来自实例方法的具有静态 void 的 Objective C Cordova 回调

Posted 2023-03-15

【中文标题】来自实例方法的具有静态 void 的 Objective C Cordova 回调

【英文标题】：Objective C Cordova callbacks with static void from instance method

【发布时间】：2014-12-17 08:13:46

【问题描述】：

我正在构建一个可以执行 DNS 查询的 Cordova 插件。由于操作是异步的，我需要使用回调来返回值。

我有

#import <dns_sd.h>

....

- (void)dnsQuery:(CDVInvokedUrlCommand*)command

    id domain = [command.arguments objectAtIndex:0];

    DNSServiceRef serviceRef;

    DNSServiceQueryRecord(&serviceRef, 0, 0, "hmspl.de", kDNSServiceType_TXT,
                      kDNSServiceClass_IN, queryCallback, command);

    DNSServiceProcessResult(serviceRef);
    DNSServiceRefDeallocate(serviceRef);

然后是回调，也就是static void:

static void queryCallback(DNSServiceRef sdRef, DNSServiceFlags flags, uint32_t interfaceIndex,
                      DNSServiceErrorType errorCode, const char *fullname, uint16_t rrtype,
                      uint16_t rrclass, uint16_t rdlen, const void *rdata, uint32_t ttl, void *context) 

if (errorCode == kDNSServiceErr_NoError && rdlen > 1) 
    NSMutableData *txtData = [NSMutableData dataWithCapacity:rdlen];

    for (uint16_t i = 1; i < rdlen; i += 256) 
        [txtData appendBytes:rdata + i length:MIN(rdlen - i, 255)];
    

    NSString *theTXT = [[NSString alloc] initWithBytes:txtData.bytes length:txtData.length encoding:NSASCIIStringEncoding];
    NSLog(@"%@",    

    //PROBLEM HERE
    [self.commandDelegate sendPluginResult:theTXT callbackId:context.callbackId]; 
   


@end

我需要用初始方法返回一个回调：

[self.commandDelegate sendPluginResult:theTXT callbackId:command.callbackId];

但我不能在static void 方法中使用self。

如何将值 theTXT 返回到 cordova 并将 command.callbackId 从原始方法传递给回调？

【参考方案1】：

DNSServiceQueryRecord 的最后一个参数是应用程序上下文，而不是传递cordova 的命令，而是将self 作为参数传递

在您的 .h 中

@property (strong, nonatomic) NSString * callbackId;

在你的 .m 中

- (void)dnsQuery:(CDVInvokedUrlCommand*)command

    self.callbackId = command.callbackId;

    id domain = [command.arguments objectAtIndex:0];

    DNSServiceRef serviceRef;

    DNSServiceQueryRecord(&serviceRef, 0, 0, "hmspl.de", kDNSServiceType_TXT,
                          kDNSServiceClass_IN, queryCallback, (__bridge void*)self);

    DNSServiceProcessResult(serviceRef);
    DNSServiceRefDeallocate(serviceRef);

所以你现在可以在 queryCallback 中使用它

static void queryCallback(DNSServiceRef sdRef, DNSServiceFlags flags, uint32_t interfaceIndex,
                      DNSServiceErrorType errorCode, const char *fullname, uint16_t rrtype,
                      uint16_t rrclass, uint16_t rdlen, const void *rdata, uint32_t ttl, void *context) 

if (errorCode == kDNSServiceErr_NoError && rdlen > 1) 
    NSMutableData *txtData = [NSMutableData dataWithCapacity:rdlen];

    for (uint16_t i = 1; i < rdlen; i += 256) 
        [txtData appendBytes:rdata + i length:MIN(rdlen - i, 255)];
    

    NSString *theTXT = [[NSString alloc] initWithBytes:txtData.bytes length:txtData.length encoding:NSASCIIStringEncoding];
    NSLog(@"%@",    

    [context.commandDelegate sendPluginResult:theTXT callbackId:context.callbackId];