TweetFollow Us on Twitter

Jun 97 - Newton Q and A

Volume Number: 13 (1997)
Issue Number: 6
Column Tag: develop

Newton Q&A: Ask the Llama

by Apple Developer Technical Support Group

Q: I'm probably missing something obvious, but when I try to use an asynchronous output call in some situations, I get an exception, while synchronous calls seem to work fine. For instance, this code fails consistently with bus errors:

endpoint:output(headerCache,
   nil,
   {async: true,
   form: 'string,
   completionScript: func(ep, options, result)
      self:SendData(endpoint, qfCursor)});

On the other hand, this code works fine:

endpoint:output(headerCache, nil, nil);
self:SendData(endpoint, qfCursor);

I'd really prefer to use asynchronous calls, but I keep running into problems. Do you have any suggestions?

A: The key thing you're missing is that self (that is, the receiver) is not what you expect in your asynchronous callback. In your first example, you pass a completion frame as the third argument of the Output message. It's this frame that will be self (that is, that will be the context of the completionScript). This means that you send the sendData message to that completion frame.

What you probably want is to send the message to the ep argument passed to the completionScript. This will be the endpoint to which you sent the Output message. In general, you will have set this endpoint to have a _parent slot that points to your application. Assuming that the sendData method is in either the endpoint or your application, you would modify the body of the completionScript to be

ep:sendData(endpoint, qfCursor);

The same restrictions apply for Input and Option calls as well.


Q: I have a pop-up view that has an icon with some text, and I'd like the user to be able to edit the icon. I call MakeShape on the icon and draw it into a bitmap. I then have an interface for the user to modify the icon. The problem occurs when I try to display the modified icon in the pop-up. It either doesn't show up, has incorrect bounds, or throws an exception. Before I modify the icon, it looks like something that would be returned by GetPictAsBits:

{data: <bits, Length 42>, bounds: {0,0,15,15}, }

Once I call MakeShape on the icon, it looks like this:

{class: bitmap, bounds: <boundsRect, Length 8>,
   data: <pixels, Length 54>, }

The pop-up chokes on this when I try to display it. First it threw an exception because it was expecting a frame instead of a binary object in the bounds frame. So I called SetBounds to set the bounds frame to {0,0,15,15}. This enabled the pop-up to open, but the icon wasn't in the right place. Fiddling with the bounds frame didn't seem to help. So I'm guessing that the next problem is that I have pixels instead of bits in the data slot. I tried calling SetClass on the slot to change it from pixels to bits. That actually didn't throw an exception, but the length is still different and it didn't look right. How can I get my shape or bitmap back into a form that the pop-up will be happy with?

A: The basic problem is that the binary object used by MakeShape to represent the picture (that is, <pixels, Length 54>) is not the same as that used in the bitmap structure (<bits, Length 42>). You have a couple of choices. Since the formats are documented, you can write some code to convert the object returned by MakeShape into a NewtonScript bitmap object. The other option, which seems more complex but is probably easier to implement, is to use the MakeShape representation only for your icon editor. Let the user modify the MakeShape representation, but keep track of the changes and use them to modify the bitmap. So, while the user is editing the icon, there will be two data objects: the original icon representation using the bitmap data structure and the MakeShape representation that the user sees and modifies. As the user changes the MakeShape object, your code is also modifying the bitmap object.

As a related side note, you can use DrawIntoBitmap to get the bits that represent the shape.


Q: In an application I'm building, I want to keep a serial communication session open with a GPS unit 24 hours a day, unattended by the user. Both the MessagePad and the GPS unit are powered by the car. The GPS unit sends out data approximately every two seconds. I'm using the "Basic Serial" Newton DTS sample code as the starting point. The communications code in the application works fine except that occasionally I get a -18003 exception, which results in a kMessage_BufferOverrun message. I've tried turning on useSoftFlowControl and useHardFlowControl in the kCMOInputFlowControlParms parameter frame inside the MBuildConfigOptions method, but that doesn't seem to help.

Can you explain when/why this exception is raised? Can I safely ignore the exception by revising the MNotifyError method? What can I do to prevent the occurrence of the exception in the first place?

A: A -18003 error can indicate several things, including bad parity or a framing error. Usually it indicates that the Newton's UART (SCC chip) buffer has overrun. You can just ignore this error, repost the input specification, and go on your merry way.

