How to truncate a string so that it fits in a container?

Question

There are many questions (EG: 1 , 2 , 3 , 4 , 5 ) asking how you can truncate a string to the required number of characters. But I want the text fragment to be truncated to fit into the container. (IE: crop the string in pixels , not characters ).

This is easy if you use WPF, but not so much in WinForms ...

So: how can you truncate a string to fit in a container?

Answer 1

After a day of coding, I found a solution, and I wanted to share it with the community.

First of all: there is no built-in truncation function for a string or winforms TextBox. If you use a shortcut, you can use the AutoEllipsis property.

FYI: An ellipsis is a punctuation mark made up of three dots. IE: ...

This is why I did it:

public static class Extensions { /// <summary> /// Truncates the TextBox.Text property so it will fit in the TextBox. /// </summary> static public void Truncate(this TextBox textBox) { //Determine direction of truncation bool direction = false; if (textBox.TextAlign == HorizontalAlignment.Right) direction = true; //Get text string truncatedText = textBox.Text; //Truncate text truncatedText = truncatedText.Truncate(textBox.Font, textBox.Width, direction); //If text truncated if (truncatedText != textBox.Text) { //Set textBox text textBox.Text = truncatedText; //After setting the text, the cursor position changes. Here we set the location of the cursor manually. //First we determine the position, the default value applies to direction = left. //This position is when the cursor needs to be behind the last char. (Example:"…My Text|"); int position = 0; //If the truncation direction is to the right the position should be before the ellipsis if (!direction) { //This position is when the cursor needs to be before the last char (which would be the ellipsis). (Example:"My Text|…"); position = 1; } //Set the cursor position textBox.Select(textBox.Text.Length - position, 0); } } /// <summary> /// Truncates the string to be smaller than the desired width. /// </summary> /// <param name="font">The font used to determine the size of the string.</param> /// <param name="width">The maximum size the string should be after truncating.</param> /// <param name="direction">The direction of the truncation. True for left (…ext), False for right(Tex…).</param> static public string Truncate(this string text, Font font, int width, bool direction) { string truncatedText, returnText; int charIndex = 0; bool truncated = false; //When the user is typing and the truncation happens in a TextChanged event, already typed text could get lost. //Example: Imagine that the string "Hello Worl" would truncate if we add 'd'. Depending on the font the output //could be: "Hello Wor…" (notice the 'l' is missing). This is an undesired effect. //To prevent this from happening the ellipsis is included in the initial sizecheck. //At this point, the direction is not important so we place ellipsis behind the text. truncatedText = text + "…"; //Get the size of the string in pixels. SizeF size = MeasureString(truncatedText, font); //Do while the string is bigger than the desired width. while (size.Width > width) { //Go to next char charIndex++; //If the character index is larger than or equal to the length of the text, the truncation is unachievable. if (charIndex >= text.Length) { //Truncation is unachievable! //Throw exception so the user knows what going on. throw new IndexOutOfRangeException("The desired width of the string is too small to truncate to."); } else { //Truncation is still applicable! //Raise the flag, indicating that text is truncated. truncated = true; //Check which way to text should be truncated to, then remove one char and add an ellipsis. if (direction) { //Truncate to the left. Add ellipsis and remove from the left. truncatedText = "…" + text.Substring(charIndex); } else { //Truncate to the right. Remove from the right and add the ellipsis. truncatedText = text.Substring(0, text.Length - charIndex) + "…"; } //Measure the string again. size = MeasureString(truncatedText, font); } } //If the text got truncated, change the return value to the truncated text. if (truncated) returnText = truncatedText; else returnText = text; //Return the desired text. return returnText; } /// <summary> /// Measures the size of this string object. /// </summary> /// <param name="text">The string that will be measured.</param> /// <param name="font">The font that will be used to measure to size of the string.</param> /// <returns>A SizeF object containing the height and size of the string.</returns> static private SizeF MeasureString(String text, Font font) { //To measure the string we use the Graphics.MeasureString function, which is a method that can be called from a PaintEventArgs instance. //To call the constructor of the PaintEventArgs class, we must pass a Graphics object. We'll use a PictureBox object to achieve this. PictureBox pb = new PictureBox(); //Create the PaintEventArgs with the correct parameters. PaintEventArgs pea = new PaintEventArgs(pb.CreateGraphics(), new System.Drawing.Rectangle()); pea.Graphics.PageUnit = GraphicsUnit.Pixel; pea.Graphics.PageScale = 1; //Call the MeasureString method. This methods calculates what the height and width of a string would be, given the specified font. SizeF size = pea.Graphics.MeasureString(text, font); //Return the SizeF object. return size; } } 

Usage: This is a class that you can copy and paste into the namespace containing the winforms form. Make sure you enable " using System.Drawing; "

This class has two extension methods called Truncate. You can basically do this:

 public void textBox1_TextChanged(object sender, EventArgs e) { textBox1.Truncate(); } 

Now you can enter something in textBox1, and if necessary, it will automatically truncate your line to fit in textBox, and it will add an ellipsis.

Overview: This class currently contains 3 methods:

• Truncation (extension for TextBox)
• Truncation (extension for string)
• MeasureString

Truncation (extension for TextBox)

This method automatically trims the TextBox.Text property. The direction of truncation is limited by the TextAlign property. (EG: "Truncate for left alignment ...", "... ncation for proper alignment".) Please note: this method may require some modification to work with other writing systems, such as Hebrew or Arabic.

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Truncation (extension for string)

To use this method, you must pass two parameters: the font and the desired width. The font is used to calculate the width of the line, and the required width is used as the maximum width allowed after truncation.

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MeasureString

This method is closed in a piece of code. Therefore, if you want to use it, you must first transfer it to the publication. This method is used to measure the height and width of a line in pixels. Two parameters are required for this: the text to be measured and the font of the text.

Hope I helped someone with this. Perhaps there is another way to do this, I found this answer by Hans Passant that truncates ToolTipStatusLabel, which is quite impressive. My .NET skills are not close to Hans Passant anywhere, so I couldn’t convert this code to work with something like TextBox ... But if you succeeded or have another solution, I would love to see it! :)

Answer 2

I tested the Jordy code and compared the result with this code, there is no difference, they both crop / truncate quite well, but not very well in some cases, this may be the size measured by MeasureString() , is not accurate. I know that this code is just a simplified version, I publish it here if someone cares about it and uses it because it is short, and I tested: there is no difference in how exactly this code can crop / truncate string compared to Jordy code, Of course, its code is some kind of full version supporting 3 methods.

 public static class TextBoxExtension { public static void Trim(this TextBox text){ string txt = text.Text; if (txt.Length == 0 || text.Width == 0) return; int i = txt.Length; while (TextRenderer.MeasureText(txt + "...", text.Font).Width > text.Width) { txt = text.Text.Substring(0, --i); if (i == 0) break; } text.Text = txt + "..."; } //You can implement more methods such as receiving a string with font,... and returning the truncated/trimmed version. }