在Swift中将闭包存储为变量 [英] store a closure as a variable in Swift
问题描述
在Objective-C中,您可以定义一个块的输入和输出,存储传递给方法的那些块,然后再使用该块:
// in .h
typedef void(^ APLCalibrationProgressHandler)(float percentComplete);
typedef void(^ APLCalibrationCompletionHandler)(NSInteger measuredPower,NSError * error);
// in .m
@property(strong)APLCalibrationProgressHandler progressHandler;
@property(strong)APLCalibrationCompletionHandler completionHandler;
- (id)initWithRegion:(CLBeaconRegion *)region completionHandler:(APLCalibrationCompletionHandler)handler
{
self = [super init];
if(self)
{
...
_completionHandler = [handler copy];
..
}
return self;
}
- (void)performCalibrationWithProgressHandler:(APLCalibrationProgressHandler)处理程序
{
...
self.progressHandler = ];
...
dispatch_async(dispatch_get_main_queue(),^ {
_completionHandler(0,error);
}
...
}
所以我试图做在Swift中:
var completionHandler:(Float) - > Void = {}
init(){
locationManager = CLLocationManager()
region = CLBeaconRegion()
timer = NSTimer()
}
方便init(region:CLBeaconRegion,handler:((Float) - > Void)){
self.init()
locationManager.delegate = self
self.region = region
completionHandler = handler
rangedBeacons = NSMutableArray()
}
像完成声明的Handler。
不是我的责任,但我如何定义一个闭包编译器在
上投诉 var completionHandler:(Float) - > Void = {}
,因为右侧不是适当签名的关闭,即关闭采用
a float参数。下面将给
完成处理程序分配一个do nothing闭包:
var completionHandler:(Float) > Void = {
(arg:Float) - >无效于
}
,可缩短为
var completionHandler:(Float) - > Void = {arg in}
$
初始化为
nil
,方法与将Objective-C实例变量初始化为
nil
相同。在Swift 中,这可以通过可选实现:
var completionHandler:( Float) - > Void)?
现在该属性自动初始化为 nil
(没有价值)。
在Swift中,您将使用可选绑定检查
完成处理程序是否具有值
if let handler = completionHandler {
handler(result)
}
:
completionHandler?(result)
In Objective-C, you can define a block's input and output, store one of those blocks that's passed in to a method, then use that block later:
// in .h
typedef void (^APLCalibrationProgressHandler)(float percentComplete);
typedef void (^APLCalibrationCompletionHandler)(NSInteger measuredPower, NSError *error);
// in .m
@property (strong) APLCalibrationProgressHandler progressHandler;
@property (strong) APLCalibrationCompletionHandler completionHandler;
- (id)initWithRegion:(CLBeaconRegion *)region completionHandler:(APLCalibrationCompletionHandler)handler
{
self = [super init];
if(self)
{
...
_completionHandler = [handler copy];
..
}
return self;
}
- (void)performCalibrationWithProgressHandler:(APLCalibrationProgressHandler)handler
{
...
self.progressHandler = [handler copy];
...
dispatch_async(dispatch_get_main_queue(), ^{
_completionHandler(0, error);
});
...
}
So I'm trying to do the equivilant in Swift:
var completionHandler:(Float)->Void={}
init(){
locationManager = CLLocationManager()
region = CLBeaconRegion()
timer = NSTimer()
}
convenience init(region: CLBeaconRegion, handler:((Float)->Void)){
self.init()
locationManager.delegate = self
self.region = region
completionHandler = handler
rangedBeacons = NSMutableArray()
}
The compiler doesn't like that declaration of completionHandler. Not that I blame it, but, how do I define a closure that can be set and used later in Swift?
The compiler complains on
var completionHandler: (Float)->Void = {}
because the right-hand side is not a closure of the appropriate signature, i.e. a closure taking a float argument. The following would assign a "do nothing" closure to the completion handler:
var completionHandler: (Float)->Void = {
(arg: Float) -> Void in
}
and this can be shortened to
var completionHandler: (Float)->Void = { arg in }
due to the automatic type inference.
But what you probably want is that the completion handler is initialized to nil
in the same way that an Objective-C instance variable is inititialized to nil
. In Swift
this can be realized with an optional:
var completionHandler: ((Float)->Void)?
Now the property is automatically initialized to nil
("no value").
In Swift you would use optional binding to check of a the
completion handler has a value
if let handler = completionHandler {
handler(result)
}
or optional chaining:
completionHandler?(result)
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