HUDInventory.cs

using UnityEngine;
using System.Collections;

public class HUDInventory : MonoBehaviour {



//Inventory Variables
public int InventoryFieldSelected = 1;
public int ActiveItem = 0;
public int InventoryFromTop = 600;
public int ItemToPickUp = 0;
public int SlotToTransferPickUp = 0;

//  Slots Background Textures
public Texture Slot1Background;
public Texture Slot2Background;
public Texture Slot3Background;
public Texture Slot4Background;
public Texture Slot5Background;
public Texture Slot6Background;
public Texture Slot7Background;
public Texture Slot8Background;
public Texture Slot9Background;
public Texture Slot0Background;

//Item Icons generally
    //0
static public Texture InventoryIconEmpty;
    //1
public Texture InventoryIconHammer;
    //2
public Texture InventoryIconPipe;

//Item Icon for Slot
public Texture ItemIconSlot1 = InventoryIconEmpty;
public Texture ItemIconSlot2;
public Texture ItemIconSlot3;
public Texture ItemIconSlot4;
public Texture ItemIconSlot5;
public Texture ItemIconSlot6;
public Texture ItemIconSlot7;
public Texture ItemIconSlot8;
public Texture ItemIconSlot9;
public Texture ItemIconSlot0;

// What Item is in Slot?
public int ItemInSlot1 = 0;
public int ItemInSlot2 = 0;
public int ItemInSlot3 = 0;
public int ItemInSlot4 = 0;
public int ItemInSlot5 = 0;
public int ItemInSlot6 = 0;
public int ItemInSlot7 = 0;
public int ItemInSlot8 = 0;
public int ItemInSlot9 = 0;
public int ItemInSlot0 = 0;

    // Use this for initialization
    void Start () {

    }

    // Update is called once per frame
    void Update () {

    //Select Fields per Keyboard
    if(Input.GetKeyUp("1")){InventoryFieldSelected = 1;}
    if(Input.GetKeyUp("2")){InventoryFieldSelected = 2;}
    if(Input.GetKeyUp("3")){InventoryFieldSelected = 3;}
    if(Input.GetKeyUp("4")){InventoryFieldSelected = 4;}
    if(Input.GetKeyUp("5")){InventoryFieldSelected = 5;}
    if(Input.GetKeyUp("6")){InventoryFieldSelected = 6;}
    if(Input.GetKeyUp("7")){InventoryFieldSelected = 7;}
    if(Input.GetKeyUp("8")){InventoryFieldSelected = 8;}
    if(Input.GetKeyUp("9")){InventoryFieldSelected = 9;}
    if(Input.GetKeyUp("0")){InventoryFieldSelected = 0;}
    //TEST PICK UP HAMMER
    if(Input.GetKeyUp("h")){ItemToPickUp = 1; PickUpItem();}

    //Set ActiveItem
    if (InventoryFieldSelected == 1){ActiveItem = ItemInSlot1;}
    if (InventoryFieldSelected == 2){ActiveItem = ItemInSlot2;}
    if (InventoryFieldSelected == 3){ActiveItem = ItemInSlot3;}
    if (InventoryFieldSelected == 4){ActiveItem = ItemInSlot4;}
    if (InventoryFieldSelected == 5){ActiveItem = ItemInSlot5;}
    if (InventoryFieldSelected == 6){ActiveItem = ItemInSlot6;}
    if (InventoryFieldSelected == 7){ActiveItem = ItemInSlot7;}
    if (InventoryFieldSelected == 8){ActiveItem = ItemInSlot8;}
    if (InventoryFieldSelected == 9){ActiveItem = ItemInSlot9;}
    if (InventoryFieldSelected == 0){ActiveItem = ItemInSlot0;}

    //Send ActiveItem to PlayerAttack.cs
    PlayerAttack.ActiveItem = ActiveItem;
    }




    void OnGUI ()
    {
    GUI.BeginGroup(new Rect(500, InventoryFromTop, 640, 64));
    //GUI.contentColor = Color.yellow;

    //InventoryField1
    //======= first problem ====================================
    //==========================================================
    //== I want to Add the following line the all Slots ========
    //== to display an image of the Item that is in this Slot
    //== If i add this line, the whole inventory isnt displayed anymore
    //==========================================================
    //==========================================================
    //GUI.DrawTexture(new Rect(0,0,64,64), ItemIconSlot1);
    if (GUI.Button(new Rect(0, 0, 64, 64), Slot1Background))
        {InventoryFieldSelected = 1;}

