文章摘自: http://www.cocoachina.com/ios/20150127/11037.html
JSContext/JSValue
JSContext 即JavaScript代码的运行环境。一个Context就是一个JavaScript代码执行的环境,也叫作用域。当在浏览器中运行 JavaScript代码时,JSContext就相当于一个窗口,能轻松执行创建变量、运算乃至定义函数等的JavaScript
//Objective-C
JSContext *context = [[JSContext alloc] init];
[context evaluateScript:@
"var num = 8 + 5"
];
[context evaluateScript:@
"var names = ['Grace', 'Ada', 'Margaret']"
];
[context evaluateScript:@
"var triple = function(value) { return value * 3 }"
];
JSValue *tripleNum = [context evaluateScript:@
"triple(num)"
];
NSLog(@
"Tripled: %d"
, [tripleNum toInt32]);
//Swift
let context = JSContext()
context.evaluateScript(
"var num = 5 + 5"
)
context.evaluateScript(
"var names = ['Grace', 'Ada', 'Margaret']"
)
context.evaluateScript(
"var triple = function(value) { return value * 3 }"
)
let tripleNum: JSValue = context.evaluateScript(
"triple(num)"
)
println(
"Tripled: \(tripleNum.toInt32())"
)
JSValue *names = context[@
"names"
];
JSValue *initialName = names[0];
NSLog(@
"The first name: %@"
, [initialName toString]);
//Swift
let names = context.objectForKeyedSubscript(
"names"
)
let initialName = names.objectAtIndexedSubscript(0)
println(
"The first name: \(initialName.toString())"
)
//Objective-C
JSValue *tripleFunction = context[@
"triple"
];
JSValue *result = [tripleFunction callWithArguments:@[@5] ];
NSLog(@
"Five tripled: %d"
, [result toInt32]);
//Swift
let tripleFunction = context.objectForKeyedSubscript(
"triple"
)
let result = tripleFunction.callWithArguments([5])
println(
"Five tripled: \(result.toInt32())"
)
//Objective-C
context.exceptionHandler = ^(JSContext *context, JSValue *exception) {
NSLog(@
"JS Error: %@"
, exception);
};
[context evaluateScript:@
"function multiply(value1, value2) { return value1 * value2 "
];
// JS Error: SyntaxError: Unexpected end of script
//Swift
context.exceptionHandler = { context, exception
in
println(
"JS Error: \(exception)"
)
}
context.evaluateScript(
"function multiply(value1, value2) { return value1 * value2 "
)
// JS Error: SyntaxError: Unexpected end of script
JavaScript函数调用
了 解了从JavaScript环境中获取不同值以及调用函数的方法,那么反过来,如何在JavaScript环境中获取Objective-C或者 Swift定义的自定义对象和方法呢?要从JSContext中获取本地客户端代码,主要有两种途径,分别为Blocks和JSExport协议。
Blocks (块)
在JSContext中,如果Objective-C代码块赋值为一个标识 符,JavaScriptCore就会自动将其封装在JavaScript函数中,因而在JavaScript上使用Foundation和Cocoa类 就更方便些——这再次验证了JavaScriptCore强大的衔接作用。现在CFStringTransform也能在JavaScript上使用了, 如下所示:
//Objective-C
context[@
"simplifyString"
] = ^(NSString *input) {
NSMutableString *mutableString = [input mutableCopy];
CFStringTransform((__bridge CFMutableStringRef)mutableString, NULL, kCFStringTransformToLatin, NO);
CFStringTransform((__bridge CFMutableStringRef)mutableString, NULL, kCFStringTransformStripCombiningMarks, NO);
return
mutableString;
};
NSLog(@
"%@"
, [context evaluateScript:@
"simplifyString('?????!')"
]);
//Swift
let simplifyString: @objc_block String -> String = { input
in
var
mutableString = NSMutableString(string: input) as CFMutableStringRef
CFStringTransform(mutableString, nil, kCFStringTransformToLatin, Boolean(0))
CFStringTransform(mutableString, nil, kCFStringTransformStripCombiningMarks, Boolean(0))
return
mutableString
}
context.setObject(unsafeBitCast(simplifyString, AnyObject.self), forKeyedSubscript:
"simplifyString"
)
println(context.evaluateScript(
"simplifyString('?????!')"
))
// annyeonghasaeyo!
内存管理(Memory Management)
代码块可以捕获变量引用,而JSContext 所有变量的强引用都保留在JSContext中,所以要注意避免循环强引用问题。另外,也不要在代码块中捕获JSContext或任何JSValues, 建议使用[JSContext currentContext]来获取当前的Context对象,根据具体需求将值当做参数传入block中。
JSExport协议
借助JSExport协议也可以在JavaScript上使用自定义对象。在JSExport协议中声明的实例方法、类方法,不论属性,都能自动与JavaScrip交互。文章稍后将介绍具体的实践过程。
JavaScriptCore实践
我们可以通过一些例子更好地了解上述技巧的使用方法。先定义一 个遵循JSExport子协议PersonJSExport的Person model,再用JavaScript在JSON中创建和填入实例。有整个JVM,还要NSJSONSerialization干什么?
