Create a Slider Custom Control in an MDK App (Using Metadata Approach)

The extension control that you will be creating to extend the functionality of your app can be used as base controls by registering it using the MDK editor.

1. Download this image and save it locally. This image will be used as a display image on the page editor to represent the extension control.

2. Drag & drop slider.png file on Images folders.

   

3. Right-click Extensions | select MDK: Register Extension Control.

   

4. In Template Selection step, select New and register Metadata Extension Control. Click Next.

   

5. In the Basic Information step, provide the below information:

   Field	Value
   Control Name	mdk_slider
   Module	MySliderModule
   Control	MySliderExtension
   Class	MySliderClass
   Display	bind it to slider.png file

   Here is the basic definition for properties you defined above:

   Module: It is used to identify the extension control. The path to the extension module under <MetadataProject>/Extensions/.

   Control: The name of the file under the <MetadataProject>/Extensions/<Module>/controls that contains the extension class. If not specified, module name would be used as the value for this property.

   Class: The class name of your custom extension class. The client will check for this class at runtime and if it’s found, your extension will be instantiated. Otherwise, a stub with an error message will be shown.

   Display: This property is used for the image to be displayed on the page editor to represent the extension control.

   

6. In Schema Information step, fill schema details in Schema column and click Next.

   {
   	"type": "object",
   	"BindType": "",
   	"properties": {
   		"MaxValue": {
   			"type": "number",
   			"BindType": ""
   		},
   		"MinValue": {
   			"type": "number",
   			"BindType": ""
   		},
   		"Title": {
   			"type": "string",
   			"BindType": ""
   		}
   	}
   }
   

   

   Above schema will add these predefined properties (MaxValue, MinValue and Title) in the map extension control. You will provide values for these properties in next step.

7. Click Finish to confirm.

   Some additional files and folders are added to the Extensions folder. You will learn more about it in following steps.

   

   You can find more details about registering extension control in this guide.

You will add this registered control in a Form Cell page.

1. Create a new page of Form Cell type.

   Right-click the Pages folder | MDK: New Page | Form Cell Page | Next.

   

   A Form Cell Page is suitable for pages that generate new objects or modify existing objects. It includes a form cell container by default. You can add form sections, multiple containers or action controls to this page. Under each container section, you can add various container items.

   You can find more details about Form Cell page.

2. Enter the Page Name as SliderExtension and click Next and the Finish on the Confirmation step.

   

3. In MDK Page Editor, drag & drop the registered mdk_slider control on the page area.

   

   You can find more details about the Section Extension in this guide.

4. In the Properties section, provide the below value:

   Field	Value
   Name	MyExtensionControlName
   Height	72
   MaxValue	200
   MinValue	10
   Title	Counter

   

5. Create a new Message action.

   Right-click the Actions folder | MDK: New Action | choose MDK Message Actions in Category | click Message Action | Next.

   

   Provide the below information:

   Property	Value
   Action Name	ShowMessage
   Type	Select Message from the dropdown
   Message	#Control:MyExtensionControlName/#Value
   Title	Value of the Slider is:
   OKCaption	OK
   OnOK	--None--
   CancelCaption	leave it blank
   OnCancel	--None--

   

   Here MyExtensionControlName is the name of the control that you renamed in code editor.

   Click Next and then Finish on the confirmation step.

6. You will add an item on action bar in SliderExtension.page and set ShowMessage.action on its onPress event.

   In SliderExtension.page, drag and drop an Action Bar Item to the upper right corner of the action bar.

   

7. Click the link icon to open the object browser for the System Item property.

   Double click the Save type and click OK.

   

8. In the Properties pane | Events tab, click the 3 dots icon for the OnPress property to open the Object Browser, bind it to ShowMessage.action.

   

9. You can also add an input field where you can provide a manual entry for the slider value and the counter will adapt accordingly.

   For this, first you will write a business logic to set the extension value and then bind it to the input field.

   Right-click the Rules folder | MDK: New Rule File | select Empty JS Rule.

   

   Enter the Rule name SetExtensionValue, click Next and then Finish on the confirmation step.

   

   Replace the generated snippet with below code.

   export default function SetExtensionValue(context) {
       console.log("In SetExtensionValue");
       let srcValue = context.getValue();
       let targetCtrl = context.evaluateTargetPath("#Page:SliderExtension/#Control:MyExtensionControlName");
       targetCtrl.setValue(srcValue);
   }
   

   

10. Save the changes to the SetExtensionValue.js file.

11. In SliderExtension.page, drag and drop a Simple Property item control below the slider control.

    

12. Provide the following information:

    Property	Value
    Caption	Manual Entry
    placeholder	Enter number to set the slider ext's value

    

13. Navigate to Events tab, click the 3 dots icon for the OnValueChange property to open the Object Browser, bind it to SetExtensionValue.js.

