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Shawn Oster · Guest

I'm pulling my hair out, anyone care to help prevent further hair loss?

I have what I *think* is a fairly solid data-aware framework. It allows
registering of heterogeneous data sources (not TDataSources) to a central
data broker (TMyDataBroker). My model requires data from all types of
sources, a database, from the model itself, from the environment, etc.
Every data-aware object has a link to a TDataField which knows how to get
the needed data, regardless of type. So far so good, works like a charm and
is fast.

Now the big hiccup. I need two different views of this data. I need the
live view (which basically pulls it's data from the database) and a sample
or design view. The first idea that comes to mind is to simply add a
property to the TMyDataBroker, something like UseSampleData: boolean. The
problem is that my data-aware objects are only linked to the TDataField,
which is contained in a TDataFieldList, which is owned by a TDataProvider,
which is contained in a TDataProviderList, which is finally owned by the
TMyDataBroker. The TDataField would have to follow an Owner chain 4 levels
up to find out if it should return real data or sample data.

Any thoughts on how to determine what the current state is inside my model
so I know what data to retrieve? I've asked a similar question like this
before about drawing routines and the suggestion was to have two different
views, so in this case a TLiveDataBroker and a TSampleDataBroker. That
worked wonderfully for drawing (thanks everyone) but that doesn't work in
this case because each object has a link to a TDataField. The model is
linked directly to the data.

My design below...

// base class for a single data field. I have a few descendant classes that
// work with concrete types, such as a DateTime, another that triggers
// an event when GetValue is called
TDataField = class
protected
procedure GetName(): string; virtual;
procedure GetValue(): string; virtual;
public
property Name: string read GetName();
property Value: string read GetValue();
end;

// type-safe TObjectList that holds TDataFields
TDataFieldList = class;

// holds a category of TDataFields. One of the categories is 'SystemInfo'
// with the fields being 'DefaultPrinter', 'MachineName'. Another is
'ModelInfo'
// with such fields as 'DocumentTitle', etc. Yet another is
'DatabaseProvider' which
// has a connection to a TDataSet. For each TField in the TDataSet there is
a mirrored
// TDataField in the provider.
TDataProvider = class;
public
DataFieldList: TDataFieldList;
end;

// type-safe TObjectList that holds TDataProviders
TDataProviderList = class;

// holds all the TDataProviders. Each TDataProvider is registered with the
broker with
// a category name. This way I can display all the categories (almost like
different tables)
// and their contained TDataFields for selection.
TDataBroker = class;
public
DataProviderList: TDataProviderList;
end;

// Holds a reference to a TDataField. Acts as a link between a data-bound
object
// and a TDataField, vary similar to a TFieldDataLink in DBCtrls. Also used
to pull
// just a subset of the TDataField's data. Some data-bound objects only
want the
// first character, or the last 3, etc.
TDataReference = class;
public
DataField: TDataField;
Length: integer;
StartPos: integer;
function GetValue(): string;
end;

// any data bound object
TSomeObject = class
public
DataReference: TDataReference;
end;

Thanks!

Shawn Oster

Eric Hill · Guest

Marc Rohloff · Guest

Shawn Oster wrote on Tue, 9 Dec 2003 14:44:45 -0700 ...
<3fd64249 (AT) newsgroups (DOT) borland.com>

Shawn Oster · Guest

"Marc Rohloff" <dont (AT) mailme (DOT) com> wrote

Marc Rohloff · Guest

Shawn Oster wrote on Fri, 12 Dec 2003 15:42:43 -0700 ...