ios开发中常用的几种辅助方法

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//1.Keychain本地长期键值存储//删除+(void)deleteStringForKey:(NSString *)aKey{    NSMutableDictionary *query = [NSMutableDictionary dictionary];    [query setObject:(__bridge id)kSecClassGenericPassword forKey:(__bridge  id)kSecClass];    [query setObject:(id)aKey forKey:(__bridge id)kSecAttrAccount];    OSStatus status = SecItemDelete((__bridge CFDictionaryRef)query);    if (status != noErr) {        // NSLog(@"[KeychainAccessor]>>> SecItemDelete result in error:(%d)", (int)status);    }}//存储+ (void)setString:(NSString *)aString forKey:(NSString *)aKey{    NSData *savingData = [aString dataUsingEncoding:NSUTF8StringEncoding];    NSMutableDictionary *attributes = [NSMutableDictionary dictionary];    [attributes setObject:(__bridge id)kSecClassGenericPassword forKey:(__bridge id)kSecClass];    [attributes setObject:(id)aKey forKey:(__bridge id)kSecAttrAccount];    [attributes setObject:savingData forKey:(__bridge id)kSecValueData];    OSStatus status = SecItemAdd((__bridge CFDictionaryRef)attributes, NULL);    if ((int)status==-25299) {        //  NSLog(@"delete old data add new data");        [self deleteStringForKey:aKey];        SecItemAdd((__bridge CFDictionaryRef)attributes, NULL);    }    if (status != noErr) {        //  NSLog(@"[KeychainAccessor]>>> SecItemAdd result in error:(%d)",(int)status);    }}//查询+ (NSString *)stringForKey:(NSString *)aKey {    NSMutableDictionary *query = [NSMutableDictionary dictionary];    [query setObject:(__bridge id)kSecClassGenericPassword forKey:(__bridge  id)kSecClass];    [query setObject:(id)aKey forKey:(__bridge id)kSecAttrAccount];    [query setObject:(__bridge id)kCFBooleanTrue forKey:(__bridge id)kSecReturnData];    [query setObject:(__bridge id)kSecMatchLimitOne forKey:(__bridge id)kSecMatchLimit];    CFDataRef result = nil;    OSStatus status = SecItemCopyMatching((__bridge CFDictionaryRef)query, (CFTypeRef*)&result);    if (status != noErr) {        if (status == errSecItemNotFound) {            //NSLog(@"[KeychainAccessor]>>> SecItemCopyMatching result NOT-FOUND.");        } else {            //NSLog(@"[KeychainAccessor]>>> SecItemCopyMatching result in error:(%d)", (int)status);        }        return @"";    }    NSData *theValue = [(__bridge NSData*)result copy];    return [[NSString alloc] initWithData:theValue encoding:NSUTF8StringEncoding];}//2.压缩图片到指定尺寸大小+ (UIImage *)compressOriginalImage:(UIImage *)image toSize:(CGSize)size{    UIImage *resultImage = image;    UIGraphicsBeginImageContext(size);    [resultImage drawInRect:CGRectMake(0, 0, size.width, size.height)];    UIGraphicsEndImageContext();    return resultImage;}//3.压缩图片到指定文件大小+ (NSData *)compressOriginalImage:(UIImage *)image toMaxDataSizeKBytes:(CGFloat)size{    NSData *data = UIImageJPEGRepresentation(image, 1.0);    CGFloat dataKBytes = data.length/1000.0;    CGFloat maxQuality = 0.9f;    CGFloat lastData = dataKBytes;    while (dataKBytes > size && maxQuality > 0.01f) {        maxQuality = maxQuality - 0.01f;        data = UIImageJPEGRepresentation(image, maxQuality);        dataKBytes = data.length/1000.0;        if (lastData == dataKBytes) {            break;        }else{            lastData = dataKBytes;        }    }    return data;}//全屏截图+ (UIImage *)shotScreen{    UIWindow *window = [UIApplication sharedApplication].keyWindow;    UIGraphicsBeginImageContext(window.bounds.size);    [window.layer renderInContext:UIGraphicsGetCurrentContext()];    UIImage *image = UIGraphicsGetImageFromCurrentImageContext();    UIGraphicsEndImageContext();    return image;}
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