首先要獲取cache資料夾路徑

#define cachePath [NSSearchPathForDirectoriesInDomains(NSCachesDirectory, NSUserDomainMask, YES) firstObject]

//
//  LLFileTool.h
//  BuDeJie
//
//  Created by llkj on 2017/10/13.
//  Copyright © 2017年 LayneCheung. All rights reserved.
//  處理檔案快取

#import <Foundation/Foundation.h>

@interface LLFileTool : NSObject
/**
 刪除資料夾所有檔案

 @param
 
 directoryPath 資料夾路徑
 */
+ (void)removeDirectoryPath:(NSString *)directoryPath;

/**
 獲取資料夾尺寸

 @param directoryPath 資料夾路徑
 @param completion 資料夾尺寸
 */
+ (void)getFileSize:(NSString *)directoryPath completion:(void(^)(NSInteger totalSize))completion;
@end

//
//  LLFileTool.m
//  BuDeJie
//
//  Created by llkj on 2017/10/13.
 

//  Copyright © 2017年 LayneCheung. All rights reserved.
//

#import "LLFileTool.h"

@implementation LLFileTool

+ (void)removeDirectoryPath:(NSString *)directoryPath {
    //獲取檔案管理者
    NSFileManager *mgr = [NSFileManager defaultManager];

    BOOL isDirectoey;
    BOOL isExist = [mgr fileExistsAtPath:directoryPath isDirectory:&isDirectoey];

    if
 
 (!isExist || !isDirectoey) {
        NSException *exception = [NSException exceptionWithName:@"PathError" reason:@"需要傳入的是資料夾路徑，並且路徑要存在！" userInfo:nil];
        [exception raise];
    }
    //獲取cache資料夾下所有檔案，不包括子路徑的子路徑
    NSArray *subPaths = [mgr contentsOfDirectoryAtPath:directoryPath error:nil];
    for (NSString *subPath in subPaths) {
        //拼接完整路徑
        NSString *filePath = [directoryPath stringByAppendingPathComponent:subPath];
        //刪除路徑
        [mgr removeItemAtPath:filePath error:nil];
    }
}

+ (void)getFileSize:(NSString *)directoryPath completion:(void(^)(NSInteger totalSize))completion {
    NSFileManager *mgr =[NSFileManager defaultManager];
    BOOL isDirectory;
    BOOL isExist = [mgr fileExistsAtPath:directoryPath isDirectory:&isDirectory];
    if (!isDirectory || !isExist) {
        NSException *exception = [NSException exceptionWithName:@"PathError" reason:@"需要傳入的是資料夾路徑，並且路徑要存在！" userInfo:nil];
        [exception raise];
    }
    dispatch_async(dispatch_get_global_queue(0, 0), ^{
        //獲取資料夾下所有檔案，包括子路徑的子路徑
        NSArray *subPaths = [mgr subpathsAtPath:directoryPath];
        NSInteger totalSize = 0;
        for (NSString *subPath in subPaths) {
            //獲取檔案全路徑
            NSString *filePath = [directoryPath stringByAppendingPathComponent:subPath];

            //判斷隱藏檔案
            if ([filePath containsString:@".DS"]) continue;

            //判斷是否資料夾
            BOOL isDircetory;

            //判斷檔案是否存在，並判斷是否是資料夾
            BOOL isExist = [mgr fileExistsAtPath:filePath isDirectory:&isDircetory];
            if (isDircetory || !isExist) continue;

            //獲取檔案屬性
           NSDictionary *attr = [mgr attributesOfItemAtPath:filePath error:nil];
            NSInteger size = [attr fileSize];

            totalSize += size;
        }

        //計算完成回撥
        dispatch_sync(dispatch_get_main_queue(), ^{
            if (completion) {
                completion(totalSize);
            }
        });
    });
}
@end

注意：返回的單位是（B），下面是單位換算

- (NSString *)cacheSizeStr {
    NSInteger totalSize = _totalSize;
    NSString *sizeStr = @"清除快取";
    if (totalSize > 1000 * 1000) {
        CGFloat sizeF = totalSize / 1000.0 / 1000.0;
        sizeStr = [NSString stringWithFormat:@"%@(%.1fMB)", sizeStr, sizeF];
    } else if (totalSize > 1000) {
        CGFloat sizeF = totalSize / 1000.0;
        sizeStr = [NSString stringWithFormat:@"%@(%.1fKB)", sizeStr, sizeF];
    } else if (totalSize > 0) {
        sizeStr = [NSString stringWithFormat:@"%@(%.ldB)", sizeStr, totalSize];
    }
    return sizeStr;
}