I'm trying to create my own class object and use it to store various data types for my application, this all works fine when using Published Properties, I can stream these to disk and back with no problems. But I need to stream some Arrays of both integer and strings data types as well.
I understand that Arrays, amongst other data types can't be published properties because Delphi doesn't know how to stream them, I was led to believe you need to use DefineProperties to accomplish this, I've created a test Array of String as a Public property, I can read and write to it just fine, however I need to stream it to disk so i can save it for future use.
The only thing i can find that touches on this subject is here:
Array of a custom class as a property
I've attempted to copy this code and manipulate it to archive what I need but I cannot get it to save, I'm seemingly missing something obvious, my test code I'm using is below, I get no errors with this code, published properties stream to disk ok but my private array does not. Any help would be greatly appreciated.
Thanks.
unit UnitDataSet;
//------------------------------------------------------------------------------
interface
uses System.Classes;
{$M+}
//------------------------------------------------------------------------------
type
TDataStrings = Array [1..50] of String;
TDataSet = class(TComponent)
protected
procedure DefineProperties(Filer: TFiler); override;
procedure ReadArray(Reader: TReader);
procedure WriteArray(Writer: TWriter);
private
FArrayToSave : TDataStrings;
FPStr : String;
function GetItem(I: Integer): String;
procedure SetItem(I: Integer; Value: string);
public
constructor Create(aOwner: TComponent); override;
destructor Destroy; override;
procedure LoadFromStream(const Stream: TStream);
procedure LoadFromFile(const FileName: string);
procedure SaveToStream(const Stream: TStream);
procedure SaveToFile(const FileName: string);
property Items[I: Integer]: String read GetItem write SetItem;
published
property StringItem : String read FPStr write FPStr;
end;
//------------------------------------------------------------------------------
var
DataSet: TDataSet;
implementation
uses TypInfo, Sysutils;
{ TDataSet }
//------------------------------------------------------------------------------
procedure TDataSet.DefineProperties(Filer: TFiler);
begin
inherited;
Filer.DefineProperty('DataArray', ReadArray, WriteArray, True);
end;
//------------------------------------------------------------------------------
destructor TDataSet.Destroy;
begin
inherited;
end;
//------------------------------------------------------------------------------
function TDataSet.GetItem(I: Integer): string;
begin
Result := '';
if (I > 0) and (I < Length(FArrayToSave)) then
Result := FArrayToSave[I];
end;
//------------------------------------------------------------------------------
procedure TDataSet.SetItem(I: Integer; Value: string);
begin
if (I > 0) and (I < Length(FArrayToSave)) then
FArrayToSave[I] := Value;
end;
//------------------------------------------------------------------------------
procedure TDataSet.LoadFromFile(const FileName: string);
var
Stream: TStream;
begin
Stream := TFileStream.Create(FileName, fmOpenRead or fmShareDenyWrite);
try
LoadFromStream(Stream);
finally
Stream.Free;
end;
end;
//------------------------------------------------------------------------------
procedure TDataSet.LoadFromStream(const Stream: TStream);
var
Reader: TReader;
PropName, PropValue: string;
begin
Reader := TReader.Create(Stream, $FFF);
Stream.Position := 0;
Reader.ReadListBegin;
while not Reader.EndOfList do
begin
PropName := Reader.ReadString;
PropValue := Reader.ReadString;
SetPropValue(Self, PropName, PropValue);
end;
FreeAndNil(Reader);
end;
//------------------------------------------------------------------------------
procedure TDataSet.SaveToFile(const FileName: string);
var
Stream: TStream;
begin
Stream := TFileStream.Create(FileName, fmCreate);
try
SaveToStream(Stream);
finally
Stream.Free;
end;
end;
//------------------------------------------------------------------------------
procedure TDataSet.SaveToStream(const Stream: TStream);
var
PropName, PropValue: string;
cnt: Integer;
lPropInfo: PPropInfo;
lPropCount: Integer;
lPropList: PPropList;
lPropType: PPTypeInfo;
Writer: TWriter;
begin
lPropCount := GetPropList(PTypeInfo(ClassInfo), lPropList);
Writer := TWriter.Create(Stream, $FFF);
Stream.Size := 0;
Writer.WriteListBegin;
for cnt := 0 to lPropCount - 1 do
begin
lPropInfo := lPropList^[cnt];
lPropType := lPropInfo^.PropType;
if lPropType^.Kind = tkMethod then Continue;
PropName := lPropInfo.Name;
PropValue := GetPropValue(Self, lPropInfo);
Writer.WriteString(PropName);
Writer.WriteString(PropValue);
end;
Writer.WriteListEnd;
FreeAndNil(Writer);
end;
//------------------------------------------------------------------------------
constructor TDataSet.Create(aOwner: TComponent);
begin
inherited;
end;
//------------------------------------------------------------------------------
procedure TDataSet.ReadArray(Reader: TReader);
var
N: Integer;
begin
N := 0;
Reader.ReadListBegin;
while not Reader.EndOfList do begin
Reader.ReadListBegin;
FArrayToSave[N] := Reader.ReadString;
Reader.ReadListEnd;
Inc(N);
end;
Reader.ReadListEnd;
end;
//------------------------------------------------------------------------------
procedure TDataSet.WriteArray(Writer: TWriter);
var
I: Integer;
begin
Writer.WriteListBegin;
for I := 1 to High(FArrayToSave) do begin
Writer.WriteListBegin;
Writer.WriteString(FArrayToSave[I]);
Writer.WriteListEnd;
end;
Writer.WriteListEnd;
end;
//------------------------------------------------------------------------------
initialization
DataSet := TDataSet.Create(Nil);
finalization
FreeAndNil(DataSet);
end.