    //InventoryField2
    if (GUI.Button(new Rect(64, 0, 64, 64), Slot2Background))
        {InventoryFieldSelected = 2;}

    //InventoryField3
    if (GUI.Button(new Rect(128, 0, 64, 64), Slot3Background))
        {InventoryFieldSelected = 3;}

    //InventoryField4
    if (GUI.Button(new Rect(192, 0, 64, 64), Slot4Background))
        {InventoryFieldSelected = 4;}

    //InventoryField5
    if (GUI.Button(new Rect(256, 0, 64, 64), Slot5Background))
        {InventoryFieldSelected = 5;}

    //InventoryField6
    if (GUI.Button(new Rect(320, 0, 64, 64), Slot6Background))
        {InventoryFieldSelected = 6;}

    //InventoryField7
    if (GUI.Button(new Rect(384, 0, 64, 64), Slot7Background))
        {InventoryFieldSelected = 7;}

    //InventoryField8
    if (GUI.Button(new Rect(448, 0, 64, 64), Slot8Background))
        {InventoryFieldSelected = 8;}

    //InventoryField9
    if (GUI.Button(new Rect(512, 0, 64, 64), Slot9Background))
        {InventoryFieldSelected = 9;}

    //InventoryField0
    if (GUI.Button(new Rect(576, 0, 64, 64), Slot0Background))
        {InventoryFieldSelected = 0;}

    GUI.EndGroup();

    }

    void PickUpItem()
    {
    //=============================================
    //== FIND FREE SLOT // CHANGE ITEMINSLOT VAR ==
    //=============================================
    //Transfer ItemToPickUp into Slot1 if free
    if (ItemInSlot1 == 0){ItemInSlot1 = ItemToPickUp; SlotToTransferPickUp = 1; ItemToPickUp = 0;}

    //Transfer ItemToPickUp into Slot2 if free
    if (ItemInSlot2 == 0){ItemInSlot2 = ItemToPickUp; SlotToTransferPickUp = 2; ItemToPickUp = 0;}

    //Transfer ItemToPickUp into Slot3 if free
    if (ItemInSlot3 == 0){ItemInSlot3 = ItemToPickUp; SlotToTransferPickUp = 3; ItemToPickUp = 0;}

    //Transfer ItemToPickUp into Slot4 if free
    if (ItemInSlot4 == 0){ItemInSlot4 = ItemToPickUp; SlotToTransferPickUp = 4; ItemToPickUp = 0;}

    //Transfer ItemToPickUp into Slot5 if free
    if (ItemInSlot5 == 0){ItemInSlot5 = ItemToPickUp; SlotToTransferPickUp = 5; ItemToPickUp = 0;}

    //Transfer ItemToPickUp into Slot6 if free
    if (ItemInSlot6 == 0){ItemInSlot6 = ItemToPickUp; SlotToTransferPickUp = 6; ItemToPickUp = 0;}

    //Transfer ItemToPickUp into Slot7 if free
    if (ItemInSlot7 == 0){ItemInSlot7 = ItemToPickUp; SlotToTransferPickUp = 7; ItemToPickUp = 0;}

    //Transfer ItemToPickUp into Slot8 if free
    if (ItemInSlot8 == 0){ItemInSlot8 = ItemToPickUp; SlotToTransferPickUp = 8; ItemToPickUp = 0;}

    //Transfer ItemToPickUp into Slot9 if free
    if (ItemInSlot9 == 0){ItemInSlot9 = ItemToPickUp; SlotToTransferPickUp = 9; ItemToPickUp = 0;}

    //Transfer ItemToPickUp into Slot0 if free
    if (ItemInSlot0 == 0){ItemInSlot0 = ItemToPickUp; SlotToTransferPickUp = 0; ItemToPickUp = 0;}

        PickUpItem2();

    }

    void PickUpItem2()
    {
        //=============================================
        //== CHANGE SLOT TEXTURE TO ITEM ICON =========
        //=============================================
        //== second problem ===========================
        if (ItemToPickUp == 1){
            if (SlotToTransferPickUp == 1){ItemIconSlot1 = InventoryIconHammer;}

        }


    }

}