02. A class, in this context, is a text file with a set of instructions and information about an object. In this case, we need to create a file for the class we just created: ‘MO’. Choose File > New, then from the Type list select ActionScript File. We’ll enter all the code for MO into this file. Save the file as MO.as.

03. Enter the following code into your MO.as file (you can copy and paste it from the file Step 3 on the cover CD), then save the file and return to the main Flash movie. class MO extends MovieClip { var movedelta = 10; function onEnterFrame() { if( Key.isDown(Key.RIGHT) ) { _x = _x + movedelta; } if( Key.isDown(Key.LEFT) ) { _x = _x - movedelta; } if( Key.isDown(Key.UP) ) { _y = _y - movedelta; } if( Key.isDown(Key.DOWN) ) { _y = _y + movedelta; } } } Select Control > Test Movie to test whether the movement works when you press the arrows on your keyboard.

04. The code we just created sets up the class MO as a sub-class of the MovieClip class; that is to say, we’re using the existing MovieClip class and giving it some extra instructions. We create a variable called movedelta and give it a value of 10. This is the amount, in pixels, that the character will move each time a button is depressed. We also added four conditional statements inside a function. The function is special, as it’s built into the MovieClip class. onEnterFrame executes every time a frame is encountered in the movie. As our movie is running at 30fps, this function will execute 30 times a second. The conditional statements check each arrow key in turn to see if it is pressed down and if it is, the position of the character is updated on the X or Y axis, as appropriate.

05. We’ve now got Madame Octopus happily moving around the screen in response to the arrow keys. The next stage is to add some objects for her to avoid. We’ll make use of the bubble movie clip that we used last month. Locate the bubble MovieClip in your library, right-click (Ctrl + click) on it and choose Duplicate. Name the duplicate ‘evilBubble’, and again tick Export for ActionScript, giving the MovieClip an identifier of ‘EB’ and a class of ‘EB’. If you didn’t complete last month’s tutorial, open the file EB.as from the cover CD.