block语法基础与应用

1.block变量的声明定义void (^block) (void);此处void是返回值类型，block是块变量名，(void)是形参［不难发现block的声明与函数指针的声明类似：void (*point) (void)］这只是一种block类型，根据不同的返回值类型或者形参可以定义各种 block变量：例如：（1） int (^block1) (int,float)(2) NSString * (^block2) (NSInteger , NSString *)etc..2.创建block

block = ^(void) {
NSLog(@"hello");
};

同样还有：

block1 = ^int(int a, float b){
return a+b;
};
block2 = ^NSString *(NSInteger a,NSString *b){
NSLog(@"a = %ld,b = %@",a,b);
};
etc..

3.调用block

block();

void (^myBlock) (int);
myBlock = ^(int a){
NSLog(@"%d",a);
};
myBlock(3);

int (^block1) (int);
block1 = ^(int b){
return b;
};
int ss = block1(90);
NSLog(@"%d",ss);

4.typedef 的使用使用typedef可以简洁block代码，如：

typedef void (^Type1) (void);
typedef NSString* (^Type2) (NSString *);
typedef int (^Type3) (int,int);

调用时：

Type1 block2 = ^(void) {
NSLog(@"TYPE block2");
};
block2();

Type2 block3 = ^(NSString *str) {

return [NSString stringWithFormat:@"hahahaha %@",str];
};
NSString *str = block3(@"hyr");
NSLog(@"%@",str);

Type3 block4 = ^(int a,int b) {
return a*b;
};
NSLog(@"%d",block4(2,6));

5.block做方法的参数

[self testBlock1:^NSString*(NSString *str){
return [NSString stringWithFormat:@"hahahaha %@",str];
}];

6.应用用block方式完成弹出窗口中内容的回传：（1）主视图中有个label和button0（2）点击button后弹出一个视图A（3）视图A上有个输入框和button1（4）在输入框中输入文字后，点击button1后视图A消失，并将输入框中输入的文字显示在label上ViewController.h

#import <UIKit/UIKit.h>
#import "OpenView.h"

@interface ViewController : UIViewController
{
UILabel *_label;
OpenView *view;
}

@end

ViewController.m

#import "ViewController.h"

#define kWidth [UIScreen mainScreen].bounds.size.width
#define kHeight [UIScreen mainScreen].bounds.size.height

typedef void (^Type) (void);

@interface ViewController ()

@end

@implementation ViewController

- (void)viewDidLoad {
[super viewDidLoad];
// Do any additional setup after loading the view, typically from a nib.
_label = [[UILabel alloc] initWithFrame:CGRectMake(20, 70, kWidth-40, 400)];
_label.numberOfLines = 0;
_label.backgroundColor = [UIColor lightGrayColor];

[self.view addSubview:_label];

UIButton *button = [[UIButton alloc] initWithFrame:CGRectMake(70, 500, kWidth-140, 50)];
button.backgroundColor = [UIColor greenColor];
[button addTarget:self action:@selector(buttonAction) forControlEvents:UIControlEventTouchUpInside];
[self.view addSubview:button];

view = [[OpenView alloc] initWithFrame:CGRectMake(50, 100,kWidth-100 , 300)];
view.backgroundColor = [UIColor blackColor];
view.hidden = YES;
[self.view addSubview:view];

Type block = ^{
_label.text = view.textView.text;
};
[view setBlo:block];
//    _label.text = [view ];
}

- (void)buttonAction {
view.hidden = NO;
}

- (void)didReceiveMemoryWarning {
[super didReceiveMemoryWarning];
// Dispose of any resources that can be recreated.
}

@end

OpenView.h

#import <UIKit/UIKit.h>
typedef void (^Type) (void);

@interface OpenView : UIView
{

UIButton *_btn;
Type _block;
}
@property (nonatomic, retain)  UITextView *textView;

- (void)setBlo:(Type)block;
@end

OpenView.m

#import "OpenView.h"

@implementation OpenView

- (instancetype)initWithFrame:(CGRect)frame {self= [super initWithFrame:frame];if (self) {_textView = [[UITextView alloc] initWithFrame:CGRectMake(5, 5, self.bounds.size.width-10, 200)];_textView.backgroundColor = [UIColor yellowColor];[self addSubview:_textView];_btn = [[UIButton alloc] initWithFrame:CGRectMake(20, 210+20, self.bounds.size.width-40, 40)];_btn.backgroundColor = [UIColor blueColor];[_btn addTarget:self action:@selector(btnAction:) forControlEvents:UIControlEventTouchUpInside];[self addSubview:_btn];}return self;}- (void)btnAction:(UIButton *)btn {_block();self.hidden = YES;}- (void)setBlo:(Type)block {_block = [block copy];}@end