MeasureString always thinks spaces will match

Question

I am trying to perform some tests when testing on strings (I want to get the char index from offset x), but I am encountering problems with the dimension string.

This is essentially the code I use

     StringFormat sf = new StringFormat(StringFormatFlags.MeasureTrailingSpaces | StringFormatFlags.NoWrap | StringFormatFlags.LineLimit);
     e.Graphics.MeasureString("test    string", this.Font, new SizeF(xHitTestPosition, this.Font.Height), sf, out charFitted, out linesFilled);

The charFitted value should be set to the number of characters that it can fit in the size it gives (I give it a size based on the point at which I am trying to hit the test).

This works fine until the area is large enough to hold the string "test". at this point, charFitted jumps from 3 ('tes') to 8 ('test'). It basically always includes all the spaces, regardless of the place that he gave.

I tried communicating with StringFormat settings but nothing helps ...

I have included a test application below that demonstrates this

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Windows.Forms;

namespace WindowsFormsApplication2
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }

        private void Form1_Load(object sender, EventArgs e)
        {
            trackBar1.Maximum = this.ClientRectangle.Width;
        }

        protected override void OnPaint(PaintEventArgs e)
        {
            string sample = "abc                       def";
            int charFitted, linesFilled;

            e.Graphics.DrawString(sample, this.Font, Brushes.Black, PointF.Empty);
            e.Graphics.DrawLine(Pens.Red, trackBar1.Value, 0, trackBar1.Value, 100);

            StringFormat sf = new StringFormat(StringFormatFlags.MeasureTrailingSpaces | StringFormatFlags.NoWrap | StringFormatFlags.LineLimit);
            sf.Trimming = StringTrimming.Character;
            e.Graphics.MeasureString(sample, this.Font, new SizeF(trackBar1.Value, this.Font.Height), sf, out charFitted, out linesFilled);
            textBox1.Text = "[" + sample.Substring(0, charFitted) + "]";

            base.OnPaint(e);
        }

        private void trackBar1_Scroll(object sender, EventArgs e)
        {
            Invalidate();
        }

        /// <summary>
        /// Required designer variable.
        /// </summary>
        private System.ComponentModel.IContainer components = null;

        /// <summary>
        /// Clean up any resources being used.
        /// </summary>
        /// <param name="disposing">true if managed resources should be disposed; otherwise, false.</param>
        protected override void Dispose(bool disposing)
        {
            if (disposing && (components != null))
            {
                components.Dispose();
            }
            base.Dispose(disposing);
        }

        #region Windows Form Designer generated code

        /// <summary>
        /// Required method for Designer support - do not modify
        /// the contents of this method with the code editor.
        /// </summary>
        private void InitializeComponent()
        {
            this.trackBar1 = new System.Windows.Forms.TrackBar();
            this.textBox1 = new System.Windows.Forms.TextBox();
            ((System.ComponentModel.ISupportInitialize)(this.trackBar1)).BeginInit();
            this.SuspendLayout();
            // 
            // trackBar1
            // 
            this.trackBar1.Location = new System.Drawing.Point(13, 184);
            this.trackBar1.Name = "trackBar1";
            this.trackBar1.Size = new System.Drawing.Size(259, 45);
            this.trackBar1.TabIndex = 0;
            this.trackBar1.Scroll += new System.EventHandler(this.trackBar1_Scroll);
            // 
            // textBox1
            // 
            this.textBox1.Location = new System.Drawing.Point(22, 229);
            this.textBox1.Name = "textBox1";
            this.textBox1.Size = new System.Drawing.Size(237, 20);
            this.textBox1.TabIndex = 1;
            // 
            // Form1
            // 
            this.AutoScaleDimensions = new System.Drawing.SizeF(6F, 13F);
            this.AutoScaleMode = System.Windows.Forms.AutoScaleMode.Font;
            this.ClientSize = new System.Drawing.Size(284, 261);
            this.Controls.Add(this.textBox1);
            this.Controls.Add(this.trackBar1);
            this.Name = "Form1";
            this.Text = "Form1";
            this.Load += new System.EventHandler(this.Form1_Load);
            ((System.ComponentModel.ISupportInitialize)(this.trackBar1)).EndInit();
            this.ResumeLayout(false);
            this.PerformLayout();

        }

        #endregion

        private System.Windows.Forms.TrackBar trackBar1;
        private System.Windows.Forms.TextBox textBox1;
    }
}

Answer 1

The problem is that the lengths of "abc" and "abc" are the same. Since you are not printing trailing spaces, the graphic representation is the same. I would add a character at the end, and then measure the string and delete the length of the added character.

Minimize your OnPaint and it seems to work:

    protected override void OnPaint(PaintEventArgs e) {
        string sample = "abc                       def";

        e.Graphics.DrawString(sample, this.Font, Brushes.Black, PointF.Empty);
        e.Graphics.DrawLine(Pens.Red, trackBar1.Value, 0, trackBar1.Value, 100);

        StringFormat sf = new StringFormat(StringFormatFlags.MeasureTrailingSpaces | StringFormatFlags.NoWrap | StringFormatFlags.LineLimit);
        sf.Trimming = StringTrimming.Character;

        var underscoreWidth = e.Graphics.MeasureString("_", this.Font).Width;

        for (int i = 0; i < sample.Length; i++) {
            var s = sample.Substring(0, i + 1) + "_";
            var size = e.Graphics.MeasureString(s, this.Font).Width - underscoreWidth;
            if (size > trackBar1.Value) {
                if (s.Length > 0) {
                    var ok = s.Substring(0, s.Length - 2);
                    textBox1.Text = "[" + ok + "]";
                    base.OnPaint(e);
                    return;
                }
            }
        }

        textBox1.Text = "[" + sample + "]";
        base.OnPaint(e);
    }

Answer 2

I really don't like this solution, but so far this is the only working solution that I have. Its based on a solution from @FSDaniel, but I noticed that the results of Graphics.MeasureString and Graphics.DrawString drift even if you pass them the same StringFormat.

, , TextRenderer TextFormatFlags.TextBoxControl.

, ( ) , , 3/4 , 5/8 .., .

, , - - , !

    protected override void OnPaint(PaintEventArgs e)
    {
        string sample = "abc                       defXXXXXXXXXXXXiiiiiiiX";

        TextFormatFlags flags = TextFormatFlags.NoPadding | TextFormatFlags.TextBoxControl | TextFormatFlags.SingleLine | TextFormatFlags.NoPrefix;

        TextRenderer.DrawText(e.Graphics, sample, this.Font, Point.Empty, Color.Black, flags);
        e.Graphics.DrawLine(Pens.Red, trackBar1.Value, 0, trackBar1.Value, 100);

        string measuredString = sample;
        for (int i = 0; i < sample.Length; i++)
        {
            Size size = TextRenderer.MeasureText(e.Graphics, sample.Substring(0, i+1), this.Font, new Size(10000000, 1000000), flags);
            if (size.Width > trackBar1.Value)
            {
                textBox1.Text = "[" + sample.Substring(0,i+1) + "]";
                break;
            }
        }

        base.OnPaint(e);
    }