TAILIEUCHUNG - Lập trình iphone chuyên nghiệp part 8

Handling Touch Interactions and Events Một phần thiết yếu của bất kỳ ứng dụng Web là khả năng đáp ứng với các sự kiện được kích hoạt bởi người dùng hoặc bởi một điều kiện xảy ra trên máy khách. Các cách nhấn vào một nút. Các cách nhấn một phím | Handling Touch Interactions and Events An essential part of any Web application is the ability to respond to events triggered by the user or by a condition that occurs on the client. The clicking of a button. The pressing of a key. The scrolling of a window. While the user interacts with an HTML element the entire document or the browser window JavaScript serves as the watchful eye behind the scenes that monitors all of this activity taking place and fires off events as they occur. With its touch screen interface iPhone is all about direct interactivity with the user. As a result you would expect any iPhone iPod touch application you create to be able to handle the variety of finger taps flicks swipes and pinches that a user naturally performs as they interact with their mobile device. However because of the current capabilities of Mobile Safari browser you have to work with these interactions differently than what you might expect. How iPhone Handles Events When working with touch interactions and events for iPhone keep in mind that the finger is not a mouse. As a result the traditional event model that Web developers are so used to working with does not always apply in this new context. This is both good news and bad news for the application developer. The good news is that much of the touch interaction that iPhone and iPod touch are famous for is built right into Mobile Safari. As a result you do not need to write any code to handle the basic touch interactions of the user. Flick-scrolling pinching and unpinching and one-finger scrolling are those sorts of user inputs that come for free. The bad news is that the developer is greatly constrained in his or her ability to work with the full suite of JavaScript events and override built-in behavior. As a result certain user interactions that have become a staple to Web developers now are impossible to utilize or require tricky dumbed-down workarounds. Chapter 5 Handling Touch Interactions and Events The general

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