBox tb)
{
int lc = 0;
while (tb.GetFirstCharIndexFromLine(lc) != -1)
{
++lc;
}
return lc;
}
The code Works well, but in my subclass it does not. The above static method is called only from the method UpdateVisibleScrollBars, which is called only in the following places:
- from the subclass' c-tor
OnTextChangedOnFontChangedOnResize
The only speciality of this subclass is that it has a placeholder when the user did not enter anything in the TextBox, and this UpdateVisibleScrollBars. In this subclass NumberOfPhysicalLinesInTextBox does not return, it loops indefinitely because the GetFirstCharIndexFromLine always returns 0 when the text is the placeholder: "Enter text here...".
Update: I do not use Lines because I need the physical lines (the lines that result after Word-wrapping), so I can know if I need to show or hide the vertical scrollbar. The TextBox is set with WordWrap = true. Here is the GetFirstCharIndexFromLine method's official documentation.
Update 2: All the class' code is below (without non-English comments):
class EnhancedTextBox : TextBox
{
internal string PlaceholderText = "Enter text here...";
internal string ActualText
{
get
{
return PlaceholderShown ? "" : Text;
}
set
{
if (value == "" || value == null)
{
if (Text == PlaceholderText)
{
PlaceholderShown = true;
ActualTextChanged?.Invoke(this, EventArgs.Empty);
}
else
{
if (!Focused)
{
BeforeActualTextChanged?.Invoke(this, EventArgs.Empty);
ProgrammaticTextChange = true;
Text = PlaceholderText;
ProgrammaticTextChange = false;
PlaceholderShown = true;
ActualTextChanged?.Invoke(this, EventArgs.Empty);
}
else
{
PlaceholderShown = false;
ActualTextChanged?.Invoke(this, EventArgs.Empty);
}
}
}
else
{
if (Text != value)
{
BeforeActualTextChanged?.Invoke(this, EventArgs.Empty);
ProgrammaticTextChange = true;
Text = value;
ProgrammaticTextChange = false;
}
PlaceholderShown = false;
ActualTextChanged?.Invoke(this, EventArgs.Empty);
}
}
}
internal Color _PlaceholderForeColor = Utils.GrayByPercent(50);
internal Color PlaceholderForeColor
{
get
{
return _PlaceholderForeColor;
}
set
{
if (_PlaceholderForeColor != value)
{
_PlaceholderForeColor = value;
Invalidate();
}
}
}
internal Color _NormalForeColor = Color.Empty;
internal Color NormalForeColor
{
get
{
return _NormalForeColor;
}
set
{
if (_NormalForeColor != value)
{
_NormalForeColor = value;
Invalidate();
}
}
}
internal bool _PlaceholderShown = true;
internal bool PlaceholderShown
{
get
{
return _PlaceholderShown;
}
set
{
if (_PlaceholderShown != value)
{
_PlaceholderShown = value;
ForceUpdatePlaceholderShown(value);
}
}
}
internal void ForceUpdatePlaceholderShown(bool value)
{
ForeColor = value ? PlaceholderForeColor :
NormalForeColor;
Invalidate();
}
public EnhancedTextBox() : base()
{
NormalForeColor = ForeColor;
ProgrammaticTextChange = true;
Text = PlaceholderText;
ProgrammaticTextChange = false;
PlaceholderShown = true;
ForceUpdatePlaceholderShown(true);
UpdateVisibleScrollBars();
}
protected override void OnEnter(EventArgs e)
{
HidePlaceholder();
base.OnEnter(e);
}
private void HidePlaceholder()
{
if (PlaceholderShown)
{
ProgrammaticTextChange = true;
Text = "";
ProgrammaticTextChange = false;
PlaceholderShown = false;
}
}
protected override void OnLeave(EventArgs e)
{
ShowPlaceholder();
base.OnLeave(e);
}
private void ShowPlaceholder()
{
if (Text == "")
{
ProgrammaticTextChange = true;
Text = PlaceholderText;
ProgrammaticTextChange = false;
PlaceholderShown = true;
}
}
internal static int NumberOfPhysicalLinesInTextBox(TextBox tb)
{
int lc = 0;
while (tb.GetFirstCharIndexFromLine(lc) != -1)
{
++lc;
}
return lc;
}
internal bool ProgrammaticTextChange = false;
/// <summary>
/// Do not use this event using handlers. Use ActualTextChanged instead.
