MVC Approach

If you have read previous chapters, constructing the user interface for the example application should not be a big problem. Let's look at the layout first and ignore the details.

Layout in chapter4/todolist-mvc.zul


<?link rel="stylesheet" type="text/css" href="/style.css"?>
<window apply="org.zkoss.essentials.chapter4.mvc.TodoListController"
    border="normal" hflex="1" vflex="1" contentStyle="overflow:auto">
    <caption src="/imgs/todo.png" sclass="fn-caption" label="Todo List (MVC)"/>
    <borderlayout>
        <center autoscroll="true" border="none">
            <vlayout hflex="1" vflex="1">
                <!-- todo creation function-->
                <!-- todo list -->
            </vlayout>
        </center>
        <east id="selectedTodoBlock" visible="false"
        width="300px" border="none" collapsible="false"
        splittable="true" minsize="300" autoscroll="true">
            <vlayout >
                <!-- detail editor -->
            </vlayout>
        </east>
    </borderlayout>
</window>

Line 5: We construct the user interface with a Border Layout to separate user interface into 2 areas.
Line 6: The center area contains a todo creation function and a todo list.
Line 12, 13: The east area is a todo item detail editor which is invisible if no item selected.

Read

As we talked in previous chapters, we can use Template to define how to display a data model list with implicit variable each.

Display a ToDo List

...
    <listbox id="todoListbox" vflex="1">
        <listhead>
            <listheader width="30px" />
            <listheader/>
            <listheader hflex="min"/>
        </listhead>
        <template name="model">
            <listitem sclass="${each.complete?'complete-todo':''}"
                value="${each}">
                <listcell>
                    <checkbox forward="onCheck=todoListbox.onTodoCheck"
                        checked="${each.complete}"/>
                </listcell>
                <listcell>
                    <label value="${each.subject}"/>
                </listcell>
                <listcell>
                    <button forward="onClick=todoListbox.onTodoDelete"
                        image="/imgs/cross.png" width="36px"/>
                </listcell>
            </listitem>
        </template>
    </listbox>
...

Line 8: The default value for the required attribute name is "model".
Line 10: The ${each} is an implicit variable that you can use without declaration inside Template, and it represents each object of the data model list. We can implement simple presentation logic with EL expressions. Here we apply different styles according to a flag each.complete. We also set a whole object in value attribute, and later we can get the object in the controller.
Line 13: The each.complete is a boolean variable so that we can assign it to checked. By doing this, the Checkbox will be checked if the todo item's complete variable is true.
Line 12, 19: The forward attribute is used to forward events to another component and we will talk about it in later sections.

In the controller, we should provide a data model for the Listbox.

public class TodoListController extends SelectorComposer<Component>{


    //wire components
    ...
    @Wire
    Listbox todoListbox;

    ...

    //services
    TodoListService todoListService = new TodoListServiceChapter4Impl();

    //data for the view
    ListModelList<Todo> todoListModel;
    ListModelList<Priority> priorityListModel;
    Todo selectedTodo;


    @Override
    public void doAfterCompose(Component comp) throws Exception{
        super.doAfterCompose(comp);

        //get data from service and wrap it to list-model for the view
        List<Todo> todoList = todoListService.getTodoList();
        todoListModel = new ListModelList<Todo>(todoList);
        todoListbox.setModel(todoListModel);

        ...
    }
...
}

Line 25 ~ 27: We initialize the data model in doAfterCompose(). Get data from the service class todoListService and create a ListModelList object. Then set it as the data model of todoListbox.

There is a priority radiogroup in todo item detail editor appeared on the right hand side when you select an item.

Todo Item's Priority Radiogroup

</div> In our application, its priority labels come from an enumerating Priority instead of a static text. We can still use Template to define how to create each Radio under a Radiogroup. The zul looks like as follows:

...
        <row>
            <cell sclass="row-title">Priority :</cell>
            <cell>
                <radiogroup id="selectedTodoPriority">
                    <template name="model">
                        <radio label="${each.label}"/>
                    </template>
                </radiogroup>
            </cell>
        </row>
...

