将一个RunLoop的一些耗时任务分拆到多个RunLoop里面处理
需求：cell 里面需要加载大图（3M），保证Cell滚动的时候，UITableView不卡顿
卡顿原因：
在一次runloop中绘制大量的图片，所以UI会卡顿
解决方案：(一次runloop，只绘制一张图片)
- 1、监听Runloop 循环，循环一次，调用一次回调函数
- 2、回调函数里面做加载图片的事情（执行一次任务）
- 3、提供一个添加任务的方法，不要直接加载图片，你将加载图片的代码都给RunLoop
- 4、回调函数里面将任务一个一个取出来
- 5、手动向 RunLoop 中添加 Source 任务（由应用发起和处理的是 Source 0 任务）。通过开启定时，NSTimeInterval = 0.001
#import "ViewController.h"
typedef BOOL(^RunloopBlock)(void);
static NSString *IDENTIFIER = @"IDENTIFIER";
static CGFloat CELL_HEIGHT = 135.f;
@interface ViewController () <UITableViewDataSource, UITableViewDelegate>
@property (nonatomic, strong) NSMutableArray *tasks;
@property (nonatomic, strong) NSMutableArray *tasksKeys;
@property (nonatomic, assign) NSUInteger max;
@property (nonatomic, strong) NSTimer * timer;
@property (nonatomic, strong) UITableView *exampleTableView;
@end
@implementation ViewController
- (void)viewDidLoad {
[super viewDidLoad];
_max = 20;
_tasks = [NSMutableArray array];
_tasksKeys = [NSMutableArray array];
self.exampleTableView = [[UITableView alloc] initWithFrame:self.view.bounds];
self.exampleTableView.delegate = self;
self.exampleTableView.dataSource = self;
[self.exampleTableView registerClass:[UITableViewCell class] forCellReuseIdentifier:IDENTIFIER];
[self.view addSubview:self.exampleTableView];
_timer = [NSTimer scheduledTimerWithTimeInterval:0.001 target:self selector:@selector(_timerFiredMethod) userInfo:nil repeats:YES];
[self addRunloopObserver];
}
- (void)_timerFiredMethod{
}
+ (void)addImage1With:(UITableViewCell *)cell{
UIImageView *imageView = [[UIImageView alloc] initWithFrame:CGRectMake(5, 20, 85, 85)];
imageView.tag = 1;
NSString *path1 = [[NSBundle mainBundle] pathForResource:@"spaceship" ofType:@"png"];
UIImage *image = [UIImage imageWithContentsOfFile:path1];
imageView.contentMode = UIViewContentModeScaleAspectFit;
imageView.image = image;
[UIView transitionWithView:cell.contentView duration:0.3 options:(UIViewAnimationOptionCurveEaseInOut | UIViewAnimationOptionTransitionCrossDissolve) animations:^{
[cell.contentView addSubview:imageView];
} completion:nil];
}
+ (void)addImage2With:(UITableViewCell *)cell{
UIImageView *imageView1 = [[UIImageView alloc] initWithFrame:CGRectMake(105, 20, 85, 85)];
imageView1.tag = 2;
NSString *path1 = [[NSBundle mainBundle] pathForResource:@"spaceship" ofType:@"png"];
UIImage *image1 = [UIImage imageWithContentsOfFile:path1];
imageView1.contentMode = UIViewContentModeScaleAspectFit;
imageView1.image = image1;
[UIView transitionWithView:cell.contentView duration:0.3 options:(UIViewAnimationOptionCurveEaseInOut | UIViewAnimationOptionTransitionCrossDissolve) animations:^{
[cell.contentView addSubview:imageView1];
} completion:nil];
}
+ (void)addImage3With:(UITableViewCell *)cell{
UIImageView *imageView2 = [[UIImageView alloc] initWithFrame:CGRectMake(200, 20, 85, 85)];
imageView2.tag = 3;
NSString *path1 = [[NSBundle mainBundle] pathForResource:@"spaceship" ofType:@"png"];
UIImage *image2 = [UIImage imageWithContentsOfFile:path1];
imageView2.contentMode = UIViewContentModeScaleAspectFit;
imageView2.image = image2;
[UIView transitionWithView:cell.contentView duration:0.3 options:(UIViewAnimationOptionCurveEaseInOut | UIViewAnimationOptionTransitionCrossDissolve) animations:^{
[cell.contentView addSubview:imageView2];
} completion:nil];
}
#pragma mark - UITableViewDelegate
- (CGFloat)tableView:(UITableView *)tableView heightForRowAtIndexPath:(NSIndexPath *)indexPath {
return CELL_HEIGHT;
}
#pragma mark - UITableViewDataSource
- (NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section {
return 399;
}
- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath {
UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:IDENTIFIER];
cell.selectionStyle = UITableViewCellSelectionStyleNone;
for (NSInteger i = 1; i <= 3; i++) {
[[cell.contentView viewWithTag:i] removeFromSuperview];
}
//不要直接加载图片!! 你将加载图片的代码!都给RunLoop!!
[self addTask:^BOOL{
[ViewController addImage1With:cell];
return YES;
} withKey:indexPath];
[self addTask:^BOOL{
[ViewController addImage2With:cell];
return YES;
} withKey:indexPath];
[self addTask:^BOOL{
[ViewController addImage3With:cell];
return YES;
} withKey:indexPath];
return cell;
}
#pragma mark - <RunLoop>
- (void)addTask:(RunloopBlock)unit withKey:(id)key{
[self.tasks addObject:unit];
[self.tasksKeys addObject:key];
if (self.tasks.count > self.max) {
[self.tasks removeObjectAtIndex:0];
[self.tasksKeys removeObjectAtIndex:0];
}
}
//定义一个回调函数 一次RunLoop来一次
static void Callback(CFRunLoopObserverRef observer, CFRunLoopActivity activity, void *info){
ViewController * vc = (__bridge ViewController *)(info);
if (vc.tasks.count == 0) {
return;
}
BOOL result = NO;
while (result == NO && vc.tasks.count) {
RunloopBlock unit = vc.tasks.firstObject;
//执行任务
result = unit();
[vc.tasks removeObjectAtIndex:0];
[vc.tasksKeys removeObjectAtIndex:0];
}
}
// 添加一个监听者
- (void)addRunloopObserver{
CFRunLoopRef runloop = CFRunLoopGetCurrent();
CFRunLoopObserverContext context = {
0,
( __bridge void *)(self),
&CFRetain,
&CFRelease,
NULL
};
static CFRunLoopObserverRef defaultModeObsever;
defaultModeObsever = CFRunLoopObserverCreate(NULL,
kCFRunLoopBeforeWaiting,
YES,
NSIntegerMax - 999,
&Callback,
&context
);
//添加当前RunLoop的观察者
CFRunLoopAddObserver(runloop, defaultModeObsever, kCFRunLoopDefaultMode);
CFRelease(defaultModeObsever);
}
另一种解决方案：
利用RunLoop空闲时间执行预缓存任务（孙源大神的UITableView-FDTemplateLayoutCell）
需求：
利用RunLoop空闲时间执行预缓存任务（cell高度的计算）
解决方案：
- 1、分解成多个RunLoop Source任务
- 2、RunLoop 处于休眠状态，则唤醒它处理事件
- 3、每个 RunLoopObserver 回调时都把第一个任务拿出来分发
假设列表有 20 个 cell，加载后展示了前 5 个，那么开启估算后 table view 只计算了这 5 个的高度，此时剩下 15 个就是“预缓存”的任务，而我们并不希望这 15 个计算任务在同一个 RunLoop 迭代中同步执行，这样会卡顿 UI，所以应该把它们分别分解到 15 个 RunLoop 迭代中执行，这时就需要手动向 RunLoop 中添加 Source 任务（由应用发起和处理的是 Source 0 任务）
NSMutableArray *mutableIndexPathsToBePrecached = self.fd_allIndexPathsToBePrecached.mutableCopy;
CFRunLoopObserverRef observer = CFRunLoopObserverCreateWithHandler(kCFAllocatorDefault, kCFRunLoopBeforeWaiting, true, 0, ^(CFRunLoopObserverRef observer, CFRunLoopActivity _) {
if (mutableIndexPathsToBePrecached.count == 0) {
CFRunLoopRemoveObserver(runLoop, observer, runLoopMode);
CFRelease(observer); // 注意释放，否则会造成内存泄露
return;
}
NSIndexPath *indexPath = mutableIndexPathsToBePrecached.firstObject;
[mutableIndexPathsToBePrecached removeObject:indexPath];
[self performSelector:@selector(fd_precacheIndexPathIfNeeded:)
onThread:[NSThread mainThread]
withObject:indexPath
waitUntilDone:NO
modes:@[NSDefaultRunLoopMode]];
});
每个任务都被分配到下个“空闲” RunLoop 迭代中执行，其间但凡有滑动事件开始，Mode 切换成 UITrackingRunLoopMode，所有的“预缓存”任务的分发和执行都会自动暂定，最大程度保证滑动流畅。
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