Is there a `AcceptsOneWidget` which also `Provides

问题:

I have a composite which extends ResizeComposite and has a DockLayoutPanel as its root. I can stick it directly into RootLayoutPanel and it works because DockLayoutPanel ProvidesResize.

However, I'm wanting to use the MVP facilities in GWT 2.2, and RootLayoutPanel can't be passed to ActivityManager#setDiplay(AcceptsOneWidget) (since it's a multi-widget container).

At first glance, ScrollPanel appears to meet the dual requirement of implementing AcceptsOneWidget and both ProvidesResize and RequiresResize.

But I am finding that when I put my widget into a ScrollPanel, that it has a 'zero size', and I have to size it manually in order to see it, and I'm having trouble knowing what size to give it. I'd rather a Panel that didn't necessarily scroll.

回答1:

You can add ProvidesResize to any widget by implementing it yourself, which is relatively simple - you just pass along all of the resize notifications you get to every sub-child that RequiresResize.

Alternatively, if you just want your panel to take up all of the available space, you might try setting the width and height on the ScrollPanel to "100%".

Finally, here's my implementation of a LayoutPanel that AcceptsOneWidget:

public class PanelForView extends LayoutPanel implements AcceptsOneWidget
{
    IsWidget myWidget = null;

    @Override
    public void setWidget(IsWidget w)
    {
        if (myWidget != w)
        {
            if (myWidget != null)
            {
                remove(myWidget);
            }

            if (w != null)
            {
                add(w);
            }

            myWidget = w;
        }
    }

}

I've been using this in my commercial app for months without any problems, and it's easy to swap views in and out of it. Feel free to use this code yourself.

回答2:

There will be a SimpleLayoutPanel in GWT 2.3, described as:

A simple panel that {@link ProvidesResize} to its one child.