QVariantMap loss of pointers

I'm passing pointers for instance in one of my classes around as an element of a QVariantMap. 98% of the time it works well, while 2% is killing me. Sometimes when I extracted the pointer elsewhere in my app it comes out as NULL rather than this pointer valid that was on there.

Here's an example of how to get the pointer in the QVariantMap:

MyClass* myClassPtr;
QVariantMap map;

myClassPtr = &myClassInstance;
map["title"] = "Pointer to my class";Q_ASSERT(myClassPtr);
map["myClass"] = QVariant::fromValue( myClassPtr );Q_ASSERT(map["settings"].value());

Once the 'map' is filled with other values too happening around in the application by various means, such as a signal when the user does something. In contrast, when I need the pointer back, I do the following:

MyClass* myClassPtr = map["settings"].value();Q_ASSERT(myClassPtr);

As I said, 98% of the time this works as expected, but the remaining time the pointer spell back as NULL, which obviously has critical implications when I try to call functions of the object of it. Strangely, the "title" element always comes out correctly even when the pointer is not. I know that the pointer is lost in transit because the first and the second fire Q_ASSERTs never, even when the third. Either way, I am trying to retrieve the pointer to the same place in the code every time. It will work fine 10, 20, 40 times in a row, then next time... boom!

I can not understand what is happening here.

Update: on the off-chance that it might be useful, I'll explain how the QVariantMap happening around. Only the first block of code is a class that generates a QList and use it to fill a GroupDataModel.

The second block is a function that is triggered when the user clicks on one of the items in the ListView that uses this GroupDataModel, and it gets the path of the index of the item that the user has typed as a parameter. To develop this second block:

QVariantMap map = dataModel->data( indexPath ).value();
QString title = map["title"].toString();
myClass* myClassPtr = map["settings"].value();
Q_ASSERT(myClassPtr);

AsI said before "title" comes out correctly, and usually 'settings', but not always. Maybe someone notices something wrong with this additional detail.

UPDATE: Turns out that I was running a red herring, because it has nothing to do with QVariantMap. After weeks of having my app "randomly" close last night, I realized that there was a reason after all and I learned something new about ListView.

What I didn't know, is that numbers of ListView by triggered() report not ONLY when you tap an item in the list, but also when you tap on a header. My articles are quite large while my headers are very narrow. What was going on, it was that a few times out of a hundred, I got a little sloppy typing element and hit header instead. This triggered a function which should receive a path index pointing to a QVariantMap of the datamodel that had been filled with the item "settings". When I typed in the header error, it was not to do the QVariantMap with the 'settings' so when I cast to MyClass * liquidation was always NULL.

What made it particularly difficult to identify, it is that I'm very rarely enough botched hit header by mistake, and there was no indication that I had done, so I thought the app was going to die when I was the ListView element you tapoterez normally. I didn't know that ListView sends a signal triggered() for valves header too.

I fixed it by checking the length of row in the slot in onTriggered of the ListView. If the length is two then an item has been exploited, so I call the function. However, if the length is one then this is a header instead, so I did nothing.

Tags: BlackBerry Developers

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Editor-in-Chief of cell customized JTable loss of focus

It is a follow-up of Re: tutorial on the AWT/Swing control flow in which I ask for pointers to help me understand the source of behavior lost focus in the custom my JTable cell editor.

I've done some research more and it turns out that loss of focus is a more general problem with the custom cell editors who call other windows. Even the demo of the pipette in the JTable tutorial at http://download.oracle.com/javase/tutorial/uiswing/examples/components/index.html#TableDialogEditDemo has this problem, IF you add a text field or both to the setting in FRONT of the table. Only in the demo table loses focus when the color picker appears, it is because the table is the only thing in the window!

Here's the code for demo, increased with two text fields, which are certainly bad here, but which serve the desired purpose:

/*
 * Copyright (c) 1995, 2008, Oracle and/or its affiliates. All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 *
 *   - Redistributions of source code must retain the above copyright
 *     notice, this list of conditions and the following disclaimer.
 *
 *   - Redistributions in binary form must reproduce the above copyright
 *     notice, this list of conditions and the following disclaimer in the
 *     documentation and/or other materials provided with the distribution.
 *
 *   - Neither the name of Oracle or the names of its
 *     contributors may be used to endorse or promote products derived
 *     from this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS
 * IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO,
 * THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
 * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE COPYRIGHT OWNER OR
 * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
 * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
 * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
 * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
 * LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
 * NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
 * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */

import javax.swing.*;
import javax.swing.border.Border;
import javax.swing.table.AbstractTableModel;
import javax.swing.table.TableCellEditor;
import javax.swing.table.TableCellRenderer;
import java.awt.*;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;

public class TableDialogEditDemo extends JPanel {
    public class ColorEditor extends AbstractCellEditor
            implements TableCellEditor,
            ActionListener {
        Color currentColor;
        JButton button;
        JColorChooser colorChooser;
        JDialog dialog;
        protected static final String EDIT = "edit";

        public ColorEditor() {
            //Set up the editor (from the table's point of view), which is a button.
            //This button brings up the color chooser dialog, which is the editor from the user's point of view.
            button = new JButton();
            button.setActionCommand(EDIT);
            button.addActionListener(this);
            button.setBorderPainted(false);

            //Set up the dialog that the button brings up.
            colorChooser = new JColorChooser();
            dialog = JColorChooser.createDialog(button, "Pick a Color", true,  //modal
                    colorChooser, this,  //OK button handler
                    null); //no CANCEL button handler
        }

