iOS 8人机交互指南（8）
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8. 动画（Animation）
Beautiful, subtle animation pervades the iOS UI and makes the app experience more engaging and dynamic. Appropriate animation can:
（1）Communicate status and provide feedback
（2）Enhance the sense of direct manipulation
（3）Help people visualize the results of their actions
优美、巧妙的动画遍布 iOS UI 的各处，使得 app 的用户体验更迷人、动感。恰当的动画可以：
（1）显示状态、提供反馈；
（2）加强直接操作感；
（3）帮助人们将操作结果可视化。
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Add animation cautiously, especially in apps that don’t provide an immersive experience. Animation that seems excessive or gratuitous can obstruct app flow, decrease performance, and distract users from their task.
In particular, use motion effects and UIKit dynamic behaviors with purpose and restraint, and be sure to test the results. Used appropriately, these effects can increase users’ understanding and enjoyment; overusing them can make an app seem disorienting and difficult to control.
慎重考虑添加动画，尤其是在 app 并没有提供拟真体验的时候。过度或不必要的动画会阻碍 app 的流程，降低性能，转移用户对任务的注意力。
特别注意，要带有目的或限制来使用手势效果和 UIKit 动态行为，而且一定要验证这些效果。恰当的使用这些效果可以增加用户的理解力和愉悦感；过度的使用则会让 app 看上去迷失方向、很难控制。
When appropriate, make custom animation consistent with built-in animation. People are accustomed to the subtle animation used in the built-in iOS apps. In fact, people tend to regard the smooth transitions between views, the fluid response to changes in device orientation, and the physics-based scrolling as an expected part of the iOS experience. Unless you’re creating an app that enables an immersive experience—such as a game—custom animation should be comparable to the built-in animations.
适当地考虑让自定义动画与内置动画保持一致。用户已经习惯于 iOS app 中内置的那些巧妙动画。事实上，用户倾向于将视图间的流畅切换、设备方向改变时的流畅响应、基于物理的滚动看做是 iOS 体验的一部分。除非正在开发一款拟真体验的 app ——例如游戏——否则自定义动画还是应当同内置动画保持一致。
Use animation consistently throughout your app. As with other types of customization, it’s important to use custom animation consistently so that users can build on the experience they gain as they use your app.
在 app 中使用一致的动画。与其他的自定义类型一样，保持自定义动画的一致性非常重要，这样用户可以随着对 app 的使用建立起他们的使用体验。
In general, strive for realism and credibility in custom animation. People tend to be willing to accept artistic license in appearance, but they can feel disoriented when they experience movement that doesn’t make sense or appears to defy physical laws. For example, if you reveal a view by sliding it down from the top of the screen, you should dismiss it by sliding it back up because doing so helps users remember where the view comes from. If you dismiss the same view by sliding it down beyond the bottom of the screen, you break the user’s mental model of a view that’s available above the top of the screen.
通常情况下，要争取自定义动画现实可靠。用户倾向于愿意接受外观上充满美感的协议，但当动作体验无意义或看上去违背物理规则时他们会感到迷失方向。例如，如果你从屏幕顶部向下滑动来显示视图，那如果让它消失的话就需要反向滑动，因为这样做会让用户记住视图来自哪里。如果在屏幕底部向下滑动该视图来让它消失，那就破坏了用户对视图的心理模型。
后一篇：iOS 8人机交互指南（9）
