OC基础数据类型-NSData-NSMutableData-NSString

NSData和NSMutableData存储的是二进制数据，在文件操作，网络，以及核心图形图像中使用较广泛。NSData创建后不可以再修改，NSMutableData可以再次修改。

1.NSString和NSData之间的转换

 //NSString转换成NSData类型
   NSString * str = @"hello, world!";
   NSData * data = [str dataUsingEncoding:NSUTF8StringEncoding];
   NSLog(@"%s", data.bytes);

   //NSData转换成NSString类型
   NSString * newStr = [[NSString alloc] initWithData:data encoding:NSUTF8StringEncoding];
   NSLog(@"%@", newStr);

2.UIImage和NSData之间的转换　　　

 //获取图片路径
  NSString *imgPath = [[NSBundle mainBundle] pathForResource:@"01loading.png" ofType:nil];
  NSData *imgData = [NSData dataWithContentsOfFile:imgPath];
//直接使用，也可写入文件

  self.imageView.image = [UIImage imageWithData:imgData];
　>.数据库里存储图片 存储图片路径 /images/car@2x.png；
　>.如果图片是较小的 可以将UIImage转换成NSData存数据库。

3.NsMutableData 使用

NsMutableData* md = [NSMutableData data];
NSMutableData* md=[[NSMutableData alloc]initWithLength:];
//追加data内容:
[md appendData: dt];
//设置Data内容：
[md setData:dt];
//变更size内容：
[md setLength:];

4.NSString 使用

//1、创建常量字符串
    NSString *astring = @"This is a String!";
//2、创建空字符串，给予赋值。
    NSString *astring = [[NSString alloc] init];
    astring = @"This is a String!";
    [astring release];
    NSLog(@"astring:%@",astring);
//3、在以上方法中，提升速度:initWithString方法
    NSString *astring = [[NSString alloc] initWithString:@"This is a String!"];
    NSLog(@"astring:%@",astring);
    [astring release];
//4、用标准c创建字符串:initWithCString方法
    char *Cstring = "This is a String!";
    NSString *astring = [[NSString alloc] initWithCString:Cstring];
    NSLog(@"astring:%@",astring);
    [astring release];
//5、创建格式化字符串:占位符（由一个%加一个字符组成）
    int i = ;
    int j = ;
    NSString *astring = [[NSString alloc] initWithString:[NSString stringWithFormat:@"%d.This is %i string!",i,j]];
    NSLog(@"astring:%@",astring);
    [astring release];
//6、创建临时字符串
    NSString *astring;
    astring = [NSString stringWithCString:"This is a temporary string"];
    NSLog(@"astring:%@",astring);
//7、从文件创建字符串
    NSString *path = [[NSBundlemainBundle] pathForResource:@"astring.text"ofType:nil];
    NSString *astring = [[NSString alloc] initWithContentsOfFile:path];
    NSLog(@"astring:%@",astring);
    [astring release];
//8、用字符串创建字符串，并写入到文件
    NSString *astring = [[NSString alloc] initWithString:@"This is a String!"];
    NSLog(@"astring:%@",astring);
    NSString *path = @"astring.text";
    [astring writeToFile: path atomically: YES];
    [astring release];
注：此路径path只只是示意，真实路径并非如此

//9、用C比较:strcmp函数
    char string1[] = "string!";
    char string2[] = "string!";
    if(strcmp(string1, string2) == )
    {
        NSLog(@"");
    }

//10、isEqualToString方法
    NSString *astring01 = @"This is a String!";
    NSString *astring02 = @"This is a String!";
    BOOL result = [astring01 isEqualToString:astring02];
    NSLog(@"result:%d",result);

//11、compare方法(comparer返回的三种值)
    NSString *astring01 = @"This is a String!";
    NSString *astring02 = @"This is a String!";
    BOOL result = [astring01 compare:astring02] == NSOrderedSame;    //NSOrderedSame判断两者内容是否相同
    NSLog(@"result:%d",result);
    NSString *astring01 = @"This is a String!";
    NSString *astring02 = @"this is a String!";
    BOOL result = [astring01 compare:astring02] == NSOrderedAscending;    //NSOrderedAscending判断两对象值的大小(按字母顺序进行比较，astring02大于astring01为真)
    NSLog(@"result:%d",result);
    NSString *astring01 = @"this is a String!";
    NSString *astring02 = @"This is a String!";
    BOOL result = [astring01 compare:astring02] == NSOrderedDescending;   //NSOrderedDescending判断两对象值的大小(按字母顺序进行比较，astring02小于astring01为真)
    NSLog(@"result:%d",result);  

