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];
　1>.数据库里存储图片 存储图片路径 /images/car@2x.png；
　2>.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:100];
//追加data内容:
[md appendData: dt];
//设置Data内容：
[md setData:dt];
//变更size内容：
[md setLength:50];

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 = 1; 
    int j = 2; 
    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) == 0)
    { 
        NSLog(@"1"); 
    }
 
//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:3]; 
    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:3]; 
    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(0, 4)]; 
    NSLog(@"string2:%@",string2);
 
//18、-stringWithCapacity: //按照固定长度生成空字符串
    NSMutableString *String; 
    String = [NSMutableString stringWithCapacity:40];
 
//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:0]; 
    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(0, 4) 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"] = = 1 ?  NSLog(@"YES") : NSLog(@"NO"); 
    [String1 hasSuffix:@".txt"] = = 1 ?  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]);