setter 需要retain
static NSString* _assetsPath = @"";
@implementation MyGame
@synthesize assetsPath = _assetsPath;
+(void)SetAssetsPath:(NSString *)assetsPath
{
[_assetsPath release];
_assetsPath = [NSString stringWithString:assetsPath];//系统托管的String
[_assetsPath retain];//防止在界面变换时，string被系统回收
}
