Using prefabs with arrays

Let's have a bit more fun with Prefabs. So far we've instantiated them in predictable places at predictable times. In our little game the player will start out in the staging area. It's small, and there's nothing of interest in it, but we might need to motivate him into leaving it. A bunch of rocks falling on him just might do the job. Now it would look pretty odd if all the rocks were the same size, but the Instantiate function doesn't have a Scale parameter. So the first thing we need to do is import the LotsOfRocks package from the right-click menu.

Import Package > Custom Package, and from our Assets folder we are going to bring in LotsOfRocks. In the Prefabs folder, you can see Rock1, Rock2, Rock3, and Rock4. I've added to each a Mesh collider set to Convex, a Physics material, a Rigidbody, and an Audio Source. Let's drag the four new rocks into the scene near the original rock pile, and then lift them up above the Rock Zone's collider.

Rock1, Rock2, Rock3, and Rock4, and I'll use Shift to select them all and drag them up a little ways. I'm going to deselect them, and click Play, and watch them fall. We'll exit Play mode. And now we need to update each Rock's Prefab by clicking Apply in the selector to make sure it knows where the new location is.

Apply, Apply, Apply, and Apply, and now we can delete the rocks in our scene, Delete, and there we go, so far so good. Let's make a new Rock script in the Game Scripts folder by duplicating the original. So I'll select it and use Ctrl+D, and I want to name this one RockDropper.

Let's open it in the Script editor and make a few changes, double-click, make sure we're on RockDropper. And the first change we are going to make is the variable. Instead of 1 of type transform we're going to make it an array. Unity uses two types of arrays, the usual Javascript type array, and its own version. The Unity array must be declared as a particular type, and it can show up in the Inspector where we can change its size and load up its elements.

A Javascript array doesn't store types causing the #pragma strict to report an error. With Unity's emphasis on mobile we're better off to stick to the Unity arrays. If you're already familiar with Javascript arrays you may want to read through the scripting reference on arrays to see the differences. So in the RockDropper script, let's change the variable line to their Prefabs, I'm adding an S, and then transform and then open and shut bracket.

This is what tells us it's going to be an array. Next we need to change the instantiate line. To access an element of an array we need to put the element number in brackets. So Prefabs and open bracket, I'm going to start with element 0 and close bracket. Arrays always start with element 0. Let's save the script now and get back to the editor. We can replace the original script with this one on the Rock Zone object.

And we can do that to the browser, and we'll choose RockDropper. If you click Play, and use the S key to back into the collider, you'll get an IndexOutOfRangeException Error on the console. Let's look at that. That's because we haven't filled out the array with anything yet, and then we're trying to instantiate element 0. So let's exit Play mode and fix that.

I'll close the console, exit Play mode. And in the Rock Zone, we need to open up Prefabs, set its size to four. And drag the Rock into each parameter. Now we can click Play, press S to back into the zone, and we get lots and lots of rocks.

Let's stop before we get too many. So this time the Rock Prefab from element 0 drops into the scene. And it keeps dropping because each rock triggers the zone on entry. In this case that's a serendipitous side effect. It will eventually shut itself off when it fills up. The problem now is that the same rock is being used over and over. We'll fix that in the next video.