C#将动态转换为字符串的最佳方法

Question

The following gets a field from a DataTable and converts it to string. Is there a cleaner way to convert dynamic to string?

dynamic value = dataTable.Rows[i].Field<dynamic>(columnName);
value = (value == null) ? null : value.ToString();

Answer 1

string value = Convert.ToString(dataTable.Rows[i][columnName]);

标准格式将启动，无需泛型、扩展方法或动态等内容。

Answer 2

First of all as Marc mentioned in his answer " the standard formatting will kick in, without the need for things like generics, extension methods or dynamic " , so in your case you don't have to use dynamic keyword , you can just convert directly to string, but talking about converting from dynamic to string I have two ways:

First way

string x = Convert.ToString(value) // value is a dynamic object

pros: this is a good way of conversion if you are not sure whether the compiled data type supports casting to string or it's hard coded as int for instance,

cons: this way can cause errors if your are trying to make Convert.ToString(value) // value is a dynamic object inside an Extension Method , when I do so it gives me this error : "Extension methods cannot be dynamically dispatched. Consider casting the dynamic arguments or calling the extension method without the extension method syntax" .

so if you are for example using Asp.Net Core HttpContext.Session.SetString() and you put Convert.ToString(value) // value is dynamic object as an inline conversion in the arguements it will give you the error in the cons secion, to resolve this you can assign a variable outside the function arguments to the Covert.ToString(value) result then send the variable to the extension function arguements :

dynamic value = 10;
HttpContext.Session.SetString("key",Convert.ToString(value));  <-- error

resolve:

dynamic value = 10;
string x = Convert.ToString(value);
HttpContext.Session.SetString("key",x);  // works fine

or use the second way (casting), make sure the compiled data type supports casting to string

HttpContext.Session.SetString("key",(string)value);

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Second Way
cast dynamic to string if the compiled data type supports it

string x = (string)value;  //value is dynamic object

pros: -it's useful if you want to make inline conversion inside an Extension method arguements -also useful if you want to make sure that the compiled data type supports casting to string and generate an exception based on this

cons: this doesn't work on all data types so if you want a more generic conversion method the first way is recommended

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as mentioned here in MS docs "The dynamic type enables the operations in which it occurs to bypass compile-time type checking . Instead, these operations are resolved at run time. "

So the dynamic variable's data type is compiled at run time and takes a type other than dynamic , and you can use casting if the interpreted object supports it or use Convert.ToString() for more generic type conversion.

PS: if you are converting to a data type other than string you may face data loss , like converting float to int , so be aware of that.

Answer 3

I have a case where the dynamic should be a string, but in an error case is a number (code I call into and can't change is doing that).

In my case I do:

string x = value as string;
if (x == null)
{
   // error condition
} else {
   //use x here
}

Answer 4

Convert.ToString doesn't work for me since my data are double[][] and result will be "System.Double[][]"

double[,] figure_geometry = new double[2, 2] { { 1.0, 1.0 }, { 2.0, 2.0 } };
string geometry = JsonSerializer.Serialize(figure_geometry);

Works well