Line 6 ~8: Define how to create each Radio with Template and assign each.label to label attribute.

We also need to provide a data model for the Radiogroup in the controller:

public class TodoListController extends SelectorComposer<Component>{


    //wire components
    ...
    @Wire
    Listbox todoListbox;

    ...
    @Wire
    Radiogroup selectedTodoPriority;
    ...

    //services
    TodoListService todoListService = new TodoListServiceChapter4Impl();

    //data for the view
    ListModelList<Todo> todoListModel;
    ListModelList<Priority> priorityListModel;
    Todo selectedTodo;

    @Override
    public void doAfterCompose(Component comp) throws Exception{
        super.doAfterCompose(comp);

        //get data from service and wrap it to list-model for the view
        List<Todo> todoList = todoListService.getTodoList();
        todoListModel = new ListModelList<Todo>(todoList);
        todoListbox.setModel(todoListModel);

        priorityListModel = new ListModelList<Priority>(Priority.values());
        selectedTodoPriority.setModel(priorityListModel);
    }
...
}

Line 31, 32: Create a ListModelList with Priority and set it as a model of selectedTodoPriority.

Create

After typing the todo item name, we can save the item by either clicking the button with the plus icon () or pressing "Enter" key. Therefore, we have to listen to 2 events: onClick and onOK. For handling other key pressing events, please refer to ZK_Developer's_Reference/UI_Patterns/Keystroke_Handling.

public class TodoListController extends SelectorComposer<Component>{

    //wire components
    @Wire
    Textbox todoSubject;

    //services
    TodoListService todoListService = new TodoListServiceChapter4Impl();

    //data for the view
    ListModelList<Todo> todoListModel;
    ListModelList<Priority> priorityListModel;
    Todo selectedTodo;

    ...

    //when user clicks on the button or enters on the textbox
    @Listen("onClick = #addTodo; onOK = #todoSubject")
    public void doTodoAdd(){
        //get user input from view
        String subject = todoSubject.getValue();
        if(Strings.isBlank(subject)){
            Clients.showNotification("Nothing to do ?",todoSubject);
        }else{
            //save data
            selectedTodo = todoListService.saveTodo(new Todo(subject));
            //update the model of listbox
            todoListModel.add(selectedTodo);
            //set the new selection
            todoListModel.addToSelection(selectedTodo);

            //refresh detail view
            refreshDetailView();

            //reset value for fast typing.
            todoSubject.setValue("");
        }
    }
...
}

Line 18: Listen the button's onClick event and "Enter" key pressing event: onOK.
Line 19: This method adds a todo item, update the data model of Listbox, change the selection to a newly created one, then reset the input field of the Textbox.
Line 21: Get user input in the Textbox todoSubject by getValue().
Line 23: Show a notification at the right hand side of the Textbox todoSubject.
Line 28: When you change (add or remove) items in a ListModelList object, it will automatically render in the Listbox's.
Line 30: Call addToSelection() to assign a component's selection and it will automatically reflect to the corresponding widget's selection.

Update

To update a todo item, you should select an item first then detail editor will appear. The following codes demonstrate how to listen a "onSelect" event and display the item's detail.

public class TodoListController extends SelectorComposer<Component>{


    //wire components
    @Wire
    Textbox todoSubject;
    @Wire
    Button addTodo;
    @Wire
    Listbox todoListbox;

    @Wire
    Component selectedTodoBlock;
    @Wire
    Checkbox selectedTodoCheck;
    @Wire
    Textbox selectedTodoSubject;
    @Wire
    Radiogroup selectedTodoPriority;
    @Wire
    Datebox selectedTodoDate;
    @Wire
    Textbox selectedTodoDescription;
    @Wire
    Button updateSelectedTodo;


