你如何提取从TGraphicField位图？ [英] How do you extract a bitmap from a TGraphicField?

问题描述

我要疯了。

下面是我在做什么。

1. 放入一个TClientDataSet，一个的TImage，并在窗体上一个TButton。


2. 将Clientdataset1.Filename到biolife.xml



3. 按钮双击并添加下列code：

    程序TForm31.Button1Click（发件人：TObject的）;
   VAR
     BF：TBlobField;
     BS：TStream;
     BM：TBitmap;
   开始
     ClientDataset1.Open;
     ClientDataset1.First;
     BF：= ClientDataSet1.FieldByName（'平面'）作为TBlobField;
     BS：= ClientDataSet1.CreateBlobStream（BF，bmRead）;
     BS.Position：= 0;
     BM：= TBitmap.Create;
     尝试
       BM.LoadFromStream（BS）;
     最后
       BM.Free;
     结束;
   结束;
    

运行它。当我这样做，我得到位图图像无效。

咦？该数据一直是位年 - ？什么是错

解决方案

  

图形字段是二进制大对象（BLOB）领域，其中的一种形式
  在数据包括BLOB头描述的编码
  图形化的价值。

BLOB头是误导那里，它似乎是图形备忘录悖论存储格式的残余。

 （*从DB *）{悖论图形BLOB头}
类型
  TGraphicHeader =记录
    字数：字; {1}固定
    HTYPE：字; {在$ 0100固定}
    尺寸：Longint型; {尺寸不包括报头}
  结束;
程序TForm1.FormClick（发件人：TObject的）;
常量
  HeaderSize =中SizeOf（TGraphicHeader）;
VAR
  现场：TGraphicField;
  流：TClientBlobStream;
开始
  现场：= ClientDataSet1.FieldByName（'平面'）作为TGraphicField;
  流：= ClientDataSet1.CreateBlobStream（场，bmRead）为TClientBlobStream;
  Stream.SaveToFile（'dump.bin'）; //检查BLOB，看到额外的字节preceding BITMAPFILEHEADER
  断言（Stream.Position = 0）;
  Stream.Seek（+ HeaderSize，soFromCurrent）; //丢弃报头，它不包含使用任何反正
  Image1.Picture.Bitmap.LoadFromStream（流）;  ClientDataSet1.Next;
结束;
 

I am going nuts.

Here's what I am doing

1. Drop a TClientDataset, a TImage, and a TButton on a form.
2. Set the Clientdataset1.Filename to biolife.xml

3. Double click on the button and add the following code:

   procedure TForm31.Button1Click(Sender: TObject);
   var
     BF: TBlobField;
     BS: TStream;
     BM: TBitmap;
   begin
     ClientDataset1.Open;
     ClientDataset1.First;
     BF :=  ClientDataSet1.FieldByName('Graphic') as TBlobField;
     BS := ClientDataSet1.CreateBlobStream(BF, bmRead);
     BS.Position := 0;
     BM := TBitmap.Create;
     try
       BM.LoadFromStream(BS);
     finally
       BM.Free;
     end;
   end;
   

Run it. When I do, I get "Bitmap image is not valid".

Huh? That data has been a bitmap for years -- what is wrong?

解决方案

Graphics fields are a form of binary large object (BLOB) field where the data includes a BLOB header describing the encoding of the graphical value.

"BLOB header" is misleading there, it appears to be a remnant of Paradox storage format for graphic memos.

(* from DB *)

{ Paradox graphic BLOB header }
type
  TGraphicHeader = record
    Count: Word;                { Fixed at 1 }
    HType: Word;                { Fixed at $0100 }
    Size: Longint;              { Size not including header }
  end;


procedure TForm1.FormClick(Sender: TObject);
const
  HeaderSize = SizeOf(TGraphicHeader);
var
  Field: TGraphicField;
  Stream: TClientBlobStream;
begin
  Field := ClientDataSet1.FieldByName('Graphic') as TGraphicField;
  Stream := ClientDataSet1.CreateBlobStream(Field, bmRead) as TClientBlobStream;
  Stream.SaveToFile('dump.bin');            // examine BLOB and see extra bytes preceding BITMAPFILEHEADER
  Assert(Stream.Position = 0);
  Stream.Seek(+HeaderSize, soFromCurrent);  // discard header, it does not contain anything of use anyways
  Image1.Picture.Bitmap.LoadFromStream(Stream);

  ClientDataSet1.Next;
end;

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