JavascriptCore：在JSExport中将javascript函数作为参数传递 [英] JavascriptCore: pass javascript function as parameter in JSExport

问题描述

JavascriptCore是iOS7支持的新框架。我们可以使用JSExport协议将部分objc类暴露给JavaScript。

JavascriptCore is a new framework supported in iOS7. We can use the JSExport protocol to expose parts of objc class to JavaScript.

在javascript中，我尝试将函数作为参数传递。就像这样：

In javascript, I tried to pass function as parameter. Just like this:

function getJsonCallback(json) {
        movie = JSON.parse(json)
        renderTemplate()
}
viewController.getJsonWithURLCallback("", getJsonCallback)

在我的objc viewController中，我定义了我的协议：

In my objc viewController, I defined my protocol:

@protocol FetchJsonForJS <JSExport>
 - (void)getJsonWithURL:(NSString *)URL
               callback:(void (^)(NSString *json))callback;
 - (void)getJsonWithURL:(NSString *)URL
         callbackScript:(NSString *)script;
@end

在javascript中，viewController.getJsonWithURLCallbackScript工作，但是，viewController.getJsonWithURLCallback无效。

In javascript, viewController.getJsonWithURLCallbackScript works, however, viewController.getJsonWithURLCallback not work.

我在JSExport中使用了块有什么错误吗？ thx。

Is there any mistake that I used block in JSExport? Thx.

推荐答案

问题是你已经将回调定义为采用NSString arg的Objective-C块但javascript没有知道如何处理这个并在你尝试评估viewController.getJsonWithURLCallback（，getJsonCallback）时产生异常 - 它认为第二个参数的类型是'undefined'

The problem is you have defined the callback as an Objective-C block taking a NSString arg but javascript doesn't know what to do with this and produces an exception when you try to evaluate viewController.getJsonWithURLCallback("", getJsonCallback) - it thinks the type of the second parameter is 'undefined'

相反，您需要将回调定义为javascript函数。

Instead you need to define the callback as a javascript function.

您可以使用JSValue在Objective-C中执行此操作。

You can do this in Objective-C simply using JSValue.

对于那里的其他读者，这是一个完整的工作示例（有异常处理）：

For other readers out there, here's a complete working example (with exception handling):

TestHarnessViewController.h：

#import <UIKit/UIKit.h>
#import <JavaScriptCore/JavaScriptCore.h>

@protocol TestHarnessViewControllerExports <JSExport>
- (void)getJsonWithURL:(NSString *)URL callback:(JSValue *)callback;
@end

@interface TestHarnessViewController : UIViewController <TestHarnessViewControllerExports>
@end

TestHarnessViewController.m：
（如果使用复制/粘贴，删除evaluateScript中的换行符 - 为了清楚起见添加了这些换行符）：

TestHarnessViewController.m: (if using copy/paste, remove the newlines inside the evaluateScript - these were added for clarity):

#import "TestHarnessViewController.h"

@implementation TestHarnessViewController {
    JSContext *javascriptContext;
}

- (void)viewDidLoad
{
    [super viewDidLoad];

    javascriptContext  = [[JSContext alloc] init];
    javascriptContext[@"consoleLog"] = ^(NSString *message) {
        NSLog(@"Javascript log: %@",message);
    };
    javascriptContext[@"viewController"] = self;

    javascriptContext.exception = nil;
    [javascriptContext evaluateScript:@"
        function getJsonCallback(json) {
            consoleLog(\"getJsonCallback(\"+json+\") invoked.\");
            /* 
            movie = JSON.parse(json); 
            renderTemplate(); 
            */
        } 

        viewController.getJsonWithURLCallback(\"\", getJsonCallback);
    "];
    JSValue *e = javascriptContext.exception;
    if (e != nil && ![e isNull])
        NSLog(@"Javascript exception occurred %@", [e toString]);
}

- (void)getJsonWithURL:(NSString *)URL callback:(JSValue *)callback {
    NSString *json = @""; // Put JSON extract from URL here
    [callback callWithArguments:@[json]];
}

- (void)didReceiveMemoryWarning
{
    [super didReceiveMemoryWarning];
    // Dispose of any resources that can be recreated.
}

@end

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