Unit 9

1. Unit 9 • Completed a whistle-stop tour of programming language and C# basics • Now we will write a program or two from scratch Learning to Program with C# - 9

2. A word on program styles • Rocketry is an animation, or simulation • Animation: drawing and redrawing graphical shapes to give the appearance of movement • Simulation: modelling the behaviour of a real world system • Many other program styles • Data processing • read data in, process it, output it again • Search programs • look for a solution to a problem by creating and assessing multiple different possibilities along the way • Windows-based application – you're used to seeing them • Takes time to learn about a new style • so here, we will stick with the animation/simulation style Learning to Program with C# - 9

3. Problem • Draw a spoked wheel rolling across the screen • Great. Now what? • Problem solvers apply a huge number of heuristics in the problem solving process. You will learn these over time • We'll apply some of them here Learning to Program with C# - 9

4. Heuristic 1: Can I solve a simpler, related, problem first? • Version 2 • Draw a rotating spoked wheel, not moving • Version 3 • Draw a single rotating spoke, like a second hand on a watch • Version 4 • Draw a dot rotating about a fixed point – the end of the spoke/second hand • If I can solve each one of these in turn • it is a relatively simple step to get to the next one Learning to Program with C# - 9

5. Heuristic 2: Play with the problem • Often, take pen & paper, and mess around until the light dawns – until you make connections with things you do know about • e.g. I might get: • Realisations come fromthis playing: • position of moving point isdependent on theangle, and the radiusof the point from the centre of rotation • using trigonometry, thedistances x and y can becalculated • if we know the central pointwe can calculate the outerpoint x y Radius Route of point Angle Learning to Program with C# - 9

6. Heuristic 3: What kind of behaviour am I considering? • Primarily, is it • a sequence of steps? • a repetitive activity? • a conditional activity? • It's repetitive • repeatedly • erase previous drawing of ball • recalculate the position of the ball • draw in new version of ball • delay a moment, so we can see it • Notice that primarily it's repetitive, but that on each repeat, we're performing a sequence of instructions Learning to Program with C# - 9

7. Heuristic 4: What tools do I have available, and will they help? • Trigonometric functions • available in Math class, in System namespace • good, because sine and cosine are needed to calculate the point's position • Animation class • this contains a graphics canvas object that has drawing functions defined on it • good, because we need to go drawing • Repetition and sequence instructions available • good, because we're doing that kind of activity Learning to Program with C# - 9

8. Heuristic 5: What objects needed? • A RotatingPoint object • it can draw itself • it knows where it is and how to work out where to go next • An Animation object • for the Point to draw on • this has already been written, we simply reuse it • An Animate class to set it off • it will run a timer, repeatedly telling the point to redraw itself • later, it could handle many objects • a driver or startup class (like ExecuteMission) Learning to Program with C# - 9

9. So, how to get started on a new project… • Open up AnimateObjects.sln • found in AnimateObjects folder • This is a bare minimum starting point • contains a skeleton version of the Animate class • We need a new class • RotatingPoint • Press mouse button 2 in the class viewer, then choose Add/Add Class • In the Add Class wizard • type in RotatingPoint for the name of the class • and a description – manages a point rotating round a fixed centre – or something Learning to Program with C# - 9

10. Add a method to RotatingPoint • In Class View, select RotatingPoint • press button 2, then Add/AddMethod • In the wizard • method name is Redraw • give a description – something like redraw the point assuming a time interval has passed • ignore the rest, there will be no parameters and we are not returning anything • See what the wizard produces • you could have typed this yourself – once you have become proficient, you may find it easier! Learning to Program with C# - 9

11. Add a field member to the class • In Class View, with RotatingPoint selected • button 2/Add/Add Field • Field Access – choose private • we don't want external classes to see this value • Field Type – choose int • for integer or whole numbers • Field Name – type X • this is going to represent the X position of the point • type in a description explaining this • Once Finished, see the addition to the code in the class's window Learning to Program with C# - 9

