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Problem
How do I implement a virtual grid? I want to supply cell contents on demand.
Cause
Action
Here is an example how you can override GetStyleRowCol() and StoreStyleRowCol() and implement a virtual grid. See also the browsevw.cpp/.h sample in gridapp.
| BOOL CBrowserView::GetStyleRowCol(ROWCOL nRow, ROWCOL nCol, CGXStyle& style, GXModifyType mt, int nType) { |
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| if (mt == gxRemove) // not supported | |||
| return FALSE; | |||
| // Note: I do not distinct between // gxApplyNew, gxCopy and gxOverride ASSERT(nRow <= LONG_MAX); long nRecord = (long) nRow; if (nType == -1) |
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| // Here you can return the style // for a complete row, column or // table return CGXGridWnd::GetStyleRowCol(nRow, nCol, style, mt, nType); |
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| } else if (nRow == 0 && nCol == 0) { |
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| // Style for the top-left button return FALSE; |
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| } else if (nRow == 0) { |
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| // Column headers style.SetValue(nCol); |
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| } else { |
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| // Cell in the grid style.SetValue(myData[nRow][nCol].text); // - Or - style.SetValue("World"); return TRUE; |
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| }
return FALSE; |
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| } | |||
You should also override StoreStyleRowCol() to store the value in your data structure if the user did change it. The grid always calls this method to store values.
Example:
| BOOL CBrowserView::StoreStyleRowCol(ROWCOL nRow, ROWCOL nCol, const CGXStyle* pStyle, GXModifyType mt, int nType) { |
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| if (mt == gxRemove) // not supported | |||
| return FALSE; | |||
| // Note: I do not distinct between // gxApplyNew, gxCopy and gxOverride if (nType == -1) { |
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| // Here you could store the // style for a complete row, // column or table return FALSE; |
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| } else if (nRow == 0 && nCol == 0) { |
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| // style for the top-left button return FALSE; |
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| } else if (nRow == 0) { |
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| // Column headers return FALSE; |
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| } else { |
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| // cell myData[nRow][nCol].text = style.GetValue(); return TRUE; |
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| }
// unreferenced: return FALSE; |
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| } | |||
You might also override GetRowCount() to return the number of rows in your data structure.
Example:
| ROWCOL CBrowserView::GetRowCount() { |
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| return myData.GetRowCount(); | ||
| } | ||
When the grid starts drawing any cells, it loads all cells it needs to draw into memory. At this time the GetStyleRowCol() method will be called for each cell. The grid keeps all the cells of the last drawing action in memory until the next drawing action occurs. Then, it frees the memory and loads the new cells that need to be drawn.
