解决: NSDebugDescription=Unable to convert data to string around character.m

Sometimes, we will get this error:

> Error Domain=NSCocoaErrorDomain Code=3840 "Unable to convert data to string around character 28." UserInfo={NSDebugDescription=Unable to convert data to string around character 28.}

The reason that causes this error is that the encoding(GBK for example) of the response data is not compatible with the default encoding(UTF-8) of iOS.
To resolve this, we need to convert the encoding of response data to UTF-8.

Here is the inline method of converting the encoding to UTF-8:

```objc
static NSString *GBK2UTF8(NSData *data) {
    NSStringEncoding enc =CFStringConvertEncodingToNSStringEncoding(kCFStringEncodingGB_18030_2000);
    NSString *gbkString = [[NSString alloc] initWithData:data encoding:enc];
    return gbkString;
}
```

After define the inline method, go to the lines where response data transfer happens.
First, transfer the binary data to `NSString` with the inline method above:

```objc
NSString *dataString = GBK2UTF8(data); // data is the binary response data
```

Then, create a new data object using UTF-8 encoding with the dataString:


```objc
data = [dataString dataUsingEncoding:NSUTF8StringEncoding];
```

Finally, the encoding of the data turns to UTF-8.