Question

I’m modifying an example of the built-in-ds. The way this example works is that you need to select a datasource, and then a table gets filled with data from there. The idea is to show how the same component can adapt to multiple data sources. I’ve managed to run the example and it works, but I’m trying to modify it so you skip the first step – there’s only one data source that gets loaded “into” the table. What puzzles me is that this should be trivial but for some reason it’s not. I’ll paste just the different parts of code, this one works:

    // we create a list of datasources
    ListGrid grid = new ListGrid();
    grid.setLeft(20);
    grid.setTop(75);
    grid.setWidth(130);
    grid.setLeaveScrollbarGap(false);
    grid.setShowSortArrow(SortArrow.NONE);
    grid.setCanSort(false);
    grid.setFields(new ListGridField("dsTitle", "Select a DataSource"));
    // I'm just loading the one I need
    grid.setData(new ListGridRecord[] { new DSRecord("predmeti", "predmeti")});
    grid.setSelectionType(SelectionStyle.SINGLE);
    grid.addRecordClickHandler(new RecordClickHandler() {
        public void onRecordClick(RecordClickEvent event) {
            DSRecord record = (DSRecord) event.getRecord();
            bindComponents(record.getDsName());
        }
    });

    grid.draw();

and this is the bindComponents method:

private void bindComponents(String dsName) {
    DataSource ds = DataSource.get(dsName);
    boundList.setDataSource(ds);
    boundViewer.setDataSource(ds);
    boundForm.setDataSource(ds);
    boundList.fetchData();
    newBtn.enable();
    saveBtn.disable();
}

and this works as it should. Now, since I only have one data source, I can skip the grid and just make the call to bindComponents:

bindComponents();

And bindComponents looks like this:

private void bindComponents() {
    DataSource ds = DataSource.get("predmeti");
    boundList.setDataSource(ds);
    boundViewer.setDataSource(ds);
    boundForm.setDataSource(ds);
    boundList.fetchData();
    newBtn.enable();
    saveBtn.disable();
}

I can’t see why the second doesn’t work, it breaks on boundList.setDataSource(ds);. I inspected it in Debug mode, an object is returned and it looks “the same” in both cases but for some reason it doesn’t work in the second example, so I’m guessing I’m instancing the data source too early or, somehow, just plain wrong 🙂

Answer 1

Everything was fine with the datasources, the problem is trivial and I must have just been tired – the boundList object at the time of this call boundList.setDataSource(ds); was not yet instantiated. I kept getting Null pointer exception, but I thought there was something wrong with the DataSource.