    

1. In Extensions folder, create additional files & folders. You will write individual implementation for Android and iOS platform. Final structure should look like as per below.

   

   ├── Extensions
     ├── MySliderModule
      │   └── controls
      │       ├── MySliderExtension.ts
      │       └── MySliderPlugin
      │           ├── MySlider.ts
      │           ├── android
      │           │   └── MySlider.ts
      │           └── ios
      │               └── MySlider.ts
      └── mdk_slider.extension
   

2. In MySliderPlugin/android/MySlider.ts file, copy and paste the following code.

   import { Observable } from '@nativescript/core/data/observable';
   import {​​​​​​ Device, View, Utils }​​​​​​ from'@nativescript/core';
   /*
     This is a way to keep iOS and Android implementation of your extension separate
     We will encapsulate the MySlider class definition inside a function called GetMySliderClass
     This is so that the class definition won't be executed when you load this javascript
     via require function.
     The class definition will only be executed when you execute GetMySliderClass
   */
   declare var com: any;
   declare var android: any;
   export function GetMySliderClass() {
       /**
        * IMPLEMENT THE ANDROID VERSION OF YOUR PLUGIN HERE
        * In this sample you have 2 controls a label and a seekbar (slider)
        * You extends this control with Observable (View) class so that you can accept listeners
        *  and notify them when UI interaction is triggered
        */
       function getPadding() {
           // Return left & right padding in dp
           // For tablet you want 24dp, for other type you use 16dp
           return Device.deviceType === 'Tablet' ? 24 : 16;
       }
   
       class MySlider extends View {
           private _androidcontext;
           private _label;
           private _labelText = "";
           private _seekbar;
           private _layout;
           private _value = 0;
           private _min = 0; //Used to track min for API 25 or lower
   
           private updateText() {
               this._label.setText(this._labelText + "(" + this._value + ")")
           }
   
           public constructor(context: any) {
               super();
               this._androidcontext = context;
               this.createNativeView();
           }
   
           /**
            * Creates new native controls.
            */
           public createNativeView(): Object {
               //Create an Android label
               this._label = new android.widget.TextView(this._androidcontext);
               const labelBottomPaddingInPx = Utils.layout.round(Utils.layout.toDevicePixels(8)); // For top & bottom padding, always 16dp
               this._label.setPadding(0, 0, 0, labelBottomPaddingInPx);
               this._label.setLayoutParams(new android.view.ViewGroup.LayoutParams(-1, -2));
   
               //Create an Android seekbar
               this._seekbar = new android.widget.SeekBar(this._androidcontext);
               this._seekbar.setLayoutParams(new android.view.ViewGroup.LayoutParams(-1, -2));
   
               //Create a LinearLayout container to contain the label and seekbar
               this._layout = new android.widget.LinearLayout(this._androidcontext);
               this._layout.setOrientation(android.widget.LinearLayout.VERTICAL);
               this._layout.setLayoutParams(new android.view.ViewGroup.LayoutParams(-1, -1));
   
               const hortPaddingInPx = Utils.layout.round(Utils.layout.toDevicePixels(getPadding()));
               const vertPaddingInPx = Utils.layout.round(Utils.layout.toDevicePixels(16)); // For top & bottom padding, always 16dp
               this._layout.setPadding(hortPaddingInPx, vertPaddingInPx, hortPaddingInPx, vertPaddingInPx);
               this._layout.addView(this._label);
               this._layout.addView(this._seekbar);
               this.setNativeView(this._layout);
               return this._layout;
           }
   
           /**
            * Initializes properties/listeners of the native view.
            */
           initNativeView(): void {
               console.log("initNativeView called");
               // Attach the owner to nativeView.
               // When nativeView is tapped you get the owning JS object through this field.
               (<any>this._seekbar).owner = this;
               (<any>this._layout).owner = this;
               super.initNativeView();
   
