Block 語法基礎

Declaring and Using a Block（定義和使用Block）

1— 無參的block

// 1 無參
        void (^myblocks) (void) = NULL;//聲明
        myblocks = ^(void){
            NSLog(@"myblocks");
        };// 給myblcok 賦值
myblocks(); //調用

2— 帶參的block

 

int multiplier = 7;
int (^myBlock)(int) = ^(int num) {
    return num * multiplier;
};
printf("%d",myBlock(3));
// prints "21"

 

 

3—— 有返回值，帶參block

 

int (^myblocks2) (int a, int b) = ^(int a ,int b){
            int c = a+b;
            return c;
        };
int ret = myblocks2(2,3);
   // prints  "5"

 

 

 

截至到目前位置，都先聲明瞭block，再對block 賦值！其實你完全可以直接使用一個block

 

Using a Block Directly

 

In many cases, you don’t need to declare block variables;（大部分情況下，你無需聲明一個block 變量）

本例子：將數組逆序

char *myCharacters[3] = { "TomJohn", "George", "Charles Condomine" };

qsort_b(myCharacters, 3, sizeof(char *), ^(const void *l, const void *r) {
    char *left = *(char **)l;
    char *right = *(char **)r;
    return strncmp(left, right, 1);
});

// myCharacters is now { "Charles Condomine", "George", "TomJohn" }

Blocks with Cocoa

 

Several methods in the Cocoa frameworks take a block as an argument, typically
either to perform an operation on a collection of objects, or to use as a callback
 after an operation has finished. The following example shows how to use a block with
 the NSArray method sortedArrayUsingComparator:. The method takes a single argument—the
 block. For illustration, in this case the block is defined as an NSComparator local
variable:

 take a block as an argument,（將block 作爲參數） typically either to perform an operation on a collection of objects, or to use as a callback after an operation has finished.（通常要麼執行操作在對象集合、或者操作回調）下面簡單的例子展示瞭如何在NSArray 的方法 sortedArrayUsingComparator: 中使用block，該方法將block作爲一個參數。爲了解釋說明，本例子的block被定義爲一個NSComparator 的本地變量。

本例子：NSArray 排序

NSArray *stringsArray = [NSArray arrayWithObjects:
                                 @"string 1",
                                 @"String 21",
                                 @"string 12",
                                 @"String 11",
                                 @"String 02", nil];

static NSStringCompareOptions comparisonOptions = NSCaseInsensitiveSearch | NSNumericSearch |
        NSWidthInsensitiveSearch | NSForcedOrderingSearch;
NSLocale *currentLocale = [NSLocale currentLocale];

NSComparator finderSortBlock = ^(id string1, id string2) {

    NSRange string1Range = NSMakeRange(0, [string1 length]);
    return [string1 compare:string2 options:comparisonOptions range:string1Range locale:currentLocale];
};

NSArray *finderSortArray = [stringsArray sortedArrayUsingComparator:finderSortBlock];
NSLog(@"finderSortArray: %@", finderSortArray);

/*
Output:
finderSortArray: (
    "string 1",
    "String 02",
    "String 11",
    "string 12",
    "String 21"
)
*/

__block Variables（__block 變量（關鍵字））

__block 修飾臨時變量，可讓其變爲全局的變量。（引用自身作用域外的變量）

__block 參數全局聲明

__block int sum = 0;
int (^myblock3) (int a,int b) = ^(int a ,int b){
    sum = a+b;
    return sum;
};
ret = myblock3(2,3);
NSLog(@"block3 %d",ret);

NSArray *stringsArray = [NSArray arrayWithObjects:
                         @"string 1",
                         @"String 21", // <-
                         @"string 12",
                         @"String 11",
                         @"Strîng 21", // <-
                         @"Striñg 21", // <-
                         @"String 02", nil];

NSLocale *currentLocale = [NSLocale currentLocale];
__block NSUInteger orderedSameCount = 0;

NSArray *diacriticInsensitiveSortArray = [stringsArray sortedArrayUsingComparator:^(id string1, id string2) {

    NSRange string1Range = NSMakeRange(0, [string1 length]);
    NSComparisonResult comparisonResult = [string1 compare:string2 options:NSDiacriticInsensitiveSearch range:string1Range locale:currentLocale];

    if (comparisonResult == NSOrderedSame) {
        orderedSameCount++;
    }
    return comparisonResult;
}];

NSLog(@"diacriticInsensitiveSortArray: %@", diacriticInsensitiveSortArray);
NSLog(@"orderedSameCount: %d", orderedSameCount);

/*
Output:

diacriticInsensitiveSortArray: (
    "String 02",
    "string 1",
    "String 11",
    "string 12",
    "String 21",
    "Str\U00eeng 21",
    "Stri\U00f1g 21"
)
orderedSameCount: 2
*/