iOS -- block的正确使用

1. block相关内容

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2. block的使用

block的使用步骤：

1.正确声明 block

2.判断block是否被实现

3.block的调用

2.1 block的书写

#import <UIKit/UIKit.h>

//=================通用(1,2,3可直接把完整的block改为block名,为了加深印象暂时不用改名)
//=================通用
typedef void(^choiceCity3)(NSString *cityStr);

@interface SearchController : UIViewController
@property(nonatomic, strong)NSArray * dataArry;//存放所有的城市信息
//=================1
@property (nonatomic, copy) void(^choiceCity1)();

//=================2
@property (nonatomic, copy) void(^choiceCity2)(NSString * cityStr);

//================3
@property(nonatomic, copy)choiceCity3 choiceCity3;
- (void)choiceCityComplete:(void(^)(NSString *cityStr)) choiceCity3;

@end

2.2 block的判断

//在需要调用block的地方先判断block是否被实现。如果不做判断将会出错.

（可理解为:如果(block)方法有被实现了,那么就执行该方法(block))。

所以如果没有判断该方法是否被实现就去执行方法自然会错咯

- (void)tableView:(UITableView *)tableView didSelectRowAtIndexPath:(NSIndexPath *)indexPath{
NSArray * currentCityArray = self.citysArray[indexPath.section];
ModelCity *currentCity = currentCityArray[indexPath.row];
if (self.choiceCity1) {
self.choiceCity1();
}
if (self.choiceCity2) {
self.choiceCity2(currentCity.name);
}
if (self.choiceCity3) {
self.choiceCity3(_test3);//点击选择了才去执行block
}

[self dismissViewControllerAnimated:YES completion:nil];
}
- (void)choiceCityComplete:(void (^)(NSString *))choiceCity3{
self.choiceCity3 = choiceCity3;
}

2.3 block的调用

- (void)presentVC{
SearchController *searchVC = [[SearchController alloc]init];
searchVC.dataArry = _cityArray;

searchVC.choiceCity1=^(){
NSLog(@"无参调用,在这里执行你想做的事");
};
searchVC.choiceCity2=^(NSString *cityName){
NSLog(@"属性参数:%@",cityName);
};

[searchVC choiceCityComplete:^(NSString *cityStr) {
NSLog(@"传来的参数是:%@",cityStr);
_choiceLabel.text = cityStr;
}];

[self presentViewController:searchVC animated:YES completion:nil];

}