C#成神之路<8> C#引用数据类型详述

1、字符串变量

属性：用于存储文本数据。（比如文本框对象中的Text属性实际上就是字符串变量，TryParse方法就是把字符串数据转换成数值数据类型。）

(1)定义字符串引用变量

VS编译器处理字符串变量的方法和之前的数值数据类型存储方式相同。唯一不同是，其rvalue的值如果程序中没有赋值，那么系统默认为“null”。

注：C#语言默认使用Unicode字符集。

(2)引用类型不同于值类型的原因

I.在必要时，引用变量可以与不同大小的数据关联。

II.固定字节数非常适合于值数据类型，但是并不适用于字符串数据。

(3)引用变量规则

I.引用变量的rvalue只能有两种值：null和内存地址。

II.如果引用变量的rvalue为null，引用变量就不包含有用的数据。

III.如果引用变量的rvalue不是null，他就包含存储与引用变量相关联的数据的地址。

和值类型不同，字符串数据中的rvalue不存放在程序中使用的实际数据的引用变量。因为引用的rvalue的值只能存放null和内存地址，所以引用变量的大小总是4字节，这意味着引用变量的bucket的大小总是相同。

(4)C#传值传引用的比较

按引用传递：

I.省时省力，节省内存。

II.使用引用变量的方法具有直接访问数据的权限

III.传递实际内存位置的方式。（直接访问原始数据）

IV.代价：数据有污染的可能性。

按值传递：

I.使用值类型方法接受用户的值是值的副本而不是值的本身。这种方法不能够永远的改变用户的值。

II.内存中有两个桶：原始桶和包含副本的桶。（保护了原始数据，更改的只是副值）

(5)提高效率

一行代码能够完成的任务，尽量用一行代码完成。代码量越少，只要完成相同任务，就可以提升程序速度。

同时也是为了减少输入量。

(6)使用字符串变量

字符串链接：+

简化赋值：+=（只有这种简化版的赋值运算符对字符串有用。）

(7)字符串操作

.Length : 返回字符串对象的length属性。

注：属性是与对象关联的变量，因此，他们不要求在对象后面有圆括号。

而方法后面必须有圆括号。

using System;
using System.Windows.Forms;
public class frmMain : Form
{
private Label label2;
private Label label3;
private Label label4;
private Label label5;
private Label label6;
private Label label7;
private Label label8;
private Label label9;
private Label label10;
private Label label11;
private Label label12;
private Button btnTest_Click;
private TextBox txtInput;
private TextBox txtLength;
private TextBox txtToUpper;
private TextBox txtToLower;
private TextBox txtSearchChar;
private TextBox txtSearchIndex;
private TextBox txtLastChar;
private TextBox txtLastIndexOf;
private TextBox txtStartIndex;
private TextBox txtEndIndex;
private Label lblSubstring;
private TextBox txtSubstringResault;
private TextBox txtRemove;
private TextBox txtRemoveResault;
private TextBox txtReplaceChars;
private TextBox txtReplaceWith;
private TextBox txtReplaceResault;
private Button btnExit;
private Label lblIndexOf;
private Label lblLastIndexOf;
private Label label1;
#region Windows code
private void InitializeComponent()
{
this.label1 = new System.Windows.Forms.Label();
this.label2 = new System.Windows.Forms.Label();
this.label3 = new System.Windows.Forms.Label();
this.label4 = new System.Windows.Forms.Label();
this.label5 = new System.Windows.Forms.Label();
this.label6 = new System.Windows.Forms.Label();
this.label7 = new System.Windows.Forms.Label();
this.label8 = new System.Windows.Forms.Label();
this.label9 = new System.Windows.Forms.Label();
this.label10 = new System.Windows.Forms.Label();
this.label11 = new System.Windows.Forms.Label();
this.label12 = new System.Windows.Forms.Label();
this.btnTest_Click = new System.Windows.Forms.Button();
this.txtInput = new System.Windows.Forms.TextBox();
this.txtLength = new System.Windows.Forms.TextBox();
this.txtToUpper = new System.Windows.Forms.TextBox();
this.txtToLower = new System.Windows.Forms.TextBox();
this.txtSearchChar = new System.Windows.Forms.TextBox();
this.txtSearchIndex = new System.Windows.Forms.TextBox();
this.txtLastChar = new System.Windows.Forms.TextBox();
this.txtLastIndexOf = new System.Windows.Forms.TextBox();
this.txtStartIndex = new System.Windows.Forms.TextBox();
this.txtEndIndex = new System.Windows.Forms.TextBox();
this.lblSubstring = new System.Windows.Forms.Label();
this.txtSubstringResault = new System.Windows.Forms.TextBox();
