ios – 将值传递给UIView返回nil

我有一个UIViewController GamePlayViewController和一个UIView JoystickView.

我试图设置一个浮动值到JoystickView.

在GamePlayViewController.m中

JoystickView *joystick = [[JoystickView alloc] initWithFrame:CGRectMake(0, 0, 100, 100)];

joystick.velocity = 123.0f;
[self.view addSubview:joystick];

在JoystickView.h中

@property(nonatomic) float velocity;

.M

@synthesize velocity;
-(id)initWithFrame:(CGRect)frame {
self = [super initWithFrame:frame];
if (self) {
    NSLog(@"%f", velocity);        //output is 0
}
return self;
}

我错过了什么？

您可以通过创建initWithFrameAndVelocity方法来覆盖initWithFrame

-(id)initWithFrame:(CGRect)frame andVelocity:(float)v {
self = [super initWithFrame:frame];
if (self) {
velocity = v;
    NSLog(@"%f", velocity);        //output is 0
}
return self;
}