Hi, I modified this for gwt 2.2.0, and some minor fixes (selecting a tab was
causing scoll to 0)
BTW thanks to Matt for the first version, it saved me a lot of work
package com.gwtscrolledtablayoutpanel.ui;
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.logical.shared.SelectionEvent;
import com.google.gwt.event.logical.shared.SelectionHandler;
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.*;
/**
* 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;
private static final int SCROLL_INTERVAL = 60;
private HandlerRegistration selectionHandler;
private int lastScroll = 0;
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 w) {
super.add(w);
checkIfScrollButtonsNecessary();
}
@Override
public void add(Widget child, String text) {
super.add(child, text);
checkIfScrollButtonsNecessary();
}
@Override
public void add(Widget child, String text, boolean asHtml) {
super.add(child, text, asHtml);
checkIfScrollButtonsNecessary();
}
@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();
}
});
}
if (selectionHandler == null) {
selectionHandler = addSelectionHandler(new SelectionHandler<Integer>()
{
public void onSelection(SelectionEvent<Integer> selectedEvent) {
doOnSelectTab(selectedEvent.getSelectedItem());
}
});
}
}
@Override
protected void onUnload() {
super.onUnload();
if (windowResizeHandler != null) {
windowResizeHandler.removeHandler();
windowResizeHandler = null;
}
if (selectionHandler != null) {
selectionHandler.removeHandler();
selectionHandler = null;
}
}
private void doOnSelectTab(int selected) {
Scheduler.get().scheduleDeferred(new Scheduler.ScheduledCommand() {
public void execute() {
scrollTo(lastScroll);
}
});
}
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 -
diff / 2))) {
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(+SCROLL_INTERVAL));
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(-1 *
SCROLL_INTERVAL));
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() {
public void execute() {
//@Override
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);
lastScroll = pos;
}
private boolean isScrollingNecessary() {
Widget lastTab = getLastTab();
return lastTab != null && 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;
}
}
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