iOS—emoji表情处理

在发送网络请求时，由于用户输入了emoji表情，服务端返回错误提示信息。为了解决服务器不能验证emoji编码的问题，需要在本地进行emoji的输入控制（正常情况下应该由服务器在数据库中添加emoji对应的转码表以支持客户端发送emoji表情），在网上搜了下iOS端解决办法如下：
1.当用户切换键盘为Emoji表情时，输入的表情不响应（即表情符号不显示到UITextView或UITextField）。这里可以通过UITextView或UITextField的回调和是否为emoji键盘：

[[[textView textInputMode] primaryLanguage] isEqualToString:@"emoji"]
-(BOOL)textField:(UITextField *)textField shouldChangeCharactersInRange:(NSRange)range replacementString:(NSString *)string{

    //不支持系统表情的输入
    if ([[[UITextInputMode currentInputMode ]primaryLanguage] isEqualToString:@"emoji"]) {
        return NO;
    }
    return YES;
}

2.通过过滤用户输入的emoji来实现

//过滤表情
+ (NSString *)filterEmoji:(NSString *)string {
    NSUInteger len = [string lengthOfBytesUsingEncoding:NSUTF8StringEncoding];
    const char *utf8 = [string UTF8String];
    char *newUTF8 = malloc( sizeof(char) * len );
    int j = 0;

    //0xF0(4) 0xE2(3) 0xE3(3) 0xC2(2) 0x30---0x39(4)
    for ( int i = 0; i < len; i++ ) {  
        unsigned int c = utf8;
        BOOL isControlChar = NO;
        if ( c == 4294967280 ||
            c == 4294967089 ||
            c == 4294967090 ||
            c == 4294967091 ||
            c == 4294967092 ||
            c == 4294967093 ||
            c == 4294967094 ||
            c == 4294967095 ||
            c == 4294967096 ||
            c == 4294967097 ||
            c == 4294967088 ) {
            i = i + 3;
            isControlChar = YES;
        }
        if ( c == 4294967266 || c == 4294967267 ) {
            i = i + 2;
            isControlChar = YES;
        }
        if ( c == 4294967234 ) {
            i = i + 1;
            isControlChar = YES;
        }
        if ( !isControlChar ) {
            newUTF8[j] = utf8;
            j++;
        }
    }
    newUTF8[j] = '\0';
    NSString *encrypted = [NSString stringWithCString:(const char*)newUTF8
                                             encoding:NSUTF8StringEncoding];
    free( newUTF8 );
    return encrypted;
}

3.通过判断用户输入的字符串时候含有表情来进行对应的操作

+ (NSString *)filterEmoji:(NSString *)string {
    NSUInteger len = [string lengthOfBytesUsingEncoding:NSUTF8StringEncoding];
    const char *utf8 = [string UTF8String];
    char *newUTF8 = malloc( sizeof(char) * len );
    int j = 0;

    //0xF0(4) 0xE2(3) 0xE3(3) 0xC2(2) 0x30---0x39(4)
    for ( int i = 0; i < len; i++ ) {  
        unsigned int c = utf8;
        BOOL isControlChar = NO;
        if ( c == 4294967280 ||
            c == 4294967089 ||
            c == 4294967090 ||
            c == 4294967091 ||
            c == 4294967092 ||
            c == 4294967093 ||
            c == 4294967094 ||
            c == 4294967095 ||
            c == 4294967096 ||
            c == 4294967097 ||
            c == 4294967088 ) {
            i = i + 3;
            isControlChar = YES;
        }
        if ( c == 4294967266 || c == 4294967267 ) {
            i = i + 2;
            isControlChar = YES;
        }
        if ( c == 4294967234 ) {
            i = i + 1;
            isControlChar = YES;
        }
        if ( !isControlChar ) {
            newUTF8[j] = utf8;
            j++;
        }
    }
    newUTF8[j] = '\0';
    NSString *encrypted = [NSString stringWithCString:(const char*)newUTF8
                                             encoding:NSUTF8StringEncoding];
    free( newUTF8 );
    return encrypted;
}

4. emoji在NSUTF8StringEncoding编码下占用4个字节，中文编码占用3个字节,可以根据- (BOOL)textField:(UITextField *)textField shouldChangeCharactersInRange:(NSRange)range replacementString:(NSString *)string方法，把string做处理，依据

NSUInteger stringUtf8Length = [string lengthOfBytesUsingEncoding:NSUTF8StringEncoding];
if(stringUtf8Length >= 4 && (stringUtf8Length / string.length != 3)) {
return NO;
}

判断,可排出大多数表情符号，还有少量的符号排除不了，比如^_ ，占3个字符。
代码不实用在九宫格键盘上的，可以在输入时打断点查看内容或直接输出%x查看。