C# winform 显示编辑ip地址，无需重绘textBox或者重写textBox方法，只需要在原生textBox控件对应事件中实现对应的算法即可。
1、textBox keyUp事件
private void textBoxKeyUp(object sender, KeyEventArgs e){if (e.KeyCode == Keys.Back)return;String text = textBoxIP.Text;string[] subs = text.Split('.');bool update = false;int index = 0;foreach (var sub in subs){Debug.WriteLine($"Substring: {sub}");if(sub != String.Empty){if (Convert.ToUInt16(sub) > 255){subs[index] = "255";update = true;}}else{update = true;}if((subs.Length == (index+1)) &&(sub.Length >= 3)){update = true;}index++;}if (update){textBoxIP.Text = "";index = 0;foreach (var sub in subs){if (sub == String.Empty)continue;if(index < 3){textBoxIP.Text += String.Format("{0}.", sub);}else if (index == 3){textBoxIP.Text += String.Format("{0}", sub);}if(index >= 4){update = true;}index++;}textBoxIP.SelectionStart = textBoxIP.Text.Length;//设置光标在末尾 }}
2、textBox click事件
private void textBoxClick(object sender, EventArgs e){String text = textBoxIP.Text;if (textBoxIP.SelectionStart >= text.Length)return;int offset_start = text.LastIndexOf('.', textBoxIP.SelectionStart, textBoxIP.SelectionStart);Debug.WriteLine("offset_start:{0}", offset_start);if (offset_start == -1){textBoxIP.SelectionStart = 0;}else{textBoxIP.SelectionStart = offset_start+1;}int offset_end = text.IndexOf('.',textBoxIP.SelectionStart, textBoxIP.Text.Length- textBoxIP.SelectionStart);Debug.WriteLine("offset_end:{0}", offset_end);if(offset_end == -1){textBoxIP.SelectionLength = textBoxIP.Text.Length - textBoxIP.SelectionStart;}else{textBoxIP.SelectionLength = offset_end - textBoxIP.SelectionStart;}}
3、实现功能
a)自动补充'.'b)限制大于255输入c)点击自动选择
