Java实现Qt的SIGNAL-SLOT机制

SIGNAL-SLOT是Qt的一大特色，使用起来十分方便。在传统的AWT和Swing编程中，我们都是为要在

监听的对象上添加Listener监听器。被监听对象中保存有Listener的列表，当相关事件发生时，被监听

对象会通知所有Listener。而在Qt中，我们只需通过connect方法连接两个对象上的方法就可以了，非常

方便、优雅地实现了传统的观察者Observer模式。

 

Qt是如何办到的呢？对于发出SIGNAL的对象，我们需要在其头文件定义中声明Q_Object宏，之后Qt的

预处理器MOC会为我们自动添加上相应的代码来实现SIGNAL-SLOT机制。这与AspectJ自定义了Javac

编译器很类似，都是通过增强编译器来自动添加相应的代码。

 

增强编译或增加预处理太复杂，怎样能够简单的实现这种机制呢？首先我们实现一个类似的QObject类，

需要发射SIGNAL的类都要继承它。在QObject类中，我们自动为其子类提供监听器列表，查找SLOT方法，

信号发射等功能。

 

QObject.java

 

1.在连接方法中，我们将信号和新建的ReceiverSlot类保存到Map中，从而将它们关联起来。

public static void connect(QObject sender, String signal, Object receiver, String slot) {
    if (sender.signalSlotMap == null)
        sender.signalSlotMap = new HashMap<String, List<ReceiverSlot>>();

    List<ReceiverSlot> slotList = sender.signalSlotMap.get(signal);
    if (slotList == null) {
        slotList = new LinkedList<ReceiverSlot>();
        sender.signalSlotMap.put(signal, slotList);
    }
    slotList.add(createReceiverSlot(receiver, slot));
}

static class ReceiverSlot {
    Object receiver;
    Method slot;
    Object[] args;
}

 

2.在创建ReceiverSlot时，我们解析SLOT方法名，如将slot(String,String)解析为方法slot，参数两个String。

如果解析失败我们就认为该SLOT仍是一个信号，也就是SIGNAL-SIGNAL的连接。这种情况下，我们需要

传递调用的不是receiver的SLOT方法，而是emit方法继续发射信号。

private static ReceiverSlot createReceiverSlot(Object receiver, String slot) {
    ReceiverSlot receiverSlot = new ReceiverSlot();
    receiverSlot.receiver = receiver;

    Pattern pattern = Pattern.compile("(\w+)\(([\w+,]*)\)");
    Matcher matcher = pattern.matcher(slot);
    if (matcher.matches() && matcher.groupCount() == 2) {
        // 1.Connect SIGNAL to SLOT
        try {
            String methodName = matcher.group(1);
            String argStr = matcher.group(2);
            ArrayList<String> argList = new ArrayList<String>();

            pattern = Pattern.compile("\w+");
            matcher = pattern.matcher(argStr);
            while (matcher.find())
                argList.add(matcher.group());
            String[] arguments = argList.toArray(new String[0]);

            receiverSlot.slot = findMethod(receiver, methodName, arguments);
            receiverSlot.args = new Object[0];
        }
        catch (Exception e) {
            e.printStackTrace();
        }
    }
    else {
        // 2.Connect SIGNAL to SIGNAL
        if (receiver instanceof QObject) {
            receiverSlot.slot = emitMethod;
            receiverSlot.args = new Object[] { slot };
        }
    }

    return receiverSlot;
}

private static Method emitMethod;

protected Map<String, List<ReceiverSlot>> signalSlotMap;

static {
    try {
        emitMethod = QObject.class.getDeclaredMethod("emit", String.class, Object[].class);
    } catch (Exception e) {
        e.printStackTrace();
    }
}

 

3.解析后，如果是SIGNAL-SLOT的连接，那我我们根据方法名和参数找到该方法，准备反射调用。

private static Method findMethod(Object receiver, String methodName, String[] arguments)
        throws NoSuchMethodException {

    Method slotMethod = null;

    if (arguments.length == 0)
        slotMethod = receiver.getClass().getMethod(methodName, new Class[0]);
    else {
        for (Method method : receiver.getClass().getMethods()) {

            // 1.Check method name
            if (!method.getName().equals(methodName))
                continue;

            // 2.Check parameter number
            Class<?>[] paramTypes = method.getParameterTypes();
            if (paramTypes.length != arguments.length)
                continue;

            // 3.Check parameter type
            boolean isMatch = true;
            for (int i = 0; i < paramTypes.length; i++) {
                if (!paramTypes[i].getSimpleName().equals(arguments[i])) {
                    isMatch = false;
                    break;
                }
            }
            if (isMatch) {
                slotMethod = method;
                break;
            }
        }

        if (slotMethod == null)
            throw new NoSuchMethodException("Cannot find method[" + methodName +
                    "] with parameters: " + Arrays.toString(arguments));
    }

    return slotMethod;
}

 

4.发射信号时，我们取到所有与该SIGNAL关联的ReceiverSlot类，逐个发射信号。

protected void emit(String signal, Object... args) {
    System.out.println(getClass().getSimpleName() + " emit signal " + signal);

    if (signalSlotMap == null)
        return;

    List<ReceiverSlot> slotList = signalSlotMap.get(signal);
    if (slotList == null || slotList.isEmpty())
        return;

    for (ReceiverSlot objSlot : slotList) {
        try {
            if (objSlot.slot == emitMethod)
                objSlot.slot.invoke(objSlot.receiver, objSlot.args[0], args);
            else
                objSlot.slot.invoke(objSlot.receiver, args);
        }
        catch (Exception e) {
            e.printStackTrace();
        }
    }
}

