Why is happened property write error?

Question

c++ : Run time error is happened with error message like this:

RevStrings1->Height of reading included in error: The property is write-protected.
RevStrings1->Height の読み込中のエラー : プロパティは書き込み禁止です.

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I'm using c++ builder 3.

This source code can be successfully compiled setting library, include path and etc.

But run time error is happened.

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I guess that this problem is about property read & write.

How can I simplly fix the problem ?

A variable RevStrings1 is created by a class TRevStrings.

//---------------------------------------------------------------------------
#ifndef RevStringsH
#define RevStringsH
//---------------------------------------------------------------------------
#include <SysUtils.hpp>
#include <Controls.hpp>
#include <Classes.hpp>
#include <Forms.hpp>
#include <Grids.hpp>
//---------------------------------------------------------------------------
class PACKAGE TRevStrings : public TStringGrid
{
private:
//  void __fastcall SetWidth(int W);
//  int __fastcall GetWidth(void);
//  int FColCount ;
  int FRowCount;
  int FFixedCols ;
  int FFixedRows ;
  int FDefaultColWidth ;
  int FDefaultRowHeight ;
  int FHeight;
//  int FWidth;
  int FScrollBars;
  int FMaxLength;
  bool ColColors[24];

protected:
public:
    __fastcall TRevStrings(TComponent* Owner);
  void __fastcall DrawCellText(TRect ARect,int ALeft,String S);
  virtual void __fastcall DrawCell(int ACol, int ARow,const Windows::TRect &ARect, TGridDrawState AState);
  void __fastcall SetColor_Col(int Col,int Row);
  void __fastcall SetColorFlag(int Col,bool flag);
  bool __fastcall GetColorFlag(int Col);
  void __fastcall SetEditText(int ACol, int ARow,const System::AnsiString Value);
  void __fastcall Clear(bool ALLorONE,int Position);
  void __fastcall DblClick(void);
__published:
//  __property int ColCount = {read = FColCount};//FColCount};
  __property int RowCount = {read=FRowCount};
  __property int FixedCols = {read=FFixedCols};
  __property int FixedRows = {read=FFixedRows};
  __property int DefaultColWidth = {read=FDefaultColWidth};
  __property int DefaultRowHeight = {read=FDefaultRowHeight};
  __property int Height = {read=FHeight};
//  __property int Width = {read=GetWidth,write=SetWidth};
  __property int ScrollBars = {read=FScrollBars};
  __property int MaxLength = {read=FMaxLength,write=FMaxLength};
/*
*/
};
//---------------------------------------------------------------------------
#endif

Answer 1

never heard of TRevStrings before

so it is either BCB 3 discontinued stuff (my BDS2006 does not have it at disposal) or you have some 3th party custom package installed but the header file suggest it is based on TStringGrid so if below text does not work for it then you can switch to TStringGrid instead.

in TStringGrid

size properties are accessible normaly:

StringGrid1->Height=256;
StringGrid1->Width=128;

if you want to have size-able col/rows then do not forget to open Options property and set goRowSizing,goColSizing to true and starting sizes are DefaultColWidth,DefaultRowHeight. Here example of usage

// resize the grid
StringGrid1->Height=128;
StringGrid1->Width=256;
// access to Cell AnsiStings
StringGrid1->Cells[0][0]="(0,0)";
StringGrid1->Cells[1][1]="(1,1)";
StringGrid1->Cells[1][2]="(1,2)";
StringGrid1->Cells[2][1]="(2,1)";
// resizing row/col
StringGrid1->RowHeights[0]=15;
StringGrid1->RowHeights[1]=20;
StringGrid1->ColWidths[0]=20;
StringGrid1->ColWidths[1]=15;

As your class is derived from this so this should work also for it if not the there are more possibilities:

1. you have unrelated bug somewhere

   overwriting what you should not damaging the C++ engine your App is running on or have memory leak somewhere or your memory manager is invalidated see

   • bds 2006 C hidden memory manager conflicts

   but that is probably not the case or you are calling VCL/Winapi visual stuff from threads.

To check for all this:

create empty application, add your TRevString and try to set its height on runtime. If no error occurs you have a bug somewhere if error occurs then:

2. this component is not able to resize on runtime this way

   try to use functions like SetSize,SetBounds instead or place the component on some panel align to Client and resize panel

3. if even this does not help switch to standard TStringGrid

   you can also try to cast you RevString to StringGrid first

   ((TStringGrid*)(RevString1))->Height=25;
   

4. Borland compilers sometimes get weird

   few times (around 10) over the years I use BCB/BDS the compiler sometimes compile wrongly. The app is running but some code gets distorted or discarted so what helps?

   • close IDE or even restart Windows
   • delete all map,obj,tds temp files prior to compiling rebuilding
   • sometimes is needed that you add empty line of code or swap 2 lines of code

5. Identifiers/Names collisions

   if you name your stuff in similar way to VCL functions then you ask for problems usual error is to name function Draw() ... (use draw() instead and you are fine)

6. for big projects

   if you add your source code as new unit to project instead of just include it (it is present in Object Manager) then in big projects you will got big problems. It looks like units are compiled differently then normal included files in units are expected Formulars and other VCL stuff components so if you got your own non visual classes as units they sometimes stop working as expected creating weird behavior (even your error could be caused by it).

   I observe this on BCB5 and BDS2006. In BCB3,BCB4 I did not make big enough projects to spot this and BCB6 is so buggy so its unusable with big projects anyway. By big projects I mean > 1 MB of pure C++ code

Answer 2

The error is self-explanatory - the Height property of the RevStrings1 object is not allowing its value to be assigned. This is evident by looking at the declaration of the Height property in the TRevStrings class:

__property int Height = {read=FHeight};

TRevStrings is going out of its way to make the Height property read-only, overriding the native read-write Height property that is inherited from TControl:

__property int Height = {read=FHeight, write=SetHeight, nodefault};

This is odd for TRevString to do, as it is a visual component that needs to be sizable. Unless it requires a specific height that the user cannot change (in which case declaring the Height property as read-only is not the correct way to handle that - the component should override the virtual SetBounds() method instead and just ignore any new Height value being assigned).

That being said, the reason you see the error at run-time is because the IDE is storing the design-time Height value of the RevStrings1 object in the parent Form's DFM resource at compile-time. That is why you are not finding any RevStrings1->Height in your code - it is coming from the Form Designer instead. The TRevStrings class is not overriding DFM behavior for the Height property, so when the VCL's DFM streaming system parses the Form's DFM resource at run-time, it sees the stored Height value and detects that the object's Height property is actually read-only, and so throws an exception to cancel DFM streaming (and thus the Form's construction).

This is a bug in the TRevStrings implementation. At the very least, if the author had wanted to prevent the Height from being streamed (thus preventing the run-time error), the Height property should have been declared like this instead:

__property Height = {read=FHeight, stored=false};

On a side note, most of the TRevStrings data members (FColCount, FRowCount, FFixedCols, FFixedRows, etc) should never have been declared at all, but instead should have been inherited from the base TStringGrid class.

Whoever wrote this component clearly did not know what they were doing.