Last week I explained how we can use display custom items in a standard Matlab combobox (popup/dropdown), using its underlying Java component. Today I will show how we can use this Java component for other nice customizations of the combobox’s popup:
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Underlying Java component
The first step is to find the underlying Java component of the Matlab combobox (aka popup) uicontrol. This is done using my findjobj utility:
% Create the Matlab combobox items = {'<HTML><FONT color="red">Hello</Font></html>', 'world', ... '<html><font style="font-family:impact;color:green"><i>What a', ... '<Html><FONT color="blue" face="Comic Sans MS">nice day!</font>'}; hCombobox = uicontrol('Style','popup', 'Position',[10,100,120,20], 'String',items); % Find the uicontrol's underlying Java component jCombobox = findjobj(hCombobox);
For findjobj to work, the Matlab uicontrol needs to be visible – it will not have a Java component before it is rendered onscreen for the first time. If everything is successful, jCombobox should now be a reference to the underlying om.mathworks.hg.peer.ComboboxPeer$MLComboBox Java component, which is an extension of the standard Swing JComboBox, as can be seen using my checkClass utility:
>> jCombobox.checkClass private com.mathworks.hg.peer.ComboboxPeer$MLComboBox (uiinspect) Superclass: com.mathworks.mwswing.MJComboBox Superclass: javax.swing.JComboBox Methods in JComboBox missing in ComboboxPeer$MLComboBox: JComboBox() JComboBox(java.lang.Object[]) JComboBox(java.util.Vector) JComboBox(javax.swing.ComboBoxModel) Methods in ComboboxPeer$MLComboBox missing in JComboBox: ComboboxPeer$MLComboBox(com.mathworks.hg.peer.ComboboxPeer) isPopupWidthConstrained() : boolean isTipWhenTruncatedEnabled() : boolean processEvent(java.awt.AWTEvent) registerWithKeyBindingManager(com.mathworks.mwswing.binding.KeyBindingManager, java.lang.String) setConstrainPopupWidth(boolean) setEditorColumnCount(int) setTipWhenTruncatedEnabled(boolean) Methods inherited & modified by ComboboxPeer$MLComboBox: getInsets() : java.awt.Insets setBackground(java.awt.Color) updateUI() Interfaces in JComboBox missing in ComboboxPeer$MLComboBox: java.awt.ItemSelectable java.awt.event.ActionListener javax.accessibility.Accessible javax.swing.event.ListDataListener
We shall now use three properties of this object to customize the control’s popup:
MaximumRowCount
The MaximumRowCount numeric property (default=20) sets the maximal number of drop-down items to display in the visible portion of the popup, before requiring a scrollbar. This basically controls the popup’s height:
% Get the current MaximumRowCount value numItems = get(jCombobox, 'MaximumRowCount'); numItems = jCombobox.MaximumRowCount; % equivalent - access the property directly numItems = jCombobox.getMaximumRowCount; % equivalent - use Java's accessor method (best way) % Set the MaximumRowCount value set(jCombobox,'MaximumRowCount',3); jCombobox.MaximumRowCount = 3; % equivalent - access the property directly jCombobox.setMaximumRowCount(3); % equivalent - use Java's accessor method (best way)
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MaximumRowCount=20
(default)
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MaximumRowCount=3
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MaximumRowCount=2
Note that MaximumRowCount is a Matlab extension to the standard Swing JComboBox, so if we use a JComboBox directly in our code (using javacomponent) we will not have this feature. Creating the ComboboxPeer$MLComboBox component instead is possible, but is beyond the scope of this article, because MathWorks chose for this class not to have JComboBox‘s standard constructors but rather only a constructor that accepts a com.mathworks.hg.peer.ComboboxPeer object.
PopupVisible
The PopupVisible property (default=false) is a boolean flag which controls whether the popup window is currently (or should be) displayed. If this property is updated, then the focus is automatically transferred to the popup window for easy item selection using the keyboard (up/down/enter keys). There are also equivalent convenience methods showPopup()/hidePopup():
% Is the popup currently shown? isShown = get(jCombobox, 'PopupVisible'); isShown = jCombobox.PopupVisible; % equivalent - access the property directly isShown = jCombobox.isPopupVisible; % equivalent - use Java's accessor method (best way) % Display the popup set(jCombobox,'PopupVisible',true); % NOT 'on' - this is a Java property, not a Matlab HG one! jCombobox.PopupVisible = true; % equivalent - access the property directly jCombobox.setPopupVisible(true); % equivalent - use Java's accessor method (best way) % Hide the popup set(jCombobox,'PopupVisible',false); % NOT 'off' - this is a Java property, not a Matlab HG one! jCombobox.PopupVisible = false; % equivalent - access the property directly jCombobox.setPopupVisible(false); % equivalent - use Java's accessor method (best way)
Note that PopUpVisible is not a Matlab extension – it exists in the original Swing JComboBox. Unfortunately, it was not included in the list of properties that are exposed to the user by the high-level Matlab uicontrol, so we need to use the underlying Java component.
On a Windows platform the PopupVisible property is toggled, thereby showing/hiding the popup window, whenever the user clicks <Alt-Up> or <Alt-Down> when the combo-box has focus.
PopupWidthConstrained
The PopupWidthConstrained property (default=false) is a boolean flag which is another Matlab extension to the standard Swing JComboBox. It is apparently used to constrain the width of the drop-down list to the width of the text field. MathWorks took the trouble to add this feature because Swing JComboBox‘s width is constrained, causing a difficulty in distinguishing between popup values when the control is relatively narrow; Matlab’s MJComboBox‘s default unconstrained behavior is much more user-friendly:
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PopupWidthConstrained=false
(default)
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PopupWidthConstrained=true
Note that the PopupWidthConstrained property’s read accessor methods is the expected isPopupWidthConstrained(), thereby also enabling the expected Matlab-standard format of get(‘PopupWidthConstrained’). However, the property update accessor method is not the expected setPopupWidthConstrained(flag) but rather a non-standard setConstrainPopupWidth(flag). For this reason, it is impossible to set this property using set(‘PopupWidthConstrained’,…), but only via the Java setConstrainPopupWidth() accessor method:
>> set(jCombobox,'PopupWidthConstrained',true) ??? Changing the 'PopupWidthConstrained' property of javahandle_withcallbacks.com.mathworks.hg.peer.ComboboxPeer$MLComboBox is not allowed. >> jCombobox.setPopupWidthConstrained(true) ??? No appropriate method or public field setPopupWidthConstrained for class javahandle_withcallbacks.com.mathworks.hg.peer.ComboboxPeer$MLComboBox. >> jCombobox.setConstrainPopupWidth(true) % this is ok
For additional customizations of Matlab comboboxes, refer to section 6.7 of my Matlab-Java programming book.
R2014b
We’re all eagerly awaiting the much-anticipated R2014b release. As you all know, this is an important release with major functionality and engine improvements. It is therefore not surprising that the release date (which should normally have been September 1) is somewhat delayed. MathWorkers are hard at work fixing problems in the pre-release beta. This delay was actually anticipated, as can be seen from the pre-release expiry date.
We should all be patient and let MathWorks fix these issues without pressure. This release could be a real home-run and MathWorks should do all it can to ensure that it works as transparently and as backward-compatible as possible so that it indeed becomes a home run rather than an outfield foul ball. Let’s not have a repeat of R2010b, which required two separate service-pack updates. I urge MathWorks to take their time – better safe than sorry. I urge everyone else to be patient – it’s worth the wait.
When 14b is finally out, I will be here with a planned series of articles explaining how we can make good use of all its new goodies. Start drooling…
Happy Jewish New Year everybody!
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