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Tausche .NET gegen Web: Desktop-Apps als PWA entwickeln

Tausche .NET gegen Web: Desktop-Apps als PWA entwickeln

Für .NET-Entwickler ist völlig klar: Wenn eine Desktopanwendung entwickelt werden muss, greift man zu Windows Forms oder WPF. In dieser DevSession nehmen wir eine alternative Technologie unter die Lupe: Progressive Web Apps. Dieses Anwendungsmodell auf Basis von Webtechnologien bietet nicht nur eine erstklassige Unterstützung für Desktopanwendungen, sondern läuft auf Basis desselben Quelltextes auch noch im Browser oder auf Mobilgeräten. Microsoft ist einer der wesentlichen Treiber der Progressive Web Apps – und das nicht erst, seitdem der eigene Browser Edge auf dem Chrome-Unterbau Chromium basiert. Im Rahmen von Project Fugu kooperiert Microsoft mit Intel und Google, um mächtige Schnittstellen für Webanwendungen einzuführen: Das schließt Dateizuordnungen, Zugriff auf das native Dateisystem oder die Zwischenablage sowie Sprunglisteneinträge mit ein. In dieser Session zeigt Ihnen Christian Liebel von Thinktecture, wie Sie erstklassige Produktivitätsapps für den Desktop als PWA entwickeln können – und ganz nebenbei auch noch Apps für den Browser und Mobilgeräte herausfallen.

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Christian Liebel
PRO

November 24, 2020
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  1. Tausche .NET gegen Web Desktop-Apps als PWA entwickeln Christian Liebel

    @christianliebel Consultant
  2. Hello, it’s me. Tausche .NET gegen Web Desktop-Apps als PWA

    entwickeln Christian Liebel Twitter: @christianliebel Email: christian.liebel @thinktecture.com Angular & PWA Slides: thinktecture.com /christian-liebel
  3. 09:00–10:00 Block 1 10:00–10:15 Break 10:15–11:30 Block 2 11:30–11:45 Break

    11:45–13:00 Block 3 Tausche .NET gegen Web Desktop-Apps als PWA entwickeln Timetable
  4. Things NOT to expect - Blueprint for PWA development -

    No AuthN/AuthZ - No hands-on Things To Expect - Extensive/up-to-date insights into PWA and Project Fugu - A productivity app use case that works on your desktop & smartphone - Lots of fun Desktop-Apps als PWA entwickeln Tausche .NET gegen Web
  5. https://paint.js.org – Productivity app – Draw images – Lots of

    actions & tools – Installable – Read/save files – Copy/paste images from/to clipboard – Share files to other apps – Register for file extensions Tausche .NET gegen Web Desktop-Apps als PWA entwickeln Demo Use Case
  6. (Workshop Edition) – Productivity app – Draw images – Lots

    of actions & tools – Installable – Read/save files – Copy/paste images from/to clipboard – Share files to other apps – Register for file extensions Tausche .NET gegen Web Desktop-Apps als PWA entwickeln Demo Use Case
  7. Paint PWA Capabilities Progressive Enhancement Tausche .NET gegen Web Desktop-Apps

    als PWA entwickeln Agenda
  8. Paint PWA Capabilities Progressive Enhancement Tausche .NET gegen Web Desktop-Apps

    als PWA entwickeln Agenda
  9. Canvas – Plain bitmap for the web – Cross-platform, hardware-

    accelerated graphics operations – Supports different contexts (2D, 3D: WebGL, WebGL 2.0) – Supported on all evergreen browsers and on IE 9+ Tausche .NET gegen Web Desktop-Apps als PWA entwickeln Paint
  10. Canvas Add a canvas element to index.html (line 11): <canvas

    id="canvas" width="600" height="480"></canvas> Query the canvas element in app.js (line 1): const canvas = document.querySelector('#canvas'); Tausche .NET gegen Web Desktop-Apps als PWA entwickeln Paint EX #1
  11. Canvas 2D Context fillRect(x, y, width, height) strokeRect(x, y, width,

    height) beginPath() moveTo(x, y) lineTo(x, y) fill() stroke() Tausche .NET gegen Web Desktop-Apps als PWA entwickeln Paint
  12. Canvas 2D Context Get the 2D context and prepare the

    canvas in app.js: const canvas = document.querySelector('#canvas'); const ctx = canvas.getContext('2d'); ctx.fillStyle = 'white'; ctx.fillRect(0, 0, canvas.width, canvas.height); ctx.fillStyle = 'black'; Tausche .NET gegen Web Desktop-Apps als PWA entwickeln Paint EX #2
  13. Low-latency Rendering Tausche .NET gegen Web Desktop-Apps als PWA entwickeln

