上一篇阅读了RACSignal订阅过程的一些源码,这一篇来看看流的一系列操作Mapping,Filtering
本文主要内容:
1.map操作的源码阅读;(其实是flattenMap:的源码)
2.filter操作
3.空信号RACEmptySignal
RACStream
RACStream是RACSignal和RACSequence的父类,所以很多方法定义在RACStream中,RACStream是一个抽象类.
来看看RACStream中定义了些什么东西
1 | @interface RACStream : NSObject |
Map操作
如果把RACStream比作是水流的话,Map操作可以是一个个加工工厂,比如一个可乐工厂,水流流进工厂,工厂处理过后,流出了可乐流,在可乐流上接了龙头,打开阀门就可以喝可乐了.
写个栗子:
1 | RACSignal *signal = [RACSignal createSignal:^RACDisposable *(id<RACSubscriber> subscriber) { |
从栗子中可以看到,流进可乐工厂产生了新的可乐流,而不是将原先的水流全部转化成了可乐流,我还想喝水还能喝.
来看看map的实现
1 | //RACStream.m中 |
为了看清楚些,转化下源码的代码1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29//map方法
- (instancetype)map:(id (^)(id value))block {
NSCParameterAssert(block != nil);
Class class = self.class;
RACStream *(^innerBlock)(id value)=^(id value)
{
return [class return:block(value)];
};
RACStream *stream=[self flattenMap:innerBlock];
//-(instancetype)flattenMap:(RACStream * (^)(id value))block;方法
return [stream setNameWithFormat:@"[%@] -map:", self.name];
}
//flattenMap方法
- (instancetype)flattenMap:(RACStream * (^)(id value))block {
Class class = self.class;
RACStreamBindBlock bindBlock = ^(id value, BOOL *stop)
{
id stream = block(value) ?: [class empty];
return stream;
};
RACStreamBindBlock (^A_Block_That_Return_A_RACStreamBindBlock)(void)=^RACStreamBindBlock(void)
{
return bindBlock;
};
RACStream *stream=[self bind:A_Block_That_Return_A_RACStreamBindBlock];
//- (RACSignal *)bind:(RACStreamBindBlock (^)(void))block;方法
//typedef RACStream * (^RACStreamBindBlock)(id value, BOOL *stop);
return [stream setNameWithFormat:@"[%@] -flattenMap:", self.name];
}
从转化后的代码可以看到
1.map:方法内,调用flattenMap:需要一个RACStream类型的block
2.那么把这个block写明白点,命名为innerBlock,然后将innerBlock传给flattenMap:方法
3.flattenMap:方法内,调用bind:方法需要一个RACStreamBindBlock (^)(void)类型的block
4.看到RACStreamBindBlock是一个返回RACStream类型,参数是value和stop指针的block
5.所以RACStreamBindBlock (^)(void)这个block的作用就是返回一个RACStreamBindBlock类型的block
恩,map的工作就是传了很多block,好了,来看看RACSignal中的bind做了什么1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35//bind方法
- (RACSignal *)bind:(RACStreamBindBlock (^)(void))block {
RACSignal *mappedSignalA=[RACSignal createSignal:^(id<RACSubscriber> subscriber) {
//(以下一大段代码就是被保存在了signal的`mappedSignalA`属性中)
//(订阅逻辑修炼一有介绍)
RACStreamBindBlock bindingBlock = block();
NSMutableArray *signals = [NSMutableArray arrayWithObject:self];
void (^completeSignal)(RACSignal *, RACDisposable *)//一个completeSignal block
...
void (^addSignal)(RACSignal *)//一个addSignal block
...
