TextBox.TextChanged和“CTRL-a”

Question

I write simply code:

using System.Windows.Forms;

namespace Test01
{
    partial class Form1
    {
        /// <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.textBox1 = new System.Windows.Forms.TextBox();
            this.checkBox1 = new System.Windows.Forms.CheckBox();
            this.SuspendLayout();
            // 
            // textBox1
            // 
            this.textBox1.Location = new System.Drawing.Point(33, 32);
            this.textBox1.Name = "textBox1";
            this.textBox1.Size = new System.Drawing.Size(186, 20);
            this.textBox1.TabIndex = 0;
            this.textBox1.Text = "Text";
            this.textBox1.TextChanged += new System.EventHandler(this.textBox1_TextChanged);
            // 
            // checkBox1
            // 
            this.checkBox1.AutoSize = true;
            this.checkBox1.Location = new System.Drawing.Point(38, 65);
            this.checkBox1.Name = "checkBox1";
            this.checkBox1.Size = new System.Drawing.Size(80, 17);
            this.checkBox1.TabIndex = 1;
            this.checkBox1.Text = "checkBox1";
            this.checkBox1.UseVisualStyleBackColor = true;
            // 
            // Form1
            // 
            this.AutoScaleDimensions = new System.Drawing.SizeF(6F, 13F);
            this.AutoScaleMode = System.Windows.Forms.AutoScaleMode.Font;
            this.ClientSize = new System.Drawing.Size(234, 86);
            this.Controls.Add(this.checkBox1);
            this.Controls.Add(this.textBox1);
            this.Name = "Form1";
            this.Text = "Form1";
            this.ResumeLayout(false);
            this.PerformLayout();

        }

        void textBox1_TextChanged(object sender, System.EventArgs e)
        {
            if (this.checkBox1.Checked)
                this.checkBox1.CheckState = CheckState.Unchecked;
            else
                this.checkBox1.CheckState = CheckState.Checked;
        }

        #endregion

        private System.Windows.Forms.TextBox textBox1;
        private System.Windows.Forms.CheckBox checkBox1;
    }
}

And:

namespace Test01
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }
    }
}

I get a windows with textbox("Text") and checkbox. When i focus on textbox and press Ctrl A checkbox toggle state, because TextBox.TextChanged raised and textBox1_TextChanged executed. But, i can`t understand why TextChanged event raised on Ctrl A ?

Answer 1

I met the same problem, use this code below:

private void textBox1_TextChanged(Object sender, EventArgs e) 
{
    if (textBox1.SelectedText == textBox1.Text && textBox1.Text != "")
        return;
}

Answer 2

You can suppress this behaviour by adding the condition below:

    void textBox1_TextChanged(object sender, System.EventArgs e) 
    {
        if (ModifierKeys == Keys.Control)
            return;

        //rest of the code
    }

Answer 3

Workaround for my problem:

void textBox1_TextChanged(object sender, System.EventArgs e)
{
    if (_oldText.Equals(this.textBox1.Text))
        return;
    _oldText = this.textBox1.Text;
    //rest of code
}

I can`t find better solution.