關於Blcok,我們經常使用,在Swift中,閉包更是無處不在。那麼,關於Block,我們到底瞭解多少呢?這篇文章旨在對Block做一次全面的總結,從簡單應用,到案例講解再到易錯點,以及原理和內存機制,爭取一文寫清楚Block。
拒絕搬磚,手寫代碼,全部測試。
知識點:
小小擴展:關於值的類型
1.Block的幾種用法
(1)作爲局部變量;
(2)作爲全局變量;
(3)Block作爲函數參數;
(4)Block作爲函數返回值;
(5)Block中使用局部變量和全局變量;
2.Block在項目中常用案例
(1)頁面傳值;
(2)代替代理使用;
(3)作爲參數傳值;
3.Block的循環引用問題
(1)問題產生原因;
(2)如何解決;
4.Block內存機制
5.Block原理
小小擴展:關於值的類型
我們知道,無論是變量、常量還是參數,都會有它的類型,我們一開始接觸一門語言的時候,都會詳細的介紹這門語言的各種類型。比如C的int, float, double, char, const char, char *, *, 等等類型,比如OC的NSString, NSArray, NSSet, NSValue等等類型。我們也知道,這些類型用來標誌一個值在內存中的存儲方式。把某個類型放在值的前面,用於聲明這個值的類型。比如:
int a;
char b;
NSString * name;
那麼,Block作爲匿名函數,它也是有類型的,不過它的類型比較複雜一些,是由簡單類型組合起來的類型。比如:
void (^block) (void)
類型是: void (^) (void)
NSString * (^block1) (void)
類型是:NSString * (^) (void)
NSInteger (^block3) (NSInteger, NSInteger)
類型是: NSInteger (^) (NSInteger, NSInteger)
明白了Block的類型,我們就可以把Block跟其他簡單類型一樣作爲參數,作爲變量進行使用了。
1.Block的幾種用法
(1)作爲局部變量;
//block作爲局部變量
-(void)test1 {
/**
返回值類型 (^Block名稱)(參數列表) = ^ 返回值類型 (參數列表){
實現代碼
}
*/
void (^block) (void) = ^ {
NSLog(@"返回值爲空,參數爲空的block");
};
//使用block
block();
NSString * (^block1) (void) = ^{
NSString * temp = @"返回值爲字符串,參數爲空的block";
return temp;
};
//使用
NSLog(@"%@", block1());
NSInteger (^block2) (NSInteger) = ^ NSInteger (NSInteger a){
NSInteger t = a * 10;
return t;
};
NSInteger test2 = block2(3);
NSLog(@"test2: %ld", (long)test2);
//求兩個數的和
NSInteger (^block3) (NSInteger, NSInteger) = ^ NSInteger (NSInteger a, NSInteger b) {
return a + b;
};
NSInteger test3 = block3(2, 7);
NSLog(@"test3: %ld", test3);
//求兩個數的乘積
double (^block4) (double, double) = ^double (double a, double b) {
return a * b;
};
NSLog(@"test4: %.2f", block4(2.3, 4.7));
//求兩個數的加減乘除運算
double (^block5) (double, double, NSString*) = ^ double (double a, double b, NSString* mark){
if ([mark isEqualToString:@"+"]) {
return a + b;
} else if ([mark isEqualToString:@"-"]) {
return a - b;
} else if ([mark isEqualToString:@"*"]) {
return a * b;
} else if ([mark isEqualToString:@"/"]) {
if (b == 0) {
return -1;
}
return a / b;
} else {
return -1;
}
};
NSLog(@"test5: %f", block5(4.0, 6.5, @"+"));
NSLog(@"test6: %f", block5(7.8, 6.5, @"-"));
NSLog(@"test7: %f", block5(2.4, 6.5, @"*"));
NSLog(@"test8: %f", block5(4.8, 2.4, @"/"));
//block賦值
double (^block6) (double, double) = block4;
//調用
NSLog(@"test9: %.2f", block6(2.1, 3.8));
}
打印結果:
(2)作爲全局變量;
//給block起別名
typedef NSInteger (^SumBlock) (NSInteger, NSInteger);
@interface BlockTestViewController ()
@property(nonatomic, copy)SumBlock block7;
@end
//block作爲全局變量
-(void)test2 {
self.block7 = ^ NSInteger (NSInteger a, NSInteger b) {
NSInteger sum = 0;
for (NSInteger i = a; i < b + 1; i++) {
sum = sum + I;
}
NSLog(@"從 %ld 到 %ld 的和爲 %ld", a, b, sum);
return sum;
};
if (self.block7) {
//調用
self.block7(0, 100);
self.block7(0, 50);
}
}
打印結果:
(3)Block作爲函數參數;
//請求成功
typedef void (^SuccessBlock)(NSDictionary* json, int code);
//請求失敗
typedef void (^FailBlock)(NSString* msg);
//調用test3系列:block作爲參數
-(void)test4 {
//有參數,有返回值的block作爲參數
[self test3:^NSString *(NSString *name) {
