Introduction to Computer Science with Scratch and App Inventor

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Now that we have the mole on the canvas, let’s think about how we are going to get him to move around. The way that Whack-a-Mole works: The mole shows up at random locations The mole is only visible for a short period of time Then the mole moves to a new random location This means that we will need some sort of way to control how long the mole is visible each time it appears. Luckily, just like Scratch had a built in timer that we could use, App Inventor has a Clock element that we can add to our program. Drag a Clock block from the Basic palate onto the MoleMash screen in the Viewer pane. Instead of showing up on the screen, the clock will show up underneath in a section labeled non-visible components. Now that the clock is added, rename it MoleTimer. Also, under Properties, set the interval to be 500. The interval is in milliseconds – there are 1000 milliseconds in a second, so by setting the interval to 500, our clock will trigger every half-second. Now we are all ready to write the code that will move our mole around the screen! So far we have been using the interface builder in App Inventor. To write code, we need to open the Blocks Editor To open the Blocks Editor, click the button in the upper right-hand corner of your screen. You may see some security warnings from Windows. Blocks Editor is 100% safe to run, so click OK or Run on the warning dialog boxes that pop up. mbrace Game Development Workbook Page 38
Your Blocks Editor Screen should look something like this: Here is the menu of blocks that you can use in your programs. There are two tabs. Built-in contains blocks that can be used in any program. My Blocks contains blocks that are specific to the user interface elements in your app. If you click on the My Blocks tab you should see a list of the elements we have used. Clicking on any element or category will open a menu of blocks that you can use Drag the blocks into this center area to create a program. In our game, we are going to need to move the mole twice: 1) The mole will move every time the timer expires 2) The mole will move every time the user successfully touches it We could write two separate pieces of code to move the mole, however the movement is the same in each case – the mole disappears and reappears at a new random location on the screen. Instead of writing the movement code twice, we are going to write one procedure that moves our mole. A procedure (may also be called a method or function) is a way to give a name a chunk of code. Then, you can use the name to call the procedure from multiple places in your program. Each call to a procedure runs the code associated with it. The Blocks Editor gives us an easy way to create methods. In the Built-In blocks, under Definition we can use the to procedure arg block to define a new procedure. Drag a to procedure arg block into the middle area of the screen to add it to your program. If you make a mistake and need to delete a block, drag it to the trash can in the bottom right hand corner. mbrace Game Development Workbook Page 39
Page 1 and 2: Introduction to Computer Science wi
Page 3 and 4: LESSON 1: Getting Started with Scra
Page 5 and 6: I decided to pick a dinosaur. You c
Page 7 and 8: The direction that your sprite move
Page 9 and 10: Let’s add some yellow wait blocks
Page 11 and 12: Changing the Background on the Stag
Page 13 and 14: To use an if block to control the m
Page 15 and 16: Costumes and Animation Now that you
Page 17 and 18: Other useful blocks are the say and
Page 19 and 20: ? Now we know how to tell when the
Page 21 and 22: Here is one script that works. To m
Page 23 and 24: After you create a variable, you wi
Page 25 and 26: Winning, Losing, and Game Play Our
Page 27 and 28: You might have noticed that when th
Page 29 and 30: Click the checkbox next to timer to
Page 31 and 32: Scratch Review Now you have built y
Page 33 and 34: App Inventor Interface The App Inve
Page 35 and 36: The first thing that we will do is
Page 37: To add the mole to our program, we
Page 41 and 42: We know that our X and Y locations
Page 43 and 44: Our mole shows up in the emulator,
Page 45 and 46: The last thing we need is the value
Page 47 and 48: Team Project Worksheet We have lear

Introduction to Computer Science with Scratch and App Inventor

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