//12、不考虑大小写比较字符串
    //1.
    NSString *astring01 = @"this is a String!";
    NSString *astring02 = @"This is a String!";
    BOOL result = [astring01 caseInsensitiveCompare:astring02] == NSOrderedSame;        //NSOrderedDescending判断两对象值的大小(按字母顺序进行比较，astring02小于astring01为真)
    NSLog(@"result:%d",result);
    //2.
    NSString *astring01 = @"this is a String!";
    NSString *astring02 = @"This is a String!";
    BOOL result = [astring01 compare:astring02
    options:NSCaseInsensitiveSearch | NSNumericSearch] == NSOrderedSame;    //NSCaseInsensitiveSearch:不区分大小写比较 NSLiteralSearch:进行完全比较，区分大小写 NSNumericSearch:比较字符串的字符个数，而不是字符值。
    NSLog(@"result:%d",result); 

//13、输出大写或者小写字符串
    NSString *string1 = @"A String";
    NSString *string2 = @"String";
    NSLog(@"string1:%@",[string1 uppercaseString]);//大写
    NSLog(@"string2:%@",[string2 lowercaseString]);//小写
    NSLog(@"string2:%@",[string2 capitalizedString]);//首字母大小
 
//14、-rangeOfString: //查找字符串某处是否包含其它字符串
    NSString *string1 = @"This is a string";
    NSString *string2 = @"string";
    NSRange range = [string1 rangeOfString:string2];
    int location = range.location;
    int leight = range.length;
    NSString *astring = [[NSString alloc] initWithString:[NSString stringWithFormat:@"Location:%i,Leight:%i",location,leight]];
    NSLog(@"astring:%@",astring);
    [astring release];

//15、-substringToIndex: 从字符串的开头一直截取到指定的位置，但不包括该位置的字符
    NSString *string1 = @"This is a string";
    NSString *string2 = [string1 substringToIndex:];
    NSLog(@"string2:%@",string2);
 
//16、-substringFromIndex: 以指定位置开始（包括指定位置的字符），并包括之后的全部字符
    NSString *string1 = @"This is a string";
    NSString *string2 = [string1 substringFromIndex:];
    NSLog(@"string2:%@",string2);

//17、-substringWithRange: //按照所给出的位置，长度，任意地从字符串中截取子串
    NSString *string1 = @"This is a string";
    NSString *string2 = [string1 substringWithRange:NSMakeRange(, )];
    NSLog(@"string2:%@",string2);

//18、-stringWithCapacity: //按照固定长度生成空字符串
    NSMutableString *String;
    String = [NSMutableString stringWithCapacity:];

//19、-appendString: and -appendFormat: //把一个字符串接在另一个字符串的末尾
    NSMutableString *String1 = [[NSMutableString alloc] initWithString:@"This is a NSMutableString"];
    [String1 appendString:@", I will be adding some character"];
    [String1 appendFormat:[NSString stringWithFormat:@", I will be adding some character"]];
    NSLog(@"String1:%@",String1);

//20、-insertString: atIndex: //在指定位置插入字符串
    NSMutableString *String1 = [[NSMutableString alloc] initWithString:@"This is a NSMutableString"];
    [String1 insertString:@"Hi! " atIndex:];
    NSLog(@"String1:%@",String1);

//21、-setString:
    NSMutableString *String1 = [[NSMutableString alloc] initWithString:@"This is a NSMutableString"];
    [String1 setString:@"Hello Word!"];
    NSLog(@"String1:%@",String1);

//22、-replaceCharactersInRange: withString: //用指定字符串替换字符串中某指定位置、长度的字符串
    NSMutableString *String1 = [[NSMutableString alloc] initWithString:@"This is a NSMutableString"];
    [String1 replaceCharactersInRange:NSMakeRange(, ) withString:@"That"];
    NSLog(@"String1:%@",String1);

//23、-hasPrefix: //检查字符串是否以另一个字符串开头
    NSString *String1 = @"NSStringInformation.txt";
    [String1 hasPrefix:@"NSString"] = =  ?  NSLog(@"YES") : NSLog(@"NO");
    [String1 hasSuffix:@".txt"] = =  ?  NSLog(@"YES") : NSLog(@"NO");

//24、扩展路径
    NSString *Path = @"~/NSData.txt";
    NSString *absolutePath = [Path stringByExpandingTildeInPath];
    NSLog(@"absolutePath:%@",absolutePath);
    NSLog(@"Path:%@",[absolutePath stringByAbbreviatingWithTildeInPath]);

//25、文件扩展名
    NSString *Path = @"~/NSData.txt";
    NSLog(@"Extension:%@",[Path pathExtension]);