I have an block that stores its content when broken via the loot table functions, like this:
 

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{
  "type": "minecraft:block",
  "pools": [
    {
      "name":"pool1",
      "rolls": 1,
      "entries": [
        {
          "type": "minecraft:item",
          "functions": [
            {
              "function": "minecraft:copy_name",
              "source": "block_entity"
            },
            {
              "function": "minecraft:copy_nbt",
              "source": "block_entity",
              "ops": [
                {
                  "source": "inv",
                  "target": "BlockEntityTag.inv",
                  "op": "replace"
                }
              ]
            },
            {
              "function": "minecraft:set_contents",
              "entries": [
                {
                  "type": "minecraft:dynamic",
                  "name": "minecraft:contents"
                }
              ]
            }
          ],
          "name": "bedres:ritual_pedestal"
        }
      ],
      "conditions": [
        {
          "condition": "minecraft:survives_explosion"
        }
      ]
    }
  ]
}

im not sure how to acces that information from the ItemStack#addInformation method, at the moment i have this in my tile, which all works, breaking and placing stays with the same item and variable values:

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@Override
public void read(CompoundNBT tag) {
    CompoundNBT compound = tag.getCompound("inv");
    handler.ifPresent(h -> {
        ((INBTSerializable<CompoundNBT>) h).deserializeNBT(compound);
    });
    item = compound.getString("name");
    super.read(tag);
}

@Override
public CompoundNBT write(CompoundNBT tag) {
    handler.ifPresent(h ->{
        CompoundNBT compound = ((INBTSerializable<CompoundNBT>)h).serializeNBT();
        tag.put("inv",compound);

        compound.put("items", ((INBTSerializable<CompoundNBT>) h).serializeNBT());
        compound.putString("name",item);

    });

    return super.write(tag);
}

and on the add info i have this, which i knew it wouldn't work, but im not sure how to approach it:

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@Override
public void addInformation(ItemStack stack, @Nullable IBlockReader worldIn, List<ITextComponent> tooltip, ITooltipFlag flagIn) {

    CompoundNBT compoundNBT = stack.getTag();
    if(compoundNBT != null) {
        String s = compoundNBT.getString("name");
        tooltip.add(new StringTextComponent(TextFormatting.DARK_GRAY + ("Item: " +s)));
    }
    super.addInformation(stack, worldIn, tooltip, flagIn);
}

 

Edited November 6, 20195 yr by AlexVR

Take a look at the shulker box code. I believe it might help you.

1 hour ago, [NoOneButNo] said:

Take a look at the shulker box code. I believe it might help you.

But the shulker box doesn't tell you it's content on the tool tip, does it? 

2 minutes ago, AlexVR said:

But the shulker box doesn't tell you it's content on the tool tip, does it? 

It does, look at ShulkerBoxBlock#addInformation, which itself gets called inside of BlockItem to add the block's tooltips to its item.

12 minutes ago, imacatlolol said:

It does, look at ShulkerBoxBlock#addInformation, which itself gets called inside of BlockItem to add the block's tooltips to its item.

Just checked, it does, thanks so much!

Will post code for future searchers:

 

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@OnlyIn(Dist.CLIENT)
public void addInformation(ItemStack stack, @Nullable IBlockReader worldIn, List<ITextComponent> tooltip, ITooltipFlag flagIn) {
    super.addInformation(stack, worldIn, tooltip, flagIn);
    CompoundNBT compoundnbt = stack.getChildTag("BlockEntityTag");
    if (compoundnbt != null) {
        if (compoundnbt.contains("LootTable", 8)) {
            tooltip.add(new StringTextComponent("???????"));
        }
        if (compoundnbt.contains("Items", 9)) {
            NonNullList<ItemStack> nonnulllist = NonNullList.withSize(1, ItemStack.EMPTY);
            ItemStackHelper.loadAllItems(compoundnbt, nonnulllist);
            if (!nonnulllist.get(0).isEmpty()) {
                ITextComponent itextcomponent = nonnulllist.get(0).getDisplayName().deepCopy();
                itextcomponent.appendText(" x").appendText(String.valueOf(nonnulllist.get(0).getCount()));
                tooltip.add(itextcomponent);
            }
        }
    }

}