[英]Validating label content equal to null or string.Empty
我正在尝试检查标签的值是否等于null, " ", string.Empty
,但每次我运行我的编码时,都会收到以下错误:
你调用的对象是空的。
这是我的编码:
if (lblSupplierEmailAddress.Content.ToString() == "") //Error here
{
MessageBox.Show("A Supplier was selected with no Email Address. Please update the Supplier's Email Address", "Warning", MessageBoxButton.OK, MessageBoxImage.Warning);
return;
}
如何检查标签内的字符串值是否等于null? 我可能会遗漏一些简单的东西,如果是这样,请忽略我的无能:P
更改
if (lblSupplierEmailAddress.Content.ToString() == "")
至
if (String.IsNullOrEmpty((string) lblSupplierEmailAddress.Content)
当lblSupplierEmailAddress.Content
实际为null
您当然不能在其上调用ToString
,因为它会导致NullReferenceException
。 但是,静态IsNullOrEmpty
-method对此采取尊重,如果Content
为null
,则返回true
。
在C#6.0中这样做
if(lblSupplierEmailAddress?.Content?.ToString() == "")
否则,如果lblSupplierEmailAddress
始终存在,您可以简单地执行:
if(lblSupplierEmailAddress.Content?.ToString() == "")
等效代码是:
if(lblSupplierEmailAddress.Content != null)
if (lblSupplierEmailAddress.Content.ToString() == ""){
//do something
}
if( null != lblSupplierEmailAddress.Content
&& string.IsNullOrEmpty(lblSupplierEmailAddress.Content.ToString() )
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