PersonJSExports和Person
Person类执行的 PersonJSExports协议具体规定了可用的JavaScript属性。,在创建时,类方法必不可少,因为JavaScriptCore并不适用 于初始化转换,我们不能像对待原生的JavaScript类型那样使用var person = new Person()。
//Objective-C
// in Person.h -----------------
@class Person;
@protocol PersonJSExports @property (nonatomic, copy) NSString *firstName;
@property (nonatomic, copy) NSString *lastName;
@property NSInteger ageToday;
- (NSString *)getFullName;
// create and return a new Person instance with `firstName` and `lastName`
+ (instancetype)createWithFirstName:(NSString *)firstName lastName:(NSString *)lastName;
@end
@interface Person : NSObject @property (nonatomic, copy) NSString *firstName;
@property (nonatomic, copy) NSString *lastName;
@property NSInteger ageToday;
@end
// in Person.m -----------------
@implementation Person
- (NSString *)getFullName {
return
[NSString stringWithFormat:@
"%@ %@"
, self.firstName, self.lastName];
}
+ (instancetype) createWithFirstName:(NSString *)firstName lastName:(NSString *)lastName {
Person *person = [[Person alloc] init];
person.firstName = firstName;
person.lastName = lastName;
return
person;
}
@end
//Swift
// Custom protocol must be declared with `@objc`
@objc protocol PersonJSExports : JSExport {
var
firstName: String { get set }
var
lastName: String { get set }
var
birthYear: NSNumber? { get set }
func getFullName() -> String
/// create and return a new Person instance with `firstName` and `lastName`
class func createWithFirstName(firstName: String, lastName: String) -> Person
}
// Custom class must inherit from `NSObject`
@objc class Person : NSObject, PersonJSExports {
// properties must be declared as `dynamic`
dynamic
var
firstName: String
dynamic
var
lastName: String
dynamic
var
birthYear: NSNumber?
init(firstName: String, lastName: String) {
self.firstName = firstName
self.lastName = lastName
}
class func createWithFirstName(firstName: String, lastName: String) -> Person {
return
Person(firstName: firstName, lastName: lastName)
}
func getFullName() -> String {
return
"\(firstName) \(lastName)"
}
}
配置JSContext
创建Person类之后,需要先将其导出到JavaScript环境中去,同时还需导入Mustache JS库,以便对Person对象应用模板。
//Objective-C
// export Person class
context[@
"Person"
] = [Person class];
// load Mustache.js
NSString *mustacheJSString = [NSString stringWithContentsOfFile:... encoding:NSUTF8StringEncoding error:nil];
[context evaluateScript:mustacheJSString];
//Swift
// export Person class
context.setObject(Person.self, forKeyedSubscript:
"Person"
)
// load Mustache.js
if
let mustacheJSString = String(contentsOfFile:..., encoding:NSUTF8StringEncoding, error:nil) {
context.evaluateScript(mustacheJSString)
}
JavaScript数据&处理
以下简单列出一个JSON范例,以及用JSON来创建新Person实例。
注 意:JavaScriptCore实现了Objective-C/Swift的方法名和JavaScript代码交互。因为JavaScript没有命名 好的参数,任何额外的参数名称都采取驼峰命名法(Camel-Case),并附加到函数名称上。在此示例中,Objective-C的方法 createWithFirstName:lastName:在JavaScript中则变成了 createWithFirstNameLastName()。
//JSON
[
{
"first"
:
"Grace"
,
"last"
:
"Hopper"
,
"year"
: 1906 },
{
"first"
:
"Ada"
,
"last"
:
"Lovelace"
,
"year"
: 1815 },
{
"first"
:
"Margaret"
,
"last"
:
"Hamilton"
,
"year"
: 1936 }
]
//JavaScript
var
loadPeopleFromJSON =
function
(jsonString) {
var
data = JSON.parse(jsonString);
var
people = [];
for
(i = 0; i < data.length; i++) {
var
person = Person.createWithFirstNameLastName(data[i].first, data[i].last);
person.birthYear = data[i].year;
people.push(person);
}
return
people;
}
//Objective-C
// get JSON string
NSString *peopleJSON = [NSString stringWithContentsOfFile:... encoding:NSUTF8StringEncoding error:nil];
// get load function
JSValue *load = context[@
"loadPeopleFromJSON"
];
// call with JSON and convert to an NSArray
JSValue *loadResult = [load callWithArguments:@[peopleJSON]];
NSArray *people = [loadResult toArray];
// get rendering function and create template
JSValue *mustacheRender = context[@
"Mustache"
][@
"render"
];
NSString *template = @
"{{getFullName}}, born {{birthYear}}"
;
// loop through people and render Person object as string
for
(Person *person
in
people) {
NSLog(@
"%@"
, [mustacheRender callWithArguments:@[template, person]]);
}
// Output:
// Grace Hopper, born 1906
// Ada Lovelace, born 1815
//Swift
// get JSON string
if
let peopleJSON = NSString(contentsOfFile:..., encoding: NSUTF8StringEncoding, error: nil) {
// get load function
let load = context.objectForKeyedSubscript(
"loadPeopleFromJSON"
)
// call with JSON and convert to an array of `Person`
if
let people = load.callWithArguments([peopleJSON]).toArray() as? [Person] {
// get rendering function and create template
let mustacheRender = context.objectForKeyedSubscript(
"Mustache"
).objectForKeyedSubscript(
"render"
)
let template =
"{{getFullName}}, born {{birthYear}}"
// loop through people and render Person object as string
for
person
in
people {
println(mustacheRender.callWithArguments([template, person]))
}
}
}
// Output:
// Grace Hopper, born 1906
// Ada Lovelace, born 1815
// Margaret Hamilton, born 1936