How to Upload Images and PDFs in Android Apps Using Retrofit

In many Android applications, the ability to upload user-selected files, such as images or PDF documents, to a server is essential. This tutorial will guide you step-by-step through the process of implementing image and PDF file uploads in your Android app. We’ll leverage the popular Retrofit library to simplify the interaction with your server-side API.

Prerequisites

• Basic understanding of Android development with Java or Kotlin.
• A working Android Studio project.
• A server-side API endpoint that can receive and process uploaded files.

Step 1: Project Setup

1. Dependencies: Add the following dependencies to your project’s build.gradle file:

dependencies {
    implementation("com.squareup.retrofit2:retrofit:2.9.0")  // Update to latest if needed
    implementation("com.squareup.retrofit2:converter-gson:2.9.0")
    implementation("com.squareup.okhttp3:okhttp:4.10.0")  // Update to latest if needed
}

Permissions: Ensure your app has storage access. Add the following line to your AndroidManifest.xml:

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

Step 2: Android Code

Here’s an improved version of your UploadPodActivity (adjusting package names and API details as needed):

import android.Manifest;
import android.content.Intent;
import android.content.pm.PackageManager; 
import android.database.Cursor;
import android.net.Uri;
import android.os.Bundle;
import android.provider.OpenableColumns;
import android.util.Log;
import android.view.View;
import android.widget.Toast; 
import androidx.activity.result.ActivityResultLauncher;
import androidx.activity.result.contract.ActivityResultContracts;
import androidx.appcompat.app.AppCompatActivity;
import androidx.core.app.ActivityCompat;
import androidx.core.content.ContextCompat;
import java.io.File;
import java.io.FileOutputStream;
import java.io.InputStream;
import okhttp3.MediaType;
import okhttp3.MultipartBody;
import okhttp3.RequestBody;
import retrofit2.Call;
import retrofit2.Callback;
import retrofit2.Response;
import retrofit2.Retrofit;
import retrofit2.converter.gson.GsonConverterFactory;

public class UploadPodActivity extends AppCompatActivity { 
    // ... (Other UI elements and SharedPreferences code)

    private static final int REQUEST_READ_STORAGE = 100;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        // ... (Existing onCreate code)

        // ... (OnClickListener setup)
    }

    private void chooseFile() {
        if (ContextCompat.checkSelfPermission(this, Manifest.permission.READ_EXTERNAL_STORAGE)
                != PackageManager.PERMISSION_GRANTED) {
            ActivityCompat.requestPermissions(this,
                    new String[]{Manifest.permission.READ_EXTERNAL_STORAGE},
                    REQUEST_READ_STORAGE);
        } else {
            openFilePicker(); 
        }
    }

    private void openFilePicker() {
        Intent intent = new Intent(Intent.ACTION_GET_CONTENT);
        intent.setType("*/*");
        String[] mimeTypes = {"image/*", "application/pdf"};
        intent.putExtra(Intent.EXTRA_MIME_TYPES, mimeTypes);
        resultLauncher.launch(intent);
    }

    private ActivityResultLauncher<Intent> resultLauncher = registerForActivityResult(
            new ActivityResultContracts.StartActivityForResult(),
            result -> {
                // ... (Handle file selection in onActivityResult)
            });

    // ... (Other utility methods: getFileFromContentUri, getFileNameFromUri)

    // ... (uploadFile