相关问题：CrashDoctor Diagnosis: Application threw exception NSRangeException: *** -[__NSCFString substringToIndex:]: Index 28 out of bounds; string length 26

下面就针对以下方法进行异常捕获 substringToIndex;、substringFromIndex、substringWithRange。添加NSString 的category 进行异常处理；核心代码如下：

// Swizzling核心代码
+ (void)load {
    static dispatch_once_t onceToken;
    dispatch_once(&onceToken, ^{
        Method fromMethod = class_getInstanceMethod(objc_getClass("__NSCFString"), @selector(substringToIndex:));
        Method toMethod = class_getInstanceMethod(objc_getClass("__NSCFString"), @selector(xd_substringToIndex:));
        method_exchangeImplementations(fromMethod, toMethod);
        
        Method fromMethod2 = class_getInstanceMethod(objc_getClass("__NSCFString"), @selector(substringFromIndex:));
        Method toMethod2 = class_getInstanceMethod(objc_getClass("__NSCFString"), @selector(xd_substringFromIndex:));
        method_exchangeImplementations(fromMethod2, toMethod2);
        
        Method fromMethod3 = class_getInstanceMethod(objc_getClass("__NSCFString"), @selector(substringWithRange:));
        Method toMethod3 = class_getInstanceMethod(objc_getClass("__NSCFString"), @selector(xd_substringWithRange:));
        method_exchangeImplementations(fromMethod3, toMethod3);
    });
}

- (id)xd_substringToIndex:(NSUInteger)index {
    if (self.length-1 < index) {
        @try {
            return [self xd_substringToIndex:index];
        }
        @catch (NSException *exception) {
            NSLog(@"---------- %s Crash Because Method %s  ----------\n", class_getName(self.class), __func__);
            NSLog(@"%@", [exception callStackSymbols]);
            return @"";
        }
        @finally {}
    }
    else {
        return [self xd_substringToIndex:index];
    }
}

- (id)xd_substringFromIndex:(NSUInteger)index {
    if (self.length-1 < index) {
        @try {
            return [self xd_substringFromIndex:index];
        }
        @catch (NSException *exception) {
            NSLog(@"---------- %s Crash Because Method %s  ----------\n", class_getName(self.class), __func__);
            NSLog(@"%@", [exception callStackSymbols]);
            return @"";
        }
        @finally {}
    }
    else {
        return [self xd_substringFromIndex:index];
    }
}

- (id)xd_substringWithRange:(NSRange)range {
    if (((range.location + range.length) > self.length) || range.location < 0) {
        @try {
            return [self xd_substringWithRange:range];
        }
        @catch (NSException *exception) {
            NSLog(@"---------- %s Crash Because Method %s  ----------\n", class_getName(self.class), __func__);
            NSLog(@"%@", [exception callStackSymbols]);
            return @"";
        }
        @finally {}
    }
    else {
        return [self xd_substringWithRange:range];
    }
}