[New Learn] explains OBJECTIVE-C's block knowledge-practice

1. Introduction

The knowledge of block is described in the previous article [New learn] explaining the block knowledge of objective-c. In this chapter we will take a practical example to briefly describe how block replaces proxies.

2. The original through the Proxy realization Way review

Using Xib to create a view in [how], we show how the Footview from the Xib table can be used to notify the controller by proxy to load more data.

Corresponding Code: Https://github.com/xufeng79x/tableView_groupbuy_test

1. In the above project we have declared an agreement in the XFLoadMoreView.h header file

@protocol Xfloadmoreviewdelegate <NSObject>/* * *when the button is clicked, notify the  agent  Implementation Object **/@optional -(void) LOADMOREVIEWDIDCLICKEDTOLOADBTN: (Xfloadmoreview *) Loadmoreview; @end

2. The proxy attribute is declared in the custom Xfloadmoreview:

ID delegate;

3. The protocol is implemented in the controller, and the Proxy property value is set to the current controller when the Xfloadmoreview instance is created to make the notification call.

@interfaceXfgoodsshowsviewcontroller () <uitableviewdatasource, xfloadmoreviewdelegate>......  //This method is called after the load button is pressed to notify this object-(void) LOADMOREVIEWDIDCLICKEDTOLOADBTN: (Xfloadmoreview *) loadmoreview{//here we simulate adding a group buy message, inserting the best line into the listXfgoodmodel *model =[[Xfgoodmodel alloc] init]; Model.image=@"image.jpg"; Model.name=@"New Food"; Model.price=123; Model.soldnum=321; //inserting secondary information into a table data source[Self.goodslist Addobject:model]; //this data needs to be plugged into the last row of the tableNsindexpath *indexpath = [Nsindexpath indexPathForItem:self.goodsList.count-1Insection:0];        [Self.goodstableview Insertrowsatindexpaths:@[indexpath] withrowanimation:uitableviewrowanimationtop]; //when the load is complete, roll the table to the newly added row, which is the last bar[Self.goodstableview Scrolltorowatindexpath:indexpath Atscrollposition:uitableviewscrollpositionbottom Animated:yes];} .... 

3. Use the block feature to override the proxy feature mechanism

We can do it by proxy without using the protocol, we can deal with it by Block:

The specific methods are:

1. Declare the Block property in the XFLoadMoreView.h file to receive a callback block from the target

// Defining notification Callbacks void (^notifyloadblock) (Xfloadmoreview *);

2. Add the block parameter to the XFLOADMOREVIEW.M class initialization method

//initialization method of notification callback using block+ (Instancetype) Loadmoreviewwithnotifyblock: (void(^) (Xfloadmoreview *)) notifyloadblock{//load view directly from XibXfloadmoreview *loadview = [[[NSBundle Mainbundle] loadnibnamed:@"Xfloadbutton"Owner:nil Options:nil] lastobject]; //beautify button to round the four corners of a buttonLoadView.loadMoreBtnView.layer.cornerRadius =5; LoadView.loadMoreBtnView.layer.masksToBounds=YES; //set Load more callback blockLoadview.notifyloadblock =Notifyloadblock; returnLoadview;}

3. When initializing the Xfloadmoreview at the controller, the specific block implementation is passed in:

    // load the TableView footview    Xfloadmoreview *loadmoreview = [Xfloadmoreview loadmoreviewwithnotifyblock:^ (Xfloadmoreview * view) {        [self Loadmoreviewdidclickedtoloadbtn:view];    }];

The methods in the original protocol method are reused here.

4. When a Load event occurs in a custom Xfloadmoreview, notify the controller to load the data:

/** * Trigger after clicking Load More button*/-(ibaction) Loadmoreclick {//hide Botton to render after loading a styleSelf.loadMoreBtnView.hidden =YES; Self.loadMoreIngView.hidden=NO; //Use this method to achieve a deferred execution effectDispatch_after (Dispatch_time (Dispatch_time_now,2.0* nsec_per_sec), Dispatch_get_main_queue (), ^{Self.loadMoreBtnView.hidden=NO; Self.loadMoreIngView.hidden=YES; //send information to the agent, because it is an optional method set in the proxy definition, you need to check whether this method is implemented before sending the information//if ([Self.delegate respondstoselector: @selector (loadmoreviewdidclickedtoloadbtn:)])//        {//[Self.delegate loadmoreviewdidclickedtoloadbtn:self];//        }                //using callbacks to load notifications        if(Nil! =self.notifyloadblock) {self.notifyloadblock (self); }    });

4. Summary

In this article, we have implemented a block approach to a function that was originally implemented by proxy.

So when should the agent adopt block?

We can refer to the following article: Http://stackoverflow.com/questions/26791548/objc-memory-usage-of-delegate-vs-block

This chapter code: Https://github.com/xufeng79x/BlockDemo

[New Learn] explains OBJECTIVE-C's block knowledge-practice