清单文件添加权限

<uses-permission android:name="android.permission.READ_EXTERNAL_STORAGE"/>

MainActivity布局代码

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".MainActivity"
    android:orientation="vertical"
    >
<Button
    android:id="@+id/Button_photo"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:text="获取图库"
    />
    <GridView
        android:id="@+id/GridView"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:numColumns="2"
        >
    </GridView>

</LinearLayout>

MainActivity代码

public class MainActivity extends AppCompatActivity {
    private GridView gridView;
    private List<String> list=new ArrayList<>();
    private Button Button_photo;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        ActivityCompat.requestPermissions(this,new String[]{Manifest.permission.READ_EXTERNAL_STORAGE},1);
        gridView=findViewById(R.id.GridView);
        Button_photo=findViewById(R.id.Button_photo);

        Button_photo.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                ContentResolver resolver = getContentResolver();
                Cursor cursor = resolver.query(MediaStore.Images.Media.EXTERNAL_CONTENT_URI, null, null, null, null);
                if(cursor!=null){
                    while(cursor.moveToNext()){
                        byte[] data = cursor.getBlob(cursor.getColumnIndex(MediaStore.Images.Media.DATA));
                        list.add(new String(data,0,data.length-1));
                    }
                    MyAdapter myAdapter = new MyAdapter(list,MainActivity.this);
                    gridView.setAdapter(myAdapter);
                }
            }
        });
        gridView.setOnItemClickListener(new AdapterView.OnItemClickListener() {
            @Override
            public void onItemClick(AdapterView<?> adapterView, View view, int i, long l) {
                View view1 = getLayoutInflater().inflate(R.layout.myview, null);
                ImageView ImageView = view1.findViewById(R.id.ImageView_look);
                ImageView.setImageBitmap(BitmapFactory.decodeFile(list.get(i)));
                new AlertDialog.Builder(MainActivity.this).setView(view1).setPositiveButton("确定",null).show();
            }
        });

    }
}

适配器代码

public class MyAdapter extends BaseAdapter {
    private List<String> list;
    private Context context;
    private LayoutInflater layoutInflater;

    public MyAdapter(List<String> list, Context context) {
        this.list = list;
        this.context = context;
        layoutInflater=LayoutInflater.from(context);
    }

    @Override
    public int getCount() {
        return list.size();
    }

    @Override
    public Object getItem(int i) {
        return list.get(i);
    }

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

    @Override
    public View getView(int i, View view, ViewGroup viewGroup) {
        ViewHoder viewHoder;
        if(view==null){
            view=layoutInflater.inflate(R.layout.item,null);
            viewHoder=new ViewHoder();
            viewHoder.imageView=view.findViewById(R.id.ImageView);
            view.setTag(viewHoder);
        }
        else{
            viewHoder = (ViewHoder) view.getTag();
        }
        Glide.with(context).load(list.get(i)).into(viewHoder.imageView);
        return view;
    }
    class ViewHoder{
        ImageView imageView;
    }
}

item布局代码

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="vertical" android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:padding="20dp"
    >
<ImageView
    android:id="@+id/ImageView"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:src="@mipmap/ic_launcher"
    />
</LinearLayout>

myview布局代码

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="vertical" android:layout_width="match_parent"
    android:layout_height="match_parent">
<ImageView
    android:id="@+id/ImageView_look"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content" />
</LinearLayout>