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  • Refresh ListGrid Periodically (Smart GWT)
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Description

ListGrid displays a list of objects in a grid, where each row represents one object and each cell in the row represents one property.

Periodically updating a ListGrid is possible in the following ways:

  • Using the invalidateCache method. This approach updates the data and will show a loading message. However, this API will disrupt the existing view.
  • Transparent update by DataSource using the fetchData method. This method updates the data but doesn't show a loading message and won't disrupt the existing view.

A working example is available in the attachment.

Transparent update

For transparent loading of the data the fetchData method should be used.

Update by DataSource
private void onRefresh() {
    DataSource dataSource = listGrid.getDataSource();
    Criteria criteria = listGrid.getCriteria();
    Integer[] visibleRows = listGrid.getVisibleRows();
    
	// request one page's worth of data on either side of the current viewport
    Integer startRow = visibleRows[0] - listGrid.getResultSet().getResultSize();
    Integer endRow = visibleRows[1] + listGrid.getResultSet().getResultSize();
    if (startRow < 0) {
        startRow = 0;
    }
    
	DSRequest request = new DSRequest();
    request.setStartRow(startRow);
    request.setEndRow(endRow);
    request.setSortBy(listGrid.getSort());
    
	dataSource.fetchData(criteria, new DSCallback() {
        @Override
        public void execute(DSResponse response, Object rawData, DSRequest request) {
            onRefreshed(response);
        }
    }, request);
}

private void onRefreshed(DSResponse response) {
    
	DataSource dataSource = listGrid.getDataSource();
    ResultSet resultSet = new ResultSet(dataSource);
    resultSet.setInitialLength(response.getTotalRows());
    
	// correctly position the result in the resultset's cache 
    Record[] result = response.getData();
    Record[] initialData = new Record[response.getTotalRows()];
    System.arraycopy(result, 0, initialData, response.getStartRow(), result.length);
    resultSet.setInitialData(initialData);
    
	resultSet.setInitialSort(listGrid.getSort());
    resultSet.setCriteria(listGrid.getCriteria());
    listGrid.setData(resultSet);
}

Attachments

  File Modified
ZIP Archive RefreshGridPeriodically.zip Jun 11, 2014 by Bill Bruyn

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