Photo_view: Proposal: PhotoViewController

[renancaraujo]

In the last months, more and more use cases of custom behavior appeared.
PhotoView as a generalist zoomable widget of zoomable must be more customizable, but in another way, cover a world of features is not our main objective here.

Customize PhotoView should be easy but use it without any config should be too.

After reading some issues, I think the best pattern to provide an optional, flexible and simple API would be a Controller.

Controller is a patter where a class define parameters of behavior and controlls state outside the widget, this would enable methods like reset (#67).

Due to the amount of issues, this is priority.

[renancaraujo]

After Some work, the controller is starting to take form. #89 will be the PR where the evolution of the controller will be placed at. Once all goals has been achieved, we will merge and release it as 0.2.0.

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To summarize its goals:

• [x] Be flexible and extensible: allow authors to customize it or even create their own controllers
• [x] Control state: scale number, scale state (initial, covered or zooming), rotation factor and position (translate) of the image
• [x] Provide a way to set the initial values for scale, rotation and position #79
• [x] Expose the state values to be accessed and changed externally #49 #66
• [x] Provide a reset method to make PhotoView go back to its initial values #67
• [x] Be sensible to layout changes: if either PhotoView or the child size changes #70 #80
• [x] Make the 'double tab' behavior customizable #69
• [x] Keep the 'go back to initial scale' behavior implemented on #76
• [x] Be externally listenable to value changes

[renancaraujo]

In order to set the next release small and let the controller with a specific concern (controlling state), we shall not include items "Customize the clamping position behavior #68" and "Customize the clamping scale behavior #85"

[renancaraujo]

Merged, sorry for the absurd long time.

[renancaraujo]

Just launched as 0.2.0