UIWindow *window=[[UIWindow alloc]initWithFrame:[[UIScreen mainScreen]bounds]];
// window.windowLevel=UIWindowLevelAlert;
_window=window;
[_window addSubview:self.tableview];
[_tableview mas_makeConstraints:^(MASConstraintMaker *make) {
make.top.mas_equalTo(@0);
make.left.right.equalTo(@0);
make.height.equalTo(@(self.view.bounds.size.height));
}];
[window makeKeyAndVisible];
//记住 需要把window设置成属性
