如何建立基于CocoaPods的ReactiveCocoa工程

ReactiveCocoa 和 CocoaPods 一样也是目前很流行的能方便和提高效率的框架.

其实不光ios 学习任何一门语音最快最直接的方法就是上手. 如果单单是看看文档只能是走马观花得到一个感性认识罢了.前两天之前一个公司的测试人员跟我联系说如何学习JAVA,我问他是怎么学的,他说从网上下了好多视频教程,一直在看视频教程,也买了一些书. 我问他敲了多少代码,他说很少. 其实跟他一样的人不少. 我觉得任何事情都不简单,因为看起来简单的事情自己没有实际做过的话往往会遇到各种各样的问题. 这也是为什么在工作中制定项目进度计划的时候我尽量给自己和团队中的人多争取时间的最主要的一个因素.

好了,自己一些啰嗦和感悟. 下面开始正式.

What is Reactive Cocoa?

RAV is an Object-C framework for Functional Reavtive Programming; 两个关键点: 1:framework 既然是framework 那就跟你用的其他framework没什么区别无非就是加到工程中引用罢了.不做多余解释 2:Functional Reavtive Programming 实时响应式编程

虾米引用被阿里收购后现在先上的mac版本的虾米音乐就是用Reactive Cocoa开发的.用阿里人自己的话来说就是

好东西啊，以前我们用 KVO 或 Notification 来自动绑定数据，改用 ReactiveCocoa 写以后，代码结构更佳简单清晰，同时代码行数直接减少 60% 以上

来点直观的对比吧,比如我们想要实现一个需求:当变量中的字符串改变后即时做出相应的反馈我们用KVO 需要如下这样做

// In your viewDidLoad/awakeFromNib/init
[self addObserver:self 
       forKeyPath:@"someString" 
          options:NSKeyValueObservingOptionNew 
          context:&someStringChangeContext];

// In dealloc
[self removeObserver:self 
          forKeyPath:@"someString" 
             context:&someStringChangeContext];

// Elsewhere in your class
- (void)observeValueForKeyPath:(NSString *)keyPath 
                      ofObject:(id)object 
                        change:(NSDictionary *)change 
                       context:(void *)context
{
    if (context == &someStringChangeContext) {
        if ([keyPath isEqualToString:@"someString"]) {        
            // Do a bunch of stuff here
        }
    }
}

上面一坨代码在应用Reactive Cocoa后只有短短一行

[RACObserve(self,someString) distinctUntilChanged] subscribeNext:^(NSString *string) {
    // Do a bunch of things here,just like you would with KVO
}];

开始动手

因为我之前安装了CocoaPods,所以我这次写的ReactiveCocoaDemo 是基于CocoaPods的.如果没有安装的可以童鞋,可以直接从github上下载ReactiveCocoa

前期工作:

1.打开xcode 创建一个工程,我命名的工程名为ReactiveCocoaDemo,

2.终端到工程路径下

cd ReactiveCocoaDemo/
pod search ReactiveCocoa

3.配置依赖文件

vi Podfile
    platform :ios,'5.0'
    pod 'ReactiveCocoa'
wq

4.下载文件

pod install /update

5:打开"Build Phases" 选中相应的target,添加 RAC 到 "Link Binary With Libraries".加上libReactiveCocoa-iOS.a

如下图

6:在Header Search Paths 中添加$(BUILD_ROOT)/../IntermediateBuildFilesPath/UninstalledProducts/include"

7:在 "Other Linker Flags" 添加 -ObjC

8:在ReactiveCocoaDemo-Prefix.pch 将RAC的头文件加进去

#import "ReactiveCocoa.h"

现在要实现如下功能

两个输入框一个提示的Lable 一个按钮,1.当两个输入框的内容相同时提示文字显示"成功" 按钮可以点击2.当任意一个输入框没有输入内容时提示文字显示"请输入" 按钮不可点击3.当输入框非空且两个输入内容不同时提示"请重新输入" 按钮不可点击

下面是部分实现代码:

@weakify(self);
[[RACObserve(self,warningText)
  filter:^(NSString *newString) {
      self.resultLabel.text = newString;
      return YES;
//          return [newString hasPrefix:@"Success"];
  }]
 subscribeNext:^(NSString *newString) {
     @strongify(self);
     self.bt.enabled = [newString hasPrefix:@"Success"];
 }];


RAC(self,self.warningText) = [RACSignal combineLatest:@[
RACObserve(self,self.input.text),RACObserve(self,self.verifyInput.text)]
reduce:^(NSString *password,NSString *passwordConfirm)
{
    if ([passwordConfirm isEqualToString:password])
    {
        return @"Success";
    }
    else if([password length] == 0 || [passwordConfirm length] ==0 )
    {
        return @"Please Input";
    }
    else
    return @"Input Error";
}
  ];

