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