Overview
I appreciate a couple of similar questions have already been asked before:
- Get/Set sub properties ussing RTTI
- Get a sub property of a component in Delphi using RTTI
- how i can set the value of a nested property using the RTTI
- How can I set/get property value through RTTI for compex things like TStringGrid.Cells?
However I am no further forward in understanding how exactly the RTTI can be used for my needs.
I have also put a lot of time and effort into writing this question so I hope it does not get closed :)
Working Examples
I have a few procedures below which can output to a TStrings list the property names, values and types of a component. The original source was not mine, I just made some minor changes to it, tidied up the code and put them into some neat reusable procedures:
The below will output the property names, such as:
- Color
- DoubleBuffered
- Enabled
- Height
- Width
procedure GetComponentPropertyNames(Component: TComponent; OutList: TStrings);
var
I: Integer;
Count, Size: Integer;
PropList: PPropList;
PropInfo: PPropInfo;
begin
OutList.BeginUpdate;
try
OutList.Clear;
Count := GetPropList(Component.ClassInfo, tkAny, nil);
Size := Count * SizeOf(Pointer);
GetMem(PropList, Size);
try
Count := GetPropList(Component.ClassInfo, tkAny, PropList);
for I := 0 to Count -1 do
begin
PropInfo := PropList^[I];
if not (PropInfo^.PropType^.Kind = tkMethod) then
begin
OutList.Add(PropInfo^.Name);
end;
end;
finally
FreeMem(PropList);
end;
finally
OutList.EndUpdate;
end;
end;
The below will output the property values, such as:
- clWindow
- False
- True
- 25
- 75
function GetComponentPropertyValue(Component: TComponent; APropName: string): string;
var
I: Integer;
Count, Size: Integer;
PropList: PPropList;
PropInfo: PPropInfo;
begin
Count := GetPropList(Component.ClassInfo, tkAny, nil);
Size := Count * SizeOf(Pointer);
GetMem(PropList, Size);
try
Count := GetPropList(Component.ClassInfo, tkAny, PropList);
for I := 0 to Count -1 do
begin
PropInfo := PropList^[I];
if not (PropInfo^.PropType^.Kind = tkMethod) then
begin
if SameText(PropInfo^.Name, APropName) then
begin
Result := System.Variants.VarToStr(GetPropValue(Component, PropInfo^.Name));
Exit;
end;
end;
end;
finally
FreeMem(PropList);
end;
end;
procedure GetComponentPropertyValues(Component: TComponent; OutList: TStrings);
var
SL: TStringList;
I: Integer;
begin
SL := TStringList.Create;
try
GetComponentPropertyNames(Component, SL);
for I := 0 to SL.Count -1 do
begin
OutList.Add(GetComponentPropertyValue(Component, SL.Strings[I]));
end;
finally
SL.Free;
end;
end;
And finally, The below will output the property types in string format, such as:
- TColor
- Boolean
- Boolean
- Integer
- Integer
function GetComponentPropertyType(Component: TComponent; APropName: string): string;
var
SL: TStringList;
I: Integer;
PropInfo: TPropInfo;
PropTypeName: string;
begin
SL := TStringList.Create;
try
GetComponentPropertyNames(Component, SL);
for I := 0 to SL.Count -1 do
begin
PropInfo := GetPropInfo(Component, SL.Strings[I])^;
if SameText(PropInfo.Name, APropName) then
begin
PropTypeName := PropInfo.PropType^.Name;
Result := PropTypeName;
Exit;
end;
end;
finally
SL.Free;
end;
end;
procedure GetComponentPropertyTypes(Component: TComponent; OutList: TStrings);
var
SL: TStringList;
I: Integer;
begin
SL := TStringList.Create;
try
GetComponentPropertyNames(Component, SL);
for I := 0 to SL.Count -1 do
begin
OutList.Add(GetComponentPropertyType(Component, SL.Strings[I]));
end;
finally
SL.Free;
end;
end;
Side by side the output for each procedure called above would show something like this:
- Color | clWindow | TColor
- DoubleBuffered | False | Boolean
- Enabled | True | Boolean
- Height | 25 | Integer
- Width | 75 | Integer
Question
All of the above at this point works, there is no issue other than I need to take some time reading the documentation a little more to try and get a bit of a better understanding and be able to digest it all.
My question (which has been bugging me for a few days now) is how to correctly get and set the sub properties. For example, take a look at this screenshot (modified for purpose) of the Delphi Object Inspector:
Just like the procedures shown before, I need the same thing to happen for those sub properties I highlighted in blue.
Ideally what I would like is a function where I can pass a component and a property name, and return True if it has sub properties, so something like:
function HasSubProperty(Component: TComponent; APropName: string): Boolean;
begin
Result := ??
end;
I am not sure how well this would work though as evident from the screenshot, some sub properties also have sub properties (such as Component>Font>Style).
Ultimately what I would like is a way of retrieving the names, values and types of sub properties. So something like:
procedure GetComponentSubPropertyNames(Component: TComponent; APropName: string;
OutList: TStrings);
begin
//
end;
When called:
GetComponentSubPropertyNames(Label1, Anchors);
Should retrieve:
- akLeft
- akTop
- akRight
- akBottom
With similar procedures to get the values and types would look like:
- akLeft | True | Boolean
- akTop | True | Boolean
- akRight | True | Boolean
- akBottom | True | Boolean
For the Font sub properties, for example:
- Charset | DEFAULT_CHARSET | TFontCharset
- Color | clWindowText | TColor
- Height | -11 | Integer
- Orientation | 0 | Integer
- Pitch | fpDefault | TFontPitch
- Quality | fqDefault | TFontQuality
- Size | 8 | Integer
Accessing another sub property (Font.Style) then poses yet another problem, unless a procedure like so is used:
procedure GetComponentSubPropertySubPropertyNames(Component: TComponent; APropName, ASubPropName: string; OutList: TStrings);
begin
//
end;
This then becomes rather silly.
Summary
Basically I need a way of digging into deeper level properties to get the names, values and types of them, put them in a list, and also be able to change the values.
I would appreciate it if someone could write some code samples of how I can achieve this (bonus with some comments in the code). I am sure for some this will be a relatively easy task but I am finding it very trivial indeed.
Having read various documentation and examples so far still leaves me rather clueless to be honest, the main concern is not knowing what types to use or how to correctly create and manage them.
