Some ways to use IOS---block (back-propagation)

A friend recently asked me how the block in iOS was used,

I told him about some of the practical applications I had learned.

Because I think this is mostly more practical,

Well nonsense not much to say that directly on the actual

------

In fact, using the block pass is usually the value, a page--> b page If it is positive, then we pass the value of the B page to A is called the reverse transfer value (or callback).

Steps:

1. Who sent the message, who wrote block (with the use of agents)

#import <UIKit/UIKit.h>

typedef void (^myblock) (NSString *str);


@interface Detailviewcontroller:uiviewcontroller

//Generate a block property
@property (nonatomic, copy) Myblock block;< c4/> @end

2. In the b.m file to pass the value---when the b page to disappear, call their own block pass value

-(void) Touchesbegan: (Nsset *) touches withevent: (Uievent *) event
{
    //calls its own block to pass it an argument
    nsstring *str = @ "Hello I am detail page incoming string";

    Block is based on the C language function, direct parameter invocation < specific implementation in the message receiver a>
    self.block (str);
    
    [Self Dismissviewcontrolleranimated:yes completion:^{
        
    }];
}

3. It is in the a page, received the value of B page passed-----< in the creation of a B page class instance, the implementation b.block receive its incoming parameters >

-(void) Touchesbegan: (Nsset *) touches withevent: (Uievent *) event
{
    Detailviewcontroller *detail = [ Detailviewcontroller alloc] init];
   
    Direct call to detail block implementation
    Detail.block = ^ (NSString *str) {
    
        //print incoming str
        NSLog (@ "str:%@", str);
    
    //Jump to Detail page
    [Self presentviewcontroller:detail animated:yes completion:^{
        
    }];
}

----------------------------This is the 3 songs used in block syntax--------------------

How is it not very simple.

Here's a look at the effect chart

============ Rear Extension ==========

Block of some of the small definition, the estimated understanding of the above has been a little read, only for reference

1.block can be used to save a piece of code, or to encapsulate a piece of code. ---> Code snippet, code block.

The logo of the 2.block is ^

3.block is like a function (in fact it is the C language function)

can save the code;

Can have a return value;

Can also have the row parameter;

Call the same way;

4. Define a block

#pragma mark block with no parameters

void (^outputblock) = ^{

NSLog (@ "------------");

};

Outputblock ();

}

5. Block with row parameters

#pragma mark-The block with parameters

Int (^sumblock) (int, int) = ^ (int a,int b) {

return a+b;

};

int sum = Sumblock (3,13);

int sum1 = Sumblock (1,2);

NSLog (@ "%d", sum1);

NSLog (@ "%d", sum);

#pragma mark-Output n horizontal line

The Declaration and implementation of block

void (^myblock) (int) = ^ (int n) {

for (int i = 0; i < n; i++) {

NSLog (@ "-----------------");

}
};

Call to block

Myblock (10);

6. If the block has no row parameters, you can omit the parentheses behind it.

7. Use a typedef to define the type of a block

typedef int (^myblock) (int,int);

Myblock Sumblock = ^ (int a,int b) {

return a+b;

}

Myblock minus = ^ (int a,int b) {

return a-b;

}

8.block can access variables outside, or modify external local variables

Must declare in advance

For example __block int a = 5;

A variable modified with __block can modify its value when the block is called

Postscript:

There's a lot of little knowledge about block, though.

Here I will first say so many, mainly can be practical, later I will as soon as possible to complete the knowledge of the block to write up for all the friends need to refer to.