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From: Michael on 20 Jul 2010 03:44
This statement yields unexpected behavior:

DynamicModule[{n = 7},
Row[{n, Button["X", --n; Print[n]]}]
]

Why doesn't the "n" that appears as the first element in Row[] change
when I click on the button? The Print[] statement clearly shows it is
being decremented. I can look at "n" outside of the DynamicModule[] and
see that it is not defined, so Button[] can't be working with a
different "n" than Row is trying to display, can it?


n2=7;
Dynamic[
Row[{n2, Button["X", --n2; Print[n2]]}]
]


This behaves as expected, but I need localization and this doesn't
provide it. Ok, I will use a Block[]. But wait...

Block[{n3 = 7},
Dynamic[
Row[{n3, Button["X", --n3; Print[n3]]}]
]
]

Mathematica highlights n3 in Red, and n3 appears to lose its value
inside the Dynamic. I have looked, but I can't find anything in the
documentation for Block[] or Dynamic[] suggesting this sort of behavior.

Ok, how about a Module[] instead of a Block[]?

Module[{n3 = 7},
Dynamic[
Row[{n3, Button["X", --n3; Print[n3]]}]
]
]

This works fine. So why doesn't DynamicModule[] work??? There is also
another problem with this approach. I might want to define a more
complex interface than just a button:

f[x_] := Button[x, --n3; Print[n3]]
Module[{n3 = 7},
Dynamic[
Row[{n3, f["X"]}]
]
]

This is why I wanted to use Block[] or even DynamicModule[], because
then f[] would see n3 in the context of the Block. But since Module[]
creates internally some name like n3$1, f[] can't see it.

I'm using Version 7.

What's going on here? Any suggestions on how I can accomplish what
seemed like any easy task but wound up eating up my entire evening with
nothing to show for it?

Thanks,

Michael


From: Patrick Scheibe on 20 Jul 2010 07:55
Hi,

even *in* a DynamicModule you have to use Dynamic to *mark* the that should be
updated dynamically

DynamicModule[{n = 7}, Row[{Dynamic[n], Button["X", --n; Print[n]]}]]

Cheers
Patrick


Am Jul 20, 2010 um 9:44 AM schrieb Michael:

> This statement yields unexpected behavior:
>
> DynamicModule[{n = 7},
> Row[{n, Button["X", --n; Print[n]]}]
> ]
>
> Why doesn't the "n" that appears as the first element in Row[] change
> when I click on the button? The Print[] statement clearly shows it is
> being decremented. I can look at "n" outside of the DynamicModule[]
> and
> see that it is not defined, so Button[] can't be working with a
> different "n" than Row is trying to display, can it?
>
>
> n2=7;
> Dynamic[
> Row[{n2, Button["X", --n2; Print[n2]]}]
> ]
>
>
> This behaves as expected, but I need localization and this doesn't
> provide it. Ok, I will use a Block[]. But wait...
>
> Block[{n3 = 7},
> Dynamic[
> Row[{n3, Button["X", --n3; Print[n3]]}]
> ]
> ]
>
> Mathematica highlights n3 in Red, and n3 appears to lose its value
> inside the Dynamic. I have looked, but I can't find anything in the
> documentation for Block[] or Dynamic[] suggesting this sort of
> behavior.
>
> Ok, how about a Module[] instead of a Block[]?
>
> Module[{n3 = 7},
> Dynamic[
> Row[{n3, Button["X", --n3; Print[n3]]}]
> ]
> ]
>
> This works fine. So why doesn't DynamicModule[] work??? There is
> also
> another problem with this approach. I might want to define a more
> complex interface than just a button:
>
> f[x_] := Button[x, --n3; Print[n3]]
> Module[{n3 = 7},
> Dynamic[
> Row[{n3, f["X"]}]
> ]
> ]
>
> This is why I wanted to use Block[] or even DynamicModule[], because
> then f[] would see n3 in the context of the Block. But since Module[]
> creates internally some name like n3$1, f[] can't see it.
>
> I'm using Version 7.
>
> What's going on here? Any suggestions on how I can accomplish what
> seemed like any easy task but wound up eating up my entire evening
> with
> nothing to show for it?
>
> Thanks,
>
> Michael
>
>


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