asked on

Accessing properties by name

Hi,

I am trying to access properties by using a text string and am not sure how to go about it, or indeed if it is possible. The sort of thing I am trying to do is as follows:

procedure TForm1.Button1Click(Sender: TObject);
var
xx : TComponent;
yy : TProperty;
ss : string;

begin
xx := FindComponent('Edit1');//find the component
yy := (xx as xx.ClassType).FindProperty('Text');//type cast the component and find the Text property
yy := 'Test Data'; //write to property
ss := yy; //read from property
end;

I know this is rubbish but it illustrates the sort of thing I am trying to do.

Please illustrate any possible answers with code.

Thanks

Chris

edey

This usenet article could be helpful: http://groups.google.com/groups?q=delphi+rtti+property+find&hl=en&lr=&safe=off&rnum=5&ic=1&selm=VA.000028f4.010144fe%40petersnewbox

GL
Mike

DidierD

Hi,

Add TypInfo to the uses. Put an editbox and a button on the form and use the code below.

procedure TForm1.Button1Click(Sender: TObject);
var
xx: TComponent;
ss : string;
PropInfo: PPropInfo;
begin
xx := FindComponent('Edit1');
PropInfo := GetPropInfo(xx.ClassInfo,'Text');
if PropInfo <> nil then
begin
if PropInfo^.PropType^.Kind = tkLString then
begin
SetStrProp(xx, PropInfo, 'test');
ShowMessage(GetStrProp(xx, PropInfo));
end;
end;
end;

See in TypInfo unit for more information. For integer check for tkInteger, etc..

TTypeKind = (tkUnknown, tkInteger, tkChar, tkEnumeration, tkFloat,
tkString, tkSet, tkClass, tkMethod, tkWChar, tkLString, tkWString,
tkVariant, tkArray, tkRecord, tkInterface, tkInt64, tkDynArray);

In typeInfo you can also find the other getters and setters.

Didier

DidierD

The other getters and setters

function GetOrdProp(Instance: TObject; PropInfo: PPropInfo): Longint; overload;
procedure SetOrdProp(Instance: TObject; PropInfo: PPropInfo;
Value: Longint); overload;

function GetEnumProp(Instance: TObject; PropInfo: PPropInfo): string; overload;
procedure SetEnumProp(Instance: TObject; PropInfo: PPropInfo;
const Value: string); overload;

function GetSetProp(Instance: TObject; PropInfo: PPropInfo;
Brackets: Boolean = False): string; overload;
procedure SetSetProp(Instance: TObject; PropInfo: PPropInfo;
const Value: string); overload;

function GetObjectProp(Instance: TObject; PropInfo: PPropInfo;
MinClass: TClass = nil): TObject; overload;
procedure SetObjectProp(Instance: TObject; PropInfo: PPropInfo;
Value: TObject); overload;
function GetObjectPropClass(Instance: TObject; PropInfo: PPropInfo): TClass; overload;

function GetStrProp(Instance: TObject; PropInfo: PPropInfo): string; overload;
procedure SetStrProp(Instance: TObject; PropInfo: PPropInfo;
const Value: string); overload;

function GetFloatProp(Instance: TObject; PropInfo: PPropInfo): Extended; overload;
procedure SetFloatProp(Instance: TObject; PropInfo: PPropInfo;
Value: Extended); overload;

function GetVariantProp(Instance: TObject; PropInfo: PPropInfo): Variant; overload;
procedure SetVariantProp(Instance: TObject; PropInfo: PPropInfo;
const Value: Variant); overload;

function GetMethodProp(Instance: TObject; PropInfo: PPropInfo): TMethod; overload;
procedure SetMethodProp(Instance: TObject; PropInfo: PPropInfo;
const Value: TMethod); overload;

function GetInt64Prop(Instance: TObject; PropInfo: PPropInfo): Int64; overload;
procedure SetInt64Prop(Instance: TObject; PropInfo: PPropInfo;
const Value: Int64); overload;

DidierD

:-(

I just checked out edey's comment and his answer is exactly the same. So don't give me the points.

Didier

Epsylon

listening...

edey

There is an alternative method - for activeX controls. Use the MS scripting control, then all of your parsing, evaluating & property/method access is taken care of. For these very reasons I've wrapped most of the common controls (very easy in pro+ ver's of delphi).

GL
Mike

ChrisBerry

ASKER

Hi Mike and Didier,

Thanks for your answers, I will check it out.

Mike, could you please amplify your scripting comment. I have never used this.

Regards

Chris

DragonSlayer

listening to what Mike has to say :)

ChrisBerry

ASKER

I have tested and it works great for simple properties such as a string, integer etc. How do I deal with a property such as a Font or TStrings etc? I know the kind returned is tkClass but I don't know how to access the methods and properties of that class.

Thanks

Chris

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edey

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ChrisBerry

ASKER

Mike,

Thanks for your help.

Regards

Chris

edey

Glad to be of service :)

GL
Mike