I often wish I could specify the placement of views — buttons, text views, etc. — within a screen by percentages: “Put one button 33% of the screen height from the top, and the other button 67% of the screen height from the top. In other words, two buttons evenly spaced vertically.” Alas…

Any app that doesn’t run solely in the background is going to need to interact with the user. Fortunately, the Android SDK provides a huge variety of methods to help an app recognize when a user does something, and respond appropriately. These are event handlers — a user click, tap…