MString 和NSData转换 ios 4.0之后

string转换成Data
wrieString=@"--------------------这个是末尾增加";
 [wrieString writeToFile:otherFile atomically:NOencoding:NSUTF8StringEncoding error:nil];//初始化一个文件

 NSMutableData*writeData=[[NSMutableData alloc] initWithData:[wrieStringdataUsingEncoding:NSUTF8StringEncoding]];


Data转换成String
 NSMutableData *readData=[[NSMutableData alloc]initWithContentsOfFile:otherFile];
 NSString*readString=[[NSString alloc] initWithData:readDataencoding:NSUTF8StringEncoding];