android - Adapter, GridView, AlertDialog

package com.example.it.myapplication9_5;

import android.app.AlertDialog;
import android.content.Context;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.view.ViewGroup;
import android.widget.BaseAdapter;
import android.widget.GridView;
import android.widget.ImageView;

public class MainActivity extends AppCompatActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        setTitle("그리드뷰 영화 포스터");

        final GridView gv = (GridView) findViewById(R.id.gridView1);
        //3요소 있어야함
        //1.위치 (액티비티)
        //2.한줄 디자인
        MyGridAdapter gAdapter = new MyGridAdapter(this);
        //3.데이터
        gv.setAdapter(gAdapter);
    }

    public class MyGridAdapter extends BaseAdapter {
        Context context;

        int [] posterID = {R.drawable.mov01, R.drawable.mov02, R.drawable.mov03,
                R.drawable.mov04, R.drawable.mov05, R.drawable.mov06,
                R.drawable.mov07, R.drawable.mov08, R.drawable.mov09, R.drawable.mov10,
                R.drawable.mov01, R.drawable.mov02, R.drawable.mov03,
                R.drawable.mov04, R.drawable.mov05, R.drawable.mov06,
                R.drawable.mov07, R.drawable.mov08, R.drawable.mov09, R.drawable.mov10,
                R.drawable.mov01, R.drawable.mov02, R.drawable.mov03,
                R.drawable.mov04, R.drawable.mov05, R.drawable.mov06,
                R.drawable.mov07, R.drawable.mov08, R.drawable.mov09, R.drawable.mov10};

        String [] posterName = {"써니", "완득이", "괴물",
                "라디오스타", "비열한거리", "왕의남자",
                "아일랜드", "웰컴투동막골", "헬보이", "백투더퓨처",
                "써니", "완득이", "괴물",
                "라디오스타", "비열한거리", "왕의남자",
                "아일랜드", "웰컴투동막골", "헬보이", "백투더퓨처",
                "써니", "완득이", "괴물",
                "라디오스타", "비열한거리", "왕의남자",
                "아일랜드", "웰컴투동막골", "헬보이", "백투더퓨처"};


        public MyGridAdapter(Context context) {
            this.context = context;
        }

        @Override
        public int getCount() { //중요1//데이터의 갯수 지정
            return posterID.length;
        }

        @Override
        public Object getItem(int position) {
            return null;
        }

        @Override
        public long getItemId(int position) {
            return 0;
        }

        @Override
        public View getView(int position, View convertView, ViewGroup parent) { //중요2 : 디자인 담당
            ImageView imageView = new ImageView(context);
            imageView.setLayoutParams(new ViewGroup.LayoutParams(100, 150));
            imageView.setScaleType(ImageView.ScaleType.FIT_CENTER);
            imageView.setPadding(5,5,5,5);

            imageView.setImageResource(posterID[position]);

            final int pos = position;
            imageView.setOnClickListener(new View.OnClickListener() {
                @Override
                public void onClick(View v) {
                    View dialogView = (View) View.inflate(MainActivity.this, R.layout.dialog, null);
                    AlertDialog.Builder dlg = new AlertDialog.Builder(MainActivity.this);
                    ImageView ivPoster = (ImageView) dialogView.findViewById(R.id.ivPoster);
                    ivPoster.setImageResource(posterID[pos]);
                    dlg.setTitle(posterName[pos]);
                    dlg.setIcon(R.drawable.ic_launcher);
                    dlg.setView(dialogView);
                    dlg.setNegativeButton("닫기", null);
                    dlg.show();
                }
            });

            return imageView;
        }

    }

}

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent"
    android:orientation="vertical" >

    <GridView
        android:id="@+id/gridView1"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:gravity="center"
        android:numColumns="4" >
    </GridView>

</LinearLayout>

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:gravity="center"
    android:orientation="vertical" >

    <ImageView
        android:id="@+id/ivPoster"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content" />

</LinearLayout>