this.txtRemove = new System.Windows.Forms.TextBox();
this.txtRemoveResault = new System.Windows.Forms.TextBox();
this.txtReplaceChars = new System.Windows.Forms.TextBox();
this.txtReplaceWith = new System.Windows.Forms.TextBox();
this.txtReplaceResault = new System.Windows.Forms.TextBox();
this.btnExit = new System.Windows.Forms.Button();
this.lblIndexOf = new System.Windows.Forms.Label();
this.lblLastIndexOf = new System.Windows.Forms.Label();
this.SuspendLayout();
//
// label1
//
this.label1.BorderStyle = System.Windows.Forms.BorderStyle.Fixed3D;
this.label1.Location = new System.Drawing.Point(52, 42);
this.label1.Name = "label1";
this.label1.Size = new System.Drawing.Size(211, 23);
this.label1.TabIndex = 0;
this.label1.Text = "String To Test";
this.label1.TextAlign = System.Drawing.ContentAlignment.TopRight;
this.label1.Click += new System.EventHandler(this.label1_Click);
//
// label2
//
this.label2.BorderStyle = System.Windows.Forms.BorderStyle.Fixed3D;
this.label2.Location = new System.Drawing.Point(52, 82);
this.label2.Name = "label2";
this.label2.Size = new System.Drawing.Size(211, 23);
this.label2.TabIndex = 1;
this.label2.Text = "String Length";
this.label2.TextAlign = System.Drawing.ContentAlignment.TopRight;
this.label2.Click += new System.EventHandler(this.label2_Click);
//
// label3
//
this.label3.BorderStyle = System.Windows.Forms.BorderStyle.Fixed3D;
this.label3.Location = new System.Drawing.Point(52, 117);
this.label3.Name = "label3";
this.label3.Size = new System.Drawing.Size(211, 23);
this.label3.TabIndex = 2;
this.label3.Text = "String ToUpper";
this.label3.TextAlign = System.Drawing.ContentAlignment.TopRight;
//
// label4
//
this.label4.BorderStyle = System.Windows.Forms.BorderStyle.Fixed3D;
this.label4.Location = new System.Drawing.Point(52, 160);
this.label4.Name = "label4";
this.label4.Size = new System.Drawing.Size(211, 23);
this.label4.TabIndex = 3;
this.label4.Text = "String To Lower";
this.label4.TextAlign = System.Drawing.ContentAlignment.TopRight;
//
// label5
//
this.label5.BorderStyle = System.Windows.Forms.BorderStyle.Fixed3D;
this.label5.Location = new System.Drawing.Point(52, 202);
this.label5.Name = "label5";
this.label5.Size = new System.Drawing.Size(211, 23);
this.label5.TabIndex = 4;
this.label5.Text = "Search for character";
this.label5.TextAlign = System.Drawing.ContentAlignment.TopRight;
//
// label6
//
this.label6.BorderStyle = System.Windows.Forms.BorderStyle.Fixed3D;
this.label6.Location = new System.Drawing.Point(52, 247);
this.label6.Name = "
1a410
label6";
this.label6.Size = new System.Drawing.Size(211, 23);
this.label6.TabIndex = 5;
this.label6.Text = "Search for last character";
this.label6.TextAlign = System.Drawing.ContentAlignment.TopRight;
this.label6.Click += new System.EventHandler(this.label6_Click);
//
// label7
//
this.label7.BorderStyle = System.Windows.Forms.BorderStyle.Fixed3D;
this.label7.Location = new System.Drawing.Point(52, 289);
this.label7.Name = "label7";
this.label7.Size = new System.Drawing.Size(211, 23);
this.label7.TabIndex = 6;
this.label7.Text = "Extract Substring from index";
this.label7.TextAlign = System.Drawing.ContentAlignment.TopRight;
//
// label8
//
this.label8.BorderStyle = System.Windows.Forms.BorderStyle.Fixed3D;
