.net 如何在c#中使用构造函数返回一个值？
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How to return a value using constructor in c#?
提问by Sanmuga Nathan
I follow a convention that I won't use any print statements in classes, but I have done a parameter validation in a constructor. Please tell me how to return that validation which I've done in the constructor to the Main function.
我遵循一个约定，即我不会在类中使用任何打印语句，但我已经在构造函数中进行了参数验证。请告诉我如何将我在构造函数中完成的验证返回给 Main 函数。
回答by Oded
The constructor does return a value - the type being constructed...
构造函数确实返回一个值 - 正在构造的类型......
A constructor is not supposed to return any other type of value.
构造函数不应返回任何其他类型的值。
When you validate in a constructor, you should throw exceptionsif the passed in values are invalid.
当您在构造函数中进行验证时，如果传入的值无效，您应该抛出异常。
public class MyType
{
public MyType(int toValidate)
{
if (toValidate < 0)
{
throw new ArgumentException("toValidate should be positive!");
}
}
}
回答by Adil
Constructors do not have a return type, but you can pass values by reference using the refkeyword. It would be better to throw an exception from the constructor to indicate a validation failure.
构造函数没有返回类型，但您可以使用ref关键字通过引用传递值。最好从构造函数抛出异常以指示验证失败。
public class YourClass
{
public YourClass(ref string msg)
{
msg = "your message";
}
}
public void CallingMethod()
{
string msg = string.Empty;
YourClass c = new YourClass(ref msg);
}
回答by nVn
Make a Constructor with Out parameter and send your return value via same.
使用 Out 参数创建一个构造函数并通过它发送您的返回值。
public class ClassA
{
public ClassA(out bool success)
{
success = true;
}
}
回答by Pawel Czapski
I think my approach might be useful also. Need to add public property to constructor, then you can access this property form other class, as in below example.
我认为我的方法也可能有用。需要向构造函数添加公共属性，然后您可以从其他类访问该属性，如下例所示。
// constructor
public class DoSomeStuffForm : Form
{
private int _value;
public DoSomeStuffForm
{
InitializeComponent();
// do some calculations
int calcResult = 60;
_value = calcResult;
}
// add public property
public int ValueToReturn
{
get
{
return _value;
}
}
}
// call constructor from other class
public statc void ShowDoSomeStuffForm()
{
int resultFromConstructor;
DoSomeStuffForm newForm = new DoSomeStuffForm()
newForm.StartPosition = System.Windows.Forms.FormStartPosition.CenterScreen;
newForm.ShowDialog();
// now you can access value from constructor
resultFromConstructor = newForm.ValueToReturn;
newForm.Dispose();
}
回答by Adi Lester
When a constructor receives an invalid argument, it's common to throw an exception. You can then catch this exception and parse the data it contains.
当构造函数接收到无效参数时，通常会抛出异常。然后，您可以捕获此异常并解析它包含的数据。
try
{
int input = -1;
var myClass = new MyClass(input);
}
catch (ArgumentException ex)
{
// Validation failed.
}
回答by Jon B
A constructor returns the type being instantiated, and, if necessary, can throw an exception. Perhaps a better solution would be to add a static method to trycreating an instance of your class:
构造函数返回被实例化的类型，并在必要时抛出异常。也许更好的解决方案是添加一个静态方法来尝试创建类的实例：
public static bool TryCreatingMyClass(out MyClass result, out string message)
{
// Set the value of result and message, return true if success, false if failure
}
