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MSApp.getHtmlPrintDocumentSourceAsync - JavaScript UWP app printing

2017 Oct 11, 5:49

The documentation for printing in JavaScript UWP apps is out of date as it all references MSApp.getHtmlPrintDocumentSource but that method has been replaced by MSApp.getHtmlPrintDocumentSourceAsync since WinPhone 8.1.

Background

Previous to WinPhone 8.1 the WebView's HTML content ran on the UI thread of the app. This is troublesome for rendering arbitrary web content since in the extreme case the JavaScript of some arbitrary web page might just sit in a loop and never return control to your app's UI. With WinPhone 8.1 we added off thread WebView in which the WebView runs HTML content on a separate UI thread.

Off thread WebView required changing our MSApp.getHtmlPrintDocumentSource API which could no longer synchronously produce an HtmlPrintDocumentSource. With WebViews running on their own threads it may take some time for them to generate their print content for the HtmlPrintDocumentSource and we don't want to hang the app's UI thread in the interim. So the MSApp.getHtmlPrintDocumentSource API was replaced with MSApp.getHtmlPrintDocumentSourceAsync which returns a promise the resolved value of which is the eventual HtmlPrintDocumentSource.

Sample

However, the usage of the API is otherwise unchanged. So in sample code you see referencing MSApp.getHtmlPrintDocumentSource the sample code is still reasonable but you need to call MSApp.getHtmlPrintDocumentSourceAsync instead and wait for the promise to complete. For example the PrintManager docs has an example implementing a PrintTaskRequested event handler in a JavaScript UWP app.

    function onPrintTaskRequested(printEvent) {    
var printTask = printEvent.request.createPrintTask("Print Sample", function (args) {
args.setSource(MSApp.getHtmlPrintDocumentSource(document));
});

Instead we need to obtain a deferral in the event handler so we can asynchronously wait for getHtmlPrintDocumentSourceAsync to complete:

    function onPrintTaskRequested(printEvent) {    
var printTask = printEvent.request.createPrintTask("Print Sample", function (args) {
const deferral = args.getDeferral();
MSApp.getHtmlPrintDocumentSourceAsync(document).then(htmlPrintDocumentSource => {
args.setSource(htmlPrintDocumentSource);
deferral.complete();
}, error => {
console.error("Error: " + error.message + " " + error.stack);
deferral.complete();
});
});
PermalinkCommentsjavascript MSApp printing programming uwp webview win10 windows

Tweet from Andy Richter

2016 Jul 30, 3:42
Back in my day when we found a Pokémon we had to beat it to death with a rotary phone
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Tweet from Jen Gentleman

2016 May 13, 3:51
You can use the curser controller just by flicking it 😉 📱 pic.twitter.com/Gl9FB5YAq6
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Retweet of SwiftOnSecurity

2016 Feb 16, 5:06
#MustRead Apple CEO Tim Cook's letter to customers on FBI's request for assistance hacking an iPhone 5c http://www.apple.com/customer-letter/ …
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Tweet from David_Risney

2015 Nov 18, 8:29
Next up: hacking phones with inaudible sounds that exploit bugs in this software http://arstechnica.com/tech-policy/2015/11/beware-of-ads-that-use-inaudible-sound-to-link-your-phone-tv-tablet-and-pc/ …
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Retweet of alvarombedoya

2015 Nov 11, 9:42
3/ This lets advertisers figure out that 'John owns this laptop AND this smartphone.' http://www.steamfeed.com/silverpush-launches-cross-device-ad-targeting-with-unique-audio-beacon-technology/ … pic.twitter.com/hci0aUeLoN
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Tweet from David_Risney

2015 Oct 13, 9:43
Neat hack: use victim's headphone wire as antenna to send audio commands to their phone's Siri http://www.wired.com/2015/10/this-radio-trick-silently-hacks-siri-from-16-feet-away/ …
PermalinkComments

Tweet from David_Risney

2015 Apr 15, 12:54
Do Faraday pants exist? Should protect left pocket for wallet & keys, and not right for phone & fitbit. Kickstarter? https://twitter.com/newsycombinator/status/588386535160033280 …
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Retweet of ncardozo

