iOS的WebView中使用javascript调用原生的api

$('.content .saveCode').on('touchstart', function () {//touchstart
        if (temp == 0) {
            jump();
        }
        if (temp == 1) { android.savePic(image.src); }
        
    });

    function jump() {//IOS
        var touchstart = true;
        window.location = "/touchstart";     //改变URL  注意：要使用"/"分隔符 
    }

    function postStr() {//IOS
        return image.src;
    }

// 当加载完网页取到imageurl
- (void)webViewDidFinishLoad:(UIWebView *)webView
{
    _urlString = [_myWebView stringByEvaluatingJavaScriptFromString:@"postStr();"];
    NSLog(@"%@",_urlString);

}

// 调用次序 - shouldStart->FinishLoad->回调block函数
- (BOOL)webView:(UIWebView *)webView shouldStartLoadWithRequest:(NSURLRequest *)request navigationType:(UIWebViewNavigationType)navigationType
{
    if ([request.mainDocumentURL.relativePath isEqualToString:@"/touchstart"]) {
        UIImageFromURL( [NSURL URLWithString:_urlString], ^( UIImage * image )
                       {
                           UIImageWriteToSavedPhotosAlbum( image, self, @selector( onSaveComplete:didFinishSavingWithError:contextInfo: ), nil );
                       }, ^(void){
                           NSLog(@"error!");
                       });

        return false;
    }
    return  true;
}

void UIImageFromURL( NSURL * URL, void (^imageBlock)(UIImage * image), void (^errorBlock)(void) )
{
    dispatch_async( dispatch_get_global_queue( DISPATCH_QUEUE_PRIORITY_DEFAULT, 0 ), ^(void)
                   {
                       NSData * data = [[NSData alloc] initWithContentsOfURL:URL];
                       UIImage * image = [[UIImage alloc] initWithData:data];
                       dispatch_async( dispatch_get_main_queue(), ^(void){
                           if( image != nil )
                           {
                               imageBlock( image );
                           } else {
                               errorBlock();
                           }
                       });
                   });
}