    Paint Web pages need to synchronize with the DOM on graphics updates causing latencies that can make drawing difficult Low-latency rendering skips syncing with the DOM with can lead to a more natural experience Supported on Chrome (Chrome OS and Windows only)
  14. Low-latency Rendering Opt-in to low-latency rendering (app.js): const ctx =

    canvas.getContext('2d', { desynchronized: true }); Tausche .NET gegen Web Desktop-Apps als PWA entwickeln Paint EX #3
  15. Pointer Events Tausche .NET gegen Web Desktop-Apps als PWA entwickeln

    Paint Users nowadays use different input methods, cross-platform apps should cover all of them Pointer Events offer an abstract interface to catch all input methods (pointerdown, pointermove, pointerup) event.offsetX/event.offsetY contain the pointer’s position relative to the listener
  16. Pointer Events Add event listeners (bottom of app.js): canvas.addEventListener('pointerdown', event

    => {}); canvas.addEventListener('pointermove', event => { // ~~ is the shorter Math.floor() ctx.fillRect(~~event.offsetX, ~~event.offsetY, 2, 2); }); canvas.addEventListener('pointerup', () => {}); Tausche .NET gegen Web Desktop-Apps als PWA entwickeln Paint EX #4
  17. Bresenham Line Algorithm The user may move faster than the

    input can be processed For this case, we need to remember the previous point and interpolate the points in between The Bresenham line algorithm calculates the missing pixels between two given points Tausche .NET gegen Web Desktop-Apps als PWA entwickeln Paint
  18. Bresenham Line Algorithm 1. Add the following import to the

    top of app.js (“.js” is required, otherwise the request will 404): import {bresenhamLine} from "./helpers.js"; 2. Then, adjust the event listeners: a) In the pointerdown event handler, store ~~event.offsetX/~~event.offsetY in a variable called previousPoint (~~ is required, otherwise Bresenham will go into an endless loop) b) In pointermove i. only draw if the pointer is down ii. retrieve the current point (event.offsetX|Y, ~~ required!) iii. In a for…of loop, call bresenhamLine() with previousPoint.x|y & currentPoint.x|y and draw a 2x2 rectangle for each returned point. iv. store current point in previousPoint c) In pointerup, set previousPoint to null again. Tausche .NET gegen Web Desktop-Apps als PWA entwickeln Paint EX #5
  19. Bresenham Line Algorithm let previousPoint = null; canvas.addEventListener('pointerdown', event =>

    previousPoint = {x: ~~event.offsetX, y: ~~event.offsetY}); canvas.addEventListener('pointermove', event => { if (previousPoint) { const currentPoint = {x: ~~event.offsetX, y: ~~event.offsetY}; for(let {x, y} of bresenhamLine(previousPoint.x, previousPoint.y, currentPoint.x, currentPoint.y)) { ctx.fillRect(x, y, 2, 2); } previousPoint = currentPoint; } }); canvas.addEventListener('pointerup', () => previousPoint = null); Tausche .NET gegen Web Desktop-Apps als PWA entwickeln Paint
  20. Color Selection For this demo, we will only implement the

    brush tool. However, we want to bring in some color. A simple method to implement a color selection is to use the HTML color-type input element that shows the native color picker: <input type="color"> Tausche .NET gegen Web Desktop-Apps als PWA entwickeln Paint
  21. Color Selection 1. In index.html, add the following input to

    the <nav> node: <input type="color" id="color"> 2. In app.js, add the following code at the bottom: const txtColor = document.querySelector('#color'); txtColor.addEventListener('change', () => { ctx.fillStyle = txtColor.value; }); Tausche .NET gegen Web Desktop-Apps als PWA entwickeln Paint EX #6
  22. Paint PWA Capabilities Progressive Enhancement Tausche .NET gegen Web Desktop-Apps

    als PWA entwickeln Agenda
  23. Desktop-Apps als PWA entwickeln Tausche .NET gegen Web Responsive Linkable

    Discoverable Installable App-like Connectivity Independent Fresh Safe Re-engageable Progressive
  24. Tausche .NET gegen Web Desktop-Apps als PWA entwickeln Web App

    Manifest Service Worker
  25. Web App Manifest Distinguishes Web Apps from Websites JSON-based file

    containing metadata for apps only Apps can be identified by search engines, app store providers, etc. Tausche .NET gegen Web Desktop-Apps als PWA entwickeln PWA
  26. manifest.webmanifest { "short_name": "Paint", "name": "Paint Workshop", "theme_color": "white", "icons":

