iOS development loads a lot of network picture optimizations

1. Overview

Reading a Web image through a URL under iOS is not as easy as other programming languages to place the picture path directly in the picture path, but requires us to load the network image through a similar stream, before the image can be placed in the image path display. Like what:

-(UIImage *) Getimagefromurl: (NSString *) FileURL {//nslog (@ "Perform picture download function");      UIImage * result;  NSData * data = [NSData Datawithcontentsofurl:[nsurl Urlwithstring:fileurl]];      result = [UIImage imagewithdata:data]; return result;}

Loading network pictures can be said to be a must in network applications. If the simple to download pictures, and not to do multi-threading, caching and other technologies to optimize, loading pictures when the effect and user experience will be very poor.

The optimization idea is:

(1) Local cache

(2) Asynchronous loading

(3) Use placeholder images before loading

2. Optimization method

Method 1: Use Nsoperation to open an asynchronous thread to download the picture and replace the placeholder picture when the download is complete

#import   "XNViewController.h" #import   "XNApp.h" @interface  XNViewController  () @property   (Nonatomic, strong)  NSArray *appList; @property   (nonatomic, strong)   nsoperationqueue *queue; @end @implementation xnviewcontroller#pragma mark -  Lazy Loading-  (nsoperationqueue *) queue {if  (!_queue)  _queue = [[nsoperationqueue alloc]  init];return _queue;} It can be extracted and written into the model-  (nsarray *) applist {if  (!_applist)  {//1. Loading plist into an array nsurl *url  = [[nsbundle mainbundle] urlforresource:@ "Apps.plist"  withExtension:nil]; Nsarray *array = [nsarray arraywithcontentsofurl:url];//2. Iterating through an array Nsmutablearray *arraym  = [NSMutableArray array]; [Array enumerateobjectsusingblock: ^ (Id obj, nsuinteger idx, bool *stop)  {    [arraym addobject:[xnapp appwithdict:objThe]];  //array is stored in the dictionary,  converted to an App object and then added to the array}];_applist = [arraym copy];} Return _applist;} -  (void) viewdidload {[super viewdidload];self.tableview.rowheight = 88;//     nslog (@ "applist-%@", _applist);} #pragma  mark -  Data source method-  (Nsinteger) TableView: (uitableview *) tableview  Numberofrowsinsection: (Nsinteger) Section {return self.applist.count;} -  (uitableviewcell *) TableView: (uitableview *) Tableview cellforrowatindexpath: (NSIndexPath  *) indexpath {static nsstring *id = @ "Cell"; uitableviewcell *cell = [tableview dequeuereusablecellwithidentifier:id];// Populate each cellxnapp *app = self.applist[indexpath.row];cell.textlabel.text = app.name; with a model   //set text//settings image:  The image in the model is nil with the default image, and download the image .  otherwise cache the image with the memory in the Model .if  (!app.image)  { cell.imageview.image = [uiimage imagenamed:@ "User_defAult "]; [Self downloadimg:indexpath];} else {//directly with the memory cache in the model Cell.imageview.image = app.image;} NSLog (@ "cell--%p",  cell); Return cell;} /** always remembers,  to modify the display .  through the model instead of trying to directly modify the display */-  (void) downloadimg: (nsindexpath *) Indexpath {xnapp  *app  = self.applist[indexpath.row]; //to get the model of the row corresponding [self.queue  addoperationwithblock: ^{    nsdata *imgdata = [nsdata  datawithcontentsofurl:[nsurl urlwithstring:app.icon]]; //Get Image Data     UIImage  *image = [uiimage imagewithdata:imgdata];    //update ui    in the main thread  [[NSOperationQueue mainQueue] addOperationWithBlock: ^{         //modify the data by modifying the model,          app.image =  image;        //refreshes the specified table row        &NBsp [Self.tableview reloadrowsatindexpaths:@[indexpath] withrowanimation:uitableviewrowanimationnone];}];}];} @end

The code above simply does the memory cache and does not have a local cache, because this method is not the focus, nor is it the preferred method. The above code is re-downloaded from the Web every time you re-enter the app. If you want to continue optimizing the above code, you need to implement the local cache yourself.

Method 2: Use a third-party framework Sdwebimage

Characteristics:

Rely on a few libraries, full-featured.

Automatic disk caching: Cached image names are named after the name of the MD5 encryption. (because the string of encryption is unique)

Set the placeholder image directly when loading the network picture: [ImageView sd_setimagewithurl:imageurl placeholderimage:[uiimage imagenamed:@ "xxxxx"].

In one way, it realizes multi-thread buffering and other effects. (Can be used with the method of parameters, specific to the document)

The code after modifying the above method with Sdwebimage can be simplified to:

#pragma  mark -  Data source method-  (Nsinteger) TableView: (uitableview *) tableview  Numberofrowsinsection: (Nsinteger) Section {return self.applist.count;} -  (uitableviewcell *) TableView: (uitableview *) Tableview cellforrowatindexpath: (NSIndexPath  *) indexpath {static nsstring *id = @ "Cell"; uitableviewcell *cell = [tableview dequeuereusablecellwithidentifier:id];// Populate each cellxnapp *app = self.applist[indexpath.row];cell.textlabel.text = app.name; with a model   //Set the text////set the image:  the image in the model is nil with the default image, and download the image .  otherwise use the memory in the model to cache the image .//if  (!cell.imageview.image)  {//cell.imageview.image = [uiimage imagenamed:@ "User_default"];////[self downloadImg : indexpath];//}//else {////directly with the memory cache in the model//cell.imageview.image = app.image;//}// Use Sdwebimage to complete the above functions .  for imageview.//A word,  automatic implementation of the asynchronous download .  picture local cache .  network download .  auto-set placeholder. [cell.imageview sd_setimagewithurl:[nsurl urlwithstring:app.icon] placeholderimage:[uiimage imagenamed:@ "User_ Default "]];return cell;} /** always remembers,  to modify the display .  through the model instead of trying to directly modify the display *///-  (void) downloadimg: (nsindexpath *) indexpath {// xnapp *app  = self.applist[indexpath.row]; //to get the model of the row corresponding////[self.queue  addoperationwithblock: ^{//    nsdata *imgdata = [nsdata  datawithcontentsofurl:[nsurl urlwithstring:app.icon]]; //Get Image Data//    uiimage  *image = [uiimage imagewithdata:imgdata];////    //update ui//  in the main thread    [[NSOperationQueue mainQueue] addOperationWithBlock: ^{//         //modifies the data by modifying the model, //        app.image  = image;//        //refreshes the specified table row//        &nBsp [self.tableview reloadrowsatindexpaths:@[indexpath] withrowanimation:uitableviewrowanimationnone];// }];//}];//} @end

Some of the parameters in the "Remarks" Sdwebimage:

*sdwebimageretryfailed = 1<< 0, default option, retry after failure

*sdwebimagelowpriority = 1<< 1, using low-priority

*sdwebimagecachememoryonly = 1<< 2, using only memory cache

*sdwebimageprogressivedownload = 1<< 3, showing current progress

*sdwebimagerefreshcached = 1<< 4, flush cache

*sdwebimagecontinueinbackground =1 << 5, continue downloading images in the background

*sdwebimagehandlecookies = 1<< 6, processing cookies

*sdwebimageallowinvalidsslcertificates= 1 << 7, allow invalid SSL authentication

*sdwebimagehighpriority = 1<< 8, high-priority

*sdwebimagedelayplaceholder = 1<< 9 delay display placeholder picture

iOS development loads a lot of network picture optimizations