2015 Apr 11, 10:58
The NSA does not have "an absolute right to gain access to every way in which two people may choose to communicate." http://arstechnica.com/tech-policy/2015/04/nsa-dreams-of-smartphones-with-split-crypto-keys-protecting-user-data/ …
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Retweet of ThatJessePorter

2015 Feb 19, 8:27
Harris' Phone/Foam Corner is one of the best part of #ComedyBangBang. http://youtu.be/AweVgPJhVFQ  #RIPHarrisWittels
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The Secret Life of SIM Cards - DEFCON 21 - simhacks

2014 Aug 16, 1:07

A DEFCON talk “The Secret Life of SIM Cards” that covers running apps on your SIM card. Surprisingly they run a subset of Java and execute semi-independent of the Phone’s OS.

PermalinkCommentstechnical phone sim-card security java

From Inside Edward Snowden’s Life as a Robot: Wizner had...

2014 Jun 23, 7:04


From Inside Edward Snowden’s Life as a Robot:

Wizner had to jump on a phone call during a meeting with his whistleblower client. When he got off the phone, he found that Snowden had rolled the bot into civil liberties lawyer Jameel Jaffer’s office and was discussing the 702 provision of the Foreign Intelligence Surveillance Act. “It was kind of cool,” Wizner says.

It is neat but they’re marketing video is at times strangely terrifying. Put different music on when the Susan-bot comes up behind the unknowing Mark and this could be a horror movie trailer.

PermalinkCommentsedward-snowden beam robot telepresence

U.S. Marshals Seize Cops’ Spying Records to Keep Them From the ACLU | Threat Level | WIRED

2014 Jun 4, 6:08

"A routine request in Florida for records detailing the use of a surveillance tool known as stingray turned extraordinary Tuesday when the U.S. Marshals Service seized the documents before local police could release them."

Also what about the part where the PD reveals that its been using the stingray a bunch without telling any court and blames that on the manufacturer’s NDA.

PermalinkCommentstechnical law security phone

Debugging anecdote - the color transparent black breaks accessibility

2014 May 22, 10:36

Some time back while I was working on getting the Javascript Windows Store app platform running on Windows Phone (now available on the last Windows Phone release!) I had an interesting bug that in retrospect is amusing.

I had just finished a work item to get accessibility working for JS WinPhone apps when I got a new bug: With some set of JS apps, accessibility appeared to be totally broken. At that time in development the only mechanism we had to test accessibility was a test tool that runs on the PC, connects to the phone, and dumps out the accessibility tree of whatever app is running on the phone. In this bug, the tool would spin for a while and then timeout with an error and no accessibility information.

My first thought was this was an issue in my new accessibility code. However, debugging with breakpoints on my code I could see none of my code was run nor the code that should call it. The code that called that code was a more generic messaging system that hit my breakpoints constantly.

Rather than trying to work backward from the failure point, I decided to try and narrow down the repro and work forwards from there. One thing all the apps with the bug had in common was their usage of WinJS, but not all WinJS apps demonstrated the issue. Using a binary search approach on one such app I removed unrelated app code until all that was left was the app's usage of the WinJS AppBar and the bug still occurred. I replaced the WinJS AppBar usage with direct usage of the underlying AppBar WinRT APIs and continued.

Only some calls to the AppBar WinRT object produced the issue:

        var appBar = Windows.UI.WebUI.Core.WebUICommandBar.getForCurrentView(); 
// appBar.opacity = 1;
// appBar.closeDisplayMode = Windows.UI.WebUI.Core.WebUICommandBarClosedDisplayMode.default;
appBar.backgroundColor = Windows.UI.Colors.white; // Bug!
Just setting the background color appeared to cause the issue and I didn't even have to display the AppBar. Through additional trial and error I was blown away to discover that some colors I would set caused the issue and other colors did not. Black wouldn't cause the issue but transparent black would. So would aqua but not white.