    //when user selects a todo of the listbox
    @Listen("onSelect = #todoListbox")
    public void doTodoSelect() {
        if(todoListModel.isSelectionEmpty()){
            //just in case for the no selection
            selectedTodo = null;
        }else{
            selectedTodo = todoListModel.getSelection().iterator().next();
        }
        refreshDetailView();
    }

    private void refreshDetailView() {
        //refresh the detail view of selected todo
        if(selectedTodo==null){
            //clean
            selectedTodoBlock.setVisible(false);
            selectedTodoCheck.setChecked(false);
            selectedTodoSubject.setValue(null);
            selectedTodoDate.setValue(null);
            selectedTodoDescription.setValue(null);
            updateSelectedTodo.setDisabled(true);

            priorityListModel.clearSelection();
        }else{
            selectedTodoBlock.setVisible(true);
            selectedTodoCheck.setChecked(selectedTodo.isComplete());
            selectedTodoSubject.setValue(selectedTodo.getSubject());
            selectedTodoDate.setValue(selectedTodo.getDate());
            selectedTodoDescription.setValue(selectedTodo.getDescription());
            updateSelectedTodo.setDisabled(false);

            priorityListModel.addToSelection(selectedTodo.getPriority());
        }
    }
...
}

Line 29: Use @Listen to listen onSelect event of the Listbox whose id is todoListbox.
Line 30: This method checks todoListModel's selection and refreshes the detail editor.
Line 35: Get user selection from data model by getSelection() which returns a Set.
Line 40: If an item is selected, it makes detail editor visible and pushes data into those input components of the editor by calling setter methods. If no item is selected, it makes detail editor invisible and clear all input components' value.
Line 53: Make the detail editor visible when selectedTodo is not null.
Line 60: Use addToSelection() to assign a component's selection and it will automatically reflect to the corresponding widget's selection.

After modifying the item's detail, you can click the "Update" button to save the modification or "Reload" to revert back original data. The following codes demonstrate how to implement these functions:

Handle clicking "update" and "reload" button

    //when user clicks the update button
    @Listen("onClick = #updateSelectedTodo")
    public void doUpdateClick(){
        if(Strings.isBlank(selectedTodoSubject.getValue())){
            Clients.showNotification("Nothing to do ?",selectedTodoSubject);
            return;
        }

        selectedTodo.setComplete(selectedTodoCheck.isChecked());
        selectedTodo.setSubject(selectedTodoSubject.getValue());
        selectedTodo.setDate(selectedTodoDate.getValue());
        selectedTodo.setDescription(selectedTodoDescription.getValue());
        selectedTodo.setPriority(priorityListModel.getSelection().iterator().next());

        //save data and get updated Todo object
        selectedTodo = todoListService.updateTodo(selectedTodo);

        //replace original Todo object in listmodel with updated one
        todoListModel.set(todoListModel.indexOf(selectedTodo), selectedTodo);

        //show message for user
        Clients.showNotification("Todo saved");
    }

    //when user clicks the update button
    @Listen("onClick = #reloadSelectedTodo")
    public void doReloadClick(){
        refreshDetailView();
    }

Line 4: Validate user input and show a notification.
Line 9 ~ 13: Update selected Todo by getting user input from components.
Line 16, 19: We save the selected Todo object and get an updated one. Then, we replace the old one in the list model with the updated one.

Complete a Todo

Click a Checkbox in front of a todo item means to finish it. To implement this feature, the first problem is: how do we know which Checkbox is checked as there are many of them. We cannot listen to a Checkbox event as they are created in template using @Listen("onCheck = #todoListbox checkbox"),thus are created dynamically. Therefore, we introduce the "Event Forwarding" feature to demonstrate ZK's flexibility. This feature can forward an event from a component to another component, so we can forward an onCheck event from each Checkbox to the Listbox that encloses it, then we can just listen to the Listbox's events instead of all events of Checkbox.

extracted from chapter4/todolist-mvc.zul

...
    <listbox id="todoListbox" vflex="1">
...
        <template name="model">
            <listitem sclass="${each.complete?'complete-todo':''}" value="${each}">
                <listcell>
                    <checkbox forward="onCheck=todoListbox.onTodoCheck" checked="${each.complete}"/>
                </listcell>
                <listcell>
                    <label value="${each.subject}"/>
                </listcell>
                <listcell>
                    <button forward="onClick=todoListbox.onTodoDelete" image="/imgs/cross.png" width="36px"/>
                </listcell>
            </listitem>
        </template>

Line 7: Forward the Checkbox's onCheck to an event onTodoCheck of a Listbox whose id is todoListbox. The onTodoCheck is a customized forward event name, and you can use whatever name you want. Then we can use @Listen to listen this special event name.

