GWT composite widget | 易学教程

问题

I try to build own GWT widget. I select the composite way of build it. But I have problem, the widget didn't see on screen. Here is the composite widget code:

public class LoginPanel extends Composite {

private static final String DEFAULT_STYLENAME = "LoginPanel";

private TextBox nameField;
private PasswordTextBox passField;
private Button loginButton;
private Label errorLbl;
private DecoratedPopupPanel decoratedPopupPanel;

public LoginPanel() {
    nameField = new TextBox();
    passField = new PasswordTextBox();
    loginButton = new Button("Login");
    loginButton.getElement().setId("loginButton");
    errorLbl = new Label();

    Grid grid = new Grid(4, 2);
    grid.setWidget(0,0, errorLbl);
    grid.setWidget(1,0, new Label("Name"));
    grid.setWidget(1,1, nameField);
    grid.setWidget(2,0, new Label("Password"));
    grid.setWidget(2,1, passField);
    grid.setWidget(3,1, loginButton);

    decoratedPopupPanel = new DecoratedPopupPanel();
    initWidget(decoratedPopupPanel);
    //decoratedPopupPanel.setAnimationEnabled(true);
    decoratedPopupPanel.setWidget(grid);
    //decoratedPopupPanel.setAnimationEnabled(true);
    decoratedPopupPanel.setPopupPositionAndShow(new PopupPanel.PositionCallback() {
        public void setPosition(int i, int i1) {
            decoratedPopupPanel.setPopupPosition(Window.getClientWidth()/2, Window.getClientHeight()/2);
        }
    });
}

}

In entry class function onModuleLoad() I have this peace of code:

LoginPanel lp = new LoginPanel();
RootPanel.get().add(lp);

When I delete in LoginPanel class rows behind initWidget() function, then all is right, but widget is not centered. Can anyone help me?

回答1:

The problem is a PopupPanel can't be used as a 'normal' widget, because it won't be attached to a parent but it attaches itself to the dom to make guarantee it's on top. So using initWidget on a popup doesn't make sense.

To make this work you should put the LoginWidget in the PopupPanel instead of the other way around. You could make the PopupPanel a member field and add a method show to your LoginPanel that calls the show on the PopupPanel field.

If you don't want the login widget to float independent of a parent or context you're using the Login widget in, you shouldn't use a PopupPanel.