iOS小知识
2016-07-20 本文已影响33人
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1. 程序进入后台继续执行代码操作
在AppDelegate文件中创建一个属性
@property (nonatomic, assign) UIBackgroundTaskIdentifier backgroundUpdateTask;
并且在下面这个方法中实现你想要执行的代码
- (void)applicationDidEnterBackground:(UIApplication *)application {
[self beingBackgroundUpdateTask];
NSLog(@"你想要执行的代码");
[self endBackgroundUpdateTask];
}
这是下面的两个方法的实现
- (void)beingBackgroundUpdateTask
{
self.backgroundUpdateTask = [[UIApplication sharedApplication] beginBackgroundTaskWithExpirationHandler:^{
[self endBackgroundUpdateTask];
}];
}
- (void)endBackgroundUpdateTask
{
[[UIApplication sharedApplication] endBackgroundTask:self.backgroundUpdateTask];
self.backgroundUpdateTask = UIBackgroundTaskInvalid;
}
2. 关键字
nullable:表示可以为空;
nonnull:表示不能为空;
null_resettable: get:不能返回为空,set可以为空;选择重写set或者get;
_Null_unspecified:不确定是否为空,暂时没发现有啥用;
- 1__kindof:表示当前类或者它的子类;
- 2__covariant(协变):用于泛型数据强转类型,可以向上强转,子类可以转成父类;
- 3__contravariant(逆变):用于泛型数据强转类型,可以向下强转,父类可以转成子类;
@property (nonatomic,strong, nullable) NSString * name;
@property (nonatomic,strong) NSString * _Nullable stu;
@property (nonatomic,strong, null_resettable) NSString * name;
@property (nonatomic,strong) NSString * _Null_unspecified name;
3. 下载苹果官方字体库
4. -w:禁止所有的编译警告;
-Wno-unused-variable:只禁止未使用变量的
的编译警告;
5. 使用函数式指针忽略警告
忽略警告：
#pragma clang diagnostic push
#pragma clang diagnostic ignored "-Warc-performSelector-leaks"
[_target performSelector:_action withObject:self];
#pragma clang diagnostic pop
如果需要忽视的警告有多处，可以定义一个宏：
#define IgnorePerformSelectorLeakWarning(Stuff) \
do {\ _Pragma("clang diagnostic push") \
_Pragma("clang diagnostic ignored \
"-Warc-performSelector-leaks\"") \
Stuff; \
_Pragma("clang diagnostic pop") \
} while (0)
使用方法：
IgnorePerformSelectorLeakWarning( [_target performSelector:_action withObject:self]);
6.HTML字符转NSString
//1.html转string
NSString * htmlString = @"<html><body> Some html string \n <font size=\"13\" color=\"red\">This is some text!</font> </body></html>";
NSAttributedString * attrStr = [[NSAttributedString alloc] initWithData:[htmlString dataUsingEncoding:NSUnicodeStringEncoding] options:@{ NSDocumentTypeDocumentAttribute: NSHTMLTextDocumentType } documentAttributes:nil error:nil];
UILabel * myLabel = [[UILabel alloc] initWithFrame:self.view.bounds];
myLabel.attributedText = attrStr;
[self.view addSubview:myLabel];
7.判断是是否为PNG/GIF图片
//通过图片Data数据第一个字节 来获取图片扩展名
- (NSString *)contentTypeForImageData:(NSData *)data {
uint8_t c;
[data getBytes:&c length:1];
switch (c) {
case 0xFF:
return @"jpeg";
case 0x89:
return @"png";
case 0x47:
return @"gif";
case 0x49:
case 0x4D:
return @"tiff";
case 0x52:
if ([data length] < 12) {
return nil;
}
NSString *testString = [[NSString alloc] initWithData:[data subdataWithRange:NSMakeRange(0, 12)] encoding:NSASCIIStringEncoding];
if ([testString hasPrefix:@"RIFF"] && [testString hasSuffix:@"WEBP"]) {
return @"webp";
}
return nil;
}
return nil;
}
- 使用方法
//假设这是一个网络获取的URL
NSString *path = @"http://pic.rpgsky.net/images/2016/07/26/3508cde5f0d29243c7d2ecbd6b9a30f1.png";
NSData *data = [NSData dataWithContentsOfURL:[NSURL URLWithString:path]];
//调用获取图片扩展名
NSString *string = [self contentTypeForImageData:data];
//输出结果为 png
NSLog(@"%@",string);
8.设置圆角的几种方法
- 1.绘图
/** 设置圆形图片(放到分类中使用) */
- (UIImage *)cutCircleImage {
UIGraphicsBeginImageContextWithOptions(self.size, NO, 0.0);
// 获取上下文
CGContextRef ctr = UIGraphicsGetCurrentContext();
// 设置圆形
CGRect rect = CGRectMake(0, 0, self.size.width, self.size.height);
CGContextAddEllipseInRect(ctr, rect);
// 裁剪
CGContextClip(ctr);
// 将图片画上去
[self drawInRect:rect];
UIImage *image = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();
return image;
}
- 1.1绘图传参
@implementation UIImage (RoundedCorner)
- (UIImage *)imageWithRoundedCornersAndSize:(CGSize)sizeToFit andCornerRadius:(CGFloat)radius
{
CGRect rect = (CGRect){0.f, 0.f, sizeToFit};
