网站怎么建设后台百度问问

目录

一、定义

二、示例

三、生成

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        使用as关键字可以将对象转换为指定类型，与is关键字不同，is关键字用于检查对象是否与给定类型兼容，如果兼容则返回true，如果不兼容则返回false。而as关键字会直接进行类型转换，如果转换成功将会返回转换后的对象，如果转换不成功则不会抛出异常而是返回NULL。

一、定义

        as关键字用于引用类型之间执行转换。

        as关键字与is关键字一样都不会抛出异常，但是相比之下as关键字要更方便一些。

二、示例

        首先创建一个字符串对象，然后将字符串对象隐式转换为object类型的对象Temp_obj，使用as关键字将Temp_obj转换为字符串对象，最后检查字符串对象是否为空。如果为空，则转换不成功；如果不为空，则转换成功并执行后面的语句块。

// 使用as关键字将对象转换为指定类型
namespace _026
{public partial class Form1 : Form{private GroupBox? groupBox1;private RadioButton? radioButton3;private RadioButton? radioButton2;private RadioButton? radioButton1;private Label? label1;private Button? button1;public Form1(){InitializeComponent();Load += Form1_Load;}private void Form1_Load(object? sender, EventArgs e){// // label1// label1 = new Label{AutoSize = true,Location = new Point(29, 21),Name = "label1",Size = new Size(43, 17),TabIndex = 0,Text = "将FileStream对象转换为："};// // radioButton1// radioButton1 = new RadioButton{AutoSize = true,Location = new Point(180, 17),Name = "radioButton1",Size = new Size(102, 21),TabIndex = 1,TabStop = true,Text = "转换为object类型",UseVisualStyleBackColor = true};// // radioButton2// radioButton2 = new RadioButton{AutoSize = true,Location = new Point(180, 41),Name = "radioButton2",Size = new Size(102, 21),TabIndex = 2,TabStop = true,Text = "转换为Stream类型",UseVisualStyleBackColor = true};// // radioButton3// radioButton3 = new RadioButton{AutoSize = true,Location = new Point(180, 65),Name = "radioButton3",Size = new Size(102, 21),TabIndex = 3,TabStop = true,Text = "转换为String类型",UseVisualStyleBackColor = true};// // groupBox1// groupBox1 = new GroupBox{Location = new Point(0, 1),Name = "groupBox1",Size = new Size(354, 103),TabIndex = 0,TabStop = false,Text = "类型转换"};groupBox1.Controls.Add(radioButton3);groupBox1.Controls.Add(radioButton2);groupBox1.Controls.Add(radioButton1);groupBox1.Controls.Add(label1);groupBox1.SuspendLayout();// // button1// button1 = new Button{Location = new Point(137, 110),Name = "button1",Size = new Size(75, 23),TabIndex = 0,Text = "转换类型",UseVisualStyleBackColor = true};button1.Click += Button1_Click;// // Form1// AutoScaleDimensions = new SizeF(7F, 17F);AutoScaleMode = AutoScaleMode.Font;ClientSize = new Size(354, 141);Controls.Add(button1);Controls.Add(groupBox1);Name = "Form1";StartPosition = FormStartPosition.CenterScreen;Text = "as关键字转换类型";           groupBox1.ResumeLayout(false);groupBox1.PerformLayout();}private void Button1_Click(object? sender, EventArgs e){if (radioButton1!.Checked)                //选择转换为object类型{using FileStream Temp_filestream =    //创建文件流对象new(@"d:\log.txt", FileMode.Create);if (Temp_filestream != null)          //判断转换是否成功{MessageBox.Show("转换为Object成功！", "提示！");}else{MessageBox.Show("转换为Object失败！", "提示！");}}if (radioButton2!.Checked)               //选择转换为stream类型{using FileStream Temp_filestream =   //创建文件流对象new(@"d:\log.txt", FileMode.Create);object Temp_obj = Temp_filestream;if (Temp_obj as Stream != null)      //判断转换是否成功{MessageBox.Show("转换为Stream成功！", "提示！");}else{MessageBox.Show("转换为Stream失败！", "提示！");}}if (radioButton3!.Checked)                //选择转换为string类型{using FileStream Temp_filestream =    //创建文件流对象new(@"d:\log.txt", FileMode.Create);object Temp_obj = Temp_filestream;if (Temp_obj as string != null)       //判断转换是否成功{MessageBox.Show("转换为String成功！", "提示！");}else{MessageBox.Show("转换为String失败！", "提示！");}}}}
}

三、生成