I've run into a problem while developing my mod where I want to send a chat message to the player when a block receives a redstone pulse. When testing the mod, I get an error:

java.lang.NullPointerException: Exception while updating neighbours

. My code:

 

 

@Override
public void onNeighborBlockChange(World w, int x, int y, int z, Block neighbor){
     if (!w.isRemote){
          if(w.isBlockIndirectlyGettingPowered(x, y, z)){
               w.getClosestPlayer((double)x, (double)y, (double)z, 0)
                    .addChatMessage(
                         new ChatComponentText("test message"));}
     }
}

 

 

The error occurs on the .addChatMessage() line.

You're trying to get the nearest player to the block in a radius of 0. You need to make sure that player is not null before trying to do anything because World#getClosestPlayer(double,double,double,int) can return null.

OK, so I added in the check to see if the player is null or not and changed the getClosestPlayer to 5 and it works now.

 

 

@Override
public void onNeighborBlockChange(World w, int x, int y, int z, Block neighbor){
     if (!w.isRemote){
          [bold]EntityPlayer player = w.getClosestPlayer((double)x, (double)y, (double)z, 5);
          if(player!=null){[/bold]
               if(w.isBlockIndirectlyGettingPowered(x, y, z)){
                    player.addChatMessage(
                         new ChatComponentText("test message"));
            }
               }
          }
}

 

 

However for some reason the chat message is firing twice. Any ideas?

I'm pretty sure it is being fired twice on the server.

Yea that's what I'm thinking. I tried adding in @SideOnly(Side.CLIENT) before the function but that didn't change anything.

Yea that's what I'm thinking. I tried adding in @SideOnly(Side.CLIENT) before the function but that didn't change anything.

 

That's not what @SideOnly is for.

I figured that out but the problem persists. Is there any way to have the message be sent to the player without it being duplicated?

Wrap the code in

if(!world.isRemote)

Wrap the code in

if(!world.isRemote)

 

I have that. As a refresher:

 

 

@Override
public void onNeighborBlockChange(World w, int x, int y, int z, Block neighbor){
     if (!w.isRemote){
          EntityPlayer player = w.getClosestPlayer((double)x, (double)y, (double)z, 5);
          if(player!=null){
               if(w.isBlockIndirectlyGettingPowered(x, y, z)){
                    player.addChatComponentMessage(new ChatComponentText("test message"));
               }
          }
     }
}

 

I have decided to go a different path with what I was trying to achieve with this. Instead of giving the player the information through a chat message, I am having the player place a sign above my mod block that automatically loads the sign with the information I want to display.

 

If you are interested in how I achieved this my code is below (sorry, I'm not formatting it this time ):

 

@Override
    public void onNeighborChange(IBlockAccess w, int x, int y, int z, int tileX, int tileY, int tileZ){
	if(w.getBlock(x, tileY, z)==Blocks.standing_sign||w.getBlock(x, tileY, z)==Blocks.wall_sign){
		this.sign = (TileEntitySign)w.getTileEntity(x, y+1, z);
		signText();
	}
    }
//This is in it's own method because I call it from elsewhere to have the sign be updated when the information changes.
private void signText(){ 
	this.sign.signText[0]="line0";
	this.sign.signText[1]="line1";
	this.sign.signText[2]="line3";
}

@Override
public boolean canPlaceBlockAt(World w, int x, int y, int z)
    {
	if(w.getBlock(x, y+1, z).isAir(w, x, y+1, z)){
		return w.getBlock(x, y, z).isReplaceable(w, z, y, z);
	}
	else return false;
    }
[/spoiler]