Question

I am trying to make a sample code for my further work. I am using gwt vanillia and new to gwt. My purpose is to populate some textboxes and a grid. for populating textboxes from database, no problem with rpc call. But I could’nt populate datagrid via using RPC call. I used Bastian Tenbergen’s tutorial
for populating some textboxes. But when i tried to populate the grid with asyncronious callback using ArrayList, code failed. I know ArrayList is also serializable but I can’t solve the issue.
Any advice is appreciated.
Here is some code for my questin.
In server package: SqlDbConnection.java

    public ArrayList<hastaGrid> callGrid(String something){
    ArrayList<hastaGrid> list = new ArrayList<hastaGrid>();
    hastagrid hastaGrid = null;     
    try {
        Statement st = conn.createStatement();
        ResultSet result = st.executeQuery("select name from TEST where name = '"+ something +"'");

        while(result.next()) {
            hastagrid = new hastaGrid(result.getString(1), result.getString(2),result.getNString(2),result.getString(3));
            list.add(hastaGrid);
            System.out.println("result: " +hastagrid.getLogin().toString()+" " + hastagrid.getPassword() +" "+ hastagrid.getName() +" " + hastagrid.getSurname());
        }
        result.close();
        st.close();                 
    } catch (Exception e) {
        e.printStackTrace();
    }       
    return list;
}

In client package: hastaGrid.java //the class also have getter and setter methods.

public class hastaGrid implements IsSerializable {

private String name;
private String surname;
private String login;
private String password;

public hastaGrid(String name,String surname, String login, String password){
    this.setName(name);
    this.setSurname(surname);
    this.setLogin(login);
    this.setPassword(password);
}}

In client package: DBConnection.java

public interface DBConnection extends RemoteService {   
public ArrayList<hastaGrid> callGrid(String name);  }

In client package: DBConnectionAsync.java

public interface DBConnectionAsync {    
public void callGrid(String name, AsyncCallback<ArrayList<hastaGrid>> callback);   }

In client package: userDetail.java

onModuleLoad() {
AsyncCallback> callback = new AuthenticationHandler1();
rpc.gridGetir(“John”,callback);
}

private class AuthenticationHandler<T> implements AsyncCallback<ArrayList<hastaGrid>>  {
    public void onFailure(Throwable ex) {
    RootPanel.get().add(new HTML("RPC call failed"));
    }
    public void onSuccess(ArrayList<hastaGrid> result) {        
    result.get(0).getName(); } } // I just want to reach some result here when debugging.

I read lots of pages on web but can’t find a specific solution. I could be wrong. Thanks for responses.

Answer 1

First you should make sure that your RPC returns the appropriate List of hastaGrid objects – and please do capitalize the class name 🙂
I use the AsyncDataProvider model quite a lot with various DataGrid implementations and create an implementing class somewhat like the following:

public class MyProvider extends AsyncDataProvider<MyModelObject> implements AsyncCallback<List<MyModelObject>> {
    static int PAGESIZE = 50;
    List<MyModelObject> cache = new ArrayList<MyModelObject>();

    @Override
    protected void onRangeChanged(HasData<MyModelObject> display) {
        final Range range = display.getVisibleRange();          
        int start = range.getStart();
        int end = start + range.getLength();
        if (start >= cache.size() - 1) {
            lastVisible = cache.size() - 1;
            gwtService.fetchRowsFromDbase(this);                
            return;
        }
        List<MyModelObject> dataInRange = cache.isEmpty() ? new ArrayList<MyModelObject>() : cache.subList(start,
                end >= cache.size() ? (cache.size()) : end);
        updateRowData(start, dataInRange);
    }

    public void onFailure(Throwable caught) {
        Window.alert(caught.getMessage());
    }

    public void onSuccess(List<MyModelObject> result) {
        if (result.isEmpty()) {
            //display a warning
            return;
        }
        for (MyModelObject a : result) {
            if (cache.indexOf(a) == -1)
                cache.add(a);
        }
        updateRowData(cache.indexOf(result.get(0)), result);
        updateRowCount(cache.size(), result.size() < PAGESIZE);
        tab.setPageSize(PAGESIZE);
        tab.setPageStart(lastVisible);
        MyModelObject last = cache.get(cache.size() - 1);
        orderOffset = last.getId();         
    }

    public List<MyModelObject> getCache() {
        return cache;
    }
}

In your DataGrid initalization code you put:

MyProvider pr = new MyProvider();
pr.addDataDisplay(yourDataGrid);

This approach works best if you also add a pager, because the dataprovider listens to range changes, triggered by clicking the pager.

SimplePager pager = new SimplePager();
pager.setDisplay(yourDataGrid);
//don't forget to add the pager widget to the DOM 

Hope this helps!