UIGraphicsBeginImageContextWithOptions(sizeToFit, NO, UIScreen.mainScreen.scale);
CGContextAddPath(UIGraphicsGetCurrentContext(),
[UIBezierPath bezierPathWithRoundedRect:rect cornerRadius:radius].CGPath);
CGContextClip(UIGraphicsGetCurrentContext());
[self drawInRect:rect];
UIImage *output = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();
return output;
}
- 2.圆角封装
UIView * circleView = [UIView new];
circleView.frame = CGRectMake(0, 0, 100, 100);
circleView.backgroundColor = [UIColor colorWithPatternImage:[UIImage imageNamed:@"image"]];
[CircleImagePic getCircleImage:circleView cornerRadius:circleView.bounds.size.width/2];
[self.view addSubview:circleView];
创建NSObject
+ (void)getCircleImage:(UIView *)circleView cornerRadius:(NSInteger)cornerRadius
{
UIBezierPath * path = [UIBezierPath bezierPathWithRoundedRect:circleView.bounds byRoundingCorners:UIRectCornerAllCorners cornerRadii:CGSizeMake(cornerRadius, 0)];
CAShapeLayer * layer = [[CAShapeLayer alloc] init];
layer.frame = circleView.bounds;
layer.path = path.CGPath;
circleView.layer.mask = layer;
circleView.layer.cornerRadius = cornerRadius;
circleView.layer.masksToBounds = YES;
}
- 3.带缓存机制的圆角
UIView * cacheImage = [UIView new];
cacheImage.frame = CGRectMake(200, 0, 100, 100);
cacheImage.backgroundColor = [UIColor colorWithPatternImage:[UIImage imageNamed:@"image"]];
cacheImage.layer.masksToBounds = YES;
cacheImage.layer.cornerRadius = cacheImage.bounds.size.width/2;
cacheImage.layer.shouldRasterize = YES;
cacheImage.layer.rasterizationScale = [UIScreen mainScreen].scale;
[self.view addSubview:cacheImage];
9.移动文件
// /Users/apple/Desktop/初始文件夹/Myfile
//文件在哪个地方(文件夹)
NSString *form = @"/Users/apple/Desktop/初始文件夹";
//要剪切到什么地方
NSString *to = @"/Users/apple/Desktop/移动到这里";
NSFileManager *manager = [NSFileManager defaultManager];
NSArray *subpaths = [manager subpathsAtPath:form];
NSDirectoryEnumerator *enumer = [manager enumeratorAtPath:to];
// NSDirectoryEnumerator *enumer = [manager directoryContentsAtPath:form];
for (NSDirectoryEnumerator *en in enumer) {
NSLog(@"%@",en);
}
//创建队列(并发队列)
dispatch_queue_t queue = dispatch_queue_create("com.downloadqueue", DISPATCH_QUEUE_CONCURRENT);
NSInteger count = [subpaths count];
dispatch_apply(count, queue, ^(size_t index) {
NSString *subpath = subpaths[index];
NSString *fullPath = [form stringByAppendingPathComponent:subpath];
//拼接目标文件全路径
NSString *fileName = [to stringByAppendingPathComponent:subpath];
//剪切操作
[manager moveItemAtPath:fullPath toPath:fileName error:nil];
});
10.NSString与NSData互转
- (NSString *)hexStringFromData:(NSData*)data{
return [[[[NSString stringWithFormat:@"%@",data]
stringByReplacingOccurrencesOfString: @"<" withString: @""]
stringByReplacingOccurrencesOfString: @">" withString: @""]
stringByReplacingOccurrencesOfString: @" " withString: @""];
}
- (NSData*)dataFormHexString:(NSString*)hexString{
hexString=[[string uppercaseString] stringByReplacingOccurrencesOfString:@" " withString:@""];
if (!(hexString && [hexString length] > 0 && [hexString length]%2 == 0)) {
return nil;
}
Byte tempbyt[1]={0};
NSMutableData* bytes=[NSMutableData data];
for(int i=0;i<[hexString length];i++)
{
unichar hex_char1 = [hexString characterAtIndex:i]; ////两位16进制数中的第一位(高位*16)
int int_ch1;
if(hex_char1 >= '0' && hex_char1 <='9')
int_ch1 = (hex_char1-48)*16; //// 0 的Ascll - 48
else if(hex_char1 >= 'A' && hex_char1 <='F')
int_ch1 = (hex_char1-55)*16; //// A 的Ascll - 65
else
return nil;
i++;
unichar hex_char2 = [hexString characterAtIndex:i]; ///两位16进制数中的第二位(低位)
int int_ch2;
if(hex_char2 >= '0' && hex_char2 <='9')
int_ch2 = (hex_char2-48); //// 0 的Ascll - 48
else if(hex_char2 >= 'A' && hex_char2 <='F')
int_ch2 = hex_char2-55; //// A 的Ascll - 65
else
return nil;
tempbyt[0] = int_ch1+int_ch2; ///将转化后的数放入Byte数组里
[bytes appendBytes:tempbyt length:1];
}
return bytes;
}
