jface databinding:可多选的widget List组件selection项目与java.util.List对象的双向数据绑定

「爱情、让人受尽委屈。」 2022-07-13 08:28 43阅读 0赞

# 需求说明 #

如下图，一个可多选的List组件，初始表有3个值，希望实现与一个java.util.List对象(保存选中的值)的双向数据绑定。当List组件中选中的内容变化时，java.util.List对象的内容也同步变化。

![这里写图片描述][SouthEast]

# 实现Observable对象 #

我们知道，`org.eclipse.jface.databinding.swt.WidgetProperties`工厂类的items()方法中为CCombo、Combo、List提供了获取表中所有条目(item)的observable对象,但是这个observable对象关注的是表中所有条目而不是选中的条目。所以不能满足需求。  
参见 org.eclipse.jface.internal.databinding.swt.ListItemsProperty的源码

public class ListItemsProperty extends ControlStringListProperty {
        
        @Override
        protected void doUpdateStringList(final Control control, ListDiff diff) {
            diff.accept(new ListDiffVisitor() {
                List list = (List) control;
    
                @Override
                public void handleAdd(int index, Object element) {
                    list.add((String) element, index);
                }
    
                @Override
                public void handleRemove(int index, Object element) {
                    list.remove(index);
                }
    
                @Override
                public void handleReplace(int index, Object oldElement,
                        Object newElement) {
                    list.setItem(index, (String) newElement);
                }
            });
        }
    
        @Override
        public String[] doGetStringList(Control control) {
            // getter方法调用List.getItems返回的是表中所有内容。
            return ((List) control).getItems();
        }
    
        @Override
        public String toString() {
            return "List.items[] <String>"; //$NON-NLS-1$
        }
    }

所以如果想实现上面的需求，就得不能用WidgetProperties工厂类提供的observable对象，要动手自己实现Observable类了，好在有了ListItemsProperty 方法的代码，参照它就可以根据自己的需求写一个新的类了。

ListSelectedItemsProperty1.java

package net.gdface.ui;
    
    import org.eclipse.core.databinding.observable.list.ListDiff;
    import org.eclipse.core.databinding.observable.list.ListDiffVisitor;
    import org.eclipse.core.databinding.property.INativePropertyListener;
    import org.eclipse.core.databinding.property.ISimplePropertyListener;
    import org.eclipse.jface.internal.databinding.swt.ListItemsProperty;
    import org.eclipse.jface.internal.databinding.swt.WidgetListener;
    import org.eclipse.swt.SWT;
    import org.eclipse.swt.widgets.Control;
    import org.eclipse.swt.widgets.List;
    
    /**
     * List组件中选中项目的Observable对象实现<br>
     * 对List组件表中内容的增加，删除操作不会改变表中内容，只会改变对应的selected状态
     * @author guyadong
     *
     */
    public class ListSelectedItemsProperty1 extends ListItemsProperty {
        
        @SuppressWarnings({ "unchecked", "rawtypes" })
        @Override
        protected void doUpdateStringList(final Control control, ListDiff diff) {
            diff.accept(new ListDiffVisitor() {
                List list = (List) control;
                @Override
                public void handleAdd(int index, Object element) {
                    // element对应的item置为selected
                    list.select(find((String) element));
                }
    
                @Override
                public void handleRemove(int index, Object element) {
                    // element对应的item置为unselected
                    list.deselect(find((String) element));
                }
    
                @Override
                public void handleReplace(int index, Object oldElement,
                        Object newElement) {
                }
                /**
                 * 在List中查找指定字符串的索引，找不到则返回-1
                 * @param element
                 * @return
                 */
                private int find(String element){
                    int count = list.getItemCount ();
                    for(int i=0;i<count;++i){
                        if(list.getItem(i).equals(element))return i;
                    }
                    return -1;
                }
            });
        }
        @Override
        public  String[] doGetStringList(Control control) {
            // 返回所有选中的item
            return ((List) control).getSelection();
        }
        // 重写adaptListener方法,返回NativePropertyListener对象，
        // 否则外部不能检测到List组件的状态变化
        @SuppressWarnings({ "rawtypes" })
        @Override
        public INativePropertyListener adaptListener(ISimplePropertyListener listener) {        
            return new WidgetListener(this, listener, new int[]{SWT.Selection}, null);
        }
    
