I put this in my block class:

public void onEntityWalk(World worldIn, BlockPos pos, Entity entityIn) {
    if (!entityIn.isSneaking()){
        entityIn.attackEntityFrom(DamageSource.FALL, 10);
    }
    super.onEntityWalk(worldIn, pos, entityIn);
}

 

When i'm in the game I don't take any damage from sneaking on it. What am I doing wrong?

Are you saying you want the entity to take damage when you are sneaking on it?  Not damage except when you're sneaking on it (i.e. magma blocks)?  If so, you'll want to check entityIn.isSneaking(), not !entityIn.isSneaking().  The latter returns true when the entity isn't sneaking.

I had set it to take damage when I am sneaking for testing, and when I removed the exclamation point I still didn't take damage sneaking

have you enabled the fall damage gamerule?

How would I do that?

15 minutes ago, Help! said:

How would I do that?

Shouldn't you use a Player object to do that?

/gamerule fallDamage

 

12 hours ago, poopoodice said:

/gamerule fallDamage

That didn't work. Any other ideas of why it isn't working?