Pick gallery Images in Android Application

Today i show the custom Gallery on you Application.Before do this You must write the Run time permissions
in AndroidManifest.xml as well write permissions code.
 
<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" />
<uses-permission android:name="android.permission.READ_EXTERNAL_STORAGE" />

Then Write below code on your app.
import android.content.Context;
import android.content.Intent;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.os.Bundle;
import android.os.Environment;
import android.support.annotation.Nullable;
import android.support.v7.app.ActionBar;
import android.support.v7.app.AppCompatActivity;
import android.support.v7.widget.Toolbar;
import android.view.LayoutInflater;
import android.view.MenuItem;
import android.view.View;
import android.view.ViewGroup;
import android.widget.BaseAdapter;
import android.widget.GridView;
import android.widget.ImageView;
import android.widget.TextView;

import com.google.android.gms.ads.AdListener;
import com.google.android.gms.ads.AdRequest;
import com.google.android.gms.ads.AdView;
import com.google.android.gms.ads.InterstitialAd;

import java.io.File;
import java.util.ArrayList;

public class GallaryView extends AppCompatActivity {

    private int count;
    private Bitmap[] thumbnails;
    private boolean[] thumbnailsselection;
    private String[] arrPath;
    private ImageAdapter imageAdapter;
    ArrayList<String> f = new ArrayList<String>();
    File[] listFile;
    @Override
    protected void onCreate(@Nullable Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.my_gallary);
        Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
        toolbar.setTitle("Gallery");
        setSupportActionBar(toolbar);

        ActionBar actionBar = getSupportActionBar();
        actionBar.setDisplayHomeAsUpEnabled(true);

        getFromSdcard();
        GridView imagegrid = (GridView) findViewById(R.id.gallary);
        imageAdapter = new ImageAdapter();
        imagegrid.setAdapter(imageAdapter);
    }
    public void getFromSdcard() {
        String root =Environment.getExternalStorageDirectory()
                .toString();
        File file = new File(root);
        if (file.isDirectory()) {
            listFile = file.listFiles();

            if (listFile.length > 0) {
                for (int i = 0; i < listFile.length; i++) {
                    f.add(listFile[i].getAbsolutePath());
                }
                ((TextView) findViewById(R.id.nodata)).setVisibility(View.GONE);
            } else {
                ((TextView) findViewById(R.id.nodata)).setVisibility(View.VISIBLE);
            }
        }
    }
    public class ImageAdapter extends BaseAdapter {
        private LayoutInflater mInflater;

        public ImageAdapter() {
            mInflater = (LayoutInflater) getSystemService(Context.LAYOUT_INFLATER_SERVICE);
        }

        public int getCount() {
            return f.size();
        }

        public Object getItem(int position) {
            return position;
        }

        public long getItemId(int position) {
            return position;
        }
        public View getView(final int position, View convertView, ViewGroup parent) {
            ViewHolder holder;
            if (convertView == null) {
                holder = new ViewHolder();
                convertView = mInflater.inflate(
                        R.layout.gallary_item, null);
                holder.imageview = (ImageView) convertView.findViewById(R.id.thumbImage);
                convertView.setTag(holder);
            } else {
                holder = (ViewHolder) convertView.getTag();
            }

            Bitmap myBitmap = BitmapFactory.decodeFile(f.get(position));
            holder.imageview.setImageBitmap(myBitmap);
            holder.imageview.setOnClickListener(new View.OnClickListener() {
                @Override
                public void onClick(View v) {
                    Intent next = new Intent(getApplicationContext(), Screen_Preview.class);
                    next.putExtra("path", f.get(position));
                    startActivity(next);
                }
            });
            return convertView;
        }
    }

    class ViewHolder {
        ImageView imageview;
    }
    @Override
    public boolean onOptionsItemSelected(MenuItem item) {

        switch (item.getItemId()) {
            case android.R.id.home:
               finish();
                break;

            default:
                break;
        }

        return super.onOptionsItemSelected(item);
    }
}