intent
intent 是一种构造，应用程序可以通过它发出请求，这就像是发出求助信号。intent 可能像下面这样：
"Wanted: An application to help me look up a contact" 或 "Wanted: An application to help me display this image" 或 "Wanted: An application to perform this geographic-based search"
应用程序可以按照相似或互补的方式进行注册，表明它们有能力或有兴趣执行各种请求或 intent。比如：
"Available: Application ready and willing to present contact records in clear, concise manner" 或 "Available: Application ready and willing to perform a geographic search"
https://www.ibm.com/developerworks/cn/education/opensource/os-eclipse-android/index.html
