可靈活收縮的頭部：BLKFlexibleHeightBar

BLKFlexibleHeightBar 可以讓你創建可靈活收縮的頭部。類似于我們在非死book, Square Cash, 和 Safari iOS應用中看到的。

BLKFlexibleHeightBarallows you to create header bars with flexible heights. Often, this sort of UI paradigm is used to hide chrome and make room for more content as a user is scrolling. This is seen in third party apps like 非死book and Square Cash, as well as first party apps like Safari.

BLKFlexibleHeightBarcan create bars that look and act any way you'd like:

• Immediate subviews of a flexible height bar define how they want to look and where they want to be depending on the height of the bar. Properties like frame, transform, and alpha can all vary depending on the current height of the bar.
• A bar's behavior can be defined using a behavior definer instance. A behavior definer can be created to emulate Safari's header behavior, 非死book's header behavior, or something entirely new. Behaviors are completely modular and aren't coupled with the appearence of the bar.

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