    [{ "src": "icon.png", "sizes": "512x512" }], "start_url": "/index.html", "display": "standalone", "shortcuts": [/* … */] } Tausche .NET gegen Web Desktop-Apps als PWA entwickeln PWA Names Icons Display Mode Shortcuts Start URL Theme color (status bar/window bar)
  27. Manifest Display Modes Tausche .NET gegen Web Desktop-Apps als PWA

    entwickeln PWA browser minimal-ui standalone fullscreen
  28. Manifest Icon Purposes (any) any context (e.g. app icon) monochrome

    different color requirements (at risk) maskable user agent masks icon as required Tausche .NET gegen Web Desktop-Apps als PWA entwickeln PWA Safe Zone Windows iOS Android
  29. Web App Manifest 1. In index.html, add the following tag

    to the document’s <head> node (e.g., after the stylesheet): <link rel="manifest" href="manifest.webmanifest"> 2. Create the new file manifest.webmanifest and set: a) name and short_name to values of your choice b) display to standalone c) theme_color to #000080 and background_color to #808080 d) start_url to /index.html and scope to / e) icons to [{ src: "icon.png", sizes: "512x512" }] 3. Test manifest in DevTools: F12 > Application > Manifest Tausche .NET gegen Web Desktop-Apps als PWA entwickeln PWA EX #7
  30. Manifest Shortcuts Tausche .NET gegen Web Desktop-Apps als PWA entwickeln

    PWA Secondary entrypoints for your application (e.g., home screen quick actions, jump lists, …) Static definition in Web App Manifest Dynamic API may follow in the future Supported by Google Chrome for Android
  31. Web App Manifest 1. In manifest.webmanifest, add (at least) the

    following shortcut: "shortcuts": [{ "name": "About Paint", "short_name": "About", "description": "Show information about Paint", "url": "/about.html", "icons": [{ "src": "icon.png", "sizes": "512x512" }] }], 2. Test in DevTools: F12 > Application > Manifest Tausche .NET gegen Web Desktop-Apps als PWA entwickeln PWA EX #8
  32. Web App Manifest – Chrome Installability Signals Web App is

    not already installed Meets a user engagement heuristic (previously: user has interacted with domain for at least 30 seconds) Includes a Web App Manifest that has short_name or name, at least a 192px and 512px icon, a start_url and a display mode of fullscreen, standalone or minimal-ui Served over HTTPS Has a registered service worker with a fetch event handler Tausche .NET gegen Web Desktop-Apps als PWA entwickeln PWA
  33. Service Worker JavaScript snippet executed in an own thread, registered

    by the website Acts as a controller, proxy, or interceptor Has a cache to store responses (for offline availability and performance) Can wake up even when the website is closed and perform background tasks (e.g., push notifications or sync) Tausche .NET gegen Web Desktop-Apps als PWA entwickeln PWA
  34. Service Worker Tausche .NET gegen Web Desktop-Apps als PWA entwickeln

    PWA Service Worker Internet Website HTML/JS Cache fetch
  35. Workbox Toolchain by Google Includes a CLI Generates a service

    worker implementation from directory contents (e.g., build output, or our development directory) Allows you to modify the service worker behavior (maximum flexibility) Tausche .NET gegen Web Desktop-Apps als PWA entwickeln PWA
  36. Service Worker 1. In your console, run: a) npm run

    workbox wizard (use “src” as project root and defaults for the rest) b) npm run workbox generateSW 2. In index.html, add the following script to the bottom of the <body> node: <script> if (navigator.serviceWorker) { navigator.serviceWorker.register('sw.js'); } </script> 3. Test in DevTools: F12 > Application > Service Worker 4. Install the app: Address Bar > ⊕ Install Tausche .NET gegen Web Desktop-Apps als PWA entwickeln PWA EX #9
  37. Service Worker Debugging More information on installed service workers can

    be found on • chrome://serviceworker- internals (Google Chrome) • about:serviceworkers (Mozilla Firefox) Tausche .NET gegen Web Desktop-Apps als PWA entwickeln PWA
  38. Service Worker Debugging Tausche .NET gegen Web Desktop-Apps als PWA

    entwickeln PWA
  39. Lighthouse Tausche .NET gegen Web Desktop-Apps als PWA entwickeln PWA

    Auditing tool by Google, integrated in Chrome DevTools Automatically checks performance metrics, PWA support, accessibility, SEO and other best practices and gives tips on how to improve Can simulate mobile devices
  40. Lighthouse 1. Make sure only one tab/window of your PWA

    is open 2. Open DevTools: F12 > Lighthouse 3. Make sure to select at least the “Progressive Web App” category 4. Click “Generate report” Tausche .NET gegen Web Desktop-Apps als PWA entwickeln PWA EX #10
  41. Paint PWA Capabilities Progressive Enhancement Tausche .NET gegen Web Desktop-Apps

    als PWA entwickeln Agenda
  42. Tausche .NET gegen Web Desktop-Apps als PWA entwickeln

