GWT: add filtering to CellTable

Question

I've been tasked with implementing sorting & filtering of data displayed in a GWT CellTable. Thankfully GWT already supports sorting, but it looks like I'll have to hack together my own filtering support.

To be more precise, what I'm trying to support is similar to the filtering offered by Excel, whereby you can click on a drop-down menu in the column headers and (for example) click checkboxes that will allow you to filter the rows based on the values for the filtered column(s). A picture is worth a thousand words:

My question: any suggestions on how to go about implementing this in GWT 2.2? Is it even possible?

One option I'm thinking about is to pass in a custom Header object to CellTable.addColumn(). If it's possible, I'll add a ClickHandler to the Header, and then open a Popup that displays a widget for filtering. Not sure how to implement this without negatively affecting the sorting behavior.

Any suggestions gladly welcome.

Edit:

Thanks to John below, I've got the following FilterableHeader class that allows me to at least put an icon into the header. Unsure how to get a ClickHandler on that icon just yet, as the image is inserted via HTML rather than using GWT widgets.

public class FilterableHeader extends Header<String>
{
    /**
     * Image resources.
     */
    public static interface Resources extends ClientBundle
    {
        ImageResource downArrow();
        ImageResource upArrow();
    }

    private static final Resources RESOURCES = GWT.create(Resources.class);
    private static final int IMAGE_WIDTH = 16;
    private static final String DOWN_ARROW = makeImage(RESOURCES.downArrow());
    private static final String UP_ARROW = makeImage(RESOURCES.upArrow());

    private static String makeImage(ImageResource resource)
    {
        AbstractImagePrototype proto = AbstractImagePrototype.create(resource);
        return proto.getHTML().replace("style='", "style='position:absolute;right:0px;top:0px;");
    }

    private String text;

    public FilterableHeader(String text)
    {
        super(new ClickableTextCell());
        this.text = text;
    }

    @Override
    public String getValue()
    {
        return text;
    }

    @Override
    public void render(Cell.Context context, SafeHtmlBuilder safe)
    {
        int imageWidth = IMAGE_WIDTH;

        StringBuilder sb = new StringBuilder();
        sb.append("<div style='position:relative;cursor:hand;cursor:pointer;");
        sb.append("padding-right:");
        sb.append(imageWidth);
        sb.append("px;'>");
        sb.append(UP_ARROW);
        sb.append("<div>");
        sb.append(text);
        sb.append("</div></div>");

        safe.append(SafeHtmlUtils.fromSafeConstant(sb.toString()));
    }
}

Answer 1

Custom headers are what is used with GWT 2.1 to do sorting. The 2.1 bikeshed has examples that use custom headers and am using one for sorting until Mvp4g moves to 2.2. To enable the filtering, just add an image with its own click handler and you should be good - it won't trigger sort behavior when it's clicked on, just the rest of the header will.

table.addColumn(new MyColumn(new MyCell()), new MyFilterHeader());

For the actual filtering, if you're using the database model from the examples (the wrapper class for the ListDataProvider), then I'd think you'd just keep two lists - the filtered list that's assigned to the ListDataProvider, and the unfiltered list it's based on.

Hope that helps!

---

In your new sample code, you might want to try a CompositeCell with the ClickableTextCell inside it, along with an ActionCell for the filtering part - if you can stick an image into the ClickableTextCell, you should be able to in the ActionCell, plus it'll have the mouseup behavior you want.

Answer 2

I develop business applications where a typical database query might return hundreds or thousands of rows. Users find the excel-like filters and column sorts to be very helpful.

Hence I have implemented a class that extends ListDataProvider for use with a CellTable that supports client-side excel-like column filtering and sorting. In all other respects it behaves much like a ListDataProvider.

It depends on implementing a the following ColumnAccessor interface to provide a symbolic name for for each column in the CellTable, to provide access to column-level data for sorting and filtering, a Comparator for the column for sorting, and display label for the header. Following is the ColumnAccessor class. It assumes that you have some sort of Data Transfer Object <T> that models the rows.

