Control JTable DnD cells?

[Jim Crowell]

I have developed a 3 column JTable with DnD capability. I use a TransferHandler subclass and an AbstractTableModel subclass. It is working fine.

However, I have some addition requirement to control the JTable DnD cells, e.g. no DnD for column 0, drag only from column 1 and drop only to column 2.

I studied the TransferHandler methods and added code to several of my override methods but I have not been successful yet.

I think that these requirement should be somewhat common but I have not been able to find any similar documentation using Google.

As is my experience, I suspect I am overlooking something basic and I am making my requirements implementation more difficult then it really is.

Any suggestion?

Regards,

[Tony Docherty]

Can you show the code for your transfer handler?
How are you determining which table column you are dropping onto are you using the JTable.DropLocation class?

[Jim Crowell]

Tony,

How are you determining which table column you are dropping onto are you using the JTable.DropLocation class?

No I am not using the 'DropLocation' class.
This is the kind of help I needed. I did not know of that class.
I just took a quick look at it and will examine it more after I complete this post.

I need to turn off Column 0, Drag from column 1 only and Drop to column 2 only.
In column 1, ideally, I should turn off some row cells also to avoid end user confusion.

FYI: I am developing on an iMac using OS X 10.6 and I am using Java 1.6.0_37.

The following is my code for the AbstractTableModel and the TransferHandler:

    //  
    //   JEmissaryModel InnerClass..  
    //  
        private static class JEmissaryModel extends AbstractTableModel  {  
        private static ArrayList<String>emissariesData;  
        private static int nCols, nRows;  
        private static String [] columnNames;  
        //  JEmissaryModel Constructor...  
        public JEmissaryModel (  
            ArrayList<String> emissariesData, String [] columnNames) {  
            JEmissaryModel.emissariesData = emissariesData;  
            JEmissaryModel.columnNames = columnNames;  
            JEmissaryModel.nCols = columnNames.length;  
            JEmissaryModel.nRows = (emissariesData.size()) / 3;  
        }   //  End 'JEmissaryModel' Constructor...  
        public void addRow(int index, String emissary, String person, String toDo)  {  
            //  Add the 'row' parameters in reverse order to the 'emissariesData' instance...  
            emissariesData.add(index, toDo);  
            emissariesData.add(index, person);  
            emissariesData.add(index, emissary);  
            //  Update the number of Rows parameter...  
            JEmissaryModel.nRows = (emissariesData.size()) / 3;  
            //  Set the Added Row Flag so that the 'eventDone' processing points to the proper row...  
            fAddedRow = true;  
            //  Notify the listeners of the inserted row...  
            fireTableDataChanged();  
        }   //  End 'addRow' method...  
        public int getColumnCount() {return nCols;}  
        public String getColumnName(int col) {return columnNames[col];}  
        public ArrayList<String> getEmissariesData() {return JEmissaryModel.emissariesData;};  
        public int getRowCount() {return JEmissaryModel.nRows;};  
        public Object getValueAt(int row, int col)      {  
            int index = 3 * row + col;  
            return  emissariesData.get(index);  
        }   //  End 'getValueAt' Method...  
        public void setValueAt(Object value, int row, int col) {  
            int index = 3 * row + col;  
            emissariesData.set(index, (String)value);  
            fireTableDataChanged();  
        }   //  End 'setValueAt' Method...  
    }   //  End 'JEmissaryManagerModel' Inner Class...  
    //  
    //  TransferHandler Sub-Class…  
    //  
    class JEmissaryReportTranserHandler extends TransferHandler {  
        public JEmissaryReportTranserHandler() {}  
        @Override  
        public int getSourceActions(JComponent c) {return MOVE;}  
        @Override  
        protected Transferable createTransferable(JComponent source) {  
            JTable table = (JTable)source;  
            int row = table.getSelectedRow();  
            int col = table.getSelectedColumn();  
            String value = (String)table.getModel().getValueAt(row, col);  
            return  
                new StringSelection(  
                    (String) (table.getModel().getValueAt(row, col)));  
        }   //  End 'createTransferable' Override Method...  
        @Override  
        protected void exportDone(JComponent source, Transferable data, int action) {  
            if (source instanceof JTable)   {  
                JTable table = (JTable) source;  
                int row = table.getSelectedRow();  
                //  Manage the 'row' = F[fAddedRow]...  
                if (fAddedRow)  {row++; fAddedRow = false;};  
                int col = table.getSelectedColumn();  
                table.getModel().setValueAt("", row, col);  
                //  Remove any 'Null' rows from the 'emissariesData' component...  
                //  LOOP on the existing 'emissariesData' ArraList...  
                for (int i=0; i<emissariesData.size(); i=i+3)    {  
                    if (    emissariesData.get(i).equals("")        &&  
                        emissariesData.get(i+1).equals("")  &&  
                        emissariesData.get(i+2).equals("")) {  
                            //  Remove the elements for the found 'Null' row...  
                            for (int j= 0; j><3; j++)  
                                emissariesData.remove(i);  
                                //  Decrement the number of Rows parameter...  
                                JEmissaryModel.nRows = (emissariesData.size()) / 3;  
                        }   //  End 'row' is 'Null' IF...   
                    }   //  End 'emissariesData' LOOP...  
                }   //  End 'source' : JTable...  
                else  
                    Util.softAbort(method, "OOPS: Unexpected 'source':"+LF+source.toString());  
        }   //  End 'exportDone' Override method...  
        @Override  
        public boolean canImport(TransferSupport support) {return true;}  
        @Override  
        public boolean importData(TransferSupport support) {  
            JTable table = (JTable) support.getComponent();  
            try {  
                String value = (String)support.getTransferable().getTransferData(DataFlavor.stringFlavor);  
                int row = table.getSelectedRow();  
                int col =   table.getSelectedColumn();  
            //  Get the current destination content...  
            String currentValue = (String)table.getValueAt(row, col);  
                //  If the currentValue is NOT the 'Null' String...  
                if (    !   currentValue.trim().equals("")) {  
                    //  Construct the new ArrayList index...  
                    int index = 3 * (row+1);  
                    //  Insert a new row with Null 'emissary', Null 'person' and given 'To-Do' value...  
                    jEmissaryModel.addRow(index, "", "", value);  
                }   //  End 'currentValue' : Null String IF...  
                //  To-Do destination has NOT been set...  
                else {  
                    //  Set the Drag Value into the table model...  
                    table.setValueAt(value, row, col);  
                }   //  End 'currentValue' : Null String ELSE...  
            } catch (UnsupportedFlavorException ex) {  
                System.out.println(ex);  
            } catch (IOException ex) {  
                System.out.println(ex);  
            }   //  End 'IOException' catch...  
            return super.importData(support);  
        }   //  End 'importData' Override method...  
    }   //  End 'JEmissaryReportTranserHandler' Inner Class...  

Thanks,
Jim...

[Tony Docherty]

I'm no expert on DND so take all this advice with a pinch of salt.

You need to limit which columns can be dragged from so I think you need to override getSourceActions() to return the type of transfer action available on the currently selected cell of the JTable. The cells which can't be dragged from return NONE.

For dropping the data you need to use the canImport() method to limit where the data can be dropped. The TransferSupport object passed into the method can be used to get the DropLocation object which can then be used to determine where the user is attempting to drop the dragged data.

BTW I take it you are setting the JTable's drop mode to a suitable value and are enabling dragging on the JTable.

[Jim Crowell]

You need to limit which columns can be dragged from so I think you need to override getSourceActions() to return the type of transfer action available on the currently selected cell of the JTable. The cells which can't be dragged from return NONE.

The above advise was just what I needed.
The following is the code that I am currently using successfully:
I probably did not need the 'instanceof' if but I use that approach a lot...

