Jul 97 - Newton Q and A
Volume Number: 13
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:
icon: ROM_routeDuplicateIcon,
routeScript: func(target, targetView)
begin
// my function here
end,},
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)
begin
// my function here
end,},
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.