/**
 * Interface to provide access to a specific
 * column within a data row.
 * @param <T> Object that contains the column
 *  values in a cell table row. Typically a Data Transfer Object.
 */
public interface ColumnAccessor<T> {
    /**
     * Filter display value for blank/null column values
     */
    public final String FILTER_SELECTOR_BLANK = "{Blank}";
    /**

     * Returns A row-unique symbolic name for the column. This name is
     * used as a Map key to access the ColumnAccessor instance by
     * name for filtering and sorting.
     * @return
     */
    public String getColumnName();

    /**
     * Returns text label to appear as column header in CellTable.
     * @return
     */
    public String getLabel();

    /**
     * Returns value of the column as a String
     * @param t Object that models the column values in a
     *          cell table row (Typically a Data Transfer Object)
     * @return
     */
    public String getValue(T t);

    /**
     * Returns Comparator for sorting data rows and for sorting
     * discrete values that appear in a filter's select/option list.
     * While the getValue() method always returns a String,
     * these comparators should sort the column's values in
     * consideration for the data type (for example, dates sorted
     * as dates, numbers sorted as numbers, strings sorted as strings).
     * @return
     */
    public Comparator comparator();

}

Following is the FilterSortDataProvider class:

import com.google.gwt.cell.client.SelectionCell;
import com.google.gwt.cell.client.ValueUpdater;
import com.google.gwt.dom.client.Element;
import com.google.gwt.dom.client.NativeEvent;
import com.google.gwt.dom.client.SelectElement;
import com.google.gwt.safehtml.shared.SafeHtmlBuilder;
import com.google.gwt.safehtml.shared.SafeHtmlUtils;
import com.google.gwt.user.cellview.client.Header;
import com.google.gwt.view.client.ListDataProvider;

import java.util.*;

/**
 * Class that extends a ListDataProvider but adds "Excel-Like" column filters and also
 * includes click on column heading sorts.
 * @param <T> Object that contains the column values in a cell table row. Typically a Data Transfer Object.
 */
public class FilterSortDataProvider<T> extends ListDataProvider {
    private List<T> rows;
    private List<T> filteredSortedRows;
    public Map<String, DataColumn> dataColumnMap = new HashMap<String, DataColumn>();
    private String lastSortColumn = "*";
    private int lastSortDirection = 0;

    /**
     * Constructs the DataProvider and columns
     * @param rows Collection of objects that contain column data for cell table rows, typically
     *             Data Transfer Objects.
     * @param columnAccessors List of ColumnAccessor instances for each column that will appear in
     *                        the cell table. Each accessor will render a sortable, filterable column header
     *                        and provides access to column-level data.
     */
    public FilterSortDataProvider(Collection<T> rows, List<ColumnAccessor> columnAccessors) {
        this.rows = new ArrayList<T>(rows);
        this.filteredSortedRows = new ArrayList<T>();
        Iterator<ColumnAccessor> columnAccessorIterator = columnAccessors.iterator();
        while (columnAccessorIterator.hasNext()) new DataColumn(columnAccessorIterator.next());
        // Initialize filters
        filter();
    }

    /**
     * Returns defensive copy of the current collection of filtered/sorted data rows
     * @return
     */
    public List<T> getFilteredSortedRows() {
        return new ArrayList(filteredSortedRows);
    }

    /**
     * Returns a CellTable Header for the named column for use when setting up the CellTable (ie:
     * used as Header value in cellTable.addColumn(TextColumn, Header) call. The header includes
     * the columnAccessor.getLabel() value as a click-to-sort header label, and a drop-down filter
     * where the options include all available values.
     * @param columnName Same value as returned by this columns ColumnAccessor.getColumnName()
     * @return
     */
    public Header getColumnHeader(final String columnName) {
        DataColumn column = dataColumnMap.get(columnName);
        return (column != null ? new FilteredCellTableHeader(column) : null);
    }

    /**
     * Called when user clicks on column header label. Repeated clicks on the same column header will
     * reverse the sort direction. Can also be called prior to display of CellTable to establish an initial
     * sort order.
     * @param sortColumnName
     */
    public void sort(String sortColumnName) {
        if (!sortColumnName.equals("*")) {
            DataColumn column = dataColumnMap.get(sortColumnName);
            if (column != null) {
                // Sort ascending
                Collections.sort(this.filteredSortedRows, column);
                // Re-Sort of same column
                if (sortColumnName.equals(lastSortColumn)) {
                    lastSortDirection *= -1;
                }
                else {
                    lastSortDirection = 1;
                    lastSortColumn = sortColumnName;
                }
                if (lastSortDirection == -1) Collections.reverse(filteredSortedRows);
            }
        }
        this.setList(filteredSortedRows);
    }