               //Attach a listener to be notified whenever the native Seekbar is changed so that you can notify the MDK Extension
               this._seekbar.setOnSeekBarChangeListener(new android.widget.SeekBar.OnSeekBarChangeListener({
                   onStartTrackingTouch(seekBar: any) {
                       // You do not have any use for this event, so do nothing here
                   },
                   //This handler function will be called when user let go of the handle
                   // This is where you will trigger an event called "OnSliderValueChanged" to the MDK Extension Class
                   onStopTrackingTouch(seekBar: any) {
                       var eventData = {
                           eventName: "OnSliderValueChanged",
                           object: seekBar.owner,
                           value: seekBar.owner._value
                       };
                       seekBar.owner.notify(eventData);
                   },
                   //This handler function will be called whenever the slider's value is changed
                   // i.e. whenever user drag the slider's handle
                   onProgressChanged(seekBar: any, progress: number, fromUser: boolean) {
                       seekBar.owner._value = progress;
                       seekBar.owner.updateText();
                   }
               }));
           }
   
           /**
            * Clean up references to the native view and resets nativeView to its original state.
            * If you have changed nativeView in some other way except through setNative callbacks
            * you have a chance here to revert it back to its original state
            * so that it could be reused later.
            */
           disposeNativeView(): void {
               // Remove reference from native view to this instance.
               (<any>this._seekbar).owner = null;
               (<any>this._layout).owner = null;
   
               // If you want to recycle nativeView and have modified the nativeView
               // without using Property or CssProperty (e.g. outside our property system - 'setNative' callbacks)
               // you have to reset it to its initial state here.
           }
   
           //Must return the native view of the control for MDK FormCell and Section Extension
           public getView(): any {
               return this._layout;
           }
   
           public setText(newText: string): void {
               if (newText != null && newText != undefined) {
                   this._labelText = newText;
                   this._label.setText(newText);
               }
           }
   
           public setValue(newVal: number): void {
               if (newVal != null && newVal != undefined) {
                   this._value = newVal;
                   this.updateText();
                   if (this._seekbar.getProgress() < this._min) {
                       this._seekbar.setProgress(this._min);
                   }
                   else {
                       this._seekbar.setProgress(newVal);
                   }
               }
           }
   
           public setMinValue(newMin: number): void {
               if (newMin != null && newMin != undefined) {
                   if (Device.sdkVersion >= 26) { //setMin is only available in set API Level 26 or newer
                       this._seekbar.setMin(newMin);
                   }
                   else {
                       this._min = newMin;
                       if (this._seekbar.getProgress() < this._min) {
                           this._seekbar.setProgress(this._min);
                       }
                   }
               }
           }
   
           public setMaxValue(newMax: number): void {
               if (newMax != null && newMax != undefined) {
                   this._seekbar.setMax(newMax);
               }
           }
       }
       return MySlider;
   }
   

   In your import function, if you see errors related to @nativescript/core, you can ignore them. There is currently no reference of such libraries in the MDK editor.

3. Save the MySliderPlugin/android/MySlider.ts file.

4. In MySliderPlugin/iOS/MySlider.ts file, copy and paste the following code.

   import {​​​​​​View}​​​​​​ from'@nativescript/core';
   /*
     This is a way to keep iOS and Android implementation of your extension separate
     You will encapsulate the MySlider class definition inside a function called GetMySliderClass
     This is so that the class definition won't be executed when you load this javascript
     via require function.
     The class definition will only be executed when you execute GetMySliderClass
   */
   export function GetMySliderClass() {
       /**
        * IMPLEMENT THE IOS VERSION OF YOUR PLUGIN HERE
        */
   
       // This is a class that handles the native event callbacks
       @NativeClass()
       class SliderHandler extends NSObject {
   
           //This handler function will be called whenever the slider's value is changed
           // i.e. whenever user drag the slider's handle
           public valueChanged(nativeSlider: UISlider, nativeEvent: _UIEvent) {
               nativeSlider.value = Math.round(nativeSlider.value);
               const owner: MySlider = (<any>nativeSlider).owner;
               if (owner) {
                   owner.setValue(nativeSlider.value);
               }
           }
   
           //This handler function will be called when user let go of the handle
           // This is where you will trigger an event called "OnSliderValueChanged" to the MDK Extension Class
           public afterValueChanged(nativeSlider: UISlider, nativeEvent: _UIEvent) {
               nativeSlider.value = Math.round(nativeSlider.value);
               const owner: MySlider = (<any>nativeSlider).owner;
               if (owner) {
                   owner.setValue(nativeSlider.value);
                   var eventData = {
                       eventName: "OnSliderValueChanged",
                       object: owner,
                       value: nativeSlider.value
                   };
                   owner.notify(eventData);
               }
           }
   
           public static ObjCExposedMethods = {
               "valueChanged": { returns: interop.types.void, params: [interop.types.id, interop.types.id] },
               "afterValueChanged": { returns: interop.types.void, params: [interop.types.id, interop.types.id] }
           };
       }
   
       const handler = SliderHandler.new();
   
       class MySlider extends View {
           private _label;
           private _labelText = "";
           private _slider;
           private _layout;
           private _value = 0;
   
           private updateText() {
               this._label.text = this._labelText + "(" + this._value + ")";
           }
   
           public constructor(context: any) {
               super();
               this.createNativeView();
           }
   
