Use of code blocks (block) for OBJECTIVE-C syntax

Code blocks are essentially similar to other variables. The difference is that the code block stores the data as a function body. With code blocks, you can pass in the number of parameters as you would call other standard functions, and get the return value.

The caret (^) is the syntax tag for the block. The return value defined by our familiar language rules and the body of the block (that is, code that can execute). How to assign a block variable to a variable's syntax explanation:

Calling the Block object variable in the way it calls the function will be able to:
int result = Myblock (4); Result is 28.

1. The number of references is the code block of nsstring*

        void (^printblock) (NSString *x);        Printblock = ^ (nsstring* str)        {            NSLog (@ "print:%@", str);        };        Printblock (@ "Hello world!");

The execution results are:Print:hello world!

2. The code is sorted in a string array

        Nsarray *stringarray = [Nsarray arraywithobjects:@ "ABC 1", @ "abc", @ "abc", @ "abc", @ "abc", nil];        Nscomparator Sortblock = ^ (ID string1, id string2)        {            return [string1 compare:string2];        };        Nsarray *sortarray = [Stringarray sortedarrayusingcomparator:sortblock];        NSLog (@ "sortarray:%@", Sortarray);

Execution Result:Sortarray: (

"ABC 05",

"ABC 1",

"ABC 12",

"ABC 13",

"ABC 21"

)

3. Recursive invocation of code blocks

Code blocks want to be called recursively, the block variable must be a global variable or a static variable, so that the code block variable is initialized when the program starts, and can be called recursively

        static void (^ const blocks) (int) = ^ (int i)        {            if (i > 0) {                NSLog (@ "num:%d", I);                Blocks (i-1);            }        };        Blocks (3);

To perform the printed result:

Num:3

Num:2

Num:1

 4. Use local variables and global variables in code blocks to use and change global variables in code blocks

int global = 1000;int main (int argc, const char * argv[]) {    @autoreleasepool {        void (^block) (void) = ^ (void)        {            global++;            NSLog (@ "global:%d", global);        };        Block ();        NSLog (@ "global:%d", global);    }    return 0;}

To perform the printed result:

global:1001

global:1001

Local variables can be used, but they cannot be changed.

        int local = $;        void (^block) (void) = ^ (void)        {//            local++;            NSLog (@ "local:%d", local);        };        Block ();        NSLog (@ "local:%d", local);

Changing the local variable compilation in the code block does not pass. How do you change local variables in a block of code? Precede a local variable with Keyword:__block

        __block int local = n;        void (^block) (void) = ^ (void)        {            local++;            NSLog (@ "local:%d", local);        };        Block ();        NSLog (@ "local:%d", local);

Execution Result:local:501

local:501

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Use of code blocks (block) for OBJECTIVE-C syntax