/// </summary>
/// <param name="e"></param>
protected override void OnTextChanged(EventArgs e)
{
if (ProgrammaticTextChange)
{
return;
}
ActualText = Text;
base.OnTextChanged(e);
UpdateVisibleScrollBars();
}
private bool busy = false;
private void UpdateVisibleScrollBars()
{
if (busy) return;
busy = true;
bool c1 = false; // chars == Text.Length; // TODO: this not working for WordWrap = false
bool c2 = NumberOfPhysicalLinesInTextBox(this) > 2;
if (c1 && c2)
{
ScrollBars = ScrollBars.Both;
}
else if (c1)
{
ScrollBars = ScrollBars.Horizontal;
}
else if (c2)
{
ScrollBars = ScrollBars.Vertical;
}
else
{
ScrollBars = ScrollBars.None;
}
ScrollToCaret();
busy = false;
}
protected override void OnFontChanged(EventArgs e)
{
base.OnFontChanged(e);
UpdateVisibleScrollBars();
}
protected override void OnResize(EventArgs e)
{
base.OnResize(e);
UpdateVisibleScrollBars();
}
public event EventHandler ActualTextChanged, BeforeActualTextChanged;
}
If I replace bool c2 = NumberOfPhysicalLinesInTextBox(this) > 2; with bool c2 = false; there is no non-ending while loop, although I see that the OnResize handler is called often in debugging with a breakpoint put on the c2 line, and repeatedly clicking Continue. Then If I press Continue really fast a few times, the program starts and is usable.
Update 3: Commenting out the UpdateVisibleScrollBars call inside the OnResize handler makes everything work. How can I make the scrollbars' visibility be changed when the TextBox is just resized?
Current code:
class EnhancedTextBox : TextBox
{
internal string _PlaceholderText = "Enter text here...";
internal string PlaceholderText
{
get
{
return _PlaceholderText;
}
set
{
_PlaceholderText = value;
Invalidate();
}
}
internal Color _PlaceholderForeColor = SystemColors.GrayText;
public Color PlaceholderForeColor
{
get
{
return _PlaceholderForeColor;
}
set
{
_PlaceholderForeColor = value;
Invalidate();
}
}
[Obsolete]
internal string ActualText
{
get
{
return Text;
}
set
{
if (Text != value)
{
Text = value;
}
}
}
internal Color _NormalForeColor = Color.Empty;
internal Color NormalForeColor
{
get
{
return _NormalForeColor;
}
set
{
if (_NormalForeColor != value)
{
_NormalForeColor = value;
ForeColor = value;
}
}
}
public EnhancedTextBox() : base()
{
NormalForeColor = ForeColor;
WordWrap = true;
}
protected override void WndProc(ref Message m)
{
base.WndProc(ref m);
if (m.Msg == 0xf)
{
if (!this.Focused && string.IsNullOrEmpty(this.Text)
&& !string.IsNullOrEmpty(this.PlaceholderText))
{
using (var g = this.CreateGraphics())
{
TextRenderer.DrawText(g, this.PlaceholderText, this.Font,
this.ClientRectangle, this.PlaceholderForeColor, this.BackColor,
TextFormatFlags.Top | TextFormatFlags.Left);
}
}
}
}
internal static int NumberOfPhysicalLinesInTextBox(TextBox tb)
{
int lc = 0;
while (tb.GetFirstCharIndexFromLine(lc) != -1)
{
++lc;
}
return lc;
}
internal bool ProgrammaticTextChange = false;
protected override void OnTextChanged(EventArgs e)
{
base.OnTextChanged(e);
ActualTextChanged?.Invoke(this, e);
UpdateVisibleScrollBars();
}
private bool busy = false;
private Size textSize = Size.Empty;
private void UpdateVisibleScrollBars()
{
if (busy) return;
busy = true;
bool c1 = false; // chars == Text.Length; // TODO: this not working for WordWrap = false
bool c2 = NumberOfPhysicalLinesInTextBox(this) > 2;
if (c1 && c2)
{
ScrollBars = ScrollBars.Both;
}
else if (c1)
{
ScrollBars = ScrollBars.Horizontal;
}
else if (c2)
{
ScrollBars = ScrollBars.Vertical;
}
else
{
ScrollBars = ScrollBars.None;
}
ScrollToCaret();
busy = false;
}
protected override void OnFontChanged(EventArgs e)
{
base.OnFontChanged(e);
UpdateVisibleScrollBars();
}
protected override void OnResize(EventArgs e)
{
base.OnResize(e);
//UpdateVisibleScrollBars();
}
[Obsolete]
public event EventHandler ActualTextChanged;
}