           /**
            * Creates new native controls.
            */
           public createNativeView(): Object {
               //Create the Stack view - this is the main view of this extension
               this._layout = UIStackView.new();
               //Configuring the paddings around the stack view
               this._layout.autoresizingMask = [UIViewAutoresizing.FlexibleHeight, UIViewAutoresizing.FlexibleWidth];
               this._layout.layoutMarginsRelativeArrangement = true;
               let inset = new NSDirectionalEdgeInsets();
               inset.top = 8; inset.leading = 16; inset.bottom = 8; inset.trailing = 16;
               this._layout.directionalLayoutMargins = inset;
               // Set the layout stacking to be vertical
               this._layout.axis = UILayoutConstraintAxis.Vertical;
   
               //Create the label view
               this._label = UILabel.new();
               this._label.font = this._label.font.fontWithSize(15); //Set font size
               this._label.textColor = UIColor.colorWithRedGreenBlueAlpha(106 / 255, 109 / 255, 112 / 255, 1.0); //Set text color
               this._layout.setCustomSpacingAfterView(4, this._label); //Set the bottom margin of label
   
               //Create the slider control
               this._slider = UISlider.new();
   
               //Assign a handler for whenever value changed i.e. when user is dragging the slider handle
               this._slider.addTargetActionForControlEvents(handler, "valueChanged", UIControlEvents.ValueChanged);
               //Assign a handler for when user let go of the handle
               this._slider.addTargetActionForControlEvents(handler, "afterValueChanged", UIControlEvents.TouchUpInside | UIControlEvents.TouchUpOutside);
   
               //Add the label and slider to the stack view
               this._layout.addArrangedSubview(this._label);
               this._layout.addArrangedSubview(this._slider);
   
               //store the native view
               this.setNativeView(this._layout);
   
               //return the stack view
               return this._layout;
           }
           /**
            * Initializes properties/listeners of the native view.
            */
           initNativeView(): void {
               // Attach the owner to nativeViews.
               // When nativeViews are tapped you get the owning JS object through this field.
               (<any>this._slider).owner = this;
               (<any>this._layout).owner = this;
               super.initNativeView();
           }
   
           /**
            * Clean up references to the native view and resets nativeView to its original state.
            * If you have changed nativeView in some other way except through setNative callbacks
            * you have a chance here to revert it back to its original state
            * so that it could be reused later.
            */
           disposeNativeView(): void {
               // Remove reference from native view to this instance.
               (<any>this._slider).owner = null;
               (<any>this._layout).owner = null;
   
               // If you want to recycle nativeView and have modified the nativeView
               // without using Property or CssProperty (e.g. outside our property system - 'setNative' callbacks)
               // you have to reset it to its initial state here.
           }
   
           //Must return the native view of the control for MDK FormCell and Section Extension
           public getView(): any {
               return this._layout;
           }
   
           public setText(newText: string): void {
               if (newText != null && newText != undefined) {
                   this._labelText = newText;
                   this._label.text = newText;
               }
           }
   
           public setValue(newVal: number): void {
               if (newVal != null && newVal != undefined) {
                   this._value = newVal;
                   this.updateText();
                   this._slider.value = newVal;
               }
           }
   
           public setMinValue(newMin: number): void {
               if (newMin != null && newMin != undefined) {
                   this._slider.minimumValue = newMin;
               }
           }
   
           public setMaxValue(newMax: number): void {
               if (newMax != null && newMax != undefined) {
                   this._slider.maximumValue = newMax;
               }
           }
       }
   
       return MySlider;
   }
   

5. Save the MySliderPlugin/iOS/MySlider.ts file.

6. In MySliderPlugin/MySlider.ts file, copy and paste the following code.

   import * as application from '@nativescript/core/application';
   export let MySlider;
   let MySliderModule;
   /*
   This is a sample of how to implement iOS and Android codes separately in a metadata extension.
   Because all ts files in metadata Extensions folder will be bundled together using webpack,
   if you execute any iOS codes in Android vice versa, it will likely cause issue such as crash.
   
