ios 如何创建自己的完成处理程序作为方法参数的一部分
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How do I create my own completion handler as part of method parameters
提问by user2070259
I want to create a completion handler for a certain class, instead of firing off the class's main code and waiting for a delegate callback. I've read through the Apple documentation and they don't seem to give a very good example of how to directly implement something like this.
我想为某个类创建一个完成处理程序，而不是触发类的主代码并等待委托回调。我已经通读了 Apple 文档，他们似乎没有给出一个很好的例子来说明如何直接实现这样的东西。
回答by Chris C
You need to treat the completion block just like a variable. The method will accept a block as part of it's parameters, then store it for later.
您需要像对待变量一样对待完成块。该方法将接受一个块作为其参数的一部分，然后将其存储以备后用。
- (void)myMethodWithCompletionHandler:(void (^)(id, NSError*))handler;
- (void)myMethodWithCompletionHandler:(void (^)(id, NSError*))handler;
You can typedef that block type for easier reading:
您可以 typedef 该块类型以便于阅读：
typedef void (^CompletionBlock)(id, NSError*);
typedef void (^CompletionBlock)(id, NSError*);
And then store your block as an instance variable:
然后将您的块存储为实例变量：
In your @interface: CompletionBlock _block;
在您的@interface 中： CompletionBlock _block;
In the myMethod.. _block = [handler copy]
在我的方法.. _block = [handler copy]
Then when you want the completion block to execute you just call it like a regular block:
然后，当您希望完成块执行时，您只需像常规块一样调用它：
_block(myData, error);
_block(myData, error);
回答by Paul.s
If it was for an asynchronous method you could do it like this
如果是异步方法，你可以这样做
- (void)asynchronousTaskWithCompletion:(void (^)(void))completion;
{
dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
// Some long running task you want on another thread
dispatch_async(dispatch_get_main_queue(), ^{
if (completion) {
completion();
}
});
});
}
this would be invoked with
这将被调用
[self asynchronousTaskWithCompletion:^{
NSLog(@"It finished");
}];
Something to note is the guard to make sure that completionis pointing to something otherwise we will crash if we try to execute it.
需要注意的是警卫要确保它completion指向某个东西，否则如果我们尝试执行它，我们就会崩溃。
Another way I often use blocks for completion handlers is when a viewController has finished and want's to be popped from a navigation stack.
我经常使用块作为完成处理程序的另一种方式是当 viewController 完成并希望从导航堆栈中弹出时。
@interface MyViewController : UIViewController
@property (nonatomic, copy) void (^onCompletion)(void);
@end
@implementation MyViewController
- (IBAction)doneTapped;
{
if (self.onCompletion) {
self.onCompletion();
}
}
@end
You would set the completion block when pushing this view onto the stack
将此视图推入堆栈时，您将设置完成块
- (void)prepareForSegue:(UIStoryboardSegue *)segue sender:(id)sender;
{
MyViewController *myViewController = segue.destinationViewController;
myViewController.onCompletion = ^{
[self.navigationController popViewControllerAnimated:YES];
};
}
回答by realtimez
Heres an example for a method that takes a String and a completion handler as variables. The completion handler can also receive a String.
这是一个将字符串和完成处理程序作为变量的方法的示例。完成处理程序也可以接收一个字符串。
Swift 2.2 Syntax
Swift 2.2 语法
Defintion:
定义：
func doSomething(input: String, completion: (result: String) -> Void {
print(input)
completion(result: "we are done!")
}
Calling the function:
调用函数：
doSomething("cool put string!") { (result) in
print(result)
}
回答by Peter
Chris C's answer is correct (and was very helpful to me) with one caveat:
Chris C 的回答是正确的（对我很有帮助），但有一个警告：
Placing the declaration CompletionBlock _block;in @interfaceis not thread safe.
将声明CompletionBlock _block;放入@interface不是线程安全的。
Put CompletionBlock _block = [handler copy];in myMethod…instead if there is any possibility that myMethod…will be called from multiple threads (or dispatch queues).
把CompletionBlock _block = [handler copy];中myMethod…，而不是是否有任何可能myMethod…会从多个线程（或调度队列）被调用。
Thanks @Chris C.
谢谢@Chris C。
