问WPF命令修改属性没能进行通知？

private double maxXValue = 1440;
/// <summary>
/// X轴最大值
/// </summary>
public double MaxXValue
{
    get { return maxXValue; }
    set { SetProperty(ref maxXValue, value); }
}


public void DecreaseXAxis() 
{
	if (MaxXValue < 1440)
	{
		MaxXValue = 1440;
	}
	else
	{
		MaxXValue -= 1440;
    }
}

DecreaseXAxisCommand = new RelayCommand(() => ProgramManange.Program.DecreaseXAxis());
//DecreaseXAxisCommand = new RelayCommand(ProgramManange.Program.DecreaseXAxis);