   By splitting the implementation into different files and encapsulate them in a function, it allows
   us to load only the required module for the platform at runtime.
   */
   if (!MySlider) {
       //Here you will check what platform the app is in at runtime.
       if (application.ios) {
           //if app is in iOS platform, load the MySlider module from ios folder
           MySliderModule = require('./ios/MySlider');
       } else {
           //otherise, assume app is in Android platform, load the MySlider module from android folder
           MySliderModule = require('./android/MySlider');
       }
       // calling GetMySliderClass() will return MySlider class for the correct platform.
       //  See the MySlider.ts in ios/andrid folder for details
       MySlider = MySliderModule.GetMySliderClass();
   }
   

7. Save the MySliderPlugin/MySlider.ts file.

8. In MySliderExtension.ts file, replace the code with the following.

   import { BaseControl } from 'mdk-core/controls/BaseControl';
   import { MySlider } from './MySliderPlugin/MySlider'
   
   export class MySliderClass extends BaseControl {
       private _slider: MySlider;
       private _minVal: number = 0;
       private _maxVal: number = 10000;
   
       public initialize(props) {
           super.initialize(props);
   
           //Create the Slider plugin control
           this.createSlider();
           //Assign the slider's native view as the main view of this extension
           this.setView(this._slider.getView());
       }
   
       private createSlider() {
           //Create MySlider and initialize its native view
           this._slider = new MySlider(this.androidContext());
           this._slider.initNativeView();
   
           this._slider.setMinValue(this._minVal);
           this._slider.setMaxValue(this._maxVal);
   
           //Set the slider's properties if "ExtensionProperties" is defined
           let extProps = this.definition().data.ExtensionProperties;
           if (extProps) {
               //In here you will use ValueResolver to resolve binding/rules for the properties
               // This will allow the app to use binding/rules to set the properties' value
   
               // Resolve title's value
               this.valueResolver().resolveValue(extProps.Title, this.context, true).then(function (title) {
                   this._slider.setText(title);
               }.bind(this));
   
               // Resolve min value
               this.valueResolver().resolveValue(extProps.MinValue, this.context, true).then(function (minVal) {
                   if (minVal !== null && minVal !== undefined) {
                       this._minVal = minVal;
                       this._slider.setMinValue(this._minVal);
                   }
               }.bind(this));
   
               // Resolve max value
               this.valueResolver().resolveValue(extProps.MaxValue, this.context, true).then(function (maxVal) {
                   if (maxVal !== null && maxVal !== undefined) {
                       this._maxVal = maxVal;
                       this._slider.setMaxValue(this._maxVal);
                   }
               }.bind(this));
   
               // Resolve value
               this.valueResolver().resolveValue(extProps.Value, this.context, true).then(function (value) {
                   this.setValue(value, false, false);
               }.bind(this));
           }
   
           //Set up listener for MySlider's OnSliderValueChanged event that will be triggered when user let of the slider's handle
           // It's eventData object contain a property 'value' that will contain the value of the slider
           this._slider.on("OnSliderValueChanged", function (eventData) {
               //We will call the setValue
               this.setValue(eventData.value, true, false);
           }.bind(this));
       }
   
       // Override
       protected createObservable() {
           let extProps = this.definition().data.ExtensionProperties;
           //Pass ExtensionProperties.OnValueChange to BaseControl's OnValueChange
           if (extProps && extProps.OnValueChange) {
               this.definition().data.OnValueChange = extProps.OnValueChange;
           }
           return super.createObservable();
       }
   
       public setValue(value: any, notify: boolean, isTextValue?: boolean): Promise<any> {
           //Check the value
           if (value != null && value != undefined && !isNaN(value)) {
               if (typeof value == "string" && value.trim() == "") {
                   return Promise.reject("Error: Value is not a number");
               }
               let val = Number.parseInt(value);
               //Don't let value go lower than permitted minimum or higher than permitted maximum
               val = val < this._minVal ? this._minVal : val;
               val = val > this._maxVal ? this._maxVal : val;
   
               if (this._slider) {
                   //Set the slider's value
                   this._slider.setValue(val);
               }
               //Store the value. The observable will trigger "OnValueChange" to the MDK app
               // MDK app can register to this event in the metadata with property "OnValueChange"
               return this.observable().setValue(val, notify, isTextValue);
           } else if (isNaN(value)) {
               return Promise.reject("Error: Value is not a number");
           }
           return Promise.resolve();
       }
   
       public viewIsNative() {
           return true;
       }
   }    
   

9. Save the MySliderExtension.ts file.