CS193p Spring 2010 Monday, April 12, 2010

Transcription

1 CS193p Spring 2010

2 Announcements Axess! Make sure your grading option matches what you were approved for Sonali s Office Hours Changed Friday 11am to 1pm Thursday 10am to noon Gates B26B Any questions about the Homework? Did everyone get the about entering numbers?

3 Communication Questions are best sent to Sending directly to instructor or TA s risks slow response. Web Site Very Important! All lectures, assignments, code, etc. will be there. This site will be your best friend when it comes to getting info.

4 Today s Topics Protocols and Delegates Views Core Graphics Demo

5 Protocols Very similar but no Foo (NSArray Classes then proclaim they implement a MyClass : NSObject

6 Protocols Declaring arguments to require a protocol - (void)givemetheobject:(id <Foo>)anObjectImplementingFoo Declaring variables to require a protocol id <Foo> obj = [[MyClass alloc] init]; [obj dosomething]; // will not warn (and should be okay) Compiler will warn of misbehavior Class says it implements protocol Foo, but doesn t implement required methods Assigning an object which does not implement Foo to a variable like obj above Passing an object which does not implement Foo through an argument which requires it (like above)

7 Delegates Used to delegate responsibility to other objects Protocol defines what the responsibility is Great way to maintain MVC but with flexibility Oftentimes View objects do this Will see example of this in demo Very common paradigm in UIKit

8 Views Rectangular area on screen Draws and handles events in that rectangle Hierarchical Only one superview: - (UIView *)superview Can have many (or zero) subviews: - (NSArray *)subviews Subview order matters: those later in the array are on top of earlier UIWindow The UIView at the top of the view hierarchy Only have one UIWindow in an iphone application (it s all about views)

9 View Hierarchy Hierarchy often constructed in IB Even custom views can be added to the hierarchy in IB How to do it in code though? - (void)addsubview:(uiview *)aview; - (void)removefromsuperview; How to manage the order of subviews - (void)insertsubview:(uiview *)sv atindex:(int)index; - (void)insertsubview:(uiview *)sv belowsubview:(uiview *)otherview; - (void)insertsubview:(uiview *)sv abovesubview:(uiview *)otherview;

10 Transparency of Views What happens when views overlap? Order of subviews list determines who s in front, but lower ones can show through transparent views on top of them When you are drawing (covered later), you can draw with transparency (partial or fully) Default is fully opaque drawing If you want to hide a view completely, you can just set the hidden property to YES No need to remove the view from the hierarchy to hide it

11 View Memory Mgmt Superviews retain their subviews Once you put a view into the hierarchy you can release your ownership if you want Note that we retain IBOutlet variables But we don t really need to as long as they are always in the hierarchy. It s more of a convention to retain them. But be careful! If you remove a view from the view hierarchy it may deallocate immediately (no autorelease happens). So, retain it first, then call removefromsuperview.

12 Coordinates CGFloat Just a floating point number, but always use CGFloat for graphics. CGPoint C struct with two CGFloats in it: x and y. Create with CGPointMake(x, y) CGSize C struct with two CGFloats in it: width and height. Create with CGSizeMake(width, height) CGRect C struct with a CGPoint origin and a CGSize size. Create with CGRectMake(x, y, width, height)

13 (0,0) increasing x Coordinates Origin of View s coordinate system is upper left Units are pixels No matter what the dps of the screen is (250, 85) View property bounds is the local coordinate space self.bounds.origin: decide what it means for your view self.bounds.size.width/height is how wide/tall your view is Use this rectangle when you are inside the implementation of a view increasing y View s frame and center properties center is the center of the View in its superview s co ordinates frame is the smallest rectangle which will contain the view So is frame.size always the same as bounds.size? No: rotation. Use center and frame to position/size the view in its superview.

14 140, , View A , 0 View B 320 View B s bounds is ((0,0),(200,250)) View B s frame is ((140,65),(320,320)) View B s center is (300, 225)

15 Creating Views Most often you create views in IB Even though custom views are not IB, you drag out generic UIView from the Library window, then use the Inspector to change the class to your custom class How do you create them in code? - (id)initwithframe:(cgrect)arect is designated initializer Example: CGRect buttonrect = CGRectMake(20, 20, 120, 37); UIButton *button = [[UIButton alloc] initwithframe:buttonrect]; button.titlelabel.text Do it! ; [window addsubview:button]; [button release];

16 Custom Views When do I want to create my own view? I want to do my own drawing on screen And/or I want to handle touch events Create a subclass of UIView To do your own drawing, implement drawrect: - (void)drawrect:(cgrect)cliprect; You can optimize by not drawing outside of cliprect, but not required NEVER call drawrect:!! EVER! Instead, let system know view is out of date and needs a redraw. It will then call your drawrect: at an appropriate time. - (void)setneedsdisplay - (void)setneedsdisplayinrect:(cgrect)cliprect

17 Custom Views To handle events, you must implement all of these - (void)touchesbegan:(nsset *)touches withevent:(uievent *)event; - (void)touchesmoved:(nsset *)touches withevent:(uievent *)event; - (void)touchesended:(nsset *)touches withevent:(uievent *)event; - (void)touchescancelled:(nsset *)touches withevent:(uievent *)event; Or use a UIGestureRecognizer We ll talk about touches and gestures later

18 Drawing How do you implement drawrect:? Draw with Quartz2D Quartz2D is part of Core Graphics Framework It is a C API (not object-oriented) Concepts Get a context to draw into Apply transformations Create paths Set colors, fonts, textures, linewidths, linecaps, etc. Stroke or fill those paths

19 Context Context determines where your drawing goes Screen Offscreen Bitmap PDF Printer UIKit sets up a context for you in drawrect: Only valid during that execution of drawrect: So never cache the context! You ll get a new one each time Get the context in drawrect: with this method - (CGContextRef)UIGraphicsGetCurrentContext(); CGContextRef context = UIGraphicsGetCurrentContext();

20 Graphics State Setup graphics state of the context Many different properties, e.g., CGContextSetLineWidth(context, 1.0); The context UIKit provides has sensible defaults Colors have some object-oriented support in UIKit UIColor *mycolor = [UIColor bluecolor]; UIColor *rgb = [UIColor colorwithred:0.5 green:1.0 blue:0.125 alpha:1.0]; [mycolor set]; [mycolor setstroke]; [rgb setfill];

21 Define a Path Begin the path CGContextBeginPath(context) Move around and add lines or arcs to the path CGContextMoveToPoint(context, 75, 10); CGContextAddLineToPoint(context, 10, 150); CGContextAddLineToPoint(context, 160, 150); Close the path (connects last point back to first) CGContextClosePath(context); // not strictly required Set any graphics state and then draw the path [[UIColor greencolor] setfill]; [[UIColor redcolor] setstroke]; CGContextDrawPath(context, kcgpathfillstroke);

22 Define a Path It s also possible to save paths and reuse them See functions in the docs that start with CGPath instead of CGContext

23 Graphics State Defining a method to draw something What if that method sets graphics state? It might mess up the graphics state of the calling method You can push the current graphics state, then pop UIGraphicsPushContext(context); <do whatever you want with the graphics state> UIGraphicsPopContext();

24 Drawing Text Use UILabel, but if you feel you must... Object in UIKit to get a font UIFont *myfont = [UIFont systemfontofsize:12.0]; UIFont *thefont = [UIFont fontwithname:@ Helvetica size:36.0]; NSArray *availablefonts = [UIFont familynames]; Special methods in NSString to draw text NSString *text =...; [text drawatpoint:(cgpoint)p withfont:thefont]; CGSize textsize = [text sizewithfont:myfont]; Check out NSString(UIStringDrawing) in docs

25 Drawing Images Use UIImageView, but if you must... Create an image from a file in your Resources UIImage *image = [UIImage imagenamed:@ foo.jpg ]; Create an image from a file or from raw data UIImage *image = [[UIImage alloc] initwithcontentsoffile:(nsstring *)path; UIImage *image = [[UIImage alloc] initwithdata:(nsdata *)data]; Create an image using CGContext functions UIGraphicsBeginImageContext((CGSize)size); <draw with CGContext functions as usual> UIImage *myimage = UIGraphicsGetImageFromCurrentContext(); UIGraphicsEndImageContext();

26 Drawing Images Blasting the bits into the current context UIImage *image =...; [image drawatpoint:(cgpoint)p]; // p is upper left corner of image [image drawinrect:(cgrect)rect]; // scales the image [image drawaspatterninrect:(cgrect)rect]; // tiles the image Aside: You can get your UIImage as PNG or JPG NSData *jpgdata = UIImageJPGRepresentation((UIImage *)myimage); NSData *pngdata = UIImagePNGRepresentation((UIImage *)myimage);

27 Demo UISlider Custom View with drawrect: Delegate Quartz 2D

28 Wednesday Application Structure & Lifecycle Application Delegate UINavigationController Demo of AppDelegate and UINavigationController Homework Explanation

29 Homework Tomorrow at 11:59pm!