Use of iOS multi-thread nsoperation

• Steps for using Nsoperation objects

The Nsoperation object describes an operation task, and the Nsoperationqueue object describes a task queue, which is equivalent to GCD dispatch_queue_t

Nsoperation and Nsoperationqueue can be task is object-oriented encapsulation above GCD

GCD provides a lower level of control, and Nsoperationqueue implements some handy features on top of GCD, which are often the best and safest choice for developers

Basic Use steps:

1) define the operation queue

2) Define the operation

3) Adding actions to the queue

Tip: Once the operation is added to the queue, the operation is immediately scheduled for execution

• Task Queue Object

Nsoperationqueue describes the task queue, using two types of queues:

1) The home row, where the task is executed only in the main thread, as in the GCD master queue

+ (Nsoperationqueue *) mainqueue

2) Custom queue, where tasks are executed in child threads, as with GCD global queues

Create using the Alloc+init method

Other ways to Nsoperationqueue:

-(void) cancelalloperations//Cancel All Tasks-(void) waituntilalloperationsarefinished//wait until all tasks end @property Nsinteger Maxconcurrentoperationcount//Queue maximum number of concurrent tasks @property (assign) dispatch_queue_t Underlyingqueue//gcd the underlying queue

• Task object and its subclasses

Nsoperation describes a task that is an abstract type and should use its subclasses

Nsblockoperation and Nsinvocationoperation

1) Nsblockoperation uses block to describe a task:

+ (Instancetype) Blockoperationwithblock: (void (^) (void)) block

You can also add a block to describe multiple tasks

-(void) Addexecutionblock: (void (^) (void)) block

2) Nsinvocationoperation How to use a task:

-(Instancetype) Initwithtarget: (ID) Target selector: (SEL) Sel object: (ID) arg

The specified method can have a return value, using the result property to get

@property (ReadOnly, retain) ID result

• Add a task to the Task level column

To use the Addoperation method of a task queue object:

-(void) Addoperation: (nsoperation *) operation//does not block execution of the current thread-(void) Addoperations: (nsarray<nsoperation *> *) Ops Waituntilfinished: (BOOL) wait//can block the current thread

There is also a way to add tasks that directly pass the BLOCK:

-(void) Addoperationwithblock: (void (^) (void)) block

Summary: Three ways to add tasks:

1) Addoperationwithblock:

2) Add Nsblockoperation task

3) Add Nsinvocationoperation task

• Download Images asynchronously

Task 1:bo1 object that describes a download task

Task 2:bo2 object that displays the downloaded image object

Task 1 is added to the custom task queue, and the child thread executes the

Task 2 is added to the primary queue and executed on the main thread

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• Dependency of the task

task dependencies make it easy to control the sequencing of multiple task executions

Add dependencies using Nsoperation's adddependency: Method

-(void) Adddependency: (nsoperation *) operation

Such as: Modify the above code

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Where Self.img is a newly added UIImage property

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Use of iOS multi-thread nsoperation