IOS block use

aviewcontroller.h@interface aviewcontroller : uiviewcontroller {     uilabel *valuelabel;//. To receive the value returned by the Secondviewcontroller} @end implement aviewcontroller.m-  (void) viewdidload{     [super viewdidload];    valuelabel = [[uilabel alloc ] initwithframe:cgrectmake (10, 100, 300, 50)];    [self.view  Addsubview:valuelabel];    uibarbuttonitem *nextbtn = [[uibarbuttonitem  alloc] initwithtitle:@ "Next"                  style:uibarbuttonitemstyleplain target:self action: @selector (NextClick )];    self.navigationitem.rightbarbuttonitem = nextbtn;} -  (void) Nextclick{   bviewcontroller *svc = [[bviewcontroller alloc]  init];    svc.backvalue = ^ (Nsstring *strvalue)  {//set the Block property of Secondviewcontroller Edge, which is the key of this program      valueLabel.text = strValue;};     [self.navigationcontroller pushviewcontroller:svc animated:yes];} bviewcontroller.h@interface bviewcontroller : uiviewcontroller@property  (nonatomic,  copy)  void  (^backvalue) (Nsstring *strvalue), @property   (nonatomic, retain)   uitextfield *text; @end implement bviewcontroller.m@implementation bviewcontroller-  (void) viewDidLoad{     [super viewdidload];    self.view.backgroundcolor =  [UIColor whiteColor];    text = [[UITextField alloc]  Initwithframe:cgrectmake (10, 50, 300, 40)];    text.borderstyle =  UITextBorderStyleRoundedRect;    [self.view addSubview:text];     uibutton *btn = [uibutton buttonwithtype:uibuttontyperoundedrect];     Btn.frame = cgrectmake (10, 110, 60, 30);     [btn settitle:@ " Back to " forstate:uicontrolstatenormal];    [btn addtarget:self action: @selector (Btnclick)                       forcontrolevents:uicontroleventtouchupinside];    [self.view  ADDSUBVIEW:BTN];} -  (void) btnclick{self.backvalue (self.text.text);//Tune block Law [self.navigationcontroller  Popviewcontrolleranimated:yes];} @end

The idea of the block passing value:

1, a class to pass a value, that is, to establish the Block property void (^backvalue) (nsstring *strvalue), and then implement it: Self.backvalue (the value to pass )

2, Class B to get the value of a is to achieve the properties of a.

Aviewcontroller *AVC = [[Aviewcontroller alloc] init]; By block value, city switch avc.backvalue = ^ (NSString *strvalue) {//Set Secondviewcontroller? Side of the Block property, which is the key to this program Self.citynam    e = strvalue; };

3, parsing the Blcok attribute

Return value-Name-parameter

Return value-name-equals sign

@property (nonatomic, copy) void (^backvalue) (NSString *strvalue); @property (nonatomic, copy) NSString *name; =

IOS block use