http://blog.csdn.net/zfpp25_/article/details/9232129
http://blog.csdn.net/zfpp25_/article/details/9236357
三、Memory management
1• Objective-C uses ARC(OC 使用ARC機制)
2• JavaScriptCore uses garbage collection (JS 使用垃圾回收機制)
■ All references are strong (JS中全部都是“強引用”)
3• API memory management is mostly automatic
4• Two situations that require extra attention: (幾乎SDK已經做好了很多事情,所以開發者只需要重點掌握以下亮點)
■ Storing JavaScript values in Objective-C objects
■ Adding JavaScript fields to Objective-C objects
(英文文檔只要被翻譯了,就難免失去原有的含義,儘量不翻譯~)
根據官方文檔關於JS-OC內存管理總結:由於JS中全部都是強引用,如果JS 與 OC互相引用時,就要防止OC也強引用JS,這樣會形成引用循環,所以OC要想辦法弱引用,但弱引用會被系統釋放,所以把可能被釋放的對象放到一個容器中來防止對象被被錯誤釋放。
看代碼(一):
JS:
function ClickHandler(button, callback) {
this.button = button;
this.button.onClickHandler = this;
this.handleEvent = callback;
};
OC:
@implementation MyButton
- (void)setOnClickHandler:(JSValue *)handler
{
_onClickHandler = handler; // Retain cycle
}
@end
如果直接保存
handler,就會出現內存泄露,因爲 JS 中引用 button 對象是強引用,如果 Button 也用強引用來保存 JS 中的 handler,這就導致了 循環引用。我們沒法改變 JavaScript 中的強引用機制,只能在 Objective-C 中弱引用 handler,爲了防止 onclick handler 被錯誤釋放, JavaScriptCore 給出的解決方案如下:
- (void)setOnClickHandler:(JSValue *)handler
{
_onClickHandler = [JSManagedValue managedValueWithValue:handler];
[_context.virtualMachine addManagedReference:_onClickHandler
withOwner:self]
}
代碼(二):
- (void)loadColorsPlugin
{
// Load the plugin script from the bundle.
NSString *path = [[NSBundlemainBundle]pathForResource:@"colors"ofType:@"js"];
NSString *pluginScript = [NSStringstringWithContentsOfFile:pathencoding:NSUTF8StringEncodingerror:nil];
_context = [[JSContextalloc]init];
// We insert the AppDelegate into the global object so that when we call
// -addManagedReference:withOwner: for the plugin object we're about to load
// and pass the AppDelegate as the owner, the AppDelegate itself is reachable from
// within JavaScript. If we didn't do this, the AppDelegate wouldn't be reachable
// from JavaScript, and there wouldn't be anything keeping the plugin object alive.
_context[@"AppDelegate"] =self;
// Insert a block so that the plugin can create NSColors to return to us later.
_context[@"makeNSColor"] = ^(NSDictionary *rgb){
return [NSColorcolorWithRed:[rgb[@"red"]floatValue] / 255.0f
green:[rgb[@"green"]floatValue] /255.0f
blue:[rgb[@"blue"]floatValue] /255.0f
alpha:1.0f];
};
JSValue *plugin = [_contextevaluateScript:pluginScript];
_colorPlugin = [JSManagedValuemanagedValueWithValue:plugin];
[_context.virtualMachineaddManagedReference:_colorPluginwithOwner:self];
[self.windowsetDelegate:self];
}
注意:
JSManagedValue:
The primary use case for JSManagedValue is for safely referencing JSValues
from the Objective-C heap. It is incorrect to store a JSValue into an
Objective-C heap object, as this can very easily create a reference cycle,
keeping the entire JSContext alive.
(將 JSValue 轉爲 JSManagedValue 類型後,可以添加到 JSVirtualMachine 對象中,這樣能夠保證你在使用過程中 JSValue 對象不會被釋放掉,當你不再需要該 JSValue 對象後,從 JSVirtualMachine 中移除該 JSManagedValue 對象,JSValue 對象就會被釋放並置空。)
JSVirtualMachine:
All instances of JSContext are associated with a single JSVirtualMachine. The
virtual machine provides an "object space" or set of execution resources.(JSVirtualMachine就是一個用於保存弱引用對象的數組,加入該數組的弱引用對象因爲會被該數組 retain,所以保證了使用時不會被釋放,當數組裏的對象不再需要時,就從數組中移除,沒有了引用的對象就會被系統釋放。)
四、Threading
• API is thread safe• Locking granularity is JSVirtualMachine
■ Use separate JSVirtualMachines for concurrency/parallelism
五、JavaScriptCore
C API
JSValue ↔ JSValueRef :
JSValueRef valueRef = XXX;
JSValue *value = [JSValue valueWithJSValueRef:valueRef inContext:context];
JSValue *value = XXX;
JSValueRef valueRef = [value JSValueRef];
JSContext ↔ JSGlobalContextRef
:
JSGlobalContextRef ctx = XXX;
JSContext *context = [JSContext contextWithJSGlobalContextRef:ctx];
JSContext *context = XXX;
JSGlobalContextRef ctx = [context JSGlobalContextRef];
五、JavaScriptCore
with a WebView (Mac)
暫不討論,Demos下載中有項目源碼。
參考資料:
https://developer.apple.com/library/mac/#documentation/Carbon/Reference/ WebKit_JavaScriptCore_Ref/
https://developer.apple.com/wwdc/schedule/details.php?id=615
https://github.com/zynga/jsbindings
https://developer.apple.com/library/mac/#documentation/Cocoa/Reference/WebKit/Protocols/WebScripting_Protocol/Reference/Reference.html
https://developer.apple.com/library/mac/#documentation/Cocoa/Reference/WebKit/Classes/WebScriptObject_Class/Reference/Reference.html#//apple_ref/doc/c_ref/WebScriptObject
Demos下載直通車:http://download.csdn.net/detail/zfpp25_/8510931(其中 TestJS 項目爲本文測試使用項目)
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