        /**
         * Handles events from the editor button and from the dialog's OK button.
         */
        public void actionPerformed(ActionEvent e) {
            if (EDIT.equals(e.getActionCommand())) {
                //The user has clicked the cell, so bring up the dialog.
                button.setBackground(currentColor);
                colorChooser.setColor(currentColor);
                dialog.setVisible(true);

                //Make the renderer reappear.
                fireEditingStopped();

            } else { //User pressed dialog's "OK" button
                currentColor = colorChooser.getColor();
            }
        }

        public Object getCellEditorValue() {
            return currentColor;
        }

        public Component getTableCellEditorComponent(JTable table,
                                                     Object value,
                                                     boolean isSelected,
                                                     int row,
                                                     int column) {
            currentColor = (Color) value;
            return button;
        }
    }

    public class ColorRenderer extends JLabel
            implements TableCellRenderer {
        Border unselectedBorder = null;
        Border selectedBorder = null;
        boolean isBordered = true;

        public ColorRenderer(boolean isBordered) {
            this.isBordered = isBordered;
            setOpaque(true);
        }

        public Component getTableCellRendererComponent(
                JTable table, Object color,
                boolean isSelected, boolean hasFocus,
                int row, int column) {
            Color newColor = (Color) color;
            setBackground(newColor);
            if (isBordered) {
                if (isSelected) {
                    if (selectedBorder == null) {
                        selectedBorder = BorderFactory.createMatteBorder(2, 5, 2, 5,
                                table.getSelectionBackground());
                    }
                    setBorder(selectedBorder);
                } else {
                    if (unselectedBorder == null) {
                        unselectedBorder = BorderFactory.createMatteBorder(2, 5, 2, 5,
                                table.getBackground());
                    }
                    setBorder(unselectedBorder);
                }
            }
            return this;
        }
    }

    public TableDialogEditDemo() {
        super(new GridLayout());

        JTextField tf1 = new JTextField("tf1");
        add(tf1);
        JTextField tf2 = new JTextField("tf2");
        add(tf2);

        JTable table = new JTable(new MyTableModel());
        table.setPreferredScrollableViewportSize(new Dimension(500, 70));
        table.setFillsViewportHeight(true);

        JScrollPane scrollPane = new JScrollPane(table);

        table.setDefaultRenderer(Color.class,
                new ColorRenderer(true));
        table.setDefaultEditor(Color.class,
                new ColorEditor());

        add(scrollPane);
    }

    class MyTableModel extends AbstractTableModel {
        private String[] columnNames = {"First Name",
                "Favorite Color",
                "Sport",
                "# of Years",
                "Vegetarian"};
        private Object[][] data = {
                {"Mary", new Color(153, 0, 153),
                        "Snowboarding", new Integer(5), new Boolean(false)},
                {"Alison", new Color(51, 51, 153),
                        "Rowing", new Integer(3), new Boolean(true)},
                {"Kathy", new Color(51, 102, 51),
                        "Knitting", new Integer(2), new Boolean(false)},
                {"Sharon", Color.red,
                        "Speed reading", new Integer(20), new Boolean(true)},
                {"Philip", Color.pink,
                        "Pool", new Integer(10), new Boolean(false)}
        };

        public int getColumnCount() {
            return columnNames.length;
        }

        public int getRowCount() {
            return data.length;
        }

        public String getColumnName(int col) {
            return columnNames[col];
        }

        public Object getValueAt(int row, int col) {
            return data[row][col];
        }

        public Class getColumnClass(int c) {
            return getValueAt(0, c).getClass();
        }

        public boolean isCellEditable(int row, int col) {
            if (col < 1) {
                return false;
            } else {
                return true;
            }
        }

        public void setValueAt(Object value, int row, int col) {
            data[row][col] = value;
            fireTableCellUpdated(row, col);
        }
    }

    private static void createAndShowGUI() {
        JFrame frame = new JFrame("TableDialogEditDemo");
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

        JComponent newContentPane = new TableDialogEditDemo();
        newContentPane.setOpaque(true);
        frame.setContentPane(newContentPane);

        frame.pack();
        frame.setVisible(true);
    }

    public static void main(String[] args) {
        javax.swing.SwingUtilities.invokeLater(new Runnable() {
            public void run() {
                createAndShowGUI();
            }
        });
    }
}

When you come back to choose a color, tf1 is given to the development, instead of the table. This is because bringing the color selector window to front raises an event lost the focus to the cell editor component; It's temporary, as it should, then, why the hell is the system to lose track of who has the focus in the window?

I see the following in #getMostRecentFocusOwner () Window:

  public Component getMostRecentFocusOwner()
  {
    if (isFocused())
    {
      return getFocusOwner();
    }
    else
    {
      Component mostRecent =
        KeyboardFocusManager.getMostRecentFocusOwner(this);
      if (mostRecent != null)
      {
        return mostRecent;
      }
      else
      {
        return (isFocusableWindow())
               ? getFocusTraversalPolicy().getInitialComponent(this)
               : null;
      }
    }
  }

My app has a custom course development policy, so I am able to see who is called, and indeed, getInitialComponent() is called. Clearly, the KeyboardFocusManager is in fact to lose track of the fact that the table was concentrated to the point where the control was transferred to the color picker! I think that is quite unreasonable, especially since, as mentioned, it is a temporary , not a permanent LostFocus event.

I would be grateful for any wisdom to solve this, since a behavior similar to this little demo - without loss of focus, of course - is an essential part of my application.

Hello
Or simpler, setFocusable (false)

 public ColorEditor() {
   button = new JButton();
   button.setActionCommand(EDIT);
   button.addActionListener(this);
   button.setBorderPainted(false);
   button.setFocusable(false); //<---- add

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thassaright wrote:

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