I made a flying command which is still in beta, I was able to make it work so you could fly whilst holding an item, CODE:

	@Override
	public void onUpdate(ItemStack itemstack, World world, Entity entity, int i, boolean flag)
	{
	     if (entity instanceof EntityPlayer)
	    	 
	     {          EntityPlayer Player = (EntityPlayer) entity;
	          if(Player.getHeldItemMainhand() != null && Player.getHeldItemMainhand().getItem() instanceof IHasModel)
	        	  
	          {
	        	  PlayerFlight.setFlight(Player, true, world);
	        	  //System.out.println("holding");
	          }
	          else
	          { 
	        	  PlayerFlight.setFlight(Player, false, world);
	          }
	     }	 
	
	     }

This works, but this doesn't, I'm suspecting that you can't cast ICommandSender to EntityPlayer, because this code will not work, the player will do nothing.

boolean val = false;
	  @Override
	  public void execute(MinecraftServer server, ICommandSender sender, String[] params) throws CommandException {
		
		World w = sender.getEntityWorld();
		EntityPlayer p = (EntityPlayer) sender;

		val = !val;
		if(w.isRemote)
		{
			PlayerFlight.setFlight(p, true, sender.getEntityWorld());
		}
		
	  }

	  @Override
	  public String getName() {
	    return "fly";
	  }

	  @Override
	  public String getUsage(ICommandSender sender) {
	    return "command.fly.usage";
	  }

And my Flying class. #Note that I know how to use hashmaps and when I get this working ill add multiplayer support.

static boolean val = false;
	public static void toggleFlight(EntityPlayer playerIn, boolean flight, World worldIn)
	{
		
		if (worldIn.isRemote)
        {
			flight = !val;
			val = !val;
			System.out.println(flight);
			//Check Activation by player
        	String var1 = playerIn.getName();
        	//playerIn.sendChatToPlayer("Activated by: " + var1 + "");

        //Make the player fly
        	playerIn.capabilities.allowFlying = flight;
        	playerIn.capabilities.isFlying = flight;
        	playerIn.capabilities.isFlying = flight;

        	playerIn.fallDistance = 0; 
        	if(flight)
        	{
        		playerIn.motionY += 1.0;
        	} else
        	{
        		playerIn.motionY += -1.0;
        	}
        	
        	//if(!flight)
        	//{
        	//	playerIn.capabilities.isCreativeMode = false;
        	//}
        	
        	playerIn.sendPlayerAbilities();
        }
        else
        {

        	
            
            return;
        }
	}
	public static void setFlight(EntityPlayer playerIn, boolean flight, World worldIn)
	{
		
		if (worldIn.isRemote)
        {
			
			//Check Activation by player
        	String var1 = playerIn.getName();
        	//playerIn.sendChatToPlayer("Activated by: " + var1 + "");

        //Make the player fly
        	playerIn.capabilities.allowFlying = flight;
        	playerIn.capabilities.isFlying = flight;
        	playerIn.capabilities.isFlying = flight;

        	playerIn.fallDistance = 0; 
        	
        	//if(!flight)
        	//{
        	//	playerIn.capabilities.isCreativeMode = false;
        	//}
        	
        	playerIn.sendPlayerAbilities();
        }
        else
        {

        	
            
            return;
        }
	}

 

Edited May 26, 20196 yr by Jaycen1000
Solved

If you couldn't cast something to something else then you would crash with a ClassCastException.

 

I think you need to send a packet to the client notifying them that they can fly now.

Actually, scratch that, your code will never work

if(w.isRemote)
		{
			PlayerFlight.setFlight(p, true, sender.getEntityWorld());
		}

Commands are executed on the server so this condition will always be false thus your flying code will never execute.

Also

11 minutes ago, Jaycen1000 said:

instanceof IHasModel

IHasModel is stupid. All items need models, no exceptions, and IHasModel makes you write redundand code a lot(as in you need 3 lines PER ITEM as a bare minimum instead of ONE line and that's it). Register your models directly in the ModelRegistryEvent.

