Make rectangle in Unity - unity3d

Question

I stuck on the basics of Unity. I want to make a scene for mobiles in which there are four different coloured rectangles that take 25% of the screen each.
I tried making an GameObject Image, "registering" it as a prefab in Inspector.
Below code is an example of how I tried to make a single red rectangle and position it on the (x,y,z) => (0,0,0) coordinates on my scene.
Several problems are present:
Rectangle did not appear
I don't know how to programatically specify width and height of the rectangle
This is how it looks:
public class SceneScript : MonoBehaviour {
public GameObject prefab;
void Start () {
Vector3 pos = new Vector3(0, 0, 0);
GameObject gameObject = Instantiate(prefab);
Image image = gameObject.GetComponent<Image>();
image.color = new Color(1.0F, 0.0F, 0.0F);
gameObject.transform.position = new Vector3(0, 0, 0);
}
// Update is called once per frame
void Update () {
}
}
Is there an easier solution, or is this the best practice + could you please provide me some hints what should I do?

Answer 1

You probably don't have a Canvas in your heirarchy. Here's how you can programmatically create your Canvas, your Image and their containing GameObjects:
Vector3 pos = new Vector3(0, 0, 0);
GameObject parentGameObject = new GameObject();
Canvas canvas = parentGameObject.AddComponent<Canvas>();
GameObject imageGameObject = new GameObject();
imageGameObject.transform.SetParent(canvas.transform);
Image image = imageGameObject.AddComponent<Image>();
image.color = new Color(1.0F, 0.0F, 0.0F);
imageGameObject.transform.position = pos;
This will create a full-screen, red rectangle. Play around with the RectTransform settings in the inspector after these are created and you should be able to figure out how to size them properly.