The difference between Swift lazy loading (lazy) and objective-c lazy loading

In programming, we often use 懒加载, as the name implies, is used to open up space, such as the most commonly used controls in iOS development UITableView, we usually write this way when we implement the data source method objective-c

-(Nsinteger) TableView: (UITableView *) TableView   numberofrowsinsection: (nsinteger) section{       return  self.dataArray.count;} -(UITableViewCell *) TableView: (UITableView *) TableView Cellforrowatindexpath: (Nsindexpath *) indexpath{      //    Xwshopcell *cell = [Xwshopcell cellwithtableview:tableview];      //     cell.wine = Self.dataarray[indexpath.row];      //     return  cell;}

In the code above,

return Self.dataArray.count;

is actually using

@property (nonatomic, strong) Nsarray *dataarray;

@propertyAttribute , a property is generated get for the and the set method, and here is the call to the get method, but the return self.dataArray.count code above is called

return _dataarray}

This call, if the member property DataArray Start No assignment, then in use, call get method, do not rewrite, will error, null pointer, so generally we will rewrite the Get method

// Override Get Method -(Nsarray *) dataarray{   if (nil = = _dataarray)       {= [Nsarray Array];   }    return _dataarray}

This prevents the member property from being assigned

In summary, objective-c lazy loading, is actually called the member property of the Get method, initialize the value, and swift lazy load, is and objective-c different

Swift

//MARK Tablview's DataSource proxy methodFunc TableView (Tableview:uitableview, numberofrowsinsection section:int)int{returnSelf.dataArray.count} func TableView (Tableview:uitableview, Cellforrowatindexpath Indexpath:nsindexpath) /c2>-uitableviewcell{//1. Get the cellLet cell =Xwshopcell.cellwithtableview (TableView)//2. Transfer ModelCell.wine =Self.dataarray[indexpath.row]//3. Callback Cell    returncell}

And this sentence

  return Self.dataArray.count

in the Swift The storage property must be initialized, confirm the type, or use an optional type, in short to confirm the type, after all Swfi T is a type-safe language, so Swift proposed a lazy Properties, Usage

//1. Analysis Nsarray is a closure of the return value, and this is a closed packet without parametersLazy var Dataarray:nsarray = { [] }()     //2. Can also be written like this lazy var Dataarray:nsarray = {return Nsarray ()} ()//3. Loading from the plist fileLazy var dataarray:array<xwwine> ={Let Winepath= Nsbundle.mainbundle (). Pathforresource ("wine.plist", Oftype:nil)!Let winesm=Nsmutablearray (Contentsoffile:winepath); var Tmparray:array<xwwine>! = []            forTmpwinedictinchwinesm!{var wine:xwwine= Xwwine.winewithdict (tmpwinedict as!nsdictionary) tmparray.append (wine)} print ("I run it one time")           returnTmparray} ()

The above code, a bit difficult to understand, if Objective-C the previous block or the C语言 function pointer understanding, can be considered a block of code, and then self.dataArray the time, the code block is executed, but repeated calls, Lazy the properties of the code block will only be called once , the lazy modification is a storage property, and the store is a closure, I think inside, should be optimized

The difference between Swift lazy loading (lazy) and objective-c lazy loading