關(guān)系
UIView是如何顯示一個(gè)頁(yè)面的贵扰？
CALayer通過(guò)代理，將需要繪制的信息傳遞給UIView浇雹；UIView通過(guò)CoreGraphics進(jìn)行繪制的操作阁谆；- 繪制好的內(nèi)容交給
CALayer，方法有兩種：
layer.contents = image- 存儲(chǔ)在
CABackingStore
- 通過(guò)
OpenGL ES/Metal(GPU)進(jìn)行顯示晾腔。
-
CALayer的調(diào)用流程
CALayer調(diào)用流程，分為布局和繪制兩部分啊犬。
- 布局部分灼擂，先會(huì)調(diào)用
CALayer的layerSublayers方法，再調(diào)用view的layoutSubViews觉至；- 繪制部分剔应，通過(guò)設(shè)置
layer的setNeedsDisplay標(biāo)記需要刷新，然后調(diào)用CALayer的display方法，再判斷UIView的displayLayer方法是否實(shí)現(xiàn)峻贮，如果實(shí)現(xiàn)走自定義繪制流程席怪，否則進(jìn)入系統(tǒng)繪制流程，會(huì)先創(chuàng)建buffer和context纤控，然后調(diào)用drawLayer:InContext:挂捻，再執(zhí)行UIView的drawRect。
流程
- 通過(guò)在
drawRect進(jìn)行斷點(diǎn)船万，查看函數(shù)調(diào)用棧：
* thread #1, queue = 'com.apple.main-thread', stop reason = breakpoint 1.1
* frame #0: 0x0000000103de7317 CALayerProcessDemo`-[LCustomLayerView drawRect:](self=0x00007ff154508f80, _cmd="drawRect:", rect=(origin = (x = 0, y = 0), size = (width = 200, height = 200))) at LCustomLayerView.m:13:5
frame #1: 0x00000001083704d3 UIKitCore`-[UIView(CALayerDelegate) drawLayer:inContext:] + 550 //默認(rèn)調(diào)取
frame #2: 0x00000001098f393d QuartzCore`-[CALayer drawInContext:] + 285
frame #3: 0x00000001097ee969 QuartzCore`CABackingStoreUpdate_ + 173 //后臺(tái)存儲(chǔ)區(qū)
frame #4: 0x00000001098fa3fc QuartzCore`___ZN2CA5Layer8display_Ev_block_invoke + 44
frame #5: 0x00000001098f3439 QuartzCore`-[CALayer _display] + 2443 //繪制
frame #6: 0x0000000109904e77 QuartzCore`CA::Layer::layout_and_display_if_needed(CA::Transaction*) + 359
frame #7: 0x000000010987424a QuartzCore`CA::Context::commit_transaction(CA::Transaction*) + 328
frame #8: 0x00000001098ab606 QuartzCore`CA::Transaction::commit() + 610
frame #9: 0x0000000107eab2c3 UIKitCore`__34-[UIApplication _firstCommitBlock]_block_invoke_2 + 128
frame #10: 0x0000000105081cbc CoreFoundation`__CFRUNLOOP_IS_CALLING_OUT_TO_A_BLOCK__ + 12
frame #11: 0x0000000105081480 CoreFoundation`__CFRunLoopDoBlocks + 336
frame #12: 0x000000010507bd04 CoreFoundation`__CFRunLoopRun + 1252
frame #13: 0x000000010507b4d2 CoreFoundation`CFRunLoopRunSpecific + 626
frame #14: 0x000000010d6bf2fe GraphicsServices`GSEventRunModal + 65
frame #15: 0x0000000107e91fc2 UIKitCore`UIApplicationMain + 140
frame #16: 0x0000000103de76a0 CALayerProcessDemo`main(argc=1, argv=0x00007ffeebe17ea8) at main.m:14:16
frame #17: 0x0000000106a00541 libdyld.dylib`start + 1
frame #18: 0x0000000106a00541 libdyld.dylib`start + 1
- 從調(diào)用棧中可以看到在調(diào)用
drawRect之前刻撒，還會(huì)調(diào)用-[CALayer _display]（視圖繪制）、-[CALayer drawInContext:]（默認(rèn)調(diào)用）耿导、-[UIView(CALayerDelegate) drawLayer:inContext:]（自定義繪制流程）等方法声怔，我們?cè)囍鴮?shí)現(xiàn)drawLayer:inContext時(shí)，發(fā)現(xiàn)drawRect不會(huì)再走舱呻。
下面我們通過(guò)自定義CALayer醋火，來(lái)分析下系統(tǒng)的CALayer到底做了什么：
@protocol LLayerDelegate <NSObject>
- (void)l_layoutSublayersOfLayer:(CALayer *)layer;
- (void)l_displayLayer:(CALayer *)layer;
- (void)l_drawLayer:(CALayer *)layer inContext:(CGContextRef)ctx;
- (CGContextRef)l_beginDraw;
- (void)l_endDraw;
@end
@interface LLayer : CALayer
@end
@implementation LLayer
- (void)layoutSublayers { //這個(gè)會(huì)調(diào)用UIView layoutSubviews
__strong id <LLayerDelegate> delegate = (id<LLayerDelegate>)self.delegate;
if ([delegate respondsToSelector:@selector(l_layoutSublayersOfLayer:)]) {
//調(diào)用代理的實(shí)現(xiàn)
}
}
- (void)display {
//詢(xún)問(wèn)代理繪制
__strong id <LLayerDelegate> delegate = (id<LLayerDelegate>)self.delegate;
CGContextRef context = [delegate l_beginDraw];
//如何繪制
[delegate l_drawLayer:self inContext:context];
[delegate l_displayLayer:self];
[delegate l_endDraw];
}
@end
@interface LCustomLayerView()<LLayerDelegate>
@end
@implementation LCustomLayerView
//下面我們模擬下layer的執(zhí)行流程
//layer走自定義的
+ (Class)layerClass {
return [LLayer class];
}
#pragma -mark LLayerDelegate
- (void)l_layoutSublayersOfLayer:(CALayer *)layer {
[self layoutSubviews];
}
- (CGContextRef)l_beginDraw {
//開(kāi)始繪制，并返回context
UIGraphicsBeginImageContextWithOptions(self.bounds.size, self.layer.opaque, self.layer.contentsScale);
CGContextRef cRef = UIGraphicsGetCurrentContext();
return cRef;
}
- (void)l_drawLayer:(CALayer *)layer inContext:(CGContextRef)ctx {
[[UIColor blueColor] set];
UIBezierPath *path = [UIBezierPath bezierPathWithRect:CGRectMake(self.bounds.size.width/2.0 - 30, self.bounds.size.height/2.0 - 30, 60, 60)];
CGContextAddPath(ctx, path.CGPath);
CGContextFillPath(ctx);
}
//自定義繪制
- (void)l_displayLayer:(CALayer *)layer {
UIImage *img = UIGraphicsGetImageFromCurrentImageContext();
dispatch_async(dispatch_get_main_queue(), ^{
layer.contents = (__bridge id _Nullable)(img.CGImage);
});
}
- (void)l_endDraw {
UIGraphicsEndImageContext();
}
@end
@implementation ViewController
- (void)viewDidLoad {
[super viewDidLoad];
// Do any additional setup after loading the view.
[self.view addSubview:self.clView];
}
- (LCustomLayerView *)clView {
if (!_clView) {
_clView = [LCustomLayerView new];
_clView.frame = CGRectMake(50, 100, 200, 200);
_clView.backgroundColor = [UIColor orangeColor];
}
return _clView;
}
@end
-
補(bǔ)充
- 重新布局方法箱吕，
layoutSubviews調(diào)用時(shí)機(jī)：
- 延時(shí)執(zhí)行
- 被添加到父視圖中
- 添加子控件
- 尺寸發(fā)生變化
- 子控件尺寸發(fā)生變化
- 滾動(dòng)
UIScrollView - 旋轉(zhuǎn)屏幕
-
setNeedsLayout芥驳，且有布局需要更新
- 立即執(zhí)行
- 調(diào)用
layoutIfNeeded時(shí)且有變化會(huì)立即觸發(fā)
- 調(diào)用
- 重新繪制方法，
drawRect調(diào)用時(shí)機(jī)
- 在
loadView殖氏，viewDidLoad方法之后調(diào)用 -
View初始化時(shí)沒(méi)有設(shè)置rect大小晚树，將直接導(dǎo)致drawRect不會(huì)被調(diào)用 - 在調(diào)用
sizeThatFits后被調(diào)用，可以先調(diào)用sizeToFit計(jì)算出size雅采，然后系統(tǒng)自動(dòng)調(diào)用drawRect - 通過(guò)設(shè)置
contentMode為UIViewContentModeRedraw爵憎，每次設(shè)置或更改frame的時(shí)候自動(dòng)調(diào)用drawRect -
rect不為0，調(diào)用setNeedsDisplay或setNeedsDisplayInRect會(huì)觸發(fā)
