IOS: Learn notes, use Performselectoronmainthread to refresh Uiimageview in time

In iOS, the interface refresh takes place in the main thread, which causes the nsurlsession remote download picture to be set directly with Uiimageview image and not refresh the interface in a timely manner.

The following code demonstrates how to use the PerformSelectorOnMainThread:withObject:waitUntilDone: method to refresh a picture in a timely manner

1. Create an empty iOS app (application).

2. Add a controller class. Modify in yyappdelegate.m

#import "MainViewController.h" @implementation yyappdelegate-(BOOL) Application: (UIApplication *) application Didfinishlaunchingwithoptions: (nsdictionary *) launchoptions{    Self.window = [[UIWindow alloc] initwithframe:[[ UIScreen mainscreen] bounds];    Override point for customization after application launch.    Self.window.backgroundColor = [Uicolor whitecolor];        Self.window.rootViewController = [[Mainviewcontroller alloc] Initwithnibname:nil Bundle:nil];        [Self.window makekeyandvisible];    return YES;}

3. Modify the Mainviewcontroller.m file

mainviewcontroller.m//uibycodedemo0602_imageview////Created by Yao_yu on 14-6-3.//Copyright (c) 2014 Yao_yu. All rights reserved.//#import "MainViewController.h" @interface Mainviewcontroller () @property (nonatomic, Strong) UILabel *header; @property (nonatomic, strong) Uiimageview *imageview; @property (nonatomic, strong) UIImage *imagedata;@ End@implementation mainviewcontroller-(ID) initwithnibname: (NSString *) Nibnameornil Bundle: (NSBundle *)    nibbundleornil{self = [super Initwithnibname:nibnameornil Bundle:nibbundleornil]; if (self) {//Custom initialization} return to self;}    -(void) viewdidload{[Super Viewdidload];        Self.imagedata = nil;    Create title Tag Self.header = [[UILabel alloc] init];    Self.header.text = @ "";    Self.header.textAlignment = Nstextalignmentcenter;    [Self.view AddSubview:self.header];        [Self.header Settranslatesautoresizingmaskintoconstraints:no];    Create picture View Self.imageview = [[Uiimageview alloc] init]; [Self.imagevIew setbackgroundcolor: [Uicolor Bluecolor]];    [Self.imageview setimage: [UIImage imagewithcontentsoffile:@ "/users/yao_yu/documents/aaa/3002302_.png"];    Self.imageView.layer.cornerRadius = 10;    [Self.view AddSubview:self.imageView];        [Self.imageview Settranslatesautoresizingmaskintoconstraints:no];    Create a Previous button UIButton *prevbutton = [[UIButton alloc] init];    Prevbutton.frame = CGRectMake (0, 20, 300, 20);    [Prevbutton Setbackgroundcolor:[uicolor Redcolor];    [Prevbutton settitle:@ "The previous one" forstate:uicontrolstatenormal];    [Prevbutton addtarget:self Action: @selector (onshowprevimage:) forcontrolevents:uicontroleventtouchupinside];    [Self.view Addsubview:prevbutton];        [Prevbutton Settranslatesautoresizingmaskintoconstraints:no];    Create the latter button UIButton *nextbutton = [[UIButton alloc] init];    Nextbutton.frame = CGRectMake (0, 20, 300, 20);    [Nextbutton Setbackgroundcolor:[uicolor Redcolor];  [Nextbutton settitle:@ "After a" forstate:uicontrolstatenormal];  [Nextbutton addtarget:self Action: @selector (onshownextimage:) forcontrolevents:uicontroleventtouchupinside];    [Self.view Addsubview:nextbutton];        [Nextbutton Settranslatesautoresizingmaskintoconstraints:no];    Constraint Nsmutablearray *contraits = [Nsmutablearray array];    Nsdictionary *metrics = [nsdictionary dictionarywithobjectsandkeys:@20, @ "Vdist", @5, @ "Padding", nil];    UILabel *header = Self.header;    Uiimageview *imageview = Self.imageview;        Nsdictionary *views = nsdictionaryofvariablebindings (header, ImageView, Prevbutton, Nextbutton); [Contraits addobjectsfromarray:[nslayoutconstraint constraintswithvisualformat:@ "H:|-Padding-[header]-Padding-|"    options:0 Metrics:metrics Views:views]]; [Contraits addobjectsfromarray:[nslayoutconstraint constraintswithvisualformat:@ "H:|-Padding-[prevButton]-(>=        0)-[nextbutton (==prevbutton)]-padding-| "options:0 metrics:metrics views:views]"; [Contraits addobjectsfromarray:[nslayoutconstraint CONSTRAINTSWITHVisualformat:@ "h:|-padding-[imageview]-padding-|" options:0 metrics:metrics views:views]; [Contraits addobjectsfromarray:[nslayoutconstraint constraintswithvisualformat:@ "V:|-VDist-[header]-Padding-[    imageview]-(>=vdist)-| "options:0 metrics:metrics views:views]"; Center vertically [Self.view addconstraint:[nslayoutconstraint Constraintwithitem:prevbutton attribute: Nslayoutattributecentery relatedby:nslayoutrelationequal ToItem:self.view Attribute:nslayoutattributecentery    Multiplier:1 constant:0]]; [Self.view addconstraint:[nslayoutconstraint Constraintwithitem:nextbutton Attribute:nslayoutattributecentery        Relatedby:nslayoutrelationequal ToItem:self.view attribute:nslayoutattributecentery multiplier:1 constant:0]];    [Self.view addconstraints:contraits]; }-(void) didreceivememorywarning{[super didreceivememorywarning];} -(void) Onshowprevimage: (ID) sender{Nsurl *url = [Nsurl urlwithstring:@ "http://img.gtimg.cn/images/hq_parts/hushen/    Stocks/300230.png "]; Nsurlrequest*request = [Nsurlrequest Requestwithurl:url];    Nsurlsession *session = [Nsurlsession sharedsession]; Nsurlsessiondatatask *task = [Session datataskwithrequest:request Completionhan                                      Dler: ^ (NSData *data, Nsurlresponse *response, Nserror *error) {                                      Self.imageView.image = nil;                                      Self.imagedata = [UIImage imagewithdata:data];                                  [Self Performselectoronmainthread: @selector (updatemyimage) Withobject:nil Waituntildone:no];        }];    [Task resume]; }-(void) Onshownextimage: (ID) sender{Nsurl *url = [Nsurl urlwithstring:@ "http://img.gtimg.cn/images/hq_parts/hushen/    Stocks/300023.png "];    Nsurlrequest *request = [Nsurlrequest Requestwithurl:url];    Nsurlsession *session = [Nsurlsession sharedsession];      Nsurlsessiondatatask *task = [Session Datataskwithrequest:request                                      Completionhandler: ^ (NSData *data, Nsurlresponse *r                                      Esponse, Nserror *error) {self.imageView.image = nil;                                      Self.imagedata = [UIImage imagewithdata:data];                                  [Self Performselectoronmainthread: @selector (updatemyimage) Withobject:nil Waituntildone:no];        }]; [Task resume];}    -(void) updatemyimage{if (!self.imageview.image) self.imageView.image = Self.imagedata; return;} @end

4. Running