To repost the input specification, call the endpoint's SetInputSpec with the relevant input specification. Before reposting the input specification, you may also want to flush the communication tools buffers using the serial discard data option (kCMOSerialDiscard) and flush the NewtonScript buffer with FlushInput. Regardless of whether you flush, you will have lost some data in the process, although for most GPS applications that should be fine. You may also want to try increasing the size of the serial input buffer; this might give you just enough time to process all the data.

A better solution would be to have the GPS receiver support some type of flow control, though this will depend on the manufacturer of the unit.


Q: I have a view with a protoKeyboard button. The input lines within the view all take numeric input, and when the user double-taps, the numeric keypad pops up. But the keyboard button brings up the full QWERTY keyboard instead. How can I make the button open the numeric keypad?

A: The keyboard button is behaving correctly. If you don't specify which keyboard to open, it will always open the global alphanumeric keyboard. There are two ways you can get the behavior you want:

  • Override the 'defaultKeyboard slot in your protoKeyboardButton. This slot contains the keyboard that you want to use. In this case you want the symbol 'numericKeyboard, which specifies the default numeric keyboard.
  • Override the buttonClickScript in the protoKeyboardButton. You can use the OpenKeypadFor function and specify your input line as the view. This will usually do the right thing since calling OpenKeypadFor has just about the same effect as the user's double-tapping in an input line.

Q: I noticed that the NTK project preferences dialog lets you compress your application. How much slower will the application run if I do this?

A: Unfortunately, there's no simple answer to this question. The speed of execution depends on a number of factors, including how many times the system has to uncompress pages from your application into a cache and how full the system heap is.

The best way to find out is to try your application with the three different compression options: none, compressed, or faster compression. Make sure that you perform your tests a number of times and under different memory-loading conditions. If your application will be doing communications, that's a good thing to test. You can also use HeapShow (which comes with NTK) to fill the system and NewtonScript heaps to simulate low-memory conditions.

 

Community Search:
MacTech Search:

Software Updates via MacUpdate

Never Gone (Games)
Never Gone 1.0.2 Device: iOS Universal Category: Games Price: $2.99, Version: 1.0.2 (iTunes) Description: ###IMPPORTANT### Never Gone's HD art resources require devices with more than 1GB RAM, so please note that iPhone 4/4s, iPad 2/... | Read more »
INKS. (Games)
INKS. 1.0 Device: iOS Universal Category: Games Price: $1.99, Version: 1.0 (iTunes) Description: From the makers of BAFTA-winning Lumino City comes INKS. INKS updates pinball for a new generation. It combines the joy of pinball with... | Read more »
How to maximise your profits in Bakery B...
Running a bakery can be an expensive venture. You’ll need to continuously upgrade your oven, your kitchen supplies, and even your ingredients to keep customers happy. Most of these renovations in Bakery Blitz cost a pretty penny, but we have a few... | Read more »
How to manage your time in Bakery Blitz
It can be tricky, especially when you risk burning your kitchen to the ground if you forget a cake in the oven, so make sure to use these time management tricks to keep your bakery running smoothly. Don’t collect the money right away [Read more] | Read more »
Model 15 (Music)
Model 15 1.0 Device: iOS iPhone Category: Music Price: $29.99, Version: 1.0 (iTunes) Description: The Moog Model 15 App is the first Moog modular synthesizer and synthesis educational tool created exclusively for iPad, iPhone and... | Read more »
How to deal with wind in Angry Birds Act...
Angry Birds Action! is a physics-based puzzler in which you're tasked with dragging and launching birds around an obstacle-littered field to achieve a set objective. It's simple enough at first, but when wind gets introduced things can get pretty... | Read more »
How to get three stars in every level of...
Angry Birds Action! is, essentially, a pinball-style take on the pull-and-fling action of the original games. When you first boot it up, you'll likely be wondering exactly what it is you have to do to get a good score. Well, never fear as 148Apps... | Read more »
The beginner's guide to Warbits
Warbits is a turn-based strategy that's clearly inspired by Nintendo's Advance Wars series. Since turn-based strategy games can be kind of tricky to dive into, see below for a few tips to help you in the beginning. Positioning is crucial [Read... | Read more »
How to upgrade your character in Spellsp...
So you’ve mastered the basics of Spellspire. By which I mean you’ve realised it’s all about spelling things in a spire. What next? Well you’re going to need to figure out how to toughen up your character. It’s all well and good being able to spell... | Read more »
5 slither.io mash-ups we'd love to...
If there's one thing that slither.io has proved, it's that the addictive gameplay of Agar.io can be transplanted onto basically anything and it will still be good fun. It wouldn't be surprising if we saw other developers jumping on the bandwagon,... | Read more »

