GWT: In a TabLayoutPanel, how do I make tabs wrap if there are too many? - gwt

Question

I'm using GWT 2.4. I have a TabLayoutPanel to which I add tabs. Each tab contains a ScrollPanel. My question is, how do I make the tabs in the tab bar wrap to the next line if the width of the tab bar exceeds the visible width?
Thanks, - Dave

Answer 1

GWT's TabLayoutPanel intentionally never wraps tabs. See lines 246-248 in TabLayoutPanel.java - (line 217 defines private static final int BIG_ENOUGH_TO_NOT_WRAP = 16384). You might be able to override this, but as #milan says, it's probably not good design.

Answer 2

Having multiple lines is, indeed, not recommended...
However, to be able to navigate left/right on a single tab bar with many tabs, you can use this recipe:
http://devnotesblog.wordpress.com/2010/06/17/scrollable-gwt-tablayoutpanel/
And an updated implementation that doesn't use the deprecated DeferredCommand:
package whatever.you.want;
import com.google.gwt.core.client.Scheduler;
import com.google.gwt.dom.client.Style.Unit;
import com.google.gwt.event.dom.client.ClickEvent;
import com.google.gwt.event.dom.client.ClickHandler;
import com.google.gwt.event.logical.shared.ResizeEvent;
import com.google.gwt.event.logical.shared.ResizeHandler;
import com.google.gwt.event.shared.HandlerRegistration;
import com.google.gwt.resources.client.ImageResource;
import com.google.gwt.user.client.Window;
import com.google.gwt.user.client.ui.FlowPanel;
import com.google.gwt.user.client.ui.Image;
import com.google.gwt.user.client.ui.LayoutPanel;
import com.google.gwt.user.client.ui.TabLayoutPanel;
import com.google.gwt.user.client.ui.Widget;
/**
* A {#link TabLayoutPanel} that shows scroll buttons if necessary
*/
public class ScrolledTabLayoutPanel extends TabLayoutPanel {
private static final int IMAGE_PADDING_PIXELS = 4;
private LayoutPanel panel;
private FlowPanel tabBar;
private Image scrollLeftButton;
private Image scrollRightButton;
private HandlerRegistration windowResizeHandler;
private ImageResource leftArrowImage;
private ImageResource rightArrowImage;
public ScrolledTabLayoutPanel(double barHeight, Unit barUnit,
ImageResource leftArrowImage, ImageResource rightArrowImage) {
super(barHeight, barUnit);
this.leftArrowImage = leftArrowImage;
this.rightArrowImage = rightArrowImage;
// The main widget wrapped by this composite, which is a LayoutPanel with the tab bar & the tab content
panel = (LayoutPanel) getWidget();
// Find the tab bar, which is the first flow panel in the LayoutPanel
for (int i = 0; i < panel.getWidgetCount(); ++i) {
Widget widget = panel.getWidget(i);
if (widget instanceof FlowPanel) {
tabBar = (FlowPanel) widget;
break; // tab bar found
}
}
initScrollButtons();
}
#Override
public void add(Widget child, Widget tab) {
super.add(child, tab);
checkIfScrollButtonsNecessary();
}
#Override
public boolean remove(Widget w) {
boolean b = super.remove(w);
checkIfScrollButtonsNecessary();
return b;
}
#Override
protected void onLoad() {
super.onLoad();
if (windowResizeHandler == null) {
windowResizeHandler = Window.addResizeHandler(new ResizeHandler() {
#Override
public void onResize(ResizeEvent event) {
checkIfScrollButtonsNecessary();
}
});
}
}
#Override
protected void onUnload() {
super.onUnload();
if (windowResizeHandler != null) {
windowResizeHandler.removeHandler();
windowResizeHandler = null;
}
}
private ClickHandler createScrollClickHandler(final int diff) {
return new ClickHandler() {
#Override
public void onClick(ClickEvent event) {
Widget lastTab = getLastTab();
if (lastTab == null)
return;
int newLeft = parsePosition(tabBar.getElement().getStyle().getLeft()) + diff;
int rightOfLastTab = getRightOfWidget(lastTab);
// Prevent scrolling the last tab too far away form the right border,
// or the first tab further than the left border position
if (newLeft <= 0 && (getTabBarWidth() - newLeft < (rightOfLastTab + 20))) {
scrollTo(newLeft);
}
}
};
}
/** Create and attach the scroll button images with a click handler */
private void initScrollButtons() {
scrollLeftButton = new Image(leftArrowImage);
int leftImageWidth = scrollLeftButton.getWidth();
panel.insert(scrollLeftButton, 0);
panel.setWidgetLeftWidth(scrollLeftButton, 0, Unit.PX, leftImageWidth, Unit.PX);
panel.setWidgetTopHeight(scrollLeftButton, 0, Unit.PX, scrollLeftButton.getWidth(), Unit.PX);
scrollLeftButton.addClickHandler(createScrollClickHandler(+20));
scrollLeftButton.setVisible(false);
scrollRightButton = new Image(rightArrowImage);
panel.insert(scrollRightButton, 0);
panel.setWidgetLeftWidth(scrollRightButton, leftImageWidth + IMAGE_PADDING_PIXELS, Unit.PX, scrollRightButton.getWidth(), Unit.PX);
panel.setWidgetTopHeight(scrollRightButton, 0, Unit.PX, scrollRightButton.getHeight(), Unit.PX);
scrollRightButton.addClickHandler(createScrollClickHandler(-20));
scrollRightButton.setVisible(false);
}
private void checkIfScrollButtonsNecessary() {
// Defer size calculations until sizes are available, when calculating immediately after
// add(), all size methods return zero
Scheduler.get().scheduleDeferred( new Scheduler.ScheduledCommand() {
#Override
public void execute() {
boolean isScrolling = isScrollingNecessary();
// When the scroll buttons are being hidden, reset the scroll position to zero to
// make sure no tabs are still out of sight
if (scrollRightButton.isVisible() && !isScrolling) {
resetScrollPosition();
}
scrollRightButton.setVisible(isScrolling);
scrollLeftButton.setVisible(isScrolling);
}
}
);
}
private void resetScrollPosition() {
scrollTo(0);
}
private void scrollTo(int pos) {
tabBar.getElement().getStyle().setLeft(pos, Unit.PX);
}
private boolean isScrollingNecessary() {
Widget lastTab = getLastTab();
if (lastTab == null)
return false;
return getRightOfWidget(lastTab) > getTabBarWidth();
}
private int getRightOfWidget(Widget widget) {
return widget.getElement().getOffsetLeft() + widget.getElement().getOffsetWidth();
}
private int getTabBarWidth() {
return tabBar.getElement().getParentElement().getClientWidth();
}
private Widget getLastTab() {
if (tabBar.getWidgetCount() == 0)
return null;
return tabBar.getWidget(tabBar.getWidgetCount() - 1);
}
private static int parsePosition(String positionString) {
int position;
try {
for (int i = 0; i < positionString.length(); i++) {
char c = positionString.charAt(i);
if (c != '-' && !(c >= '0' && c <= '9')) {
positionString = positionString.substring(0, i);
}
}
position = Integer.parseInt(positionString);
} catch (NumberFormatException ex) {
position = 0;
}
return position;
}
}