this.label8.Location = new System.Drawing.Point(394, 289);
this.label8.Name = "label8";
this.label8.Size = new System.Drawing.Size(150, 23);
this.label8.TabIndex = 7;
this.label8.Text = "for thi many characters";
this.label8.TextAlign = System.Drawing.ContentAlignment.TopRight;
//
// label9
//
this.label9.BorderStyle = System.Windows.Forms.BorderStyle.Fixed3D;
this.label9.Location = new System.Drawing.Point(52, 330);
this.label9.Name = "label9";
this.label9.Size = new System.Drawing.Size(211, 23);
this.label9.TabIndex = 8;
this.label9.Text = "txtInput.Remove()";
this.label9.TextAlign = System.Drawing.ContentAlignment.TopRight;
//
// label10
//
this.label10.BorderStyle = System.Windows.Forms.BorderStyle.Fixed3D;
this.label10.Location = new System.Drawing.Point(52, 370);
this.label10.Name = "label10";
this.label10.Size = new System.Drawing.Size(211, 23);
this.label10.TabIndex = 9;
this.label10.Text = "Find";
this.label10.TextAlign = System.Drawing.ContentAlignment.TopRight;
//
// label11
//
this.label11.BorderStyle = System.Windows.Forms.BorderStyle.Fixed3D;
this.label11.Location = new System.Drawing.Point(460, 370);
this.label11.Name = "label11";
this.label11.Size = new System.Drawing.Size(103, 23);
this.label11.TabIndex = 10;
this.label11.Text = "Replace with";
this.label11.TextAlign = System.Drawing.ContentAlignment.TopRight;
//
// label12
//
this.label12.BorderStyle = System.Windows.Forms.BorderStyle.Fixed3D;
this.label12.Location = new System.Drawing.Point(52, 407);
this.label12.Name = "label12";
this.label12.Size = new System.Drawing.Size(211, 23);
this.label12.TabIndex = 11;
this.label12.Text = "txtInput.Replace()";
this.label12.TextAlign = System.Drawing.ContentAlignment.TopRight;
//
// btnTest_Click
//
this.btnTest_Click.Location = new System.Drawing.Point(52, 455);
this.btnTest_Click.Name = "btnTest_Click";
this.btnTest_Click.Size = new System.Drawing.Size(105, 23);
this.btnTest_Click.TabIndex = 12;
this.btnTest_Click.Text = "&Test";
this.btnTest_Click.UseVisualStyleBackColor = true;
this.btnTest_Click.Click += new System.EventHandler(this.btnTest_Click_Click);
//
// txtInput
//
this.txtInput.Location = new System.Drawing.Point(278, 44);
this.txtInput.Name = "txtInput";
this.txtInput.Size = new System.Drawing.Size(734, 21);
this.txtInput.TabIndex = 13;
//
// txtLength
//
this.txtLength.BackColor = System.Drawing.SystemColors.ButtonHighlight;
this.txtLength.Location = new System.Drawing.Point(278, 83);
this.txtLength.Multiline = true;
this.txtLength.Name = "txtLength";
this.txtLength.ReadOnly = true;
this.txtLength.Size = new System.Drawing.Size(266, 21);
this.txtLength.TabIndex = 14;
//
// txtToUpper
//
this.txtToUpper.BackColor = System.Drawing.SystemColors.ButtonHighlight;
this.txtToUpper.Location = new System.Drawing.Point(278, 118);
this.txtToUpper.Multiline = true;
this.txtToUpper.Name = "txtToUpper";
this.txtToUpper.ReadOnly = true;
this.txtToUpper.Size = new System.Drawing.Size(734, 21);
this.txtToUpper.TabIndex = 15;
//
// txtToLower
//
this.txtToLower.BackColor = System.Drawing.SystemColors.ButtonHighlight;
this.txtToLower.Location = new System.Drawing.Point(278, 160);
this.txtToLower.Multiline = true;
this.txtToLower.Name = "txtToLower";
this.txtToLower.ReadOnly = true;
