Sorry if this is a stupid newb question, I am not a native java person, and I am working on my first mod here, so be gentle if I  screw up the terminology...

 

I have created a custom block, and am interested in implementing the following logic:

 

    When that block is placed, if the block under it is not opaque, cancel the placement.

 

In the block class, I have placed an override on onBlockPlaced, which seems to fire when I would want it to, but since it does not have an event argument, it does not seem like I could cancel the block placement event from there.

 

@Override

public int onBlockPlaced(World world, int x, int y, int z, int side, float xOffSet, float yOffSet, float zOffSet, int meta)

{

System.out.println("Block Placed at "+x+" "+y+" "+z);

return meta;

}

 

Is there a different event event I should use, or is there a better approach?

 

Thanks in advance.

 

You want to look at canBlockBePlacedAt

 

BlockRedstoneWire uses it.

Thank you.  The perfect internet answer.  Short, cryptic, to the point, and exactly what I needed.  My compliments, sir.

 

For reference of anyone who finds this later, what I did:

 

Snagged the canPlaceBlockAt function from RedstoneWire, as suggested, and added it to my block class as an override.

@Override
public boolean canPlaceBlockAt(World p_149742_1_, int p_149742_2_, int p_149742_3_, int p_149742_4_)
    {
	return World.doesBlockHaveSolidTopSurface(p_149742_1_, p_149742_2_, p_149742_3_ - 1, p_149742_4_) || p_149742_1_.getBlock(p_149742_2_, p_149742_3_ - 1, p_149742_4_) == Blocks.glowstone;
    }

 

Which still left me able to place on myself.  Looking into what World.doesBlockHaveSolidTopSurface is doing, I determined I had to also override what I was returning from isSideSolid:

@Override
public boolean isSideSolid(IBlockAccess world, int x, int y, int z, ForgeDirection side)
{
	if (side != DOWN) 
	{
		return false;
	}
	else
	{
		return true;
	}
}

 

This gave me the behavior I was looking for.