ios - 是否可以将多个 UIGravityBehaviors 添加到 UIDynamicAnimator？

Question

我正在尝试创建一个 View ，其中一些项目沿正常重力矢量落下，而其他项目沿相反矢量落下

self.animator = [[UIDynamicAnimator alloc] initWithReferenceView:self];

// Normal Gravity
self.gravityBehavior = [[UIGravityBehavior alloc] initWithItems:@[ ]];
self.gravityBehavior.gravityDirection = CGVectorMake(0, 1);
[self.animator addBehavior:self.gravityBehavior];

// Inverse Gravity
self.inverseGravityBehavior = [[UIGravityBehavior alloc] initWithItems:@[ ]];
self.inverseGravityBehavior.gravityDirection = CGVectorMake(0, -1);
[self.animator addBehavior:self.inverseGravityBehavior];

我想我可以只在一个行为中添加一些项目，在另一个行为中添加一些项目，但似乎添加第二个重力行为会覆盖第一个？

    [self.gravityBehavior        addItem: ballA];
    [self.inverseGravityBehavior addItem: ballB];

这是真的吗，如果是这样，还有其他方法可以达到这种效果吗？

Answer 1

这种行为绝对是可能的。但是，无法通过使用不同 UIGravityBehavior 的动画师来实现。 s。

一种解决方案是使用两个 UIDynamicAnimator实例，每个实例都有自己的 UIGravityBehavior实例。下面是一个 View Controller 的示例，它附加了两个点击手势识别器，一个用于单击，一个用于双击。单曲将添加一个对正常重力作出 react 的 View 。双击添加了一个对倒置重力使用react的 View 。显然，需要对代码进行调整以符合您的特定要求。

#import "ViewController.h"

@interface ViewController ()

@property (nonatomic, strong) UIDynamicAnimator *animator;
@property (nonatomic, strong) UIDynamicAnimator *secondAnimator;

@property (nonatomic, strong) UIGravityBehavior *normalGravity;
@property (nonatomic, strong) UIGravityBehavior *inverseGravity;

@end

@implementation ViewController

- (void)viewDidLoad {
    [super viewDidLoad];
    // Do any additional setup after loading the view, typically from a nib.
    self.animator = [[UIDynamicAnimator alloc] initWithReferenceView:self.view];

    self.normalGravity = [[UIGravityBehavior alloc] init];
    [self.animator addBehavior:self.normalGravity];

    self.secondAnimator = [[UIDynamicAnimator alloc] initWithReferenceView:self.view];
    self.inverseGravity = [[UIGravityBehavior alloc] init];
    [self.inverseGravity setAngle:self.normalGravity.angle magnitude:(-1.0 * self.normalGravity.magnitude)];
    [self.secondAnimator addBehavior:self.inverseGravity];
}

- (void)didReceiveMemoryWarning {
    [super didReceiveMemoryWarning];
    // Dispose of any resources that can be recreated.
}


- (IBAction)viewWasTapped:(id)sender {
    UIView *v = [[UIView alloc] initWithFrame:CGRectMake(30, 10, 25, 25)];
    v.backgroundColor = [UIColor redColor];
    [self.view addSubview:v];
    [self.normalGravity addItem:v];
}

- (IBAction)viewWasDoubleTapped:(id)sender {
    UIView *v = [[UIView alloc] initWithFrame:CGRectMake(90, 400, 25, 25)];
    v.backgroundColor = [UIColor greenColor];
    [self.view addSubview:v];
    [self.inverseGravity addItem:v];
}

@end

第二种选择是使用 UIPushBehavior模拟倒置重力。下面是一个类似设置的 View Controller ，但没有第二个动画师并使用推送行为。

#import "ViewController.h"

@interface ViewController ()

@property (nonatomic, strong) UIDynamicAnimator *animator;

@property (nonatomic, strong) UIGravityBehavior *normalGravity;
@property (nonatomic, strong) UIPushBehavior *pushBehavior;

@end

@implementation ViewController

- (void)viewDidLoad {
    [super viewDidLoad];
    // Do any additional setup after loading the view, typically from a nib.
    self.animator = [[UIDynamicAnimator alloc] initWithReferenceView:self.view];

    self.normalGravity = [[UIGravityBehavior alloc] init];
    [self.animator addBehavior:self.normalGravity];

    self.pushBehavior = [[UIPushBehavior alloc] initWithItems:@[] mode:UIPushBehaviorModeContinuous];
    [self.pushBehavior setAngle:self.normalGravity.angle magnitude:(-1.0 * self.normalGravity.magnitude)];
    [self.animator addBehavior:self.pushBehavior];
}

- (void)didReceiveMemoryWarning {
    [super didReceiveMemoryWarning];
    // Dispose of any resources that can be recreated.
}


- (IBAction)viewWasTapped:(id)sender {
    UIView *v = [[UIView alloc] initWithFrame:CGRectMake(30, 10, 25, 25)];
    v.backgroundColor = [UIColor redColor];
    [self.view addSubview:v];
    [self.normalGravity addItem:v];
}

- (IBAction)viewWasDoubleTapped:(id)sender {
    UIView *v = [[UIView alloc] initWithFrame:CGRectMake(90, 400, 25, 25)];
    v.backgroundColor = [UIColor greenColor];
    [self.view addSubview:v];

    [self.pushBehavior addItem:v];
}

@end

在所有情况下，请确保您正在管理受 UIDynamicAnimator 影响的项目。以及各种行为，这样您就不会不断地添加它们并让模拟陷入困境。