I have just started playing with Ceylon and I really like it...
But I ran into this problem when using Swing... I want to add components to a JPanel using a BorderLayout.
This is the code I am using:
import javax.swing {
JLabel,
SwingUtilities { invokeLater },
JFrame { exitOnClose = \iEXIT_ON_CLOSE },
JButton,
JPanel
}
import java.lang { Runnable }
import java.awt {
Dimension,
BorderLayout { north = \iNORTH, center = \iCENTER }
}
class MySwingApp() satisfies Runnable {
shared actual void run() {
value frame = JFrame();
frame.title = "Renato app";
frame.defaultCloseOperation = exitOnClose;
frame.size = Dimension(300, 200);
frame.setLocationRelativeTo(null);
value panel = JPanel();
panel.layout = BorderLayout();
frame.add(panel);
panel.add(JLabel("Hello world"), north);
panel.add(JButton("Click me"), center);
frame.visible = true;
}
}
The error is:
Exception in thread "AWT-EventQueue-0" java.lang.IllegalArgumentException: cannot add to layout: constraint must be a string (or null)
at java.awt.BorderLayout.addLayoutComponent(BorderLayout.java:426)
at java.awt.Container.addImpl(Container.java:1120)
at java.awt.Container.add(Container.java:966)
at firstModule.MySwingApp.run(run.ceylon:52)
I run the app with:
invokeLater(MySwingApp());
This appears to me to be a problem mapping Strings in Ceylon?!? Can anyone see anything I'm doing wrong (being new to Ceylon I wouldn't be surprised)??
What's happening here is that Container.add()
's second parameter is declared to be an Object
, not a java.lang.String
so the Ceylon compiler doesn't realize there's a need to unbox the Ceylon String
. According to the signature of the method any Object
is acceptable, it's just that the implementation of the method decides it actually need a Java String.
You can use the javaString()
function from the ceylon.interop.java
module to convert a Ceylon String
to a Java String
in cases like this:
panel.add(JLabel("Hello world"), javaString(north));
panel.add(JButton("Click me"), javaString(center));