有没有一种方法只在C＃中设置一次属性？
有没有一种方法只在C＃中设置一次属性？
提问于 2018-04-19 04:59:05
我正在寻找一种方法来允许C＃对象中的属性只设置一次。编写代码很容易，但我宁愿使用标准机制（如果存在的话）。
public OneShot <int> SetOnceProperty {get; 组; }
我想要发生的是，如果属性尚未设置，可以设置该属性，但如果之前已设置属性，则会抛出异常。它应该像Nullable值那样工作，我可以检查它是否已设置。
回答 2
Stack Overflow用户
发布于 2018-04-19 13:07:57
public sealed class WriteOnce<T>
{
private T value;
private bool hasValue;
public override string ToString()
{
return hasValue ? Convert.ToString(value) : "";
}
public T Value
{
get
{
if (!hasValue) throw new InvalidOperationException("Value not set");
return value;
}
set
{
if (hasValue) throw new InvalidOperationException("Value already set");
this.value = value;
this.hasValue = true;
}
}
public T ValueOrDefault { get { return value; } }
public static implicit operator T(WriteOnce<T> value) { return value.Value; }
}
然后使用，例如：
readonly WriteOnce<string> name = new WriteOnce<string>();
public WriteOnce<string> Name { get { return name; } }
Stack Overflow用户
发布于 2018-04-19 14:40:18
public class SetOnce<T>
{
private bool set;
private T value;
public T Value
{
get { return value; }
set
{
if (set) throw new AlreadySetException(value);
set = true;
this.value = value;
}
}
public static implicit operator T(SetOnce<T> toConvert)
{
return toConvert.value;
}
}您可以这样使用它：
public class Foo
{
private readonly SetOnce<int> toBeSetOnce = new SetOnce<int>();
public int ToBeSetOnce
{
get { return toBeSetOnce; }
set { toBeSetOnce.Value = value; }
}
}下面是更稳定的实现
public class SetOnce<T>
{
private readonly object syncLock = new object();
private readonly bool throwIfNotSet;
private readonly string valueName;
private bool set;
private T value;
public SetOnce(string valueName)
{
this.valueName = valueName;
throwIfGet = true;
}
public SetOnce(string valueName, T defaultValue)
{
this.valueName = valueName;
value = defaultValue;
}
public T Value
{
get
{
lock (syncLock)
{
if (!set && throwIfNotSet) throw new ValueNotSetException(valueName);
return value;
}
}
set
{
lock (syncLock)
{
if (set) throw new AlreadySetException(valueName, value);
set = true;
this.value = value;
}
}
}
public static implicit operator T(SetOnce<T> toConvert)
{
return toConvert.value;
}
}
public class NamedValueException : InvalidOperationException
{
private readonly string valueName;
public NamedValueException(string valueName, string messageFormat)
: base(string.Format(messageFormat, valueName))
{
this.valueName = valueName;
}
public string ValueName
{
get { return valueName; }
}
}
public class AlreadySetException : NamedValueException
{
private const string MESSAGE = "The value \"{0}\" has already been set.";
public AlreadySetException(string valueName)
: base(valueName, MESSAGE)
{
}
}
public class ValueNotSetException : NamedValueException
{
private const string MESSAGE = "The value \"{0}\" has not yet been set.";
public ValueNotSetException(string valueName)
: base(valueName, MESSAGE)
{
}
}页面原文内容由Stack Overflow提供。腾讯云小微IT领域专用引擎提供翻译支持
原文链接：
https://stackoverflow.com/questions/-100008191
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