在iphone指定目录写文件log

	NSString * hisPath = [[NSPathEx DocPath] stringByAppendingFormat:@"/Log.txt"];
	
	NSString* strHistory = [NSString stringWithContentsOfFile:hisPath encoding:NSUTF8StringEncoding error:nil];
	
	if (strHistory != nil) 
	{
		NSString* newStr = [strHistory stringByAppendingString:strLog];
		
		[newStr writeToFile:hisPath atomically:YES encoding:NSUTF8StringEncoding error:nil];
	}
	else 
	{
		[strLog writeToFile:hisPath atomically:YES encoding:NSUTF8StringEncoding error:nil];
	}