@Override
public int getSourceActions(JComponent c) {
	if (c instanceof JTable)	{
	    JTable table = (JTable) c;
	    int col =	table.getSelectedColumn();
	    int row =	table.getSelectedRow();
	    if (col <= 0)						return TransferHandler.NONE;
	    else if (col ==1 && row <= nRemoves)	return TransferHandler.NONE;
	    else							return TransferHandler.MOVE;
	}	//	End instanceof JTable IF...
	else
	    Util.softAbort(method, "Unexpected component:"+LF+c.toString());
	return TransferHandler.NONE;
}	//	End 'getSourceActions' method...

For dropping the data you need to use the canImport() method to limit where the data can be dropped. The TransferSupport object passed into the method can be used to get the DropLocation object which can then be used to determine where the user is attempting to drop the dragged data.

I played with this but was unable to use it as directed.
I ended up adding some custom code to both the 'canImport' override and the 'createTransferable' override methods to [I think] resolve my controls for the 'drop' capability.

I'm still tweaking and testing but I think I am close to my objective...

BTW I take it you are setting the JTable's drop mode to a suitable value and are enabling dragging on the JTable.

Yes, the following code is used:

        emissariesTable.setDragEnabled(true);
        emissariesTable.setDropMode(DropMode.USE_SELECTION);
	emissariesTable.setTransferHandler(new JEmissaryReportTranserHandler());

Thank you for the help.
Regards,

[Tony Docherty]

I played with this but was unable to use it as directed.

You should be able to cast the DropLocation object to javax.swing.JTable.DropLocation which has methods to return which column, row etc the user is trying to drop the data into.

[Jim Crowell]

You should be able to cast the DropLocation object to javax.swing.JTable.DropLocation which has methods to return which column, row etc the user is trying to drop the data into.

Thanks.
I did some analysis of my old method and the 'JTable.DropLocation' implementation
and it looked like either way the correct drop point is there once the mouse button
is released. However, the 'JTable.DropLocation' method seemed to better track the
mouse drag movement.

Below is the revised 'canImport' method with my original method commented out…

@Override
public boolean canImport(TransferSupport support) {
	//	JTable table = (JTable) support.getComponent();
    	//	int row = table.getSelectedRow();
    	//	int col = table.getSelectedColumn();
    DropLocation dl = support.getDropLocation();
    javax.swing.JTable.DropLocation dlTable = (JTable.DropLocation)dl;
    int row = dlTable.getRow();
    int col = dlTable.getColumn();
    if (col <= 1)	fTransfer = false;
    else		fTransfer = true;
    return fTransfer;
}	//	End 'canImport' Method...

I have an additional question if I may.
In my 'getSourceActions' override method I return a "TransferHandler.MOVE" int
iff the Table Model column is > 0 [i.e. == 1 of 2]…

Also my JTable [emissariesTable] setting are as follows:
emissariesTable.setDragEnabled(true);
emissariesTable.setDropMode(DropMode.USE_SELECTION);
emissariesTable.setTransferHandler(new JEmissaryReportTransferHandler());

What i need to accomplish is to have the drag String set to a Null String after the drag String is dropped in the destination column cell…

That is what I thought the DnD MOVE process would do.

To satisfy my requirement, I went and added some code to my TransferHandler.
My JTable is dynamic in that rows are added and removed during run time by my code.
Therefore, the added code was somewhat difficult [for me anyway] and still has a bug to be fixed.

My question is as follows:
Have I overlooked something in my basic DnD JTable settings so that
the MOVE will work as I expected without my "kluge" code?

