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