12. Add more field members • One for the point's Y position • Could do this using copy and paste in the RotatingPoint window • then change occurrences of X to Y • and some for centre position, angle & radius • CentreX and CentreY and Angle and Radius • note that Angle will need to be double not int • And finally another for the Canvas to draw on • this is of type Graphics, call it Canvas • In order for the system to understand where Graphics comes from, • add using System.Drawing; after using System; at the head of the class – see Animate.cs for comparison Learning to Program with C# - 9

13. Extending the constructor method • When we construct a rotating point, we need to know • centre point (x,y), radius, and graphical canvas to draw on • Extend constructor method • so these are supplied as parameters • In method called RotatingPoint • (this is the constructor) • add the following inside the () after the name Graphics g, int centreX, int centreY, int radius • each parameter is given a type then a name, and they're all separated with commas Learning to Program with C# - 9

14. The body of the constructor • We simply assign the parameter values passed to the constructor to the corresponding internal field of the object e.g. CentreX = centrex; • Do this for all four parameters • Also need to set starting values for X, Y and Angle • refer back to earlier picture • suggest Angle is zero, and so X is zero, Y is Radius relative to the centre point • set Angle… Angle = 0; • set X… X = CentreX; • set Y… Y = CentreY + Radius Learning to Program with C# - 9

15. Take a moment… • to look at what you've created • Look in the class view, at this RotatingPoint class – neat row of methods and fields • Look in the object browser • you can navigate around the various components Learning to Program with C# - 9

16. Now for action – Redraw method • Each time this is called we want to • blank out the point • can do this by drawing it in the background colour • calculate its new position • draw it at this position • Add these steps as comments to the body of the method (in between the {} ) • a comment is just some English text to help us understand what is going on • it must start with // • two forward facing slashes Learning to Program with C# - 9

17. Code to blank out the point • Under the comment about blanking out • we want to use one of the drawing methods available on our Canvas • So, type Canvas and then a dot • Visual Studio will show you a menu of all members available for a Graphics object • choose FillEllipse by double clicking on it • Then type an open bracket, because we wish to call this method • VS shows you the parameters and their types • it may indicate there are different versions of the method too • Type in exactly Animate.Background, X-1, Y-1, 3, 3 ); • See how VS assists you as you type Learning to Program with C# - 9

18. Add in the following code • Under the update comment, add Angle = Angle + (2.0 * Animate.OneDegree); X = CentreX + (int)( (double)Radius * Math.Sin( Angle ) ); Y = CentreY + (int)( (double)Radius * Math.Cos( Angle ) ); • and then repeat the drawing code for the final part • but replace Background with Foreground Learning to Program with C# - 9

19. Back in the Animate class… • Add the following code into the Main method, between the {} AnimationForm AF = new AnimationForm( 400, 400 ); RotatingPoint RP = new RotatingPoint( AF.Canvas, 200, 200, 100 ); for( int i=0; i<1000; i++ ) { RP.Redraw(); AF.Delay( 0 ); } AF.WaitForQuit(); • The first two lines create local variables, like temporary object fields, AF and RP to hold newly created AnimationForm and RotatingPoint objects • The for loop then cycles the animation 1000 times Learning to Program with C# - 9

20. You're now ready to run… • Attempt to Start the program • you may find errors from typing • if you are unable to see where the errors have crept in • look at the solution in AnimateObjectsComplete Learning to Program with C# - 9

21. Turn the point into a spoke • How could you now turn your rotating point into a sweeping second hand – one of the spokes of the wheel • Think about it… • instead of drawing a small circle on each redraw • draw a line from the centre outwards • try it out – you'll see there's a draw line method in Graphics. It takes a Pen, not a Brush – you can find Pens in Graphics.Pens – there's White and Black and many others – let Visual Studio guide you Learning to Program with C# - 9

22. And then… • 4 spokes – how could you do that? • and a rotating wheel • easy, add a circle • and a moving, rotating, wheel • that centre point needs to move on each redraw also – everything'll move along fine! Learning to Program with C# - 9

23. Summary • Created first application largely from scratch! • Briefly started looking at the problem solving process • much more work to do here • explore new program styles • become happy with using the kind of heuristics discussed here Learning to Program with C# - 9