Problem trying to update texture using glTexImage2D on iOS.

I'm creating a plugin using C&Obj-C for iphone. I use Texture.GetNativeTextureID() to get a GL texture handle and pass it into C Plugin, then use glTexImage2D to update pixels of it.But the texture displayed in my app didn't change.(On iPad) And all gl call ran with out any error. I wonder if there are any limit that using GLES on iOS or special rules I didn't know.

Here is some test code in my project.

//Code in unity3d

 public class GamePluginTest : MonoBehaviour {
     
     const int width = 512;
     const int height = 512;
     
     void OnGUI () {
         if(GUI.Button(new Rect(20, 20, 240, 60), "UpdateTexture"))
         {
             GameObject go = GameObject.Find("Plane");
             Material mat = go.renderer.material;
             if(mat.mainTexture == null)
             {
                 mat.mainTexture = new Texture2D(width, height, TextureFormat.RGB24, false);
             }
             iOSPlugin_UpdateTexture(mat.mainTexture.GetNativeTextureID(), width, height);
         }
     }
     
     [DllImport("__Internal")]
     static extern void iOSPlugin_UpdateTexture(int textureHandle, int width, int height);
 }

//Code in XCode

 void iOSPlugin_UpdateTexture(int textureHandle, int width, int height)
 {
     unsigned char* pixels = malloc(sizeof(unsigned char) * 3 * width * height);
     for(int y = 0; y < height; ++y)
     {
         for(int x = 0; x < width; ++x)
         {
             int index = (y * width + x) * 3;
             pixels[index + 0] = 0xFF;
             pixels[index + 1] = 0xFF;
             pixels[index + 2] = 0xFF;
         }
     }
     glBindTexture(GL_TEXTURE_2D, textureHandle);
     glTexImage2D(GL_TEXTURE_2D, 0, GL_RGB, width, height, 0, GL_RGB, GL_UNSIGNED_BYTE, pixels);
     free(pixels);
 }