NSLog(@"name = %@", name);
return @"哇哈哈哈哈";
}];
//有參數,無返回值的block作爲參數
[self test3_1:^(NSString *name) {
NSLog(@"我是block的參數,name = %@", name);
}];
//無參數,有返回值的block作爲參數
[self test3_2:^int{
return 10;
}];
//函數也有返回值,block也有返回值
NSArray * arr = [self test3_3:^NSArray *(NSArray *array) {
//過濾重元素
NSMutableArray * tempArray = [NSMutableArray array];
BOOL flag = NO;
for (NSNumber * num in array) {
for (NSNumber * temp in tempArray) {
if (num == temp) {
flag = YES;
}
}
if (flag == NO) {
[tempArray addObject:num];
}
flag = NO;
}
return tempArray;
}];
NSLog(@"測試的array: %@", arr);
//應用實例
[self loadDataSuccess:^(NSDictionary *json, int code) {
NSLog(@"請求成功,%@", json);
} fail:^(NSString *msg) {
NSLog(@"%@", msg);
}];
}
//block作爲函數參數-1
//有參數,有返回值的block作爲參數
-(void)test3:(NSString* (^)(NSString * name))block {
NSString * newName = NSStringFromSelector(_cmd);
NSLog(@"%@", block(newName));
}
//block作爲函數參數-2
//有參數,無返回值的block作爲參數
-(void)test3_1: (void (^)(NSString * name))block {
NSString * myName = @"丹頂鶴";
block(myName);
}
/**
block作爲函數參數-3
無參數,有返回值的block作爲參數
*/
-(void)test3_2: (int (^)(void))blcok {
NSLog(@"我是test3_2");
int a = blcok();
NSLog(@"我是block的返回值喲, a = %d", a);
}
/**
block作爲函數參數-5
函數也有返回值
*/
-(NSArray *)test3_3: (NSArray* (^)(NSArray* array))block {
NSArray * myArray = @[@1,@2,@5,@8,@5,@7,@9,@7,@2,@1];
return block(myArray);
}
/**
block作爲函數參數-4
實際應用:模擬網絡請求
*/
-(void)loadDataSuccess: (SuccessBlock)success fail:(FailBlock)fail {
NSDictionary * json = @{@"num":@1,
@"name":@"小明",
@"age":@18,
@"phone":@"12345678922",
@"email":@"[email protected]"};
int code = 200;
if (code == 200) {
success(json, code);
} else {
fail(@"請求失敗了");
}
}
打印結果:
(4)Block作爲函數返回值;
//調用test5: block作爲函數返回值
-(void)test6 {
//有返回值,無參數的block作爲函數返回值
NSString* (^block)(void) = [self test5_1];
NSLog(@"%@", block());
//有返回值,有參數的block作爲函數返回值
NSString * (^block2)(NSString * name) = [self test5_2:@"小花花"];
NSString * bReturn = block2(@"小點點");
NSLog(@"最終的值: %@", bReturn);
}
//有返回值,無參數的block作爲函數返回值
-(NSString* (^)(void))test5_1 {
NSString * (^block)(void) = ^ NSString* {
return @"我們都是好孩子";
};
return block;
}
//有返回值,有參數的block作爲函數返回值
-(NSString* (^)(NSString* name))test5_2: (NSString *)testName {
NSString * (^block)(NSString * name) = ^ NSString* (NSString* name) {
return [NSString stringWithFormat:@"block的參數:%@",name];
};
NSLog(@"函數的參數: %@",testName);
return block;
}
打印結果:
(5)Block中使用局部變量和全局變量;
@interface BlockTestViewController ()
@property(nonatomic, copy)SumBlock block7;
@property(nonatomic, assign)int num;
@end
-(void)test7 {
//1.使用局部變量
//要想在block內部使用局部變量,需要在局部變量前面加上__block
__block int a = 100;
int b = 20;
void (^block)(void) = ^{
NSLog(@"a = %d, b = %d", a,b);
a = 200;
};
block();
NSLog(@"after a = %d, b = %d", a,b);
//2.使用全局變量
self.num = 10;
double (^block1) (void) = ^{
self.num = 20;
double t = self.num * 3.14;
return t;
};
//使用block1
double r = block1();
NSLog(@"self.num = %d, r = %.2f", self.num, r);
}
- (void)dealloc
{
NSLog(@"%@銷燬了",NSStringFromClass(self.class));
}
打印結果:
未完待續······