Java tutorial
package com.google.gwt.sample.showcase.client.content.cell; import com.google.gwt.core.client.Scheduler; import com.google.gwt.core.client.Scheduler.ScheduledCommand; import com.google.gwt.dom.client.BrowserEvents; import com.google.gwt.dom.client.NativeEvent; import com.google.gwt.event.dom.client.HasKeyDownHandlers; import com.google.gwt.event.dom.client.KeyCodes; import com.google.gwt.event.dom.client.KeyDownEvent; import com.google.gwt.event.dom.client.KeyDownHandler; import com.google.gwt.sample.showcase.client.Settings; import com.google.gwt.sample.showcase.client.content.cell.ContactDatabase.ContactInfo; import com.google.gwt.user.cellview.client.AbstractHasData.DefaultKeyboardSelectionHandler; import com.google.gwt.user.cellview.client.CellList; import com.google.gwt.user.cellview.client.LoadingStateChangeEvent; import com.google.gwt.user.cellview.client.LoadingStateChangeEvent.LoadingState; import com.google.gwt.view.client.CellPreviewEvent; class CustomKeyboardHandler extends DefaultKeyboardSelectionHandler<ContactInfo> { interface SelectableWidget extends HasKeyDownHandlers { void selectWidget(); } private static final int PAGE_INCREMENT = 11; private final CellList<ContactInfo> cellList; private final SelectableWidget widgetAboveList; private boolean isEndRequestPending = false; public CustomKeyboardHandler(CellList<ContactInfo> cellList, SelectableWidget widgetAboveList) { super(cellList); this.cellList = cellList; this.widgetAboveList = widgetAboveList; cellList.addLoadingStateChangeHandler(new LoadingStateChangeEvent.Handler() { @Override public void onLoadingStateChanged(LoadingStateChangeEvent event) { onLoadingChange(event.getLoadingState()); } }); widgetAboveList.addKeyDownHandler(new KeyDownHandler() { @Override public void onKeyDown(KeyDownEvent event) { switch (event.getNativeKeyCode()) { case KeyCodes.KEY_DOWN: case KeyCodes.KEY_J: setCurrentRow(0); event.preventDefault(); break; } } }); } @Override public void onCellPreview(CellPreviewEvent<ContactInfo> event) { if (Settings.get().getKeyHandling()) { NativeEvent nativeEvent = event.getNativeEvent(); if (nativeEvent.getType() == BrowserEvents.KEYDOWN) { // A key was pushed down if (nativeEvent.getShiftKey() || nativeEvent.getAltKey() || nativeEvent.getCtrlKey() || nativeEvent.getMetaKey()) { // Ignore if a modifier key is down return; } switch (nativeEvent.getKeyCode()) { case KeyCodes.KEY_DOWN: // The down arrow key case KeyCodes.KEY_J: setCurrentRow(cellList.getKeyboardSelectedRow() + 1); cancelEvent(event); break; case KeyCodes.KEY_UP: // The up arrow key case KeyCodes.KEY_K: if (cellList.getKeyboardSelectedRow() < 1) { goAboveList(event.getValue()); } else { setCurrentRow(cellList.getKeyboardSelectedRow() - 1); } cancelEvent(event); break; case KeyCodes.KEY_PAGEDOWN: case KeyCodes.KEY_SPACE: setCurrentRow(cellList.getKeyboardSelectedRow() + PAGE_INCREMENT); cancelEvent(event); break; case KeyCodes.KEY_PAGEUP: setCurrentRow(cellList.getKeyboardSelectedRow() - PAGE_INCREMENT); cancelEvent(event); break; case KeyCodes.KEY_HOME: setCurrentRow(cellList.getPageStart()); cancelEvent(event); break; case KeyCodes.KEY_END: goToVeryEnd(); cancelEvent(event); break; } // Bypass the default handler (super-class) for all keydown events. // For keys not handled here, let the browser handle them. return; } } // Should get here only if event was not handled above. Send the event to // the default handler. super.onCellPreview(event); } void setCurrentRow(int row) { cellList.setKeyboardSelectedRow(row); // Read the current row index back, because the cellList will have clipped // it to a valid row if we tried to set it to a row that doesn't exist. int newRow = cellList.getKeyboardSelectedRow(); // Scroll row into view (needed because the default scrolling may be disabled // so that the view doesn't jump on data updates when the current // row is out of view). Also useful, if you need custom scrolling, e.g. // because of fixed elements on the page. cellList.getRowElement(newRow).scrollIntoView(); } // Re-implement DefaultKeyboardSelectionHandler.handledEvent because that's // package-private. void cancelEvent(CellPreviewEvent<ContactInfo> event) { event.setCanceled(true); event.getNativeEvent().preventDefault(); } void goAboveList(ContactInfo keyboardSelectedValue) { cellList.getSelectionModel().setSelected(keyboardSelectedValue, false); // Unselecting the row (above) will steal the focus (doesn't really need to, // but does), and do this deferred. Defer select here to come after that. Scheduler.get().scheduleDeferred(new ScheduledCommand() { @Override public void execute() { widgetAboveList.selectWidget(); } }); } // The async data loading broke the end key. The default handler only goes to // the end of what's loaded. To fix it, update the page size to request more // data, then wait until it's loaded before selecting the last row. void goToVeryEnd() { int totalRows = cellList.getRowCount(); int pageStart = cellList.getPageStart(); int pageSize = cellList.getPageSize(); int renderedRows = cellList.getVisibleItemCount(); if (cellList.isRowCountExact() && totalRows > pageStart + pageSize) { isEndRequestPending = true; cellList.setPageSize(totalRows - pageStart); // We'll select the last row after it's loaded } else { // Just go to the end of what's rendered setCurrentRow(renderedRows - 1); } } void onLoadingChange(LoadingState newState) { if (isEndRequestPending && newState == LoadingState.LOADED) { // Loading change events are sent just before any new rows are rendered. // Defer execution to let them render. Scheduler.get().scheduleDeferred(new ScheduledCommand() { @Override public void execute() { int totalRows = cellList.getRowCount(); int pageStart = cellList.getPageStart(); int pageSize = cellList.getPageSize(); int renderedRows = cellList.getVisibleItemCount(); if (pageStart + pageSize < totalRows) { // Either more rows got added, or the page size got shrunk. Fix it. cellList.setPageSize(totalRows - pageStart); } else if (renderedRows == totalRows - pageStart) { isEndRequestPending = false; setCurrentRow(renderedRows - 1); } else { // keep waiting } } }); } } }