I am adding on to my mod More Items and i'm adding material crops. I am making my diamond crop right now and I want the seed to plant the crop on a block of diamond. I added the diamond block where farmland should be but it still wont let me plant it on it.

 

Diamond Plant Registry:

GameRegistry.registerItem(diamond_seeds = new MIItemSeeds(MoreItemsCrops.diamond_crop, Blocks.diamond_block, "diamond_seeds"), "diamond_seeds");	

I'm pretty sure the farmland-block needs to cooperate as well.  Which the diamond block doesn't know anything about crops, so the calls made to allow planting fail.

Reeds (sugar cane) can be planted on any of several types of blocks. Can they be imitated? Do they need co-operation from sand, dirt etc?

 

Walk through the reed code to see if you can extend that class (or its parent) to achieve your purpose.

 

EDIT: Oh, and netherwart is a "bush" that grows on soul sand. Maybe that's what you should imitate.

There is a chunk of code somewhere that handles valid placement that wass't in the BlockCrops class, I just don't remember where it was.

I'm looking in net.minecraft.item.ItemSeeds#onItemUse right now and there's this if statement:

 

/**
     * Called when a Block is right-clicked with this Item
     */
    public boolean onItemUse(ItemStack stack, EntityPlayer playerIn, World worldIn, BlockPos pos, EnumFacing side, float hitX, float hitY, float hitZ)
    {
        if (side != EnumFacing.UP)
        {
            return false;
        }
        else if (!playerIn.canPlayerEdit(pos.offset(side), side, stack))
        {
            return false;
        }
        else if (worldIn.getBlockState(pos).getBlock().canSustainPlant(worldIn, pos, EnumFacing.UP, this) && worldIn.isAirBlock(pos.up()))
        {
            worldIn.setBlockState(pos.up(), this.crops.getDefaultState());
            --stack.stackSize;
            return true;
        }
        else
        {
            return false;
        }
    }

 

So short of creating a coremod and altering the diamond block's canSustainPlant function, you should make an item that alters the diamond block, eg turns it into a custom diamond block which overrides this method and returns true. My advice would be to take a look at net.minecraft.block.Block#canSustainPlant and net.minecraft.block.Block#canHarvestBlock methods. I may just be talking out of my ass though, someone with more knowledge can and should correct me if I am.

getBlock().canSustainPlant()

 

That's the one.  Go look at Block#canSustainPlant

However, we're not trying to plant wheat here, so we don't even need to work around ItemSeeds#onItemUse. We're trying to plant some custom thingy, so let's override the custom thing's onItemUse method to do a different test. Have it copy the early branches of the seed's version, and then look for diamond block instead of calling canSustainPlant.

 

PS: It would help if you could post the source code to MIItemSeeds. I think that's where you need to override onItemUse.

Diamond Seeds Class:

package ronaldi2001.MoreItems.crops;

import net.minecraft.block.Block;
import net.minecraft.block.BlockBush;
import net.minecraft.block.material.Material;
import net.minecraft.init.Blocks;
import net.minecraft.init.Items;
import net.minecraft.item.Item;
import net.minecraft.util.BlockPos;
import net.minecraft.util.EnumFacing;
import net.minecraft.world.World;
import ronaldi2001.MoreItems.init.MoreItemsItems;

public class MIDiamondCrop extends BlockBush {

public MIDiamondCrop(String name) {
	this.setUnlocalizedName(name);
}

public Item getSeed() {
	return MoreItemsItems.diamond_seeds;
}

public Item getCrop() {
	return Items.diamond;	
}


}

 

MIItemSeeds Class:

package ronaldi2001.MoreItems.items;

import net.minecraft.block.Block;
import net.minecraft.item.ItemSeeds;
import ronaldi2001.MoreItems.main.MoreItems;

public class MIItemSeeds extends ItemSeeds {

public MIItemSeeds(Block crops, Block soil, String name) {
	super(crops, soil);
	this.setUnlocalizedName(name);
	this.setCreativeTab(MoreItems.tabMoreItems);
}

}

You need to override #onItemUse in your custom seed class; from there, you can do any type of checking you want and plant your crop on any type of block you want. As your code is now, your seed uses the same logic as its parent class, the vanilla ItemSeed, which makes all sorts of checks for plant type / sustainability and you don't want any of that.

 

Here's an example of a seed that can be planted only on stone / rock-based blocks that are next to lava. As you can see, there is nothing that requires you to make the same checks as the vanilla seeds do.