Here is the JEmissaryReportTransferHandler with the added code to perform the MOVE:

class JEmissaryReportTranserHandler extends TransferHandler {
	public JEmissaryReportTranserHandler() {}
	@Override
	public boolean canImport(TransferSupport support) {
		DropLocation dl = support.getDropLocation();
		javax.swing.JTable.DropLocation dlTable = (JTable.DropLocation)dl;
		if (col != 2)	fTransfer = false;
		else			fTransfer = true;
    	        return fTransfer;
	}	//	End 'canImport' Method...
	@Override
	protected Transferable createTransferable(JComponent source) {
		JTable table = (JTable)source;
		int row = table.getSelectedRow();
	    	int col = table.getSelectedColumn();
	    	String value = (String)table.getModel().getValueAt(row, col);
	    	//	Get the associated emissary name from the Table Model...
	    	//	This code is required because the Emissaries column is set to a Null String if
	    	//	there is more than 1 person to be notified by the Emissary...
	    	//
	    	//	The found NON-Null Emissary name is appended to the return Transferrable String
	    	//	for usage by the 'doToDo' processing method...
	    	int rEmissary = row;
	    	String emissary = (String)table.getModel().getValueAt(rEmissary--, 0);
	    	while (	emissary.equals("")	)
	    		emissary = (String)table.getModel().getValueAt(rEmissary--, 0);
	    	return
			new StringSelection(
				(String) (table.getModel().getValueAt(row, col))+D_ITEMS+emissary);
	}	//	End 'createTransferable' Override Method...
	@Override
	protected void exportDone(JComponent source, Transferable data, int action)	{
		JTable table = (JTable) source;
		//	If a transfer was made,
		//	Then clear the 'drag' source value in the Table Model...
		if (	fTransfer	)
			table.getModel().setValueAt("", dragRow, dragCol);
		//	Remove any 'Null' rows from the 'emissariesData' component...
		//	LOOP on the existing 'emissariesData' ArrayList…
		for (int i=0; i<emissariesData.size(); i=i+3)	{
			if (	emissariesData.get(i).equals("")		&&
				emissariesData.get(i+1).equals("")	&&
				emissariesData.get(i+2).equals(""))	{
				//	Remove the elements for the found 'Null' row...
				for (int j= 0; j><3; j++)
					emissariesData.remove(i);
				//	Reset the number of Rows TableModel parameter…
				JEmissaryModel.nRows = (emissariesData.size()) / 3;
			}	//	End 'row' is 'Null' IF...
		}	//	End 'emissariesData' LOOP...
		//	Notify the listeners of the modified Table Model...
		JEmissaryManager.jEmissaryModel.fireTableDataChanged();
	}	//	End 'exportDone' Override method...
	@Override
	public int getSourceActions(JComponent c) {
		JTable table = (JTable) c;
	    	dragCol =		table.getSelectedColumn();
	    	dragRow =		table.getSelectedRow();
		if (dragCol <= 0)	return TransferHandler.NONE;
		else				return TransferHandler.MOVE;
	}	//	End 'getSourceActions' method...
	@Override
	public boolean importData(TransferSupport support)	{
		//	Process the requested DnD command...
		JTable table = (JTable) support.getComponent();
	        try {
			String dragValue =
				(String)support.getTransferable().getTransferData(DataFlavor.stringFlavor);
			int row = table.getSelectedRow();
			int col =	table.getSelectedColumn();
			//	Get the current 'ToDo' destination content...
			String currentToDo = (String)table.getValueAt(row, col);
			//	If the current ToDo Value is NOT the 'Null' String...
			if (	!	currentToDo.trim().equals(""))	{
				//	Construct the new ArrayList index...
				int index = 3 * (row+1);
				//	Insert a new row with Null 'emissary', Null 'person' and given 'To-Do' value...
				jEmissaryModel.addRow(index, "", "", dragValue);
			}	//	End 'currentValue' : Null String IF...
			else {	//	To-Do destination has NOT been set...
				//	Set the Drag Value into the table model...
				table.setValueAt(dragValue, row, col);
			}	//	End 'currentValue' : Null String ELSE...
	        }	//	End 'try'...
	        catch (UnsupportedFlavorException ex) {System.out.println(ex);}
	        catch (IOException ex) {System.out.println(ex);}
		
	        return super.importData(support);
	}	//	End 'importData' Override method...
}	//	End 'JEmissaryReportTranserHandler' Inner Class...

Regards,
Jim...