//------------------------------------------------------------------------------
Here is my Class code re-written with Arioch's suggested code modifications from below:
unit UnitCharSett;
interface
//------------------------------------------------------------------------------
uses System.Classes;
//------------------------------------------------------------------------------
type
TCustomDatSetA = Array [0..99] of String;
TCustomCharSet = class(TComponent)
public
procedure LoadFromStream(const Stream: TStream);
procedure LoadFromFile(const FileName: string);
procedure SaveToStream(const Stream: TStream);
procedure SaveToFile(const FileName: string);
end;
TZCharSet = class(TCustomCharSet)
private
FFullArray : TCustomDatSetA;
function GetItem(I: Integer): String;
procedure SetItem(I: Integer; Value: string);
protected
procedure DefineProperties(Filer: TFiler); override;
procedure ReadArray(Reader:TReader);
procedure WriteArray(Writer:TWriter);
public
property Items[Index: Integer]: string read GetItem write SetItem;
published
end;
//------------------------------------------------------------------------------
implementation
uses
System.TypInfo, System.SysUtils;
//------------------------------------------------------------------------------
procedure TCustomCharSet.LoadFromFile(const FileName: string);
var
Stream: TStream;
begin
Stream := TFileStream.Create(FileName, fmOpenRead or fmShareDenyWrite);
try
LoadFromStream(Stream);
finally
Stream.Free;
end;
end;
//------------------------------------------------------------------------------
procedure TCustomCharSet.LoadFromStream(const Stream: TStream);
begin
Stream.ReadComponent(Self);
end;
//------------------------------------------------------------------------------
procedure TCustomCharSet.SaveToFile(const FileName: string);
var
Stream: TStream;
begin
Stream := TFileStream.Create(FileName, fmCreate);
try
SaveToStream(Stream);
finally
Stream.Free;
end;
end;
//------------------------------------------------------------------------------
procedure TCustomCharSet.SaveToStream(const Stream: TStream);
begin
Stream.WriteComponent(Self);
end;
//------------------------------------------------------------------------------
{ TZCharSett }
//------------------------------------------------------------------------------
procedure TZCharSet.DefineProperties(Filer: TFiler);
begin
inherited;
Filer.DefineProperty('DataArray', ReadArray, WriteArray, True);
end;
//------------------------------------------------------------------------------
function TZCharSet.GetItem(I: Integer): string;
begin
Result := '';
if (I > -1) and (I < Length(FFullArray)) then
Result := FFullArray[I];
end;
//------------------------------------------------------------------------------
procedure TZCharSet.ReadArray(Reader: TReader);
var
N: Integer;
S: String;
begin
for N := Low(FFullArray) to High(FFullArray) do begin
FFullArray[N] := '';
end;
Reader.ReadListBegin;
N := Reader.ReadInteger;
if N = Length(FFullArray) then
begin
N := Low(FFullArray);
while not Reader.EndOfList do
begin
S := Reader.ReadString;
if N <= High(FFullArray) then
FFullArray[N] := S;
Inc(N);
end;
end;
Reader.ReadListEnd;
end;
//------------------------------------------------------------------------------
procedure TZCharSet.SetItem(I: Integer; Value: string);
begin
if (I > -1) and (I < Length(FFullArray)) then
FFullArray[I] := Value;
end;
//------------------------------------------------------------------------------
procedure TZCharSet.WriteArray(Writer: TWriter);
var
I: Integer;
begin
Writer.WriteListBegin;
Writer.WriteInteger(Length(FFullArray));
for I := Low(FFullArray) to High(FFullArray) do begin
Writer.WriteString(FFullArray[I]);
end;
Writer.WriteListEnd;
end;
//------------------------------------------------------------------------------
initialization
RegisterClasses([TZCharSet]);
//------------------------------------------------------------------------------
end.