Next, we listen to the customized event onTodoCheck and mark the todo as finished.

public class TodoListController extends SelectorComposer<Component>{
...

    //when user checks on the checkbox of each todo on the list
    @Listen("onTodoCheck = #todoListbox")
    public void doTodoCheck(ForwardEvent evt){
        //get data from event
        Checkbox cbox = (Checkbox)evt.getOrigin().getTarget();
        Listitem litem = (Listitem)cbox.getParent().getParent();

        boolean checked = cbox.isChecked();
        Todo todo = (Todo)litem.getValue();
        todo.setComplete(checked);

        //save data
        todo = todoListService.updateTodo(todo);
        if(todo.equals(selectedTodo)){
            selectedTodo = todo;
            //refresh detail view
            refreshDetailView();
        }
        //update listitem style
        ((Listitem)cbox.getParent().getParent()).setSclass(checked?"complete-todo":"");
    }
...
}

Line 5: Listen to the customized event name onTodoCheck of a Listbox todoListbox for we already forward onCheck to the Listbox in the zul.
Line 6: An event listener method can have a argument, but argument's type depends on which event you listen. As the customized event is forwarded from another component, the argument should be org.zkoss.zk.ui.event.ForwardEvent. This method set the Todo object of the selected item as complete and decorate Listitem with line-through by changing its sclass.
Line 8: You should call getOrigin() to get the original event that is forwarded. Every event object has a method getTarget() that allows you get the target component that receives the event.
Line 9: Navigate the component tree by getParent().
Line 12: Here we get Todo object of the selected todo item from value attribute that we assigned in the zul by <listitem ... value="${each}"/>

Delete

Implement deletion feature is similar to completing a todo item. We also forward each delete button's () onClick event to the Listbox that encloses those buttons.

Forward delete button's onClick

    <listbox id="todoListbox" vflex="1">
...
        <template name="model">
            <listitem sclass="${each.complete?'complete-todo':''}"
                        value="${each}">
                <listcell>
                    <checkbox forward="onCheck=todoListbox.onTodoCheck"
                                checked="${each.complete}"/>
                </listcell>
                <listcell>
                    <label value="${each.subject}"/>
                </listcell>
                <listcell>
                    <button forward="onClick=todoListbox.onTodoDelete"
                        image="/imgs/cross.png" width="36px"/>
                </listcell>
            </listitem>
        </template>
...

Line 14, 15: Forward delete button's onClick to the Listbox's as a custom forward event named onTodoDelete.

Then we can listen to the forwarded event and perform deletion.


    //when user clicks the delete button of each todo on the list
    @Listen("onTodoDelete = #todoListbox")
    public void doTodoDelete(ForwardEvent evt){
        Button btn = (Button)evt.getOrigin().getTarget();
        Listitem litem = (Listitem)btn.getParent().getParent();

        Todo todo = (Todo)litem.getValue();

        //delete data
        todoListService.deleteTodo(todo);

        //update the model of listbox
        todoListModel.remove(todo);

        if(todo.equals(selectedTodo)){
            //refresh selected todo view
            selectedTodo = null;
            refreshDetailView();
        }
    }

Line 2: Listen the customized event name onTodoDelete of a Listbox that we forward from delete button.
Line 7: Since we have set each Todo object to each Listitem's value in the zul, we can get it by getValue()

After completing the above steps, vist http://localhost:8080/zkessentials/chapter4/todolist-mvc.zul to see the result.

MVC Pattern