Step 34: Custom Controls

介绍

In this step, we are going to extend the functionality of SAPUI5 with a custom control. We want to rate the product shown on the detail page, so we create a composition of multiple standard controls using the SAPUI5 extension mechanism and add some glue code to make them work nicely together. This way, we can reuse the control across the app and keep all related functionality in one module.

1.练习效果

Step 34: Custom Controls - 第1张  | 优通SAP

2.源码

You can view and download all files at Walkthrough – Step 34.

webapp/control/ProductRating.js (New)

We create a new folder control and a file
ProductRating.js that will hold our new control. As with our
controllers and views, the custom control inherits the common control functionality
from a SAPUI5 base
object, for controls this is done by extending the base class
sap.ui.core.Control.

Custom controls are small reuse components that can be created within the app very
easily. Due to their nature, they are sometimes also referred to as “notepad” or “on
the fly” controls. A custom control is a JavaScript object that has two special
sections (metadata and renderer) and a number of
methods that implement the functionality of the control.

The metadata section defines the data structure and thus the API of
the control. With this meta information on the properties, events, and aggregations
of the control SAPUI5
automatically creates setter and getter methods and other convenience functions that
can be called within the app.

The renderer defines the HTML structure that will be added to the DOM tree of your app whenever the control is instantiated in a view. It is usually
called initially by the core of SAPUI5 and whenever a property of the control is
changed. The parameter oRM of the render function is the SAPUI5
render manager that can be used to write strings and control properties to the HTML page.

The init method is a special function that is called by the SAPUI5 core whenever
the control is instantiated. It can be used to set up the control and prepare its
content for display.

3.Note

Controls always extend sap.ui.core.Control and render themselves. You could also extend sap.ui.core.Element or sap.ui.base.ManagedObject directly if you want to reuse life cycle features of SAPUI5 including data binding for objects that are not rendered. Please refer to the API reference to learn more about the inheritance hierarchy of controls.

webapp/control/ProductRating.js

We now enhance our new custom control with the custom functionality that we need. In
our case we want to create an interactive product rating, so we define a value and
use three internal controls that are displayed updated by our control automatically.
A RatingIndicator control is used to collect user input on the
product, a label is displaying further information, and a button submits the rating
to the app to store it.

In the metadata section we therefore define several properties that
we make use in the implementation:

  • Value

    We define a control property value that will
    hold the value that the user selected in the rating. Getter
    and setter function for this property will automatically be
    created and we can also bind it to a field of the data model
    in the XML view if we like.

  • Aggregations

    As described in the first paragraph, we need three internal controls to realize our rating
    functionality. We therefore create three “hidden aggregations” by
    setting the visibility attribute to
    hidden. This way, we can use the models that are
    set on the view also in the inner controls and SAPUI5 will
    take care of the lifecycle management and destroy the controls when they
    are not needed anymore. Aggregations can also be used to hold arrays of
    controls but we just want a single control in each of the aggregations
    so we need to adjust the cardinality by setting the attribute
    multiple to false.

    • _rating: A
      sap.m.RatingIndicator control for user
      input

    • _label: A sap.m.Label to
      display additional information

    • _button: A sap.m.Button to
      submit the rating

  • 3.Note

    You can define aggregations and associations for controls. The difference is in the relation between the parent and the related control:
    • An aggregation is a strong relation that also manages the lifecycle of the related control, for example, when the parent is destroyed, the related control is also destroyed. Also, a control can only be assigned to one single aggregation, if it is assigned to a second aggregation, it is removed from the previous aggregation automatically.

    • An association is a weak relation that does not manage the lifecycle and can be defined multiple times. To have a clear distinction, an association only stores the ID, whereas an aggregation stores the direct reference to the control. We do not specify associations in this example, as we want to have our internal controls managed by the parent.

  • Change

    We specify a change event that the control will fire when the rating is submitted. It contains the current value as an event
    parameter. Applications can register to this event and process the result similar to “regular” SAPUI5 controls, which are in fact built similar to custom
    controls.