HOW do you actually try to read and write it ? I think you're trying to make complex incompatible things when there instead of using standard methods.
Why not to use standard VCL streaming procedures?
procedure TMyDataSet.SaveToStream(const Stream: TStream);
begin
Stream.WriteComponent(self);
end;
procedure TMyDataSet.LoadFromStream(const Stream: TStream);
begin
Stream.ReadComponent(self);
end;
However if instead of using TFiler and standard VCL streamer you make your custom code using RTTI (GetPropList) - then it would not call those virtual properties APi custom to TFiler and would only show real properties.
So my advice is just to use standard emthods like shown above and to streamline and harden the code.
And since RegisterClass works by the classname you'd better choose another name, not clashing with a real TDataSet from stock DB unit.
Fix the name and do register the class, so VCL streamer could find it by name! For example:
procedure TMyDataSet.ReadArray(Reader: TReader);
var
N: Integer; S: String;
begin
N := Low(FArrayToSave);
Reader.ReadListBegin;
while not Reader.EndOfList do begin
S := Reader.ReadString; // even if we would not save it - we should remove it from the input
if N <= High(FArrayToSave) then
FArrayToSave[N] := S;
Inc(N);
end;
Reader.ReadListEnd;
end;
procedure TMyDataSet.WriteArray(Writer: TWriter);
var
I: Integer;
begin
Writer.WriteListBegin;
for I := Low(FArrayToSave) to High(FArrayToSave) do begin
Writer.WriteString(FArrayToSave[I]);
end;
Writer.WriteListEnd;
end;
initialization
DataSet := TMyDataSet.Create(Nil);
RegisterClasses([TMyDataSet]);
finalization
DataSet.Free;
end.
Additionally, i think you'd better - for future extensibility - save the array length in DFM.
procedure TMyDataSet.WriteArray(Writer: TWriter);
var
I: Integer;
begin
Writer.WriteInteger(Length(FArrayToSave));
Writer.WriteListBegin;
for I := Low(FArrayToSave) to High(FArrayToSave) do begin
....
procedure TMyDataSet.ReadArray(Reader: TReader);
var
N: Integer; S: String;
begin
for N := Low(FArrayToSave) to High(FArrayToSave) do begin
FArrayToSave := ''; // in case DFM would have less elements than 50
N := Reader.ReadInteger;
if N <> Length(FArrayToSave) then... recovery from unexpected DFM version error
N := Low(FArrayToSave);
Reader.ReadListBegin;
while not Reader.EndOfList do begin
PS. you do not need {$M+} there since TComponent already is derived from TPersistent
PPS. Wanted to comment upon update in the question, but the phone refuses to do (too long?) so putting it here.
1: since we moved away from using RTTI, the Typinfo unit no more needed in uses. 2: if N = Length(FFullArray) then lacks ELSE path. Okay, now we learned that DFM is broken or incompatible, what then? I think we better raise some error. Or try to remove list of N strings, so next property could be read. Or even remove the list of elements of any type/quantity until list end. Future compatibly is never warranted, but at least some attempt can be done, even just to explicitly halt with error. Skipping reading and silently leaving the reader inside middle of property, so next properties would get crazy, I think is not the way to do it.
And generally David is correct about ignoring incorrect indices in the setter and getter. Unless you would intentionally come with some unusual pattern of implicit item creation from default template in sparse array by setting or getting with "free" "unbound" index (which is no code for either) the better approach at least in Delphi would be "fail early". That is what users of your class would expect by default. So kinda
Procedure class.CheckArrayIdx(const i: integer);
Var mx, mn : integer;
Begin
Mn := low(myarray) ; Mx := high(myarray);
If (i <= mx) and (I >= mn) then exit;
Raise ERangeError.CreateFmt('%s.Items index should be %d <= %d <= %d', [
Self.ClassName, mn, I, mx]) ;
End;
This procedure can be called as 1st line in both setter and getter. Then you can just work with surely correct index value.
来源：https://stackoverflow.com/questions/20662975/how-to-use-defineproperties-in-a-custom-class-object-for-arrays-delphi