Edited May 26, 20196 yr by V0idWa1k3r

Ok, using your feedback, I changed my flight class to this

public static void setCommandFlight(EntityPlayer playerIn, boolean flight)
	{
		
		String var1 = playerIn.getName();
        //Make the player fly
        playerIn.capabilities.allowFlying = flight;
        playerIn.capabilities.isFlying = flight;
        playerIn.capabilities.isFlying = flight;
        playerIn.fallDistance = 0; 
        playerIn.sendPlayerAbilities();
        	
        	
        	
        

	}

And my execute method to this

		World w = sender.getEntityWorld();
		EntityPlayer p = (EntityPlayer) sender;
		
		PlayerFlight.setCommandFlight(p, true);

What this does is allow you to fly for a tick (I can see my FOV getting bigger), but then after the tick, it goes off.

After a bit of testing, I got this to work.

PlayerFlight.java

static boolean val = false;
	public static void toggleFlight(EntityPlayer playerIn, boolean flight, World worldIn)
	{
		
		if (worldIn.isRemote)
        {
			flight = !val;
			val = !val;
			System.out.println(flight);
			//Check Activation by player
        	//playerIn.sendChatToPlayer("Activated by: " + var1 + "");

        	if (worldIn.isRemote)
            {
            	//Check Activation by player

            	//playerIn.sendChatToPlayer("Activated by: " + var1 + "");

            //Make the player fly
                playerIn.capabilities.allowFlying = flight;
                playerIn.capabilities.isFlying = flight;
            	playerIn.motionY += 0;
            	playerIn.capabilities.isFlying = flight;
                playerIn.fallDistance = 0; 
                playerIn.sendPlayerAbilities();
    			return;
            }
            else
            {

                
                return;
            }
        	
        	//if(!flight)
        	//{
        	//	playerIn.capabilities.isCreativeMode = false;
        	//}
        	
        	
        }
        else
        {

        	
            
            return;
        }
	}
	public static void setFlight(EntityPlayer playerIn, boolean flight, World worldIn)
	{
		
		if (worldIn.isRemote)
        {
        	//Check Activation by player
        	String var1 = playerIn.getName();
        	//playerIn.sendChatToPlayer("Activated by: " + var1 + "");

        //Make the player fly
            playerIn.capabilities.allowFlying = flight;
            playerIn.capabilities.isFlying = flight;
        	playerIn.motionY += 0;
        	playerIn.capabilities.isFlying = flight;
            playerIn.fallDistance = 0; 
            playerIn.sendPlayerAbilities();
			return;
        }
        else
        {

            
            return;
        }
        	
        	
        
	}
	public static void setCommandFlight(EntityPlayer playerIn, boolean flight)
	{
		
		String var1 = playerIn.getName();
        //Make the player fly
        playerIn.capabilities.allowFlying = flight;
        playerIn.capabilities.isFlying = flight;
    	playerIn.motionY += 1.0;
    	playerIn.capabilities.isFlying = flight;
        playerIn.fallDistance = 0; 
        playerIn.sendPlayerAbilities();
        	
        	
        	
        

	}

And FlyCommand.java

HashMap<EntityPlayer, Boolean> flying = new HashMap<EntityPlayer, Boolean>();
	boolean val = false;
	  @Override
	  public void execute(MinecraftServer server, ICommandSender sender, String[] params) throws CommandException {
		
		World w = sender.getEntityWorld();
		EntityPlayer p = (EntityPlayer) sender;
		try
		{
			flying.replace(p, !flying.get(p));
		} catch(Exception e)
		{
			
		}
		
		if(!flying.containsKey(p))
		{
			flying.put(p, true);
		}
		val = !val;
		PlayerFlight.setCommandFlight(p, flying.get(p));
		
		
	  }

	  @Override
	  public String getName() {
	    return "fly";
	  }

	  @Override
	  public String getUsage(ICommandSender sender) {
	    return "command.fly.usage";
	  }

That should work with multiplayer, also thank you V0idWa1k3r for telling me about World#isRemote.