  • In the init function that is called by SAPUI5 automatically
    whenever a new instance of the control is instantiated, we set up our internal
    controls. We instantiate the three controls and store them in the internal
    aggregation by calling the framework method setAggregation that has
    been inherited from sap.ui.core.Control. We pass on the name of the
    internal aggregations that we specified above and the new control instances. We
    specify some control properties to make our custom control look nicer and register a
    liveChange event to the rating and a press event to the button.
    The initial texts for the label and the button are referenced from our
    i18n model.

    Let’s ignore the other internal helper functions and event handlers for now and
    define our renderer. With the help of the SAPUI5 render manager
    and the control instance that are passed on as a reference, we can now render the
    HTML structure of our control. We render the start of the outer
    <div> tag as <div and call the helper
    method writeControlData to render the ID and other basic attributes
    of the control inside the div tag. Next, we add a custom CSS class
    so that we can define styling rules for the custom control in our CSS file later.
    This CSS class and others that have been added in the view are then rendered by
    calling writeClasses on the renderer instance. Then we close the
    surrounding div tag and render three internal controls by passing
    the content of the internal aggregation to the render managers
    renderControl function. This will call the renderer of the
    controls and add their HTML to the page. Finally, we close our surrounding
    <div> tag.

    The setValue is an overridden setter. SAPUI5 will generate a
    setter that updates the property value when called in a controller or defined in the
    XML view, but we also need to update the internal rating control in the hidden
    aggregation to reflect the state properly. Also, we can skip the rerendering of SAPUI5 that is usually
    triggered when a property is changed on a control by calling the
    setProperty method to update the control property with true as
    the third parameter.

    Now we define the event handler for the internal rating control. It is called every
    time the user changes the rating. The current value of the rating control can be
    read from the event parameter value of the sap.m.RatingIndicator
    control. With the value we call our overridden setter to update the control state,
    then we update the label next to the rating to show the user which
    value he has selected currently and also displays the maximum value. The string with
    the placeholder values is read from the i18n model that is assigned
    to the control automatically.

    Next, we have the press handler for the rating button that submits our
    rating. We assume that rating a product is a one-time action and first disable the
    rating and the button so that the user is not allowed to submit another rating. We
    also update the label to show a “Thank you for your rating!” message, then we fire
    the change event of the control and pass in the current value as a parameter so that
    applications that are listening to this event can react on the rating
    interaction.

    We define the reset method to be able to revert the state of the
    control on the UI to its initial state so that the user can again submit a
    rating.

    5.webapp/view/Detail.view.xml

    A new namespace wt is defined on the detail view so that we can
    reference our custom controls easily in the view. We then add an instance of the
    ProductRating control to our detail page and register an event
    handler for the change event. To have a proper layout, we also add a margin style
    class.

    6.webapp/controller/Detail.controller.js

    In the Detail controller we load the dependency to the
    sap.m.MessageToast because we will simply display a message
    instead of sending the rating to the backend to keep the example simple. The event
    handler onRatingChange reads the value of our custom change event
    that is fired when the rating has been submitted. We then display a confirmation
    message with the value in a MessageToast control.

    In the onObjectMatched private method, we call the
    reset method to make it possible to submit another rating as
    soon as the detail view is displayed for a different item.

    webapp/css/style.css

    To layout our control, we add a little padding to the root class to have some space
    around the three inner controls, and we override the alignment of the
    RatingIndicator control so that it is aligned in one line with
    the label and the button.

    We could also do this with more HTML in the renderer but this is the simplest way and
    it will only be applied inside our custom control. However, please be aware that the
    custom control is in your app and might have to be adjusted when the inner controls
    change in future versions of SAPUI5.

    webapp/i18n/i18n.properties

    The resource bundle is extended with the confirmation message and the strings that we
    reference inside the custom control. We can now rate a product on the detail page
    with our brand new control.

    7. Conventions

    • Put custom controls in the control folder of your app.

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