目录
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。
cs
// 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