  43. Project Fugu Tausche .NET gegen Web Desktop-Apps als PWA entwickeln

    Capabilities »Let’s bring the web back – API by API« Thomas Steiner, Google
  44. Tausche .NET gegen Web Desktop-Apps als PWA entwickeln Capabilities Contacts

    Picker Screen Wake Lock API File System Access API Shape Detection API
  45. Tausche .NET gegen Web Desktop-Apps als PWA entwickeln Capabilities https://goo.gle/fugu-api-tracker

  46. Tausche .NET gegen Web Desktop-Apps als PWA entwickeln Capabilities navigator.share({

    url: 'http://example.com' }); ShareIntent DataTransferManager … NSSharingServicePicker
  47. File System Access API Some applications heavily rely on working

    with files (e.g. Visual Studio Code, Adobe Photoshop, …) File System Access API allows you to open, save and override files and directories Shipped with Google Chrome 86 Tausche .NET gegen Web Desktop-Apps als PWA entwickeln Capabilities
  48. File System Access API 1. Add the following buttons to

    the <nav> bar in index.html (before the color input): <button id="open">Open</button> <button id="save">Save</button> <button id="copy">Copy</button> <button id="paste">Paste</button> <button id="share">Share</button> Tausche .NET gegen Web Desktop-Apps als PWA entwickeln Capabilities EX #11
  49. File System Access API 2. At the top of app.js,

    change the import as follows: import {bresenhamLine, getImage, toBlob} from "./helpers.js"; 3. Add the following lines at the bottom of app.js: const fileOptions = { types: [{ description: 'PNG files', accept: {'image/png': ['.png']} }] }; Tausche .NET gegen Web Desktop-Apps als PWA entwickeln Capabilities EX #11
  50. File System Access API 4. Add the following lines at

    the bottom of app.js: const btnSave = document.querySelector('#save'); btnSave.addEventListener('click', async () => { const blob = await toBlob(canvas); const handle = await window.showSaveFilePicker(fileOptions); const writable = await handle.createWritable(); await writable.write(blob); await writable.close(); }); Tausche .NET gegen Web Desktop-Apps als PWA entwickeln Capabilities EX #11
  51. File System Access API Add the following code at the

    end of app.js: const btnOpen = document.querySelector('#open'); btnOpen.addEventListener('click', async () => { const [handle] = await window.showOpenFilePicker(fileOptions); const file = await handle.getFile(); const image = await getImage(file); ctx.drawImage(image, 0, 0); }); Tausche .NET gegen Web Desktop-Apps als PWA entwickeln Capabilities EX #12
  52. Async Clipboard API Allows reading from/writing to the clipboard in

    an asynchronous manner (UI won’t freeze during long-running operations) Reading from the clipboard requires user consent first (privacy!) Supported by Chrome, Edge and Safari Tausche .NET gegen Web Desktop-Apps als PWA entwickeln Capabilities
  53. Async Clipboard API Add the following code at the end

    of app.js: const btnCopy = document.querySelector('#copy'); btnCopy.addEventListener('click', async () => { const blob = await toBlob(canvas); await navigator.clipboard.write([ new ClipboardItem({[blob.type]: blob}) ]); }); Tausche .NET gegen Web Desktop-Apps als PWA entwickeln Capabilities EX #13
  54. Async Clipboard API const btnPaste = document.querySelector('#paste'); btnPaste.addEventListener('click', async ()

    => { const clipboardItems = await navigator.clipboard.read(); for (const clipboardItem of clipboardItems) { for (const type of clipboardItem.types) { if (type === 'image/png') { const blob = await clipboardItem.getType(type); const image = await getImage(blob); ctx.drawImage(image, 0, 0); } } } }); Tausche .NET gegen Web Desktop-Apps als PWA entwickeln Capabilities EX #14
  55. Web Share API Allows sharing a title, URL, text, or

    files API can only be invoked as a result of a user action (i.e. a click or keypress) Files supported in Chrome on Android, Edge on Windows Tausche .NET gegen Web Desktop-Apps als PWA entwickeln Capabilities
  56. Web Share API const btnShare = document.querySelector('#share'); btnShare.disabled = !('canShare'

    in navigator); btnShare.addEventListener('click', async () => { const blob = await toBlob(canvas); const file = new File([blob], 'untitled.png', {type: 'image/png'}); const item = {files: [file], title: 'untitled.png'}; if (await navigator.canShare(item)) { await navigator.share(item); } }); Tausche .NET gegen Web Desktop-Apps als PWA entwickeln Capabilities EX #15
  57. File System Handling API Register your PWA as a handler

    for file extensions Requires installing the application first Declare supported extensions in Web App Manifest and add imperative code to your application logic Tausche .NET gegen Web Desktop-Apps als PWA entwickeln Capabilities
  58. File System Handling API 1. Enable the following flag in