this.txtToLower.Size = new System.Drawing.Size(734, 21);
this.txtToLower.TabIndex = 16;
//
// txtSearchChar
//
this.txtSearchChar.BackColor = System.Drawing.SystemColors.ButtonHighlight;
this.txtSearchChar.Location = new System.Drawing.Point(278, 202);
this.txtSearchChar.Name = "txtSearchChar";
this.txtSearchChar.Size = new System.Drawing.Size(101, 21);
this.txtSearchChar.TabIndex = 17;
//
// txtSearchIndex
//
this.txtSearchIndex.BackColor = System.Drawing.SystemColors.ButtonHighlight;
this.txtSearchIndex.Location = new System.Drawing.Point(879, 200);
this.txtSearchIndex.Multiline = true;
this.txtSearchIndex.Name = "txtSearchIndex";
this.txtSearchIndex.ReadOnly = true;
this.txtSearchIndex.Size = new System.Drawing.Size(133, 21);
this.txtSearchIndex.TabIndex = 18;
//
// txtLastChar
//
this.txtLastChar.Location = new System.Drawing.Point(278, 247);
this.txtLastChar.Name = "txtLastChar";
this.txtLastChar.Size = new System.Drawing.Size(101, 21);
this.txtLastChar.TabIndex = 19;
//
// txtLastIndexOf
//
this.txtLastIndexOf.BackColor = System.Drawing.SystemColors.ButtonHighlight;
this.txtLastIndexOf.Location = new System.Drawing.Point(879, 245);
this.txtLastIndexOf.Multiline = true;
this.txtLastIndexOf.Name = "txtLastIndexOf";
this.txtLastIndexOf.ReadOnly = true;
this.txtLastIndexOf.Size = new System.Drawing.Size(133, 21);
this.txtLastIndexOf.TabIndex = 20;
//
// txtStartIndex
//
this.txtStartIndex.Location = new System.Drawing.Point(278, 290);
this.txtStartIndex.Name = "txtStartIndex";
this.txtStartIndex.Size = new System.Drawing.Size(100, 21);
this.txtStartIndex.TabIndex = 21;
//
// txtEndIndex
//
this.txtEndIndex.Location = new System.Drawing.Point(551, 290);
this.txtEndIndex.Name = "txtEndIndex";
this.txtEndIndex.Size = new System.Drawing.Size(94, 21);
this.txtEndIndex.TabIndex = 22;
//
// lblSubstring
//
this.lblSubstring.BorderStyle = System.Windows.Forms.BorderStyle.Fixed3D;
this.lblSubstring.Location = new System.Drawing.Point(651, 289);
this.lblSubstring.Name = "lblSubstring";
this.lblSubstring.Size = new System.Drawing.Size(222, 23);
this.lblSubstring.TabIndex = 23;
this.lblSubstring.Text = "txtInput.Test.Substring()";
this.lblSubstring.TextAlign = System.Drawing.ContentAlignment.TopRight;
//
// txtSubstringResault
//
this.txtSubstringResault.BackColor = System.Drawing.SystemColors.ButtonHighlight;
this.txtSubstringResault.Location = new System.Drawing.Point(879, 289);
this.txtSubstringResault.Multiline = true;
this.txtSubstringResault.Name = "txtSubstringResault";
this.txtSubstringResault.ReadOnly = true;
this.txtSubstringResault.Size = new System.Drawing.Size(133, 21);
this.txtSubstringResault.TabIndex = 24;
//
// txtRemove
//
this.txtRemove.Location = new System.Drawing.Point(278, 331);
this.txtRemove.Name = "txtRemove";
this.txtRemove.Size = new System.Drawing.Size(100, 21);
this.txtRemove.TabIndex = 25;
//
// txtRemoveResault
//
this.txtRemoveResault.BackColor = System.Drawing.SystemColors.ButtonHighlight;
this.txtRemoveResault.Location = new System.Drawing.Point(394, 331);
this.txtRemoveResault.Multiline = true;
this.txtRemoveResault.Name = "txtRemoveResault";
this.txtRemoveResault.ReadOnly = true;
this.txtRemoveResault.Size = new System.Drawing.Size(618, 21);
this.txtRemoveResault.TabIndex = 26;