RACDisposable *bindingDisposable = [self subscribeNext:^(id x) {
BOOL stop = NO;
id signal = bindingBlock(x, &stop);
@autoreleasepool {
if (signal != nil) addSignal(signal);
if (signal == nil || stop) {
[selfDisposable dispose];
completeSignal(self, selfDisposable);
}
}
} error:^(NSError *error) {
[compoundDisposable dispose];
[subscriber sendError:error];
} completed:^{
@autoreleasepool {
completeSignal(self, selfDisposable);
}
}];
selfDisposable.disposable = bindingDisposable;
}
return compoundDisposable;
}
return [mappedSignalA setNameWithFormat:@"[%@] -bind:", self.name];
}
bind就是把blocks埋起来
到这里map的工作完成了,产生了新的RACSignal–栗子中的mappedSignalA,
如果不订阅,这一切都是瞎忙1
2
3
4[signal subscribeNext:^(id x) {
NSLog(@"class-%@,value-%@",[x class],x);
}];
//subscribeNext的逻辑在修炼(一)中有介绍,
map把blocks埋起来,subscribeNext开始挖
1.调用mappedSignalA中的didSubscribe保存的代码
2.第一行代码RACStreamBindBlock bindingBlock = block();这个block就是A_Block_That_Return_A_RACStreamBindBlock,从上文的代码中可以看到A_Block_That_Return_A_RACStreamBindBlock执行返回bindBlock,将bindBlock复制给bindingBlock
3.运行到RACDisposable *bindingDisposable = [self subscribeNext:^(id x) {},这里的self即栗子中的signal,x的值就是@”ABC”
4.执行id signal = bindingBlock(x, &stop);即回调bindBlock1
2
3
4
5RACStreamBindBlock bindBlock = ^(id value, BOOL *stop)
{
id stream = block(value) ?: [class empty];
return stream;
};
5.执行block(value),即回调innerBlock,value=@”ABC”1
2
3
4RACStream *(^innerBlock)(id value)=^(id value)
{
return [class return:block(value)];
};
6.RACSignal的[class return:block(value)],value=@”ABC”1
2
3+ (RACSignal *)return:(id)value {
return [RACReturnSignal return:value];
}
block(value)即1
2NSString *text=value;
return @(text.length);
返回@(3)
7.在RACReturnSignal中value=@(3)1
2
3
4
5
6
7
8@interface RACReturnSignal ()
@property (nonatomic, strong, readonly) id value;
@end
+ (RACSignal *)return:(id)value {
RACReturnSignal *signal = [[self alloc] init];
signal->_value = value;
return signal;
}
返回一个RACReturnSignal的实例,value为3;
8.结束了一大串的回调,
回到id signal = bindingBlock(x, &stop);
signal就是一个RACReturnSignal的实例,value为3
9.进入判断if (signal != nil) addSignal(signal);1
2
3
4
5
6
7
8
9
10
11
12
13
14void (^addSignal)(RACSignal *) = ^(RACSignal *signal) {
...(省略)
RACDisposable *disposable = [signal subscribeNext:^(id x) {
[subscriber sendNext:x];
} error:^(NSError *error) {
[compoundDisposable dispose];
[subscriber sendError:error];
} completed:^{
@autoreleasepool {
completeSignal(signal, selfDisposable);
}
}];
selfDisposable.disposable = disposable;
};
10.可以看到对RACReturnSignal的实例订阅,会执行RACReturnSignal重写的[subscribe o]方法1
2
3
4
5
6
7- (RACDisposable *)subscribe:(id<RACSubscriber>)subscriber {
NSCParameterAssert(subscriber != nil);
return [RACScheduler.subscriptionScheduler schedule:^{
[subscriber sendNext:self.value];
[subscriber sendCompleted];
}];
}
返回了self.value即@(3)
11.addSignal这个block中执行[subscriber sendNext:@(3)];
12.mappedSignalA的block被调用 输出:NSNumber,31
2
3[mappedSignalA subscribeNext:^(id x) {
NSLog(@"class-%@,value-%@",[x class],x);
}];
整理下过程
1.对一个RACSignal调用map:方法后,会产生新的数据流mappedSignal
2.订阅mappedSignal
3.mappedSignal内各种回调,回调到map:的处理过程,即栗子中NSString *text=value; return @(text.length);
4.内部新产生一个RACReturnSignal类型的signal保存mapd:block回调的值
5.bind:内订阅RACReturnSignal,RACReturnSignal内的方法将value返回
6.[subscriber sendNext:x];mappedSignal的订阅者获得结果
其实看似简单的一个map,内部实现起来却不容易.
