仅在wifi下下载的设置Demo

README ====== This Network Usage sample app does the following: -- Downloads an XML feed from StackOverflow.com for the most recent posts tagged "android". -- Parses the XML feed, combines feed elements with HTML markup, and displays the resulting HTML in the UI. -- Lets users control their network data usage through a settings UI. Users can choose to fetch the feed when any network connection is available, or only when a Wi-Fi connection is available. -- Detects when there is a change in the device's connection status and responds accordingly. For example, if the device loses its network connection, the app will not attempt to download the feed.