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Jul 97 - Newton Q and A

Volume Number: 13 (1997)
Issue Number: 7
Column Tag: develop

Jul 97 - Newton Q&A: Ask the Llama

by Apple Developer Technical Support Group

Q: I want to put my own custom icons in the picker that comes up when a user taps the action button. I have a slot in my base view called myTestIcon that contains the icon I want to use. But I can't figure out how to use that icon in the array of action frames in the routeScripts slot in my application. I started with the following routing item frame based on a simple "duplicate" action:

{title: "Test Action",
icon: ROM_routeDuplicateIcon,
routeScript: func(target, targetView)
	// my function here

This worked fine. Then I replaced the icon specification with this code:

icon: GetRoot().(kAppSymbol).myTestIcon,

But this won't even compile. Any ideas?

A: The problem is that you're using the GetRoot function call in your array of routing action frames. Since the array of frames is in an evaluate slot (that is, the routeScripts slot), it will be evaluated at compile time in the Newton Toolkit environment. In other words, you're asking the Newton OS to look in the root view for your application's base view frame. This assumes that your application has been installed on a Newton device. But the code is executed at compile time, so there is no Newton device, no root view, and no base application frame.

The easiest way to solve your problem is to define a constant for the icon in a text file and then use that constant in the appropriate slot that defines the action.

Let's assume that you already have a resource file with the appropriate PICT resource, and that you have a text file as part of your project (if not, just create one from the NTK File menu and add it to your project). In the text file, add a line that looks something like this:

DefineGlobalConstant('kMyIcon, GetPictAsBits("MyIcon", nil));
// Note: Earlier versions of the platform file may use DefConst instead
// of DefineGlobalConstant.

This will give you a constant named kMyIcon. (Obviously you would replace kMyIcon with your own meaningful constant name and the string "MyIcon" with the name of the appropriate PICT resource.) Do this for each of the action menu icons that you want. Note that even though the action menu calls them "icons," you get the data by reading a Macintosh PICT resource, not a Macintosh ICON resource.

In your application's routeScripts slot where you create the array of extra action button actions, use the constant names you've created:

{title: "Test Action",
icon: kMyIcon,
routeScript: func(target, targetView)
	// my function here

The other way you can solve your problem is by specifying the array of action frames at run time. Instead of specifying a routeScripts slot with your array of action frames, you can provide a GetRouteScripts method. Since this method lets you construct your array of action frames at run time in the Newton environment, the root view will exist and your application will be found.

Q: I'm using a protoLabelInputLine, which I've used many times before. In this case no user input happens in the input line. The entryFlags slot looks fine. It's set to vVisible, vClickable, vStrokesAllowed, vGesturesAllowed, and vAnythingAllowed. But strokes, gestures, and recognition do not occur. I tried adding a viewClickScript, viewStrokeScript, and viewGestureScript. The viewClickScript does get called, but none of the others do. When I remove the viewClickScript, there's still nothing. What's going on?

A: You've fallen prey to a rare gotcha that's hard to find unless you know what you're looking for. The clue is in the behavior with and without the viewClickScript. Without it, the line takes no input, so it appears as if the view is ignoring clicks. With it, you see something occurring. The key is that the viewClickScript of a clickable view will be searched for in both the proto and the parent chain. So you must have a viewClickScript defined in a parent of the protoLabelInputLine. When the user puts the pen down in the input line, the inherited script is found and executed in the context of the input line. This inherited script probably turns off the ink and then does some processing. You've seen the result.

The solution is to add a viewClickScript to your protoLabelInputLine that returns the value 'skip. This will let the protoLabelInputLine grab the stroke and allow recognition to happen. Note that simply returning true or nil would not solve the problem.

Q: The documentation for StuffLong says it "writes four bytes at the specified offset using the 30-bit signed value you pass it as a third parameter and sign-extends it to 32 bytes." Ignoring the obvious error ("32 bytes" should read "32 bits"), why does it take only 30 bits? I realize the language defines an integer as a 30-bit representation, plus a sign bit, but what's bit 31 for? More specifically, how can I use StuffLong to result in the value 0x20000000?

A: First off, the representation is not 30 bits plus a sign bit plus some other bit. NewtonScript uses a 30-bit two's complement signed representation. The other two bits are used by the OS for other purposes. So StuffLong takes integers as 30 bits because that's how NewtonScript represents integers. In the binary object, the other two bits will be the sign extension of the number you pass in. That is, they'll have the same value as the sign bit: 0 for positive, 1 for negative.

As you can probably see, it isn't possible to use StuffLong to put your long word into a binary object. The two high-order bits must be the same as the sign of the number. In your case, you have a 1 bit in the sign, but you want a 0 for both bits of the sign extension.

To stuff the data you want, you'll have to use some combination of StuffWord and/or StuffByte.

Q: I have some compile-time functions that generate frame data and some other functions that do sanity checking. Is it possible to abort the compile and give an error message once NTK has started compiling?

A: Yes. NTK implements a subset of the Newton environment. This includes the ability to throw exceptions. To abort a compile, throw an exception. If the exception is of the type '|evt.ex.msg|, any message you provide will be shown in a dialog by NTK. Here's a simple example:

throw('|evt.ex.msg|, "Invalid data at position " && theIndex);

Assuming that theIndex has the value 4, this statement will abort the current compile and display a dialog containing "Invalid data at position 4."


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