开发中可能遇到的场景:验证密码输入框的字数
密码长度大于6时候,登入按钮才可以点击1
2
3
4
5
6
7
8
9
10__weak typeof(self) weakSelf = self;
[[self.pwdTextField.rac_textSignal map:^id(id value) {
NSString *pwd=value;
return @(pwd.length);
}] subscribeNext:^(id x) {
NSLog(@"x--%@",x);
weakSelf.loginBtn.enabled=[x integerValue]>6;
} error:^(NSError *error) {
NSLog(@"error");//正常情况下这个error是不会被调用的
}];
flattenMap的一个应用场景
上一块代码中的error不会被调用,因为rac_textSignal正常下不会发error,那么我想要流有判断错误的功能怎么办呢,
1.订阅rac_textSignal,再外层重新创建一个会发送error的newSignal,然后订阅newSignal1
2
3
4
5
6
7
8
9
10
11
12__weak typeof(self) weakSelf = self;
RACSignal *newSignal=[RACSignal createSignal:^RACDisposable *(id<RACSubscriber> subscriber) {
[weakSelf.pwdTextField.rac_textSignal subscribeNext:^(NSString *text) {
text.length<6?[subscriber sendError:nil]:[subscriber sendNext:@(text.length)];
}];
return nil;
}];
[newSignal subscribeNext:^(id x) {
weakSelf.loginBtn.enabled=YES;
} error:^(NSError *error) {
weakSelf.loginBtn.enabled=NO;
}];
2.用flattenMap1
2
3
4
5
6
7
8
9
10
11
12
13__weak typeof(self) weakSelf = self;
[[self.pwdTextField.rac_textSignal flattenMap:^RACStream *(NSString *text) {
return [RACSignal createSignal:^RACDisposable *(id<RACSubscriber> subscriber) {
text.length<6?[subscriber sendError:nil]:[subscriber sendNext:@(text.length)];
return nil;
}];
}] subscribeNext:^(id x) {
NSLog(@"x--%@",x);
weakSelf.loginBtn.enabled=YES;
} error:^(NSError *error) {
NSLog(@"error");
weakSelf.loginBtn.enabled=NO;
}];
Filtering
返回YES的值才能被订阅
简单例子:1
2
3
4
5
6
7
8//密码长度大于6时候,登入按钮才可以点击
__weak typeof(self) weakSelf = self;
[[self.pwdTextField.rac_textSignal filter:^BOOL(id value) {
NSString *text=value;
return text.length>6;
}] subscribeNext:^(id x) {
weakSelf.loginBtn.enabled=YES;
}];
看看filter:内部
1 | - (instancetype)filter:(BOOL (^)(id value))block { |
有了map的理解基础,filter就很简单了,
关键在于1
2
3
4
5if (block(value)) {
return [class return:value];
} else {
return class.empty;
}
block(value)即例子中的return text.length>6;
如果判断为真,则返回值,
如果判断为假,则返回空信号量
空信号量
1 | + (RACSignal *)empty { |
在bind:内部就会调用completeSignal(self, selfDisposable);1
2
3
4
5
6
7
8
9
10
11
12
13
14//completeSignal的block
void (^completeSignal)(RACSignal *, RACDisposable *) = ^(RACSignal *signal, RACDisposable *finishedDisposable) {
BOOL removeDisposable = NO;
@synchronized (signals) {
[signals removeObject:signal];
if (signals.count == 0) {
[subscriber sendCompleted];
[compoundDisposable dispose];
} else {
removeDisposable = YES;
}
}
if (removeDisposable) [compoundDisposable removeDisposable:finishedDisposable];
};
从代码中可以看到[subscriber sendCompleted]就这样,类似发送了一个空信号,subscribeNext的block就不会被调用;