Interesting question! cc'ing Laszlo-user list, since LZX coders on there
might have some thoughts on this, or at least be interested in the
details of how states work and whether that should be changed in the
future. I did a little experimentation (see below) to remind myself how
states work, and recall a little history of how we got to where we are.
I do like the current behavior (the convenience of implementing
dragstate and friends), but I do admit that some of the nuances of
states can be confusing and I don't know if they are clearly documented.
The question is: should contraints that are overridden when a state is
applies be "put back" when a state is removed?
Conceptually when you apply a state, a bunch of stuff is added, and when
you remove it that stuff is removed; however, states are allowed to have
side effects, when attributes are modified by a state they stay
modified. So, attributes and methods when applied remain as side
effects; however, views and events are temporal and get removed. Way
back in LPS v1, Adam Wolff and I decided that constraints are
conceptually like attribute values, even if their implementation is more
like an event; which is why we have the behavior we do today.
In an abstract sense, it feels like a bug that when a state is removed,
you don't just put everything back the way it was. If you look at this
simple example, that might be your expectation:
<canvas>
<checkbox id="cbox" text="Show"
x="10" y="10" />
<state apply="${cbox.value}">
<view bgcolor="blue" x="5" y="30"
width="150" height="150" />
</state>
</canvas>
However, it is a powerful feature of states that you are allowed to
leave a side-effect behind (which is really what enables the simplicity
of dragstate and related coding patterns.) If you change the value of
an attribute, it stays that way. In the following example, after
clicking on the checkbox twice to turn it on and off again, the value of
the attribute "t" is 10, not it's original value "4"
<canvas>
<simplelayout/>
<attribute name="t" value="4"/>
<text text="${canvas.t}"/>
<checkbox id="cbox" text="Show"
x="10" y="10" />
<state apply="${cbox.value}">
<attribute name="t" value="10"/>
<view bgcolor="blue" x="5" y="30"
width="150" height="150" />
</state>
</canvas>
Now, I wonder what happens with a method. In the example below, you
will see that if I toggle the checkbox on and back off, the state's
method remains, just like an attribute.
<canvas debug="true">
<simplelayout/>
<attribute name="t" value="4"/>
<text text="${canvas.t}"/>
<checkbox id="cbox" text="Show"
x="10" y="10" />
<state apply="${cbox.value}">
<attribute name="t" value="10"/>
<view bgcolor="blue" x="5" y="30"
width="150" height="150" />
<method name="doSomething">
Debug.write('new');
</method>
</state>
<button onclick="canvas.doSomething()">doSomething</button>
<method name="doSomething">
Debug.write('orginal');
</method>
</canvas>
Events, get added and removed like views. In the example below, you end
up with two events when the state is applied, then just the original
event when the state is removed.
<canvas debug="true">
<simplelayout/>
<attribute name="t" value="4"/>
<text text="${canvas.t}"/>
<checkbox id="cbox" text="Show"
x="10" y="10" />
<state apply="${cbox.value}">
<attribute name="t" value="10"/>
<view bgcolor="blue" x="5" y="30"
width="150" height="150" />
<handler name="onmousedown" reference="LzGlobalMouse">
Debug.write('new');
</handler>
</state>
<button onclick="canvas.doSomething()">doSomething</button>
<handler name="onmousedown" reference="LzGlobalMouse">
Debug.write('original');
</handler>
</canvas>
P T Withington wrote:
As part of fixing LPP-631 in r8032, states now remove constraints that
they override when applied, and they _restore_ those constraints when
removed. This breaks dragging and resizing of the swf debugger window!
The swf debugger starts out with its dimensions defaulted to a
percentage of the canvas. Percentage values are constraints. This is
nifty, because if you resize your browser window, the debugger window
nicely resizes too.
But if you try to drag or resize the window, the drag or resize state
gets applied, the window tracks the mouse, but when you let go of the
mouse, the state gets removed and the previous percentage constraints
are reinstalled, snapping the window back to its starting position.
My question: Is this a bug in states? Should they _not_ restore
constraints they removed? Is this a bug in drag/resize states?
Should they be overriding the base state behavior of restoring
constraints? Or, is this just a bug in the swf debugger? Should it
only size to the canvas initially and not respond to canvas changes?
Or should it be improved to track the canvas until it is resized or
dragged?
