如何实现只有当某个textBox内有文字时才激活某个button?

Question

try to handle TextBox's TextChanged event

Answer 1

using System;
using System.Drawing;
using System.Collections;
using System.ComponentModel;
using System.Windows.Forms;
using System.Data;namespace CWinApp021218
{
/// <summary>
/// Summary description for Form1.
/// </summary>
public class Form1 : System.Windows.Forms.Form
{
private System.Windows.Forms.RichTextBox richTextBox1;
private System.Windows.Forms.Button button1;
/// <summary>
/// Required designer variable.
/// </summary>
private System.ComponentModel.Container components = null; public Form1()
{
//
// Required for Windows Form Designer support
//
InitializeComponent(); //
// TODO: Add any constructor code after InitializeComponent call
//
} /// <summary>
/// Clean up any resources being used.
/// </summary>
protected override void Dispose( bool disposing )
{
if( disposing )
{
if (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.richTextBox1 = new System.Windows.Forms.RichTextBox();
this.button1 = new System.Windows.Forms.Button();
this.SuspendLayout();
// 
// richTextBox1
// 
this.richTextBox1.Location = new System.Drawing.Point(48, 80);
this.richTextBox1.Name = "richTextBox1";
this.richTextBox1.Size = new System.Drawing.Size(192, 136);
this.richTextBox1.TabIndex = 0;
this.richTextBox1.Text = "richTextBox1";
this.richTextBox1.TextChanged += new System.EventHandler(this.richTextBox1_TextChanged);
// 
// button1
// 
this.button1.Location = new System.Drawing.Point(88, 24);
this.button1.Name = "button1";
this.button1.Size = new System.Drawing.Size(128, 32);
this.button1.TabIndex = 1;
this.button1.Text = "button1";
// 
// Form1
// 
this.AutoScaleBaseSize = new System.Drawing.Size(5, 13);
this.ClientSize = new System.Drawing.Size(292, 273);
this.Controls.AddRange(new System.Windows.Forms.Control[] {
  this.button1,
  this.richTextBox1});
this.Name = "Form1";
this.Text = "Form1";
this.ResumeLayout(false); }
#endregion /// <summary>
/// The main entry point for the application.
/// </summary>
[STAThread]
static void Main() 
{
Application.Run(new Form1());
} private void richTextBox1_TextChanged(object sender, System.EventArgs e)
{
if (richTextBox1.Text.Trim().Length>0) 
button1.Enabled=true;
else
button1.Enabled=false;
}
}
}

Answer 2

谢谢各位.
那如何实现只有当listBox里有项时才激活button1呢?