    /**
     * Optional call to pre-set filter before initial display of CellTable
     * @param columnName
     * @param value
     */
    public void filter(String columnName, String value) {
        DataColumn column = dataColumnMap.get(columnName);
        if (column != null) column.filter(value);
    }

    /**
     * Filters the rows based on all of the filters, and re-builds the filter drop-down
     * options.
     */
    private void filter() {
        // Build collection of rows that pass all filters
        filteredSortedRows = new ArrayList<T>();
        Iterator<T> rowIterator = this.rows.iterator();
        while (rowIterator.hasNext()) {
            T row = rowIterator.next();
            if (rowPassesFilter(row, null)) filteredSortedRows.add(row);
        }

        // Build filter select/option list for each column based on rows
        // that pass all filters EXCEPT for the column in question.
        Iterator<DataColumn> columnIterator = dataColumnMap.values().iterator();
        while (columnIterator.hasNext()) {
            DataColumn column = columnIterator.next();
            Set<String> optionsSet = new HashSet<String>();
            rowIterator = this.rows.iterator();
            while (rowIterator.hasNext()) {
                T row = rowIterator.next();
                if (rowPassesFilter(row, column)) {
                    optionsSet.add(column.filterOptionValue(row));
                }
            }
            // Sort the options using the ColumnAccessor's comparator
            List<String> optionsList = new ArrayList<String>(optionsSet);
            Collections.sort(optionsList, column.comparator());
            // Make blank option (if any) the last entry in the option list
            if (optionsList.contains(ColumnAccessor.FILTER_SELECTOR_BLANK)) {
                optionsList.remove(ColumnAccessor.FILTER_SELECTOR_BLANK);
                optionsList.add(ColumnAccessor.FILTER_SELECTOR_BLANK);
            }
            // Add the wild-card "All" as the first entry in the option list
            optionsList.add(0, "*");
            // Set the new list of options in the column
            column.filterOptions = optionsList;
        }
        // Re-sort the data with consideration for the current sort column and direction
        lastSortDirection *= -1;
        sort(lastSortColumn);
    }

    /**
     * Returns true if the specified row passes all column filters.
     * @param row Data row to test
     * @param columnToIgnore When specified, this column is assumed to allow the row
     *                       to pass the filter. This is used when building the list
     *                       of filter select/option values.
     * @return
     */
    private boolean rowPassesFilter(T row, DataColumn columnToIgnore) {
        Iterator<DataColumn> columnIterator = dataColumnMap.values().iterator();
        boolean passes = true;
        while (columnIterator.hasNext() && passes) {
            DataColumn column = columnIterator.next();
            if (column != columnToIgnore) {
                passes = column.rowPassesFilter(row);
            }
        }
        return passes;
    }

    /**
     * Inner class that models a CellTable column, its ColumnAccessor, current filter value,
     * and current filter option values.
     */
    public class DataColumn implements Comparator<T> {
        private String filterValue = "*";
        private List<String> filterOptions = new ArrayList<String>();
        private ColumnAccessor columnAccessor;

        /**
         * Constructs a filterable, sortable column
         * @param columnAccessor
         */
        public DataColumn(final ColumnAccessor columnAccessor) {
            this.columnAccessor = columnAccessor;
            FilterSortDataProvider.this.dataColumnMap.put(columnAccessor.getColumnName(), this);
        }

        /**
         * Returns symbolic name of column
         * @return
         */
        public String getName() {
            return this.columnAccessor.getColumnName();
        }

        /**
         * Returns display label for column header
         * @return
         */
        public String getLabel() {
            return columnAccessor.getLabel();
        }

        /**
         * Returns value of column
         * @param row
         * @return
         */
        public String getValue(T row) {
            return columnAccessor.getValue(row);
        }

        /**
         * Returns comparator define in ColumnAccessor for use when sorting
         * data rows and for sorting filter options.
         * @return
         */
        public Comparator comparator() {
            return columnAccessor.comparator();
        }

        /**
         * Called when user changes the value of a column filter
         * @param filterValue
         */
        public void filter(String filterValue) {
            if (this.filterOptions.contains(filterValue)) {
                this.filterValue = filterValue;
                FilterSortDataProvider.this.filter();
            }
        }

        /**
         * Called when user clicks on column label to sort rows
         */
        public void sort() {
            FilterSortDataProvider.this.sort(this.columnAccessor.getColumnName());
        }

        /**
         * Used to sort data rows. Uses comparator specified in ColumnAccessor.
         * @param row1
         * @param row2
         * @return
         */
        public int compare(T row1, T row2) {
            return comparator().compare(getValue(row1), getValue(row2));
        }

