[embedyt] https://www.youtube.com/watch?v=gqIWrNitbbk[/embedyt]
Links & DependenciesMainActivity.javaAndroidManifest.xmlactivity_main.xml
package com.codinginflow.firebaseuploadexample;

import android.content.Intent;
import android.net.Uri;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.ImageView;
import android.widget.ProgressBar;
import android.widget.TextView;

import com.squareup.picasso.Picasso;

public class MainActivity extends AppCompatActivity {

    private static final int PICK_IMAGE_REQUEST = 1;

    private Button mButtonChooseImage;
    private Button mButtonUpload;
    private TextView mTextViewShowUploads;
    private EditText mEditTextFileName;
    private ImageView mImageView;
    private ProgressBar mProgressBar;

    private Uri mImageUri;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        mButtonChooseImage = findViewById(R.id.button_choose_image);
        mButtonUpload = findViewById(R.id.button_upload);
        mTextViewShowUploads = findViewById(R.id.text_view_show_uploads);
        mEditTextFileName = findViewById(R.id.edit_text_file_name);
        mImageView = findViewById(R.id.image_view);
        mProgressBar = findViewById(R.id.progress_bar);

        mButtonChooseImage.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                openFileChooser();
            }
        });

        mButtonUpload.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {

            }
        });

        mTextViewShowUploads.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {

            }
        });
    }

    private void openFileChooser() {
        Intent intent = new Intent();
        intent.setType("image/*");
        intent.setAction(Intent.ACTION_GET_CONTENT);
        startActivityForResult(intent, PICK_IMAGE_REQUEST);
    }

    @Override
    protected void onActivityResult(int requestCode, int resultCode, Intent data) {
        super.onActivityResult(requestCode, resultCode, data);

        if (requestCode == PICK_IMAGE_REQUEST && resultCode == RESULT_OK
                && data != null && data.getData() != null) {
            mImageUri = data.getData();

            Picasso.with(this).load(mImageUri).into(mImageView);
        }
    }
}
<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.codinginflow.firebaseuploadexample">

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

    <application
        android:allowBackup="true"
        android:icon="@mipmap/ic_launcher"
        android:label="@string/app_name"
        android:roundIcon="@mipmap/ic_launcher_round"
        android:supportsRtl="true"
        android:theme="@style/AppTheme">
        <activity android:name=".MainActivity">
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />

                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>
    </application>

</manifest>
<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout 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"
    android:padding="16dp"
    tools:context="com.codinginflow.firebaseuploadexample.MainActivity">

    <Button
        android:id="@+id/button_choose_image"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Choose file" />

    <EditText
        android:id="@+id/edit_text_file_name"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_marginStart="16dp"
        android:layout_toEndOf="@+id/button_choose_image"
        android:hint="Enter file name" />

    <ImageView
        android:id="@+id/image_view"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:layout_above="@id/progress_bar"
        android:layout_below="@id/edit_text_file_name"
        android:layout_marginTop="16dp" />

    <ProgressBar
        android:id="@+id/progress_bar"
        style="@style/Widget.AppCompat.ProgressBar.Horizontal"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_above="@+id/button_upload"
        android:layout_alignParentStart="true"
        android:layout_marginBottom="16dp" />

    <Button
        android:id="@+id/button_upload"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_alignParentBottom="true"
        android:layout_centerHorizontal="true"
        android:text="Upload" />

    <TextView
        android:id="@+id/text_view_show_uploads"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_alignBottom="@+id/button_upload"
        android:layout_alignTop="@+id/button_upload"
        android:layout_marginStart="25dp"
        android:layout_toEndOf="@+id/button_upload"
        android:gravity="center"
        android:text="Show Uploads"
        android:textSize="16sp" />

</RelativeLayout>