I eventually realized that predefined WinRT color values like Windows.UI.Colors.aqua would cause the issue while JS literal based colors didn't cause the issue (Windows.UI.Color is a WinRT struct which projects in JS as a JS literal object with the struct members as JS object properties so its easy to write something like {r: 0, g: 0, b: 0, a: 0} to make a color) and I had been mixing both in my tests without realizing there would be a difference. I debugged into the backgroundColor property setter that consumed the WinRT color struct to see what was different between Windows.UI.Colors.black and {a: 1, r: 0, g: 0, b: 0} and found the two structs to be byte wise exactly the same.

On a hunch I tried my test app with only a reference to the color and otherwise no interaction with the AppBar and not doing anything with the actual reference to the color: Windows.UI.Colors.black;. This too caused the issue. I knew that the implementation for these WinRT const values live in a DLL and guessed that something in the code to create these predefined colors was causing the issue. I debugged in and no luck. Now I also have experienced crusty code that would do exciting things in its DllMain, the function that's called when a DLL is loaded into the process so I tried modifying my C++ code to simply LoadLibrary the DLL containing the WinRT color definition, windows.ui.xaml.dll and found the bug still occurred! A short lived moment of relief as the world seemed to make sense again.

Debugging into DllMain nothing interesting happened. There were interesting calls in there to be sure, but all of them behind conditions that were false. I was again stumped. On another hunch I tried renaming the DLL and only LoadLibrary'ing it and the bug went away. I took a different DLL renamed it windows.ui.xaml.dll and tried LoadLibrary'ing that and the bug came back. Just the name of the DLL was causing the issue.

I searched for the DLL name in our source code index and found hits in the accessibility tool. Grinning I opened the source to find that the accessibility tool's phone side service was trying to determine if a process belonged to a XAML app or not because XAML apps had a different accessibility contract. It did this by checking to see if windows.ui.xaml.dll was loaded in the target process.

At this point I got to fix my main issue and open several new bugs for the variety of problems I had just run into. This is a how to on writing software that is difficult to debug.

PermalinkCommentsbug debug javascript JS technical windows winrt

The decline of the mobile web...

2014 Apr 8, 6:49


The decline of the mobile web http://cdixon.org/2014/04/07/the-decline-of-the-mobile-web/

PermalinkCommentstechnical web browser mobile phone

Phone Buttons - Numberphile (by numberphile)

2013 Aug 30, 5:47


Phone Buttons - Numberphile (by numberphile)

PermalinkCommentsHistory numbers phone

Windows Store on Windows 8 Fun For Independent Developers

2013 Jun 24, 1:00
Having worked on Windows 8 I'm not in a neutral position to review aspects of it, however I'll say from a high level I love taking the following various positives from smart phone apps and app stores and applying it to the desktop:
  • Independent developers can easily publish apps.
  • One trusted place for a user to find apps.
  • User can trust apps are limited to a declared set of capabilities.
  • One common and easy way for users to buy and try apps.
  • Easy mechanism for independent developers to collect revenue.
Relieving the independent developer of software development overhead, in this case Windows taking care of distribution and sales infrastructure is wonderful for me with my third party developer hat on. This combined with my new found fun of developing in JavaScript and the new Windows Runtime APIs means I've been implementing and finishing various ideas I've had - some for fun and some for productivity on my Surface. Development notes to follow.
PermalinkCommentsstore technical windows windows-store

laughingsquid: The Truth About Phones on Airplanes

2013 Jan 7, 11:57


laughingsquid:

The Truth About Phones on Airplanes

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laughingsquid: hi-Call, A Bluetooth Handset Glove

2012 Sep 26, 6:24


laughingsquid:

hi-Call, A Bluetooth Handset Glove

PermalinkCommentshumor phone cell-phone blue-tooth video

laughingsquid: Goldfish Phone Booth Aquariums Installed in...

2012 Sep 14, 4:27


laughingsquid:

Goldfish Phone Booth Aquariums Installed in Japan by ‘Goldfish Club’

PermalinkCommentshumor fish gold-fish japan phone-booth
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