private Column<FileSystemItem, Boolean> addSelectionColumn() { Column<FileSystemItem, Boolean> checkColumn = new Column<FileSystemItem, Boolean>( new CheckboxCell(true, false) { @Override public void render(Context context, Boolean value, SafeHtmlBuilder sb) { // don't render the check box if its for the parent path if (parentPath_ == null || context.getIndex() > 0) super.render(context, value, sb); } }) { @Override public Boolean getValue(FileSystemItem item) { return selectionModel_.isSelected(item); } }; checkColumn.setVerticalAlignment(HasVerticalAlignment.ALIGN_TOP); filesDataGrid_.addColumn(checkColumn); filesDataGrid_.setColumnWidth(checkColumn, CHECK_COLUMN_WIDTH_PIXELS, Unit.PX); return checkColumn; }