Reading custom attributes

[filipk69@gmail.com]

Could someone point me in the right direction, please.

I have an enum something like this:
enum TextFieldType
{
[Description("Fi eld ABC"), FieldLabel("abc field")] FieldABC = 3000,
[Description("Fi eld XYZ"), FieldLabel("xyz field")] FieldXYZ = 3001,
…..
…..
}
Where FieldLabel is a custom attribute.

I have a class TextEntry that contains properties: TextFieldType and Content.

I have a generic list of TextEntry objects that I'm looping through and outputting
info to the screen and what I would like to do is to display the text inside
the FieldLabel attribute and the value in "Content".

abc field: Here is the content of the ABC Type field...
xyz field: Here is the content of the XYZ Type field…
…
....

Getting the "Content" is not an issue, but how do I get the value from the
"FieldLabel ". I know I have to use reflection here but the only samples I
found show retrieving custom attribute from a class or a method. I tried
to tweek the 'method' example with no success.

Any help would be appreciated.
Thanks Filip

[Larry Lard]

Re: Reading custom attributes

filipk69@gmail. com wrote:

Could someone point me in the right direction, please.
I have an enum something like this: enum TextFieldType {
[Description("Fi eld ABC"), FieldLabel("abc field")] FieldABC = 3000,
[Description("Fi eld XYZ"), FieldLabel("xyz field")] FieldXYZ = 3001,
….. ….. } Where FieldLabel is a custom attribute.

So

[System.Attribut eUsage(System.A ttributeTargets .Field)]
public class FieldLabel : System.Attribut e
{
public string text;
public FieldLabel(stri ng text)
{
this.text = text;
}
}

public enum TextFieldType
{
[Description("Fi eld ABC"), FieldLabel("abc field")]
FieldABC = 3000,
[Description("Fi eld XYZ"), FieldLabel("xyz field")]
FieldXYZ = 3001
}

I have a class TextEntry that contains properties: TextFieldType and
Content.

public class TextEntry
{
public TextFieldType TextFieldType;
public string Content;

public TextEntry(TextF ieldType type, string content)
{
this.TextFieldT ype = type;
this.Content = content;
}
}

I have a generic list of TextEntry objects that I'm looping through and
outputting info to the screen

List<TextEntryl ist = new List<TextEntry> ();

list.Add(new TextEntry(TextF ieldType.FieldA BC, "foo"));
list.Add(new TextEntry(TextF ieldType.FieldX YZ, "bar"));

foreach (TextEntry t in list)

and what I would like to do is to display
the text inside the FieldLabel attribute and the value in "Content".
abc field: Here is the content of the ABC Type field... xyz field: Here
is the content of the XYZ Type field… … ....
Getting the "Content" is not an issue, but how do I get the value from
the "FieldLabel ". I know I have to use reflection here but the only
samples I found show retrieving custom attribute from a class or a
method. I tried to tweek the 'method' example with no success.

{
FieldInfo f = typeof
(TextFieldType) .GetField(t.Tex tFieldType.ToSt ring());
object[] customatts =
f.GetCustomAttr ibutes(typeof(F ieldLabel), false);
FieldLabel fl = (FieldLabel)cus tomatts[0];
Console.WriteLi ne("Descriptio n {0} Label {1} content
{2}", t.TextFieldType .ToString(), fl.text,
t.Content);
}

>
Any help would be appreciated. Thanks Filip

However - and this is a stylistic point, so your opinion may vary - this
is pretty horrible. If you have arbitrary data of type U (here string)
to associate one-to-one with data of type T (here TextFieldType), you
don't really need to mess about with attributes and reflection.
(Personally I have always interpreted the need for reflection as a
warning that something is 'not quite right' with the design). How about
this:

// better
private static Dictionary<Text FieldType, stringfieldlabe ls =
new Dictionary<Text FieldType, string>();
static Program()
{
fieldlabels.Add (TextFieldType. FieldABC, "label for abc");
fieldlabels.Add (TextFieldType. FieldXYZ, "label for xyz");
}

// then
private static void info(List<TextE ntrylist)
{
foreach (TextEntry t in list)
{
string label = fieldlabels[t.TextFieldType];
Console.WriteLi ne("Descriptio n {0} Label {1} content
{2}", t.TextFieldType .ToString(), label,
t.Content);
}

}


--
Larry Lard
larrylard@googl email.com
The address is real, but unread - please reply to the group
For VB and C# questions - tell us which version

[Laurent Bugnion [MVP]]

Re: Reading custom attributes

Hi,

Larry Lard wrote:

filipk69@gmail. com wrote:

>Could someone point me in the right direction, please.
>I have an enum something like this: enum TextFieldType {
>[Description("Fi eld ABC"), FieldLabel("abc field")] FieldABC = 3000,
>[Description("Fi eld XYZ"), FieldLabel("xyz field")] FieldXYZ = 3001,
>….. ….. } Where FieldLabel is a custom attribute.

>
So
>
[System.Attribut eUsage(System.A ttributeTargets .Field)]
public class FieldLabel : System.Attribut e

By convention, classes deriving from System.Attribut e should have the
"Attribute" suffix. This suffix can be omitted when you use the
attribute, so it makes its usage easier.

See

http://msdn2.microsoft.com/en-us/library/84c42s56.aspx

(scroll down until "Declaring the Attribute Class").

HTH,
Laurent
--
Laurent Bugnion [MVP ASP.NET]
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