所有这些都归功于Emanuelle，因为他提出的最多代码。

All credit here goes to Emanuelle, since he came up with most of the code.

虽然我以为我会发布他的代码的修改版本，有助于设置收件人。

Though I thought I would post a modified version of his code that helps set the to recipient.

我在MFMailComposeViewController上使用了一个类别

I used a Category on MFMailComposeViewController

#import "MFMailComposeViewController+Recipient.h"
#import <objc/message.h>

@implementation MFMailComposeViewController (Recipient)

+ (void)load {
    MethodSwizzle(self, @selector(setMessageBody:isHTML:), @selector(setMessageBodySwizzled:isHTML:));
}



static void MethodSwizzle(Class c, SEL origSEL, SEL overrideSEL)
{
    Method origMethod = class_getInstanceMethod(c, origSEL);
    Method overrideMethod = class_getInstanceMethod(c, overrideSEL);

    if (class_addMethod(c, origSEL, method_getImplementation(overrideMethod), method_getTypeEncoding(overrideMethod))) {
        class_replaceMethod(c, overrideSEL, method_getImplementation(origMethod), method_getTypeEncoding(origMethod));
    } else {
        method_exchangeImplementations(origMethod, overrideMethod);
    }
}

- (void)setMessageBodySwizzled:(NSString*)body isHTML:(BOOL)isHTML
{
    if (isHTML == YES) {
        NSRange range = [body rangeOfString:@"<torecipients>.*</torecipients>" options:NSRegularExpressionSearch|NSCaseInsensitiveSearch];
        if (range.location != NSNotFound) {
            NSScanner *scanner = [NSScanner scannerWithString:body];
            [scanner setScanLocation:range.location+14];
            NSString *recipientsString = [NSString string];
            if ([scanner scanUpToString:@"</torecipients>" intoString:&recipientsString] == YES) {
                NSArray * recipients = [recipientsString componentsSeparatedByString:@";"];
                [self setToRecipients:recipients];
            }
            body = [body stringByReplacingCharactersInRange:range withString:@""];
        }
    }
    [self setMessageBodySwizzled:body isHTML:isHTML];
}

@end