//
// txtReplaceChars
//
this.txtReplaceChars.Location = new System.Drawing.Point(278, 370);
this.txtReplaceChars.Name = "txtReplaceChars";
this.txtReplaceChars.Size = new System.Drawing.Size(176, 21);
this.txtReplaceChars.TabIndex = 27;
//
// txtReplaceWith
//
this.txtReplaceWith.Location = new System.Drawing.Point(570, 369);
this.txtReplaceWith.Name = "txtReplaceWith";
this.txtReplaceWith.Size = new System.Drawing.Size(442, 21);
this.txtReplaceWith.TabIndex = 28;
//
// txtReplaceResault
//
this.txtReplaceResault.BackColor = System.Drawing.SystemColors.ButtonHighlight;
this.txtReplaceResault.Location = new System.Drawing.Point(278, 407);
this.txtReplaceResault.Multiline = true;
this.txtReplaceResault.Name = "txtReplaceResault";
this.txtReplaceResault.ReadOnly = true;
this.txtReplaceResault.Size = new System.Drawing.Size(734, 21);
this.txtReplaceResault.TabIndex = 29;
//
// btnExit
//
this.btnExit.Location = new System.Drawing.Point(920, 455);
this.btnExit.Name = "btnExit";
this.btnExit.Size = new System.Drawing.Size(92, 23);
this.btnExit.TabIndex = 30;
this.btnExit.Text = "&Exit";
this.btnExit.UseVisualStyleBackColor = true;
this.btnExit.Click += new System.EventHandler(this.btnExit_Click);
//
// lblIndexOf
//
this.lblIndexOf.BorderStyle = System.Windows.Forms.BorderStyle.Fixed3D;
this.lblIndexOf.Location = new System.Drawing.Point(394, 202);
this.lblIndexOf.Name = "lblIndexOf";
this.lblIndexOf.Size = new System.Drawing.Size(470, 23);
this.lblIndexOf.TabIndex = 31;
//
// lblLastIndexOf
//
this.lblLastIndexOf.BorderStyle = System.Windows.Forms.BorderStyle.Fixed3D;
this.lblLastIndexOf.Location = new System.Drawing.Point(394, 247);
this.lblLastIndexOf.Name = "lblLastIndexOf";
this.lblLastIndexOf.Size = new System.Drawing.Size(470, 23);
this.lblLastIndexOf.TabIndex = 32;
this.lblLastIndexOf.Text = " ";
//
// frmMain
//
this.ClientSize = new System.Drawing.Size(1034, 525);
this.Controls.Add(this.lblLastIndexOf);
this.Controls.Add(this.lblIndexOf);
this.Controls.Add(this.btnExit);
this.Controls.Add(this.txtReplaceResault);
this.Controls.Add(this.txtReplaceWith);
this.Controls.Add(this.txtReplaceChars);
this.Controls.Add(this.txtRemoveResault);
this.Controls.Add(this.txtRemove);
this.Controls.Add(this.txtSubstringResault);
this.Controls.Add(this.lblSubstring);
this.Controls.Add(this.txtEndIndex);
this.Controls.Add(this.txtStartIndex);
this.Controls.Add(this.txtLastIndexOf);
this.Controls.Add(this.txtLastChar);
this.Controls.Add(this.txtSearchIndex);
this.Controls.Add(this.txtSearchChar);
this.Controls.Add(this.txtToLower);
this.Controls.Add(this.txtToUpper);
this.Controls.Add(this.txtLength);
this.Controls.Add(this.txtInput);
this.Controls.Add(this.btnTest_Click);
this.Controls.Add(this.label12);
this.Controls.Add(this.label11);
this.Controls.Add(this.label10);
this.Controls.Add(this.label9);
this.Controls.Add(this.label8);
this.Controls.Add(this.label7);
this.Controls.Add(this.label6);
this.Controls.Add(this.label5);
this.Controls.Add(this.label4);
this.Controls.Add(this.label3);
this.Controls.Add(this.label2);
this.Controls.Add(this.label1);
this.Name = "frmMain";
this.Text = "String Test";
this.Load += new System.EventHandler(this.frmMain_Load);
this.ResumeLayout(false);
this.PerformLayout();