        /**
         * Returns true if specified row passes this column's filter
         * @param row
         * @return
         */
        public boolean rowPassesFilter(T row) {
            return filterValue.equals("*") || filterValue.equals(filterOptionValue(row));
        }

        /**
         * Returns value to appear in filter options list. Null or "blank" values appear in options
         * list as {Blank}.
         * @param row
         * @return
         */
        private String filterOptionValue(T row) {
            String value = getValue(row);
            return (value == null || value.trim().length() == 0 ? ColumnAccessor.FILTER_SELECTOR_BLANK : value);
        }

        /**
         * Renders Html Select/Options tag for column filter
         * @return
         */
        public String toHtmlSelect() {
            StringBuffer sb = new StringBuffer();
            sb.append("<select size='1' style='width: 100%;'>");
            Iterator<String> opts = filterOptions.iterator();
            while (opts.hasNext()) {
                String escapedOption = SafeHtmlUtils.htmlEscape(opts.next());
                sb.append("\t<option value='" + escapedOption);
                sb.append((escapedOption.equals(filterValue) ? "' SELECTED>" : "'>"));
                sb.append(escapedOption + "</option>\n");
            }
            sb.append("</select>\n");
            return sb.toString();
        }
    }

    /**
     * Inner class Header wrapper for FilteredSortedCellTableHeaderCell
     */
    public class FilteredCellTableHeader extends Header {
        public FilteredCellTableHeader(DataColumn column) {
            super(new FilteredSortedCellTableHeaderCell(column));
        }
        public Object getValue() {
            return null;
        }
    }

    /**
     * CellTable SelectionCell that includes filter and sort controls, renders controls, and
     * handles onBrowserEvent()
     */
    private class FilteredSortedCellTableHeaderCell extends SelectionCell {
        private DataColumn column;
        public FilteredSortedCellTableHeaderCell(final DataColumn column) {
            super(new ArrayList<String>());
            this.column = column;
        }

        /**
         * Renders Html Submit button as sort control, and Html Select/Option tag for filter.
         * @param context
         * @param value
         * @param sb
         */
        @Override
        public void render(Context context, String value, SafeHtmlBuilder sb) {
            String sortButton = "<input type='submit' value='" + SafeHtmlUtils.htmlEscape(column.getLabel()) +
                    "' style='text-align: center; width: 100%; background: none; border: none; font-weight: bold;'>";
            sb.appendHtmlConstant(sortButton);
            sb.appendHtmlConstant("<br>");
            sb.appendHtmlConstant(column.toHtmlSelect());
        }

        /**
         * Detects filter and sort user interaction events
         * @param context
         * @param parent
         * @param value
         * @param event
         * @param valueUpdater
         */
        @Override
        public void onBrowserEvent(Context context, Element parent, String value, NativeEvent event, ValueUpdater<String> valueUpdater) {
            super.onBrowserEvent(context, parent, value, event, valueUpdater);
            String type = event.getType();
            Element element = event.getEventTarget().cast();
            String tagName = element.getTagName();
            // Filter selection changed
            if ("change".equals(type) && tagName.equals("SELECT")) {
                // Set filter value and call filter routine
                SelectElement se = (SelectElement)element;
                String filterValue = se.getOptions().getItem(se.getSelectedIndex()).getValue();
                column.filter(filterValue);
            }
            // Click on sort button
            else if (type.equals("focus") && tagName.equals("INPUT")) {
                column.sort();
            }
        }
    }
}

I hope that this might be of help to someone.

Answer 3

I used the mouse-click position to add custom click events to column headers. In other words, you can set it up so that if the user clicks in the 'general area' where the image is supposed to be, you can show a filtering screen.

Here's an example where I have it ignoring click events for a text field I added:

        if(col.isFilterable()){
            if (event.getClientY() > (getInputElement(parent).getAbsoluteTop() - 2) && event.getClientY() < (getInputElement(parent).getAbsoluteBottom() + 2)) {
                //ignore on click in area of the text field
                event.preventDefault();
            } else {

//sort if user clicks anywhere else trySort(parent); }

And the because cell listens for 'keyup' events separately, the filter is executed when the user hits enter (while the cell is focused).

    if(event.getKeyCode()==13){
        event.preventDefault();
        handleSetFilterValue(parent);
        tryFilter();
    }