    Chrome Canary and restart the browser: chrome://flags/#file-handling-api 2. Add the following property to your manifest (manifest.webmanifest): "file_handlers": [{ "action": "/index.html", "accept": { "image/png": [".png"] } }] Tausche .NET gegen Web Desktop-Apps als PWA entwickeln Capabilities EX #16
  59. File System Handling API 3. Add the following code to

    the bottom of app.js: if ('launchQueue' in window) { launchQueue.setConsumer(async params => { const [handle] = params.files; if (handle) { const file = await handle.getFile(); const image = await getImage(file); ctx.drawImage(image, 0, 0); } }); } 4. Re-generate Service Worker: npm run workbox generateSW Tausche .NET gegen Web Desktop-Apps als PWA entwickeln Capabilities EX #16
  60. Summary - Project Fugu helps the web to become more

    and more capable - Project Fugu APIs could bring many more app experiences to the web (IDEs, productivity apps, etc.) - But: Web is threatened by alternative approaches and platforms, support for modern Web API varies from platform to platform - You can make a difference! - File bugs in browser engine bugtrackers - File Fugu requests: https://goo.gle/new-fugu-request Tausche .NET gegen Web Desktop-Apps als PWA entwickeln Capabilities
  61. Paint PWA Capabilities Progressive Enhancement Tausche .NET gegen Web Desktop-Apps

    als PWA entwickeln Agenda
  62. Overview Use available interfaces and functions of a system (opposite

    of Graceful Degradation) Users with modern, feature-rich browsers get a better experience Apps are available on older browsers, but with limited functionality Concept: Browser feature support should grow over time—thereby more users can enjoy an increasing number of features Tausche .NET gegen Web Desktop-Apps als PWA entwickeln Progressive Enhancement
  63. Overview if ('serviceWorker' in navigator) { navigator.serviceWorker.register(…) .then(() => /*

    … */); } In JavaScript: check whether an API/feature is available. If yes—use it! Otherwise: 1. Disable the functionality 2. Fall back to an alternative API (if available) Tausche .NET gegen Web Desktop-Apps als PWA entwickeln Progressive Enhancement
  64. Disabling unsupported features In app.js, disable the buttons in case

    the respective API does not exist, e.g.: btnOpen.disabled = !('showOpenFilePicker' in window); 1. Open: window.showOpenFilePicker() 2. Save: window.showSaveFilePicker() 3. Copy: navigator.clipboard + navigator.clipboard.read() 4. Paste: navigator.clipboard + navigator.clipboard.write() 5. Share: navigator.canShare() Tausche .NET gegen Web Desktop-Apps als PWA entwickeln Progressive Enhancement EX #17
  65. Providing an alternative implementation 1. In app.js, test for the

    existence of the showSaveFilePicker() method on the navigator object. 2. If the method does not exist, fall back to the following code for save: const anchor = document.createElement('a'); const url = URL.createObjectURL(blob); anchor.href = url; anchor.download = ''; anchor.click(); URL.revokeObjectURL(url); Tausche .NET gegen Web Desktop-Apps als PWA entwickeln Progressive Enhancement EX #18
  66. Deployment Tausche .NET gegen Web Desktop-Apps als PWA entwickeln Electron/Capacitor

    JS HTML CSS .ipa .exe .app ELF .apk .appx Single-Page Application Capacitor Electron
  67. (Simplified) Tausche .NET gegen Web Desktop-Apps als PWA entwickeln Store

    Deployments https://example.com .appx .apk Server Microsoft Store Play Store Source Files
  68. Q&A Tausche .NET gegen Web Desktop-Apps als PWA entwickeln

  69. New powerful APIs regularly ship with new releases of Chromium-based

    browsers Some only add minor finishing touches, others enable whole application categories as productivity apps to finally make the shift to the web Some APIs already made their way into other browsers (e.g., Web Share) Fugu process makes sure that capabilities are implemented in a secure, privacy-preserving manner Let’s make the web a more capable platform! Tausche .NET gegen Web Desktop-Apps als PWA entwickeln Summary
  70. Thank you for your kind attention! Christian Liebel @christianliebel christian.liebel@thinktecture.com