Price Scanner via MacPrices.net

Global Tablet Sales Slump Continues, iPad’s F...
Another miserable showing for the global slate tablet category in calendar Q1/16, with global tablet shipments falling another 1ten percent to 46.5 million units during the according to Strategy... Read more
Revel Systems to Showcase iPad POS Platform w...
Revel Systems, specialists in iPad Point of Sale management solution for brick-and-mortar retail, food businesses and more, today announced that it will showcase its innovative iPad Point of Sale... Read more
13-inch 2.5GHz MacBook Pro on sale for $999,...
B&H Photo has the 13″ 2.5GHz MacBook Pro on sale for $999 including free shipping plus NY sales tax only. Their price is $100 off MSRP. Read more
Apple refurbished 2015 iMacs available for up...
Apple now has a full line of Certified Refurbished 2015 21″ & 27″ iMacs available for up to $350 off MSRP. Apple’s one-year warranty is standard, and shipping is free. The following models are... Read more
Indian Smartphone Market Grows Annually by 12...
India’s smartphone market grew by 12 percent year-over-year, with 24.4 million units shipping in Q1 2016. The top five vendors stayed the same, with Samsung in the lead, followed by Micromax, Intex... Read more
Get Notifications When Your Friend’s Phone Ba...
Calgary, Canada based Stonelight Pictures has announced the release of Battery Share 1.0.1, its new utility for iOS 9 supported devices. The company notes that people are spending more time on their... Read more
11-inch 1.6GHz/128GB MacBook Air on sale for...
Amazon has the current-generation 11″ 1.6GHz/128GB MacBook Air (sku MJVM2LL/A) on sale for $749.99 for a limited time. Their price is $150 off MSRP, and it’s the lowest price available for this model... Read more
Price drops on clearance 2015 13-inch MacBook...
B&H Photo has dropped prices on clearance 2015 13″ MacBook Airs by up to $250. Shipping is free, and B&H charges NY sales tax only: - 13″ 1.6GHz/4GB/128GB MacBook Air (MJVE2LL/A): $799, $200... Read more
Mac minis on sale for up to $100 off MSRP
B&H Photo has Mac minis on sale for up to $100 off MSRP including free shipping plus NY sales tax only: - 1.4GHz Mac mini: $449 $50 off MSRP - 2.6GHz Mac mini: $649 $50 off MSRP - 2.8GHz Mac mini... Read more
13-inch Retina MacBook Pros on sale for up to...
B&H Photo has 13″ Retina MacBook Pros on sale for $130-$200 off MSRP. Shipping is free, and B&H charges NY tax only: - 13″ 2.7GHz/128GB Retina MacBook Pro: $1169 $130 off MSRP - 13″ 2.7GHz/... Read more

Jobs Board

Restaurant Manager (Neighborhood Captain) - A...
…in every aspect of daily operation. WHY YOU'LL LIKE IT: You'll be the Big Apple . You'll solve problems. You'll get to show your ability to handle the stress and Read more
Simply Mac *Apple* Specialist- Service Repa...
Simply Mac is the largest premier retailer of Apple products in the nation. In order to support our growing customer base, we are currently looking for a driven Read more
Restaurant Manager (Neighborhood Captain) - A...
…in every aspect of daily operation WHY YOU LL LIKE IT You ll be the Big Apple You ll solve problems You ll get to show your ability to handle the stress and Read more
*Apple* Retail - Multiple Positions (US) - A...
Job Description:SalesSpecialist - Retail Customer Service and SalesTransform Apple Store visitors into loyal Apple customers. When customers enter the store, Read more
Restaurant Manager (Neighborhood Captain) - A...
…in every aspect of daily operation. WHY YOU'LL LIKE IT: You'll be the Big Apple . You'll solve problems. You'll get to show your ability to handle the stress and Read more
All contents are Copyright 1984-2011 by Xplain Corporation. All rights reserved. Theme designed by Icreon.