c# – TextBox最大字符数(不是MaxLength)

>当然.在派生类中覆盖/隐藏AppendText和Text.见下面的代码.
> Text属性的支持字段是一个普通的旧字符串(私有字段System.Windows.Forms.Control :: text).因此,最大长度是字符串的最大长度,即“2 GB,或大约10亿个字符”(参见 System.String).
>你为什么不尝试看看？
>这取决于您的性能要求.您可以使用Lines属性,但请注意,每次调用它时,您的整个文本都将在内部解析为行.如果你推动内容长度的限制,这将是一个坏主意.因此,更快的方式(在执行方面,而不是编码)将压缩字符并计算cr / lfs.你当然需要决定你在考虑一条线的结尾.

代码：即使在以编程方式设置文本时也强制执行MaxLength属性：

using System;
using System.Windows.Forms;
namespace WindowsFormsApplication5 {
    class TextBoxExt : TextBox {
        new public void AppendText(string text) {
            if (this.Text.Length == this.MaxLength) {
                return;
            } else if (this.Text.Length + text.Length > this.MaxLength) {
                base.AppendText(text.Substring(0,(this.MaxLength - this.Text.Length)));
            } else {
                base.AppendText(text);
            }
        }

        public override string Text {
            get {
                return base.Text;
            }
            set {
                if (!string.IsNullOrEmpty(value) && value.Length > this.MaxLength) {
                    base.Text = value.Substring(0,this.MaxLength);
                } else {
                    base.Text = value;
                }
            }
        }

        // Also: Clearing top X lines with high performance
        public void ClearTopLines(int count) {
            if (count <= 0) {
                return;
            } else if (!this.Multiline) {
                this.Clear();
                return;
            }

            string txt = this.Text;
            int cursor = 0,ixOf = 0,brkLength = 0,brkCount = 0;

            while (brkCount < count) {
                ixOf = txt.IndexOfBreak(cursor,out brkLength);
                if (ixOf < 0) {
                    this.Clear();
                    return;
                }
                cursor = ixOf + brkLength;
                brkCount++;
            }
            this.Text = txt.Substring(cursor);
        }
    }

    public static class StringExt {
        public static int IndexOfBreak(this string str,out int length) {
            return IndexOfBreak(str,out length);
        }

        public static int IndexOfBreak(this string str,int startIndex,out int length) {
            if (string.IsNullOrEmpty(str)) {
                length = 0;
                return -1; 
            }
            int ub = str.Length - 1;
            int intchr;
            if (startIndex > ub) {
                throw new ArgumentOutOfRangeException();
            }
            for (int i = startIndex; i <= ub; i++) {
                intchr = str[i];
                if (intchr == 0x0D) {
                    if (i < ub && str[i + 1] == 0x0A) {
                        length = 2;
                    } else {
                        length = 1;
                    }
                    return i;
                } else if (intchr == 0x0A) {
                    length = 1;
                    return i;
                }
            }
            length = 0;
            return -1;
        }
    }
}