Think about the times you yourself have used a mobile app. Are you spending hours on just one app? Not likely. Most people use apps intermittently with a lot of interruptions. Rumor has it that people use mobile apps when they are busy, lost, or bored. The first two of these include the need for quick information, but the third does not necessarily imply extended usage. Someone bored could easily just need a quick fix to distract or entertain himself or herself for a few minutes. The best way to learn about design principles is to view Android apps through a developer's lens. Study how, when, and for how long people use mobile apps. Monitor your own app's behavior and ask others when they most often use apps. Is it when you're waiting in line? While traveling via public transport? Going to meet someone? How much time do you spend on one app before you move on to something else? Next, look analytically at apps—the ones you regularly use along with new ones. Examine everything—the fonts, the colors, and the placement of buttons or the navigation tools to see how they function and are displayed. Keep notes to track your discoveries, jotting down elements you expect to see and those that you find unexpected.

Keep in mind that mobile phone users will be navigating your app with their thumbs, so it is essential to make buttons big enough for easy navigation. If you make interactive elements too small and difficult to trigger, users could get frustrated and avoid using your app. Bottom navigation bars also make it easy for thumbs to control an app, which is why you will find this standard on many apps. Also, keep in mind that not all users have perfect vision. Create apps with high contrast colors and text that is easily viewed by people of all ages. It's a great idea to get a wide variety of people to view your app to give you feedback on things, such as colors, contrast, readability, and navigation ease.

The way you display elements in terms of weight or importance is called visual hierarchy. You can create visual importance through the use of font size, colors, position, contrast, shape, or consistency. There are some Android elements that are familiar to users, such as an action bar that houses buttons to easily move about the app. Users will expect to find consistency on each screen along with ease in navigation. For example, it should be simple to stop, play, or quit at any point during a game app. In the Event App, we showed one way to make it apparent for the user to know which screen he or she is on by changing the text color of a button. You can also use other visual cues, such as highlighting a particular navigation button or creating a contrasting background color. Some of these recommendations may seem obvious, but you will be surprised to see how many people forget the obvious once they start creating apps from scratch.

Responsive design can refer to many things. Is your app responsive to users? Does it do what users think it will do? Does the app respond to user interaction as intended? Note that responsiveness and speed are not the same thing. It's OK if your app takes time to load something as long as the app is responding to user input and the user is aware that the app is responding. Responsive design also means that an app adjusts to a user's screen size. When creating apps, you don't know whether a user will have a mobile phone or tablet. What looks good on one screen size won't necessarily display properly on another, unless you ensure that it does. Responsive designing is creating layout and content for optimal viewing on any screen size. App Inventor makes it easy to do this. In the Properties panel of Screen1, there is a property called Sizing, as shown in the following screenshot. The default option is Fixed; but if you click on the word, a second option will be displayed: Responsive.

Upon choosing Responsive, a previously grayed out option in the Viewer will become visible. Immediately, above the Viewer window, you will now be able to click on the checkbox next to Check to see Preview on Tablet size. Once you do, the text will change to "un-check" and the Viewer will display a tablet preview of your app, as shown in the following screenshot with EventApp:

This is particularly helpful to view if you don't have a tablet and want to test how your app will look on one.

If you have the desire to make mobile apps from your own ideas, it is vital to understand the app market. How do you do this? You can do so by conducting research on mobile apps. Start looking at Google Play or other Android app markets and see what apps are new and popular. And most importantly, use those apps, jot down your reactions, what you liked and didn't like, and read reviews. Discover why certain apps in a category are more popular than others, what app features appeal to you, and also which types of apps are trending. Studying apps from the perspective of a developer will help you see themes in content, design, and user experience. Read descriptions of the apps to see how, for example, one chess game summary brands itself differently than other chess games. As we have recommended throughout this book, record your observations, reactions, and top picks, because like with any market, changes occur over time. It will be helpful for you to read what you noticed in the market 6 months ago and compare it to what your research revealed last week.

If you don't have a budget to buy apps, don't worry; you can still do valuable research on free apps or the ones that lead to in-app purchases. Notice what features are free and which ones are considered more valuable that they require a fee. When you get to the point of an in-app purchase, do you want to make one? Why or why not? Do the free apps have advertisements? If so, which apps? Which ads? If you do upgrade an app, what are the differences between the freemium and the paid versions of the same app?

This type of research will prove valuable when you complete this book and need help deciding what type of app to create on your own. The easiest way to find success creating apps is by giving users what they want. You can discover what users want by studying what apps are selling and popular. Many budding app developers fail to research app markets and instead just concentrate on coming up with an idea that they like and turning that concept into a prototype, hoping people will find the app, download it, use it, and like it. By paying attention to what users are already downloading and what they are willing to pay for, you can create an app with an understanding of what already appeals to users. Then, you can decide whether to follow this trend or disrupt it. Research can help ensure that your app is more successful once you upload it into app marketplaces. And the more people that use your apps, the more valuable feedback you will get. Ratings and comments can serve to help you improve subsequent versions or guide you in future app development.

You can sketch out your app screens on index cards, notebook paper, poster size paper, or a whiteboard, or you can use some digital tools. There are a lot of free resources available to help you create paper or digital prototypes. Do a Google search for paper prototyping for mobile apps, or if you prefer the digital route, search for wire framing for mobile apps (note that we add the words mobile apps to our search because there are also a lot of resources for designing web pages). We even found a hybrid option (https://popapp.in/) that enables you to take pictures of your hand-drawn sketches and incorporate them into the app.