C++ Builder 建立自繪圖清單方塊元件

繼承 TCustomListBox 封裝 Owner-Draw 圖文混排列表框元件

利用 lbOwnerDrawVariable 風格，覆寫 OnMeasureItem 與 OnDrawItem，將圖示 (ICO/BMP) 儲存於 Items.Objects，實現每行不同高度的圖文列表。並封裝為 TImageListBox 元件，提供 AddImage 方法簡化使用。

元件標頭檔 (ImageListBox.h)

class TImageListBox : public TCustomListBox
{
private:
    Graphics::TGraphic *tmpGraphic;
protected:
    void __fastcall MyDrawItem(TWinControl *Control, int Index,
        const TRect &Rect, TOwnerDrawState State);
    void __fastcall MyMeasureItem(TWinControl *Control, int Index, int &Height);
public:
    __fastcall TImageListBox(TComponent* Owner);
    __fastcall ~TImageListBox();
    void __fastcall AddImage(AnsiString Filename, AnsiString *Str);
};

實作檔 (ImageListBox.cpp) 核心

void __fastcall TImageListBox::MyMeasureItem(TWinControl *Control, int Index, int &Height)
{
    if (tmpGraphic) Height = tmpGraphic->Height + 2;
}

void __fastcall TImageListBox::MyDrawItem(TWinControl *Control, int Index,
    const TRect &Rect, TOwnerDrawState State)
{
    const int Offset = 2;
    TCanvas *cv = ((TListBox*)Control)->Canvas;
    cv->FillRect(Rect);

    Graphics::TGraphic *img = (Graphics::TGraphic*)(Items->Objects[Index]);
    cv->Draw(Rect.Left + Offset, Rect.Top, img);

    if (img) Offset += img->Width + 4;
    cv->TextOut(Rect.Left + Offset, Rect.Top,
        ((TListBox*)Control)->Items->Strings[Index]);
}

void __fastcall TImageListBox::AddImage(AnsiString Filename, AnsiString *Str)
{
    if (Filename.Pos(".ico")) {
        tmpGraphic = new Graphics::TIcon(); tmpGraphic->LoadFromFile(Filename);
        Items->AddObject(*Str, (TObject*)tmpGraphic);
    }
    else if (Filename.Pos(".bmp")) {
        tmpGraphic = new Graphics::TBitmap(); tmpGraphic->LoadFromFile(Filename);
        Items->AddObject(*Str, (TObject*)tmpGraphic);
    }
    tmpGraphic = NULL;
}

__fastcall TImageListBox::TImageListBox(TComponent* Owner) : TCustomListBox(Owner)
{
    Style = lbOwnerDrawVariable;
    OnDrawItem = MyDrawItem;
    OnMeasureItem = MyMeasureItem;
}

__fastcall TImageListBox::~TImageListBox()
{
    for (int i = 0; i < Items->Count; i++)
        if (Graphics::TGraphic *g = (Graphics::TGraphic*)Items->Objects[i])
            delete g;
}

使用範例

// 表單建構函數
TImageListBox *Til = new TImageListBox(this);
Til->Parent = this; Til->Width = 80; Til->Height = 90;
Til->AddImage("1.ico", "First");
Til->AddImage("2.bmp", "Second");
// 表單銷毀
delete Til;

優點

• 封裝後可像標準元件一樣拖放使用，重複利用率高。
• 支援 ICO/BMP 多種圖片格式，自動釋放資源。
• 每行高度自適應圖片高度。