对应关系如下图所示

学过C++ 的应该觉得这个很类似于Qt中的信号槽机制

需要说明的是 因为RAC很大程度上是依赖于Block的.所以在RAC前面我们加上@weakify(my_variable) 避免循环引用,然后在每一个RAC块中为了防止提前释放我们需要用@strongify(my_variable)来对对象进行持有.详情点击

运行效果图如下

文档附录

Subscription

The [-subscribe…][RACSignal] methods give you access to the current and future values in a signal:

RACSignal *letters = [@"A B C D E F G H I" componentsSeparatedByString:@" "].rac_sequence.signal;

// Outputs: A B C D
[letters subscribeNext:^(NSString *x) {
    NSLog(@"%@",x);
}];

For a cold signal,side effects will be performed once per subscription:

__block unsigned subscriptions = 0;

RACSignal *loggingSignal = [RACSignal createSignal:^ RACDisposable * (id<RACSubscriber> subscriber) {
    subscriptions++;
    [subscriber sendCompleted];
    return nil;
}];

// Outputs:
// subscription 1
[loggingSignal subscribeCompleted:^{
    NSLog(@"subscription %u",subscriptions);
}];

// Outputs:
// subscription 2
[loggingSignal subscribeCompleted:^{
    NSLog(@"subscription %u",subscriptions);
}];

This behavior can be changed using a [connection][Connections].

Injecting effects

The [-do…][RACSignal+Operations] methods add side effects to a signal without actuallysubscribing to it:

__block unsigned subscriptions = 0;

RACSignal *loggingSignal = [RACSignal createSignal:^ RACDisposable * (id<RACSubscriber> subscriber) {
    subscriptions++;
    [subscriber sendCompleted];
    return nil;
}];

// Does not output anything yet
loggingSignal = [loggingSignal doCompleted:^{
    NSLog(@"about to complete subscription %u",subscriptions);
}];

// Outputs:
// about to complete subscription 1
// subscription 1
[loggingSignal subscribeCompleted:^{
    NSLog(@"subscription %u",subscriptions);
}];

Transforming streams

These operators transform a single stream into a new stream.

Mapping

The [-map:][RACStream] method is used to transform the values in a stream,andcreate a new stream with the results:

RACSequence *letters = [@"A B C D E F G H I" componentsSeparatedByString:@" "].rac_sequence;

// Contains: AA BB CC DD EE FF GG HH II
RACSequence *mapped = [letters map:^(NSString *value) {
    return [value stringByAppendingString:value];
}];

Filtering

The [-filter:][RACStream] method uses a block to test each value,including itinto the resulting stream only if the test passes:

RACSequence *numbers = [@"1 2 3 4 5 6 7 8 9" componentsSeparatedByString:@" "].rac_sequence;

// Contains: 2 4 6 8
RACSequence *filtered = [numbers filter:^ BOOL (NSString *value) {
    return (value.intValue % 2) == 0;
}];

Combining streams

These operators combine multiple streams into a single new stream.

Concatenating

The [-concat:][RACStream] method appends one stream's values to another:

RACSequence *letters = [@"A B C D E F G H I" componentsSeparatedByString:@" "].rac_sequence;
RACSequence *numbers = [@"1 2 3 4 5 6 7 8 9" componentsSeparatedByString:@" "].rac_sequence;

// Contains: A B C D E F G H I 1 2 3 4 5 6 7 8 9
RACSequence *concatenated = [letters concat:numbers];

Flattening

The [-flatten][RACStream] operator is applied to a stream-of-streams,andcombines their values into a single new stream.

Sequences are concatenated:

RACSequence *letters = [@"A B C D E F G H I" componentsSeparatedByString:@" "].rac_sequence;
RACSequence *numbers = [@"1 2 3 4 5 6 7 8 9" componentsSeparatedByString:@" "].rac_sequence;
RACSequence *sequenceOfSequences = @[ letters,numbers ].rac_sequence;

// Contains: A B C D E F G H I 1 2 3 4 5 6 7 8 9
RACSequence *flattened = [sequenceOfSequences flatten];

Signals are merged:

RACSubject *letters = [RACSubject subject];
RACSubject *numbers = [RACSubject subject];
RACSignal *signalOfSignals = [RACSignal createSignal:^ RACDisposable * (id<RACSubscriber> subscriber) {
    [subscriber sendNext:letters];
    [subscriber sendNext:numbers];
    [subscriber sendCompleted];
    return nil;
}];

RACSignal *flattened = [signalOfSignals flatten];

// Outputs: A 1 B C 2
[flattened subscribeNext:^(NSString *x) {
    NSLog(@"%@",x);
}];

[letters sendNext:@"A"];
[numbers sendNext:@"1"];
[letters sendNext:@"B"];
[letters sendNext:@"C"];
[numbers sendNext:@"2"];

Mapping and flattening

Flattening isn't that interesting on its own,but understandinghow it works is important for [-flattenMap:][RACStream].

