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I want to write a simple "compass" app with NativeScript, a fun project to be submitted to GitHub. The GPS part is done. I am using this: https://market.nativescript.org/plugins/nativescript-canvas, app created with 'tns create --ng'. The canvas is drawn once, it works, great! But I want to constantly redraw it with data from GPS and I have no idea how.

I tried to save the 'canvas' value in an instance variable of my Component, I mean the value that comes with the event to 'draw' -> event: {canvas: Canvas} But reusing the value crushes the whole app, it is actually 'undefined' which I don't understand with my limited knowledge of Angular/TypeScript. Any hint how to get the 'canvas' wherever I like? A git repo with a working example?

I followed the instruction for Angular:

and draw(event: { canvas: Canvas }) { ...

deploying it to android emulator ends with an error (see below) but adding a space anywhere in the code forces redeployment ('change detected') which deploys fine. As such this cannot be deployed to a real device, of course. But first - I need to update the canvas :) thx. 

System.err: java.lang.RuntimeException: Unable to start activity ComponentInfo{org.nativescript.HelloWorld/com.tns.NativeScriptActivity}: com.tns.NativeScriptException:
System.err: Calling js method onCreate failed
System.err:
System.err: Error: Main entry is missing. App cannot be started. Verify app bootstrap.
System.err: File: "file:///data/data/org.nativescript.HelloWorld/files/app/vendor.js, line: 21886, column: 20
System.err:
System.err: StackTrace:
System.err:     Frame: function:'push.../node_modules/tns-core-modules/ui/frame/frame.js.ActivityCallbacksImplementation.setActivityContent', file:'file:///data/data/org.nativescript.HelloWorld/files/app/vendor.js', line: 21886, column: 27
System.err:     Frame: function:'push.../node_modules/tns-core-modules/ui/frame/frame.js.ActivityCallbacksImplementation.onCreate', file:'file:///data/data/org.nativescript.HelloWorld/files/app/vendor.js', line: 21731, column: 14
System.err:     Frame: function:'push.../node_modules/tns-core-modules/ui/frame/activity.js.NativeScriptActivity.onCreate', file:'file:///data/data/org.nativescript.HelloWorld/files/app/vendor.js', line: 19544, column: 25
Gratien Asimbahwe
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Bogusz Jeliński
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  • The error dump is messy so tha main message was 'Main entry is missing'. And a tag was removed during submission of my question, so maybe the way - I put CanvasView width="100" height="100" (draw)="draw($event) ... into an XML of my HelloWorld angular template generated by initial 'create'. – Bogusz Jeliński Jul 18 '19 at 20:49

1 Answers1

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The event param also has object property which is the canvasView.

In order to redraw, you can call

event.object.redraw()

Then your draw function will be called again, and you can handle the canvas update.

dukewan
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