 

之后，我们实现一个它的子类QWidget，将常用的Swing控件都封装在QWidget的子类中，为这些控件提供

常见的预定义的SIGNAL，像Qt中的clicked和returnPressed。

 

QWidget.java

public class QWidget<T extends JComponent> extends QObject implements QSwing<T> {

    protected T widget;

    public QWidget(Class<T> clazz) {
        try {
            widget = clazz.newInstance();
        }
        catch (Exception e) {
            e.printStackTrace();
        }
    }

    @Override
    public T getSwingWidget() {
        return this.widget;
    }

}

 

以下是封装了JButton和JTextField的QWidget子类。

 

QPushButton.java

public class QPushButton extends QWidget<JButton> {

    public static final String CLICKED = "clicked";

    public QPushButton(String text) {
        super(JButton.class);

        widget.setText(text);
        widget.addActionListener(new ActionListener() {
            @Override
            public void actionPerformed(ActionEvent e) {
                emit(CLICKED);
            }
        });
    }

}

 

QLineEdit.java

public class QLineEdit extends QWidget<JTextField> {

    public static final String RETURN_PRESSED = "returnPressed";

    public QLineEdit() {
        super(JTextField.class);

        widget.addActionListener(new ActionListener() {
            @Override
            public void actionPerformed(ActionEvent e) {
                emit(RETURN_PRESSED);
            }
        });
    }

}

 

下面我们来写个测试类实验下Java版的SIGNAL-SLOT机制，依旧是之前的浏览器的例子。

 

AddressBar.java

public class AddressBar extends QWidget<JPanel> {

    /**
     * SIGNAL
     */
    public static final String NEW_BUTTON_CLICKED = "newButtonClicked";
    public static final String GO_TO_ADDRESS = "goToAddress(String,String)";

    /**
     * SLOT
     */
    public static final String HANDLE_GO_TO_ADDRESS = "handleGoToAddress()";


    private QPushButton newButton;
    private QLineEdit addressEdit;
    private QPushButton goButton;


    public AddressBar() {
        super(JPanel.class);

        // 1.Create widget
        newButton = new QPushButton("New");
        addressEdit = new QLineEdit();
        goButton = new QPushButton("Go");

        // 2.Set property
        addressEdit.getSwingWidget().setColumns(10);

        // 3.Connect signal-slot
        connect(newButton, QPushButton.CLICKED, this, NEW_BUTTON_CLICKED);
        connect(addressEdit, QLineEdit.RETURN_PRESSED, this, HANDLE_GO_TO_ADDRESS);
        connect(goButton, QPushButton.CLICKED, this, HANDLE_GO_TO_ADDRESS);

        // 4.Add to layout
        getSwingWidget().add(newButton.getSwingWidget());
        getSwingWidget().add(addressEdit.getSwingWidget());
        getSwingWidget().add(goButton.getSwingWidget());
    }

    public void handleGoToAddress() {
        emit(GO_TO_ADDRESS, addressEdit.getSwingWidget().getText(), "test string");
    }

}

 

TabBar.java

public class TabBar extends JTabbedPane {

    /**
     * SLOT
     */
    public static final String HANDLE_NEW_TAB = "handleNewTab()";
    public static final String HANDLE_GO_TO_SITE = "goToSite(String,String)";


    public TabBar() {
        handleNewTab();
    }

    public void handleNewTab() {
        WebView tab = new WebView();
        add("blank", tab);
    }

    public void goToSite(String url, String testStr) {
        System.out.println("Receive url: " + url + ", " + testStr);

        WebView tab = (WebView) getSelectedComponent();
        tab.load(url);
    }

}

 

MainWindow.java

public class MainWindow extends JFrame {

    public static void main(String[] args) {
        JFrame window = new MainWindow();
        window.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        window.setSize(320, 340);
        window.setVisible(true);
    }

    public MainWindow() {
        // 1.Create widget
        AddressBar addressBar = new AddressBar();
        TabBar tabBar = new TabBar();

        // 2.Set property

        // 3.Connect signal-slot
        QObject.connect(addressBar, AddressBar.NEW_BUTTON_CLICKED, tabBar, TabBar.HANDLE_NEW_TAB);
        QObject.connect(addressBar, AddressBar.GO_TO_ADDRESS, tabBar, TabBar.HANDLE_GO_TO_SITE);

        // 4.Add to layout
        GridBagLayout layout = new GridBagLayout();
        setLayout(layout);
        GridBagConstraints grid = new GridBagConstraints();
        grid.fill = GridBagConstraints.BOTH;
        grid.gridx = grid.gridy = 0;
        grid.weightx = 1.0;
        grid.weighty = 0.1;
        add(addressBar.getSwingWidget(), grid);
        grid.fill = GridBagConstraints.BOTH;
        grid.gridx = 0;
        grid.gridy = 1;
        grid.weightx = 1.0;
        grid.weighty = 0.9;
        add(tabBar, grid);
    }

}


@SuppressWarnings("serial")
class WebView extends JEditorPane {

    public WebView() {
        setEditable(false);
    }

    public void load(final String url) {
        SwingUtilities.invokeLater(new Runnable() {
            @Override
            public void run() {
                try {
                    WebView.this.setPage(url);
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
        });
    }

}

 

测试一下吧，运行起来的效果就是这样。

 

新建Tab页和前往该地址事件都可以成功地从AddressBar传递到TabBar。怎么样，这种Java版的

SIGNAL-SLOT是不是很方便。多开拓自己的视野，借鉴优秀的思想，我们才能做出更好的设计！

希望你喜欢本文。

 

参考：http://blog.csdn.net/dc_726/article/details/7632430