}
#endregion
//#region是C# 预处理器指令。
//#region 使您可以在使用 Visual Studio
//代码编辑器的大纲显示功能时指定可展开或折叠的代码块。
public frmMain()
{
InitializeComponent();
}

public static void Main()
{
frmMain main = new frmMain();
Application.Run(main);
}

private void label1_Click(object sender, EventArgs e)
{

}

private void label2_Click(object sender, EventArgs e)
{

}

private void label6_Click(object sender, EventArgs e)
{

}

private void btnTest_Click_Click(object sender, EventArgs e)
{
bool flag;
int index;
int start;
int howmany;
string temp;

//find length
txtLength.Text = txtInput.Text.Length.ToString();

//change cases
txtToUpper.Text = txtInput.Text.ToUpper();
txtToLower.Text = txtInput.Text.ToLower();

//index of
index = txtInput.Text.IndexOf(txtSearchChar.Text, 0);
lblIndexOf.Text = "txtInput.Text.IndexOf(\"" + txtSearchChar.Text + "\",0)= ";
txtSearchIndex.Text=index.ToString();

//last index of:
index = txtInput.Text.LastIndexOf(txtLastChar.Text);
lblLastIndexOf.Text = "txtInput.Text.LastIndexOf(\"" + txtLastChar.Text + "\")= ";
txtLastIndexOf.Text = index.ToString();

//Substring
flag = int.TryParse(txtStartIndex.Text, out start);
if (flag == false)
{
MessageBox.Show("Inporter numric input. Re-enter");
txtStartIndex.Focus();
return;
}
flag = int.TryParse(txtEndIndex.Text, out howmany);
if (flag == false)
{
MessageBox.Show("Inporter numric input. Re-enter");
txtEndIndex.Focus();
return;
}
lblSubstring.Text="txtInput.Text.Substring("+start.ToString()+","+howmany.ToString() +")=";
txtSubstringResault.Text = txtInput.Text.Substring(start,howmany);

//Remove
temp = txtInput.Text;
index = temp.IndexOf(txtRemove.Text);
if (index > 0) {
txtRemoveResault.Text = temp.Remove(index,txtRemoveResault.Text.Length);
}

//replace
temp = txtInput.Text;
txtReplaceResault.Text = temp.Replace(txtReplaceChars.Text,
txtReplaceWith.Text);
}

private void frmMain_Load(object sender, EventArgs e)
{

}

private void btnExit_Click(object sender, EventArgs e)
{
Close();

}
}

以上是对字符串的诸多应用，下面对出现的诸多方法进行详述：

（1）数据包装器

在非OOP语言中，值类型和引用类型不能很好的融合在一起。另一方面C#从开始就被设计成面向对象编程语言。C#提供了风装置类型的包装器类。值包装器认为有一个属性（它的值）以及六个方法。

（2）修改字符串的大小写

ToUpper 和ToLower。

（3）查找特定的字符

IndexOf()

假设需要在一个字符串中查找特定的字符。（计算字符串数量的时候把第一个位置称为位置0）

index = txtInput.Text.IndexOf(txtSearchChar.Text, 0);
lblIndexOf.Text = "txtInput.Text.IndexOf(\"" + txtSearchChar.Text + "\",0)= ";
txtSearchIndex.Text=index.ToString();

indexof的两个参数值为：希望查找的字符串（txtsearchchar.text）和希望从哪个索引位置开始索引。

如果找不到与传递给他的字符序列完全匹配的字符，则他会返回-1。

LastIndexOf()搜索字符串的特定字符的最后一次出现的位置。

只有一个参数，就是他要搜索的字符。如果没有找到匹配字符，则返回 -1。

（4）搜索子字符串

txtSubstringResault.Text = txtInput.Text.Substring(start,howmany);

以上的代码，从字符串中的第start+1个字符开始搜索子字符串，并复制howmany个字符。

（5）删除子字符串

temp = txtInput.Text;
index = temp.IndexOf(txtRemove.Text);
if (index > 0) {
txtRemoveResault.Text = temp.Remove(index,txtRemoveResault.Text.Length);
}

Remove的参数：第一个是字符串中目标子字符串的位置，利用length属性得到要删除字符的个数。使程序更加灵活。

（6）删除子字符串

temp = txtInput.Text;
txtReplaceResault.Text = temp.Replace(txtReplaceChars.Text,
txtReplaceWith.Text);

第一行的复制输入字符串，从而不会永久地修改txtinput文本框中的text属性。

Rplace的两个参数：第一个参数是希望替换的字符串，第二个参数是希望取代第一个参数的字符串。如果 原始字符串中不存在目标字符串，那么就不会修改原始字符串。

这里写代码片