GWT 日期选择器单元格显示"empty"日期？

Question

我使用的CellTable也DatePickerCell，我希望能够显示日期也没有设置，例如。"空"的日期。但是在实现getValue方法时，我必须返回一些东西:

        Column<EventProxy, Date> startTimeColumn = new Column<EventProxy, Date>(
            new DatePickerCell()) {
                @Override
                public Date getValue(EventProxy object) {
                    Date ret = object.getStartTime();
                    return ret != null ? ret : new Date();
                }
    };

如果object.getStartTime()是空的，这意味着它没有设置，我想这样显示它。或者使用空标签或文本"empty"。我说过，getValue方法必须返回一些东西。如果我返回null，稍后会得到异常，如果我返回具体日期，它会显示为有效日期。还有别的选择吗?一些特殊的日期标签或对象，DatePickerCell将识别为空或未设置的值?

Answer 1

您想知道如何显示日期，对吗?然后将焦点从getValue()转移到覆盖render()方法(在Column类中找到)。render()方法有一个对象参数，就像getValue()一样，还有一个SafeHtmlBuilder的参数，您可以将对象值的表示形式附加到该参数后面。测试getStartTime()，如果它是空的，追加"[unset]"(或任何)到该SafeHtmlBuilder。您甚至可以附加一个带有红色条纹的钟面图像(使用HTML img标记)，或者任何您想要的，因为渲染只是附加将被放入单元格的HTML。

与Guava Release 10中提供的一个新类没有直接关系，但可能在另一个上下文中对您有用。它是可选的。它是一个泛型，封装了您正在使用的类，在本例中为Date。它提供了一种使用所提供的方法显式区分空值和未设置值等的方法。快速阅读它——因为您正在处理空日期，这可能在您的设计的其他地方有用。

Answer 2

DatePickerCell不支持空值。重写render是不够的，因为当你点击渲染单元格时，NPE是从onEnterKeyDown方法抛出的。

你必须在"onEnterKeyDown"中实现你自己的null保护单元格:

if (date != null) {
    datePicker.setCurrentMonth(date);
}

完整类:

public class DatePickerCell extends AbstractEditableCell<Date, Date> {
private static final int ESCAPE = 27;
private final DatePicker datePicker;
private final DateTimeFormat format;
private int offsetX = 10;
private int offsetY = 10;
private Object lastKey;
private Element lastParent;
private int lastIndex;
private int lastColumn;
private Date lastValue;
private PopupPanel panel;
private final SafeHtmlRenderer<String> renderer;
private ValueUpdater<Date> valueUpdater;
/**
 * Constructs a new DatePickerCell that uses the date/time format given by
 * {@link DateTimeFormat#getFullDateFormat}.
 */
@SuppressWarnings("deprecation")
public DatePickerCell() {
    this(DateTimeFormat.getFullDateFormat(), SimpleSafeHtmlRenderer.getInstance());
}
/**
 * Constructs a new DatePickerCell that uses the given date/time format and
 * a {@link SimpleSafeHtmlRenderer}.
 * @param format a {@link DateTimeFormat} instance
 */
public DatePickerCell(DateTimeFormat format) {
    this(format, SimpleSafeHtmlRenderer.getInstance());
}
/**
 * Constructs a new DatePickerCell that uses the date/time format given by
 * {@link DateTimeFormat#getFullDateFormat} and the given
 * {@link SafeHtmlRenderer}.
 * @param renderer a {@link SafeHtmlRenderer SafeHtmlRenderer<String>}
 *            instance
 */
public DatePickerCell(SafeHtmlRenderer<String> renderer) {
    this(DateTimeFormat.getFormat(PredefinedFormat.DATE_FULL), renderer);
}
/**
 * Constructs a new DatePickerCell that uses the given date/time format and
 * {@link SafeHtmlRenderer}.
 * @param format a {@link DateTimeFormat} instance
 * @param renderer a {@link SafeHtmlRenderer SafeHtmlRenderer<String>}
 *            instance
 */
public DatePickerCell(DateTimeFormat format, SafeHtmlRenderer<String> renderer) {
    super(CLICK, KEYDOWN);
    if (format == null) {
        throw new IllegalArgumentException("format == null");
    }
    if (renderer == null) {
        throw new IllegalArgumentException("renderer == null");
    }
    this.format = format;
    this.renderer = renderer;
    this.datePicker = new DatePicker();
    this.panel = new PopupPanel(true, true) {
        @Override
        protected void onPreviewNativeEvent(NativePreviewEvent event) {
            if (Event.ONKEYUP == event.getTypeInt()) {
                if (event.getNativeEvent().getKeyCode() == ESCAPE) {
                    // Dismiss when escape is pressed
                    panel.hide();
                }
            }
        }
    };
    panel.addCloseHandler(new CloseHandler<PopupPanel>() {
        public void onClose(CloseEvent<PopupPanel> event) {
            lastKey = null;
            lastValue = null;
            lastIndex = -1;
            lastColumn = -1;
            if (lastParent != null && !event.isAutoClosed()) {
                // Refocus on the containing cell after the user selects a
                // value, but
                // not if the popup is auto closed.
                lastParent.focus();
            }
            lastParent = null;
        }
    });
    panel.add(datePicker);
    // Hide the panel and call valueUpdater.update when a date is selected
    datePicker.addValueChangeHandler(new ValueChangeHandler<Date>() {
        public void onValueChange(ValueChangeEvent<Date> event) {
            // Remember the values before hiding the popup.
            Element cellParent = lastParent;
            Date oldValue = lastValue;
            Object key = lastKey;
            int index = lastIndex;
            int column = lastColumn;
            panel.hide();
            // Update the cell and value updater.
            Date date = event.getValue();
            setViewData(key, date);
            setValue(new Context(index, column, key), cellParent, oldValue);
            if (valueUpdater != null) {
                valueUpdater.update(date);
            }
        }
    });
}
@Override
public boolean isEditing(Context context, Element parent, Date value) {
    return lastKey != null && lastKey.equals(context.getKey());
}
@Override
public void onBrowserEvent(Context context, Element parent, Date value, NativeEvent event, ValueUpdater<Date> valueUpdater) {
    super.onBrowserEvent(context, parent, value, event, valueUpdater);
    if (CLICK.equals(event.getType())) {
        onEnterKeyDown(context, parent, value, event, valueUpdater);
    }
}
@Override
public void render(Context context, Date value, SafeHtmlBuilder sb) {
    // Get the view data.
    Object key = context.getKey();
    Date viewData = getViewData(key);
    if (viewData != null && viewData.equals(value)) {
        clearViewData(key);
        viewData = null;
    }
    String s = null;
    if (viewData != null) {
        s = format.format(viewData);
    } else if (value != null) {
        s = format.format(value);
    }
    if (s != null) {
        sb.append(renderer.render(s));
    }
}
@Override
protected void onEnterKeyDown(Context context, Element parent, Date value, NativeEvent event, ValueUpdater<Date> valueUpdater) {
    this.lastKey = context.getKey();
    this.lastParent = parent;
    this.lastValue = value;
    this.lastIndex = context.getIndex();
    this.lastColumn = context.getColumn();
    this.valueUpdater = valueUpdater;
    Date viewData = getViewData(lastKey);
    Date date = (viewData == null) ? lastValue : viewData;
    if (date != null) {
        datePicker.setCurrentMonth(date);
    }
    datePicker.setValue(date);
    panel.setPopupPositionAndShow(new PositionCallback() {
        public void setPosition(int offsetWidth, int offsetHeight) {
            panel.setPopupPosition(lastParent.getAbsoluteLeft() + offsetX, lastParent.getAbsoluteTop() + offsetY);
        }
    });
}

}