如何在对话框中使用模态

Java™ SE 6 has resolved modality issues that arose in earlier versions of the platform. The new modality model enables the developer to scope, or limit, a dialog box's modality blocking.

Before proceding with the new modality model, review the following terms:

• Dialog box — A top-level pop-up window with a title and a border that typically takes some form of input from the user. A dialog box can be modal or modeless. For more information about dialog boxes, see An Overview of Dialogs in the How to Make Dialogs page.
• Modal dialog box — A dialog box that blocks input to some other top-level windows in the application, except for windows created with the dialog box as their owner. The modal dialog box captures the window focus until it is closed, usually in response to a button press.
• Modeless dialog box — A dialog box that enables you to operate with other windows while this dialog box is shown.

In Java SE 6 the behavior of both modal and modeless dialog boxes has been changed so that they always appear on top of both not only of their parent windows and of all blocked windows as well.

The following modality types are supported in Java SE 6:

• Modeless type — A modeless dialog box does not block any other window while it is visible.
• Document-modal type — A document-modal dialog box blocks all windows from the same document, except windows from its child hierarchy. In this context, a document is a hierarchy of windows that share a common ancestor, called the document root, which is the closest ancestor window without an owner.
• Application-modal type — An application-modal dialog box blocks all windows from the same application, except windows from its child hierarchy. If several applets are launched in a browser environment, the browser is allowed to treat them either as separate applications or as a single application. This behavior is implementation-dependent.
• Toolkit-modal type — A toolkit-modal dialog box blocks all windows that run in the same toolkit, except windows from its child hierarchy. If several applets are launched, all of them run with the same toolkit. Hence, a toolkit-modal dialog box shown from an applet may affect other applets and all windows of the browser instance that embeds the Java runtime environment for this toolkit.

Additionally, you can set up the modality exclusion mode:

• Exclusion mode — Any top-level window can be marked not to be blocked by modal dialogs. This property enables you to set up the modal exclusion mode. The Dialog.ModalExclusionType enum specifies the possible modal exclusion types.

The ModalityDemo example demonstrates the first three of the four modality types mentioned above.

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The following code snippet shows how to create dialog boxes of different modality types:

//The Book 1 parent frame
f1 = new JFrame("Book 1 (parent frame)");

...

//The modeless dialog box
d2 = new JDialog(f1);

...
        
//The document-modal dialog box
d3 = new JDialog(d2, "", Dialog.ModalityType.DOCUMENT_MODAL);

...

        //The Book2 parent frame
f4 = new JFrame("Book 2 (parent frame)");

...

//The modeless dialog box
d5 = new JDialog(f4);

...

//The document-modality dialog box
d6 = new JDialog(d5, "", Dialog.ModalityType.DOCUMENT_MODAL);
        
...

//The excluded frame
f7 = new JFrame("Classics (excluded frame)");
f7.setModalityExclusionType(Dialog.ModalExclusionType.APPLICATION_EXCLUDED);
        
...

//The Feedback parent frame and Confirm Dialog box
f8 = new JFrame("Feedback (parent frame)");
...

JButton b8 = new JButton("Rate yourself");
b8.addActionListener(new ActionListener() {
    public void actionPerformed(ActionEvent e) {
        JOptionPane.showConfirmationDialog(null,
                                           "I really like my book",
                                           "Question (application-modal dialog)", 
                                           JOptionPane.Yes_NO_OPTION,
                                           JOptionPane.QUESTION_MESSAGE); 
    }
});

Find the demo's complete code in the ModalityDemo.java file.

In Java SE 6 you can create a document-modal dialog box without a parent. Because the Dialog class is a subclass of the Window class, a Dialog instance automatically becomes the root of the document if it has no owner. Thus, if such a dialog box is document-modal, its scope of blocking is empty, and it behaves as if it were a modeless dialog box.

The Modality API

The JDialog class constructors enable you to create dialog boxes of various modality types.

The following table lists methods inherited from the java.awt.Dialog class.

Examples That Use Modality API

The following table lists the example that uses modality in dialogs.