cocoa touch——UIView——draw

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draw

- (void)drawRect:(CGRect)rect;- (void)setNeedsDisplay;- (void)setNeedsDisplayInRect:(CGRect)rect;@property(nonatomic)                 BOOL              clipsToBounds;              // When YES, content and subviews are clipped to the bounds of the view. Default is NO.

注意：rect参考自身坐标系

演示

@interface FBView : UIView@end@implementation FBView- (void)drawRect:(CGRect)rect{    NSLog(@"drawRect rect = %@", NSStringFromCGRect(rect));}@end

- (void)viewDidLoad{    [super viewDidLoad];    NSLog(@"viewDidLoad");        fbView = [[FBView alloc] initWithFrame:CGRectMake(10, 20, 100, 200)];    fbView.contentMode = UIViewContentModeRedraw;    [self.view addSubview:fbView];}- (void)viewWillAppear:(BOOL)animated{    [super viewWillAppear:animated];    NSLog(@"viewWillAppear");}- (void)viewDidAppear:(BOOL)animated{    [super viewDidAppear:animated];    NSLog(@"viewDidAppear");}

output：

viewDidLoadviewWillAppeardrawRect rect = {{0, 0}, {100, 200}}viewDidAppear

first display(draw)位于viewViewAppear和viewDidAppear之间

draw不要直接调用，下列情况会发生draw调用：

first display
调用setNeedsDisplay或setNeedsDisplayInRect
contentMode为UIViewContentModeRedraw，bounds change

分析：

UIView有一个draw flag和draw rect，默认draw flag为YES，draw rect为bounds，调用draw以后，draw flag设为NO，setNeedDisplay和setNeedsDisplayInRect就是设置draw flag和draw rect的(setNeedDisplay设置draw rect为bounds)，当contentMode为UIViewContentModeRedraw，bounds change时，本质就是调用setNeedDisplay

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