关于BLOCK逆向传值和PickerView的使用

block使用一般分为3步

1.声明 可以使用typedef

2.调用 可以定义一个property 属性

3.实现 在要实现效果的类中实现 传递过来数值

下面通过一个小demo来表现出来

**demo 由viewctrl push 到PushCtrl中

PushCtrl 中有一个pickerView 通过选择数值来改变 viewCtrl中的label的值**

#import "ViewController.h"
#import "PushViewController.h"
@interface ViewController (){
UILabel *label;
}

@end

@implementation ViewController

- (void)viewDidLoad {
[super viewDidLoad];

//load push button
UIButton *button = [UIButton buttonWithType:UIButtonTypeCustom];
button.frame = CGRectMake(100, 100, 100, 100);
button.backgroundColor = [UIColor redColor];
[button setTitle:@"push" forState:UIControlStateNormal];
[button addTarget:self action:@selector(buttonAction:) forControlEvents:UIControlEventTouchUpInside];
[self.view addSubview:button];

//load label
label = [[UILabel alloc]initWithFrame:CGRectMake(100, 300, 100, 100)];
label.backgroundColor = [UIColor whiteColor];

[self.view addSubview:label];

}

- (void)buttonAction:(UIButton *)button{
PushViewController *pushCtrl = [[PushViewController alloc]init];
pushCtrl.block = ^(NSString *result){
label.text = result;
};
[self.navigationController pushViewController:pushCtrl animated:YES];
pushCtrl.title = NSLocalizedString(@"Push的界面", nil);
}

PushCtrl中的代码

#import "PushViewController.h"
#define kScreenWidth      [UIScreen mainScreen].bounds.size.width
#define kScreenHeight      [UIScreen mainScreen].bounds.size.height
@interface PushViewController ()

@end

@implementation PushViewController
{
//定义一个全局的数据源
NSArray *_dataList;
UIPickerView *_pickView;
NSString *_pickerStr;
}

- (void)viewDidLoad {
[super viewDidLoad];
self.view.backgroundColor = [UIColor blackColor];

_pickView = [[UIPickerView alloc]initWithFrame:CGRectMake(0, 100, kScreenWidth, 400)];
_pickView.delegate = self;
_pickView.dataSource = self;

[self.view addSubview:_pickView];

_dataList = @[@"1",@"2",@"3",@"4",@"5",@"6",@"7",@"8",@"9",@"10"];

}

#pragma  mark - UIPickerViewDelegate and UIPickerViewDataSource
//返回几列滚轮
- (NSInteger)numberOfComponentsInPickerView:(UIPickerView *)pickerView{
return 1;
}

// returns the # of rows in each component..
//没个滚轮返回多少个选择的字段
- (NSInteger)pickerView:(UIPickerView *)pickerView numberOfRowsInComponent:(NSInteger)component{
return _dataList.count;
}

//返回每个字段的标题
- (NSString *)pickerView:(UIPickerView *)pickerView titleForRow:(NSInteger)row forComponent:(NSInteger)component{
return _dataList[row];
}
//选择字段时调用的代理方法
- (void)pickerView:(UIPickerView *)pickerView didSelectRow:(NSInteger)row inComponent:(NSInteger)component{
NSLog(@"%@",_dataList[row]);
_pickerStr = _dataList[row];

}

//在试图将要消失的时候调用BLOCK
- (void)viewWillDisappear:(BOOL)animated{
if (self.block != nil) {
self.block(_pickerStr);
}
}

#pragma mark - 让pickview 字体颜色变白色
- (NSAttributedString *)pickerView:(UIPickerView *)pickerView attributedTitleForRow:(NSInteger)row forComponent:(NSInteger)component
{

NSAttributedString *attString = [[NSAttributedString alloc] initWithString:_dataList[row] attributes:@{NSForegroundColorAttributeName:[UIColor whiteColor]}];

return attString;

}

使用代码块能够简单的回调

代理太麻烦

通知还要移除 满天飞 都不知道是哪里发出的

单例还要重新定义一个class

其他的就不说了

希望能帮到大家

4000