新人问个问题，为什么用GUI.DrawTexture显示不出纹理啊

文件夹aa和bb内都有纹理图片
private Texture2D one_texture;
private Texture2D[] all_texture;
void OnGUI()
{
if (GUI.Button(new Rect(10, 20, 100, 60), "读取一个纹理"))
{
if (one_texture == null)
{
one_texture = Resources.Load("aa/Grass") as Texture2D;
}
}
if (GUI.Button(new Rect(10, 140, 100, 60), "读取所有纹理"))
{
if (all_texture == null)
{
all_texture = Resources.LoadAll("bb") as Texture2D[];
}
}
if (one_texture != null)
{
GUI.DrawTexture(new Rect(130, 20, 120, 120), one_texture, ScaleMode.StretchToFill, true, 0);
}
if (all_texture != null)
{
//使用for循环语句遍历
for (int i = 0; i < all_texture.Length; i++)
{
GUI.DrawTexture(new Rect(130 + i * 120, 140, 120, 120), all_texture[i], ScaleMode.StretchToFill, true, 0);
}
}
}