-flattenMap: is used to transform each of a stream's values into a newstream. Then,all of the streams returned will be flattened down into a singlestream. In other words,it's -map: followed by -flatten.

This can be used to extend or edit sequences:

RACSequence *numbers = [@"1 2 3 4 5 6 7 8 9" componentsSeparatedByString:@" "].rac_sequence;

// Contains: 1 1 2 2 3 3 4 4 5 5 6 6 7 7 8 8 9 9
RACSequence *extended = [numbers flattenMap:^(NSString *num) {
    return @[ num,num ].rac_sequence;
}];

// Contains: 1_ 3_ 5_ 7_ 9_
RACSequence *edited = [numbers flattenMap:^(NSString *num) {
    if (num.intValue % 2 == 0) {
        return [RACSequence empty];
    } else {
        NSString *newNum = [num stringByAppendingString:@"_"];
        return [RACSequence return:newNum]; 
    }
}];

Or create multiple signals of work which are automatically recombined:

RACSignal *letters = [@"A B C D E F G H I" componentsSeparatedByString:@" "].rac_sequence.signal;

[[letters
    flattenMap:^(NSString *letter) {
        return [database saveEntriesForLetter:letter];
    }]
    subscribeCompleted:^{
        NSLog(@"All database entries saved successfully.");
    }];

Combining signals

These operators combine multiple signals into a single new [RACSignal][].

Sequencing

[-then:][RACSignal+Operations] starts the original signal,waits for it to complete,and then only forwards the values from a new signal:

RACSignal *letters = [@"A B C D E F G H I" componentsSeparatedByString:@" "].rac_sequence.signal;

// The new signal only contains: 1 2 3 4 5 6 7 8 9
//
// But when subscribed to,it also outputs: A B C D E F G H I
RACSignal *sequenced = [[letters
    doNext:^(NSString *letter) {
        NSLog(@"%@",letter);
    }]
    then:^{
        return [@"1 2 3 4 5 6 7 8 9" componentsSeparatedByString:@" "].rac_sequence.signal;
    }];

This is most useful for executing all the side effects of one signal,thenstarting another,and only returning the second signal's values.

Merging

The [+merge:][RACSignal+Operations] method will forward the values from manysignals into a single stream,as soon as those values arrive:

RACSubject *letters = [RACSubject subject];
RACSubject *numbers = [RACSubject subject];
RACSignal *merged = [RACSignal merge:@[ letters,numbers ]];

// Outputs: A 1 B C 2
[merged subscribeNext:^(NSString *x) {
    NSLog(@"%@",x);
}];

[letters sendNext:@"A"];
[numbers sendNext:@"1"];
[letters sendNext:@"B"];
[letters sendNext:@"C"];
[numbers sendNext:@"2"];

Combining latest values

The [+combineLatest:][RACSignal+Operations] and +combineLatest:reduce: methodswill watch multiple signals for changes,and then send the latest values fromall of them when a change occurs:

RACSubject *letters = [RACSubject subject];
RACSubject *numbers = [RACSubject subject];
RACSignal *combined = [RACSignal
    combineLatest:@[ letters,numbers ]
    reduce:^(NSString *letter,NSString *number) {
        return [letter stringByAppendingString:number];
    }];

// Outputs: B1 B2 C2 C3
[combined subscribeNext:^(id x) {
    NSLog(@"%@",x);
}];

[letters sendNext:@"A"];
[letters sendNext:@"B"];
[numbers sendNext:@"1"];
[numbers sendNext:@"2"];
[letters sendNext:@"C"];
[numbers sendNext:@"3"];

Note that the combined signal will only send its first value when all of theinputs have sent at least one. In the example above,@"A" was neverforwarded because numbers had not sent a value yet.

Switching

The [-switchToLatest][RACSignal+Operations] operator is applied toa signal-of-signals,and always forwards the values from the latest signal:

RACSubject *letters = [RACSubject subject];
RACSubject *numbers = [RACSubject subject];
RACSubject *signalOfSignals = [RACSubject subject];

RACSignal *switched = [signalOfSignals switchToLatest];

// Outputs: A B 1 D
[switched subscribeNext:^(NSString *x) {
    NSLog(@"%@",x);
}];

[signalOfSignals sendNext:letters];
[letters sendNext:@"A"];
[letters sendNext:@"B"];

[signalOfSignals sendNext:numbers];
[letters sendNext:@"C"];
[numbers sendNext:@"1"];

[signalOfSignals sendNext:letters];
[numbers sendNext:@"2"];
[letters sendNext:@"D"];

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