    }

# 测试代码 #

TestList.java

package testwb;
    
    import org.eclipse.core.databinding.observable.Realm;
    import org.eclipse.core.databinding.observable.list.WritableList;
    import org.eclipse.core.databinding.observable.sideeffect.ISideEffect;
    import org.eclipse.jface.databinding.swt.DisplayRealm;
    import org.eclipse.jface.databinding.swt.ISWTObservableList;
    import org.eclipse.jface.dialogs.Dialog;
    import org.eclipse.jface.dialogs.IDialogConstants;
    import org.eclipse.swt.graphics.Point;
    import org.eclipse.swt.widgets.Composite;
    import org.eclipse.swt.widgets.Control;
    import org.eclipse.swt.widgets.Display;
    import org.eclipse.swt.widgets.Shell;
    
    import net.gdface.ui.ListSelectedItemsProperty1;
    
    import org.eclipse.swt.widgets.List;
    import org.eclipse.swt.SWT;
    
    import org.eclipse.core.databinding.DataBindingContext;
    import org.eclipse.swt.widgets.Label;
    import org.eclipse.swt.widgets.Button;
    import org.eclipse.swt.events.SelectionAdapter;
    import org.eclipse.swt.events.SelectionEvent;
    
    public class TestList extends Dialog {
        
        private DataBindingContext m_bindingContext;
        // 数据对象
        private WritableList<String> observableList=new WritableList<String>();
        private List list;
        private Label lblSelected;
        /**
         * Create the dialog.
         * @param parentShell
         */
        public TestList(Shell parentShell) {
            super(parentShell);
        }
    
        /**
         * Create contents of the dialog.
         * @param parent
         */
        @Override
        protected Control createDialogArea(Composite parent) {
            Composite container = (Composite) super.createDialogArea(parent);
            container.setLayout(null);
            // 初始化数据对象
            observableList.add("apple");
            list = new List(container, SWT.BORDER | SWT.MULTI);
            // 初始化List组件中的内容
            list.add("apple");
            list.add("orange");
            list.add("banana");
            list.setBounds(10, 31, 231, 68);
    
            lblSelected = new Label(container, SWT.BORDER);
            lblSelected.setBounds(10, 153, 424, 32);
    
            Label label = new Label(container, SWT.NONE);
            label.setBounds(10, 130, 61, 17);
            label.setText("已选择");
    
            Button btnAdd = new Button(container, SWT.NONE);
            btnAdd.addSelectionListener(new SelectionAdapter() {
                @Override
                public void widgetSelected(SelectionEvent e) {
                    if(!observableList.contains("banana"))observableList.add("banana");
                }
            });
            btnAdd.setBounds(286, 30, 80, 27);
            btnAdd.setText("增加");
    
            Button btnClear = new Button(container, SWT.NONE);
            btnClear.addSelectionListener(new SelectionAdapter() {
                @Override
                public void widgetSelected(SelectionEvent e) {
                    observableList.clear();
                }
            });
            btnClear.setBounds(286, 105, 80, 27);
            btnClear.setText("清除");
    
            Button btnDelete = new Button(container, SWT.NONE);
            btnDelete.addSelectionListener(new SelectionAdapter() {
                @Override
                public void widgetSelected(SelectionEvent e) {
                    observableList.remove("apple");
                }
            });
            btnDelete.setBounds(286, 63, 80, 27);
            btnDelete.setText("删除");
    
            return container;
        }
    
        /**
         * Create contents of the button bar.
         * @param parent
         */
        @Override
        protected void createButtonsForButtonBar(Composite parent) {
            createButton(parent, IDialogConstants.OK_ID, IDialogConstants.OK_LABEL, true);
            createButton(parent, IDialogConstants.CANCEL_ID, IDialogConstants.CANCEL_LABEL, false);
            m_bindingContext = initDataBindings();
        }
    
        /**
         * Return the initial size of the dialog.
         */
        @Override
        protected Point getInitialSize() {
            return new Point(450, 300);
        }
        public static void main(String[] args) {
            Display display = Display.getDefault();
            Realm.runWithDefault(DisplayRealm.getRealm(display), new Runnable() {
                public void run() {
                    try {
                        TestList testList = new TestList(null);
                        testList.open();
                    } catch (Exception e) {
                        e.printStackTrace();
                    }
                }
            });
        }
        protected DataBindingContext initDataBindings() {
            DataBindingContext bindingContext = new DataBindingContext();
            // 调用ListSelectedItemsProperty1为List组件创建observable对象
            ISWTObservableList observeSelectedListObserveWidget =new ListSelectedItemsProperty1().observe(list);
            // 将List组件与数据对象observableList绑定在一起
            bindingContext.bindList(observeSelectedListObserveWidget, observableList, null, null);
            // 为查看数据对象observableList的内容，将之与Label组件进行单向绑定，
            // observableList的内容变化能及时显示在Label中
            ISideEffect.create(
                observableList::size, (s)->{
                lblSelected.setText(String.join(",", observableList));
            });
            return bindingContext;
        }
    }

# 注意 #

ListSelectedItemsProperty1.java的父类`org.eclipse.jface.internal.databinding.swt.ListItemsProperty`在jface.internal包下，也就是非公开的包，所以这个类的接口稳定性并没有保证，版本升级的时候有可能会被改变或删除。  
ListSelectedItemsProperty1中用到的WidgetListener类也是同样的问题。  
如果要解决这个问题，应该把该类及其父类的代码复制出来重写才是最保险的。  
如下为以WidgetListProperty为父类重写的ListSelectedItemsProperty2，不使用jface.internal包下的类  
ListSelectedItemsProperty2.java

package net.gdface.ui;
    
    import java.util.Arrays;
    import java.util.List;
    
    import org.eclipse.core.databinding.observable.list.ListDiff;
    import org.eclipse.core.databinding.observable.list.ListDiffVisitor;
    import org.eclipse.core.databinding.property.INativePropertyListener;
    import org.eclipse.core.databinding.property.ISimplePropertyListener;
    import org.eclipse.core.databinding.property.NativePropertyListener;
    import org.eclipse.jface.databinding.swt.WidgetListProperty;
    import org.eclipse.swt.events.SelectionEvent;
    import org.eclipse.swt.events.SelectionListener;
    
    public class ListSelectedItemsProperty2 extends WidgetListProperty {
        
        @Override
        public Object getElementType() {
            return String.class;
        }
    
        @SuppressWarnings("rawtypes")
        @Override
        protected void doSetList(Object source, List list, ListDiff diff) {
            doUpdateList(source, diff);
        }
    
        @SuppressWarnings({ "unchecked", "rawtypes" })
        @Override
        protected void doUpdateList(Object source, ListDiff diff) {
            diff.accept(new ListDiffVisitor() {
                org.eclipse.swt.widgets.List list = (org.eclipse.swt.widgets.List) source;
                @Override
                public void handleAdd(int index, Object element) {
                    list.select(find((String) element));
                }
    
                @Override
                public void handleRemove(int index, Object element) {
                    list.deselect(find((String) element));
                }
    
                @Override
                public void handleReplace(int index, Object oldElement,
                        Object newElement) {
                }
                /**
                 * 在List中查找指定字符串的索引，找不到则返回-1
                 * @param element
                 * @return
                 */
                private int find(String element){
                    int count = list.getItemCount ();
                    for(int i=0;i<count;++i){
                        if(list.getItem(i).equals(element))return i;
                    }
                    return -1;
                }
            });
        }
    
    
        @SuppressWarnings("rawtypes")
        @Override
        protected List doGetList(Object source) {
            return Arrays.asList(((org.eclipse.swt.widgets.List) source).getSelection());
        }
    
        @SuppressWarnings({ "unchecked", "rawtypes" })
        @Override
        public INativePropertyListener adaptListener(ISimplePropertyListener listener) {
            // 继承NativePropertyListener实现INativePropertyListener 接口
            return new NativePropertyListener(this,listener){
                private final SelectionListener selectionListener=new SelectionListener(){
                    @Override
                    public void widgetSelected(SelectionEvent e) {
                        fireChange(e.getSource(), null);        
                    }
                    @Override
                    public void widgetDefaultSelected(SelectionEvent e) {
                        fireChange(e.getSource(), null);                    
                    }};
                @Override
                protected void doAddTo(Object source) {
                    ((org.eclipse.swt.widgets.List)source).addSelectionListener(selectionListener);
                }
    
                @Override
                protected void doRemoveFrom(Object source) {
                    ((org.eclipse.swt.widgets.List)source).removeSelectionListener(selectionListener);
                }
            };
        }
    }

[SouthEast]: /images/20220713/cbe2dcc0fc864b6da811df50ac226880.png