GWT ImageCell: Change image dynamically in a DataGrid or CellTable - gwt

Question

I have DataGrid where one on of the columns contains images. I used this code to generate the column.
Column<Job, String> expandHideColumn = new Column<Job, String>(
imageCell) {
#Override
public String getValue(Job object) {
return null;
}
#Override
public void render(Context context, Job Object, SafeHtmlBuilder sb) {
sb.appendHtmlConstant("<img src='images/expand.jpeg' style='cursor: pointer' />");
}
}
What I want is on clicking the image it has to change. For this I added a click handler on the ImageCell like this
ImageCell imageCell = new ImageCell() {
#Override
public Set<String> getConsumedEvents() {
Set<String> events = new HashSet<String>();
events.add("click");
return events;
}
};
In the onBrowserEvent method I wrote this
#Override
public void onBrowserEvent(Context context, Element element,
Job job, NativeEvent event) {
if (element.getFirstChildElement().isOrHasChild(
Element.as(event.getEventTarget()))) {
if (element.getFirstChildElement().getPropertyString("src")
.matches("(.*)expand.jpeg")) {
element.getFirstChildElement().setPropertyString("src",
"images/collapse.jpeg");
} else {
element.getFirstChildElement().setPropertyString("src",
"images/expand.jpeg");
}
}
}
I don't think this is a good approach to change images on click event. Is there a better solution?

Answer 1

You can use a column value for know the state of the column :
Column<Job, Boolean> expandHideColumn = new Column<Job, Boolean>(new ImageExpandCollapseCell()) {
#Override
public Boolean getValue(Job object) {
return object.isExpand(); //The object know the expand state ?
}
}
expandHideColumn.setValueUpdater(new FieldUpdater<Job, Boolean>() {
void update(int index, Job object, Boolean value) {
object.setExpand(value);
}
});
The ImageExpandCollapseCell look like this :
public class ImageExpandCollapseCell extends AbstractCell<Boolean> {
final String EXPAND = "images/expand.jpeg";
final String COLLAPSE = "images/collapse.jpeg";
interface Template extends SafeHtmlTemplates {
#Template("<div style=\"float:right\"><img src=\"" + url + "\"></div>")
SafeHtml img(String url);
}
private static Template template;
/**
* Construct a new ImageCell.
*/
public ImageCell() {
super("click"); //Replace your getConsumedEvents()
if (template == null) {
template = GWT.create(Template.class);
}
}
#Override
public void render(Context context, Boolean value, SafeHtmlBuilder sb) {
if (value != null) {
sb.append(template.img(UriUtils.fromSafeConstant(value ? EXPAND : COLLAPSE)));
}
}
#Override
public void onBrowserEvent(Context context, Element element,
Boolean value, NativeEvent event, ValueUpdater<Boolean> valueUpdater) {
valueUpdate.update(!value);
}
}
I improve the proposed version of user905374
It's not a good idea to instantiate new value in the render method.
The column render method call the Cell render method, you musn't replace it !
With the FieldUpdater, you can change the state of the image : expand or collapse and update the cell display (it will be rendered again).