因此，我在 animateWithDuration 方法的帮助下完成了动画，但我需要在应用程序进入后台时停止动画，并在应用程序返回前台时恢复动画。
有什么方法可以实现这一点：-
我的动画：标签在一定时间间隔后淡入淡出；
- (void)viewDidLoad {
[super viewDidLoad];
[self MyLabelAnimation];
}
- (void)MyLabelAnimation {
self.myLabel.text = @"Text 1";
[UIView animateWithDuration:0.3 animations:^{
self.myLabel.alpha = 1.0;
} completion:^(BOOL finished) {
[UIView animateWithDuration:0.3 delay:2.7 options:UIViewAnimationOptionCurveEaseInOut animations:^{
self.myLabel.alpha = 0.0;
} completion:^(BOOL finished) {
self.myLabel.text = @"Text 2";
[UIView animateWithDuration:0.3 animations:^{
self.myLabel.alpha = 1.0;
} completion:^(BOOL finished) {
[UIView animateWithDuration:0.3 delay:2.7 options:UIViewAnimationOptionCurveEaseInOut animations:^{
self.myLabel.alpha = 0.0;
} completion:^(BOOL finished) {
self.myLabel.text = @"Text 3";
[UIView animateWithDuration:0.3 animations:^{
self.myLabel.alpha = 1.0;
} completion:^(BOOL finished) {
[UIView animateWithDuration:0.3 delay:2.7 options:UIViewAnimationOptionCurveEaseInOut animations:^{
self.myLabel.alpha = 0.0;
} completion:^(BOOL finished) {
self.myLabel.text = @"Text 4";
[UIView animateWithDuration:0.3 animations:^{
self.myLabel.alpha = 1.0;
} completion:^(BOOL finished) {
[UIView animateWithDuration:0.0 delay:4.8 options:UIViewAnimationOptionCurveEaseInOut animations:^{
self.myLabel.alpha = 0.0;
} completion:^(BOOL finished) {
[self MyLabelAnimation];
}];
}];
}];
}];
}];
}];
}];
}];
}
由于您的动画似乎是无限重复的几个较小的子动画的序列，因此您可以始终跟踪动画循环中的位置，在应用程序变为非活动状态时停止动画，并在应用程序变为非活动状态时重新启动动画再次变得活跃。
[编辑：下面添加了示例代码和解释。]
In ViewController.m:
@interface ViewController ()
{
int numStages; // 4 * 3 = 12 in our example (4 different text labels,
// with 3 substages (alpha ramping up, alpha constant, and alpha ramping down) for each)
int globalStage; // varies from 0 to numStages - 1. 0 initially
bool animationIsActive;
}
@end
@implementation ViewController
- (void)viewDidLoad {
[super viewDidLoad];
// Do any additional setup after loading the view, typically from a nib.
numStages = 4 * 3; // 4 * 3 = 12 in our example (4 different text labels,
// with 3 substages for each text label's appearance (alpha ramping up, alpha constant, and alpha ramping down))
globalStage = 0; // varies from 0 to numStages - 1. 0 initially
animationIsActive = NO;
self.myLabel.alpha = 0.0;
}
- (void)animateStage:(int)stage {
NSLog(@"animateStage called with argument stage = %d", stage);
// make a note in our instance variable of where we need to restart
// the animation THE NEXT TIME if it is interrupted or paused
// during the current animation:
globalStage = (stage + 1) % numStages;
self.myLabel.text = [NSString stringWithFormat:@"Text %d", (stage / 3) + 1];
switch (stage % 3) {
case 0: // ramp up alpha from 0 to 1
{
[UIView animateWithDuration:0.3 animations:^{
self.myLabel.alpha = 1.0;
} completion:^(BOOL finished) {
// only proceed to next stage if the animation is supposed to be active:
if (animationIsActive) {
[self animateStage:globalStage];
}
}];
}
break;
case 1: // keep alpha constant at 1 (see comment below)
{
[UIView animateWithDuration:2.7 animations:^{
self.myLabel.alpha = 0.99999; // changing the 0.99999 to 1.0 causes
// this stage to be short-circuited. probably because iOS realizes
// that alpha is not really changing in this stage and, being too clever
// by half, decides to skip this stage altogether. but 0.99999 is
// as close to 1.0 as makes no difference.
} completion:^(BOOL finished) {
// only proceed to next stage if the animation is supposed to be active:
if (animationIsActive) {
[self animateStage:globalStage];
}
}];
}
break;
case 2: // ramp down alpha from 1 to 0
{
[UIView animateWithDuration:0.3 animations:^{
self.myLabel.alpha = 0.0;
} completion:^(BOOL finished) {
// only proceed to next stage if the animation is supposed to be active:
if (animationIsActive) {
[self animateStage:globalStage];
}
}];
}
break;
default:
break;
}
}
- (void)viewWillAppear:(BOOL)animated
{
NSLog(@"viewWillAppear: called");
[[NSNotificationCenter defaultCenter]
addObserver:self
selector:@selector(didBecomeActive:)
name:UIApplicationDidBecomeActiveNotification
object:[UIApplication sharedApplication]];
[[NSNotificationCenter defaultCenter]
addObserver:self
selector:@selector(willResignActive:)
name:UIApplicationWillResignActiveNotification
object:[UIApplication sharedApplication]];
}
- (void)viewDidDisappear:(BOOL)animated
{
NSLog(@"viewDidDisappear: called");
[[NSNotificationCenter defaultCenter]
removeObserver:self
name:UIApplicationDidBecomeActiveNotification
object:[UIApplication sharedApplication]];
[[NSNotificationCenter defaultCenter]
removeObserver:self
name:UIApplicationWillResignActiveNotification
object:[UIApplication sharedApplication]];
}
- (void)didBecomeActive:(NSNotification *)notification
{
NSLog(@"view controller's didBecomeActive: called");
// start the animation is we are stopped
if (!animationIsActive)
{
NSLog(@"animation being (re)started at stage %d", globalStage);
[self animateStage:globalStage];
animationIsActive = YES;
}
}
- (void)willResignActive:(NSNotification *)notification
{
NSLog(@"view controller's willResignActive: called");
// stop the animation
NSLog(@"animation being stopped at stage %d", globalStage);
animationIsActive = NO;
}
@end
- 我已将您的动画分解并“扁平化”为 4 * 3 = 12 个阶段，以便更好地控制。
- 实例变量
globalStage and animationIsActive用于跟踪我们在动画中的位置以及动画是否正在运行。
- In
viewWillAppear:我们要求在应用程序变为活动或非活动状态时收到通知。当这些事件发生时，我们的方法didBecomeActive: or willResignActive:叫做。这两个方法是我们（重新）开始和停止动画的地方。
- 不要忘记注销这两个
UIApplication中的通知viewDidDisappear:.
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