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This merge request fixes / refers to the following issues: #2701

Pull Request Description

This is the implemntation based on #2701 draft. To solve our current implementation for stateful View Category method.

Reason

Stateful view means the UIView/NSView subclass, which has multiple image instance to set, such as UIButton setImage:forState: or UIImageView.image/UIImage.highlightedImage.

See #2701. Our image request loading model, use a Operation Key, for stateful view to load the image. It's OK because for different state, it use a different operation key, no conflict.

However, currtent these API in UIView+WebCache, it's not good:

• sd_imageURL
• sd_imageProgress
• sd_imageTransition

What if I use UIButton with sd_imageProgress to observe the progress changes ? Should it report the current state's progress, or normal progress ? or even background image's progress ? This is the root case of massive.

Solution

To solve this problem, we follow the same design model as Operation Key on image request. Now, each Operation Key will bind all the state associated to this request. I introduce a SDWebImageStateContainer class.

Each opeartion key bind a state container, and state container can be extended to include all the things we want represent the state.

• URL
• Progress
• Transition
• User-defined, such as timestamp. User may access this user-defined value in SDSetImageBlock and process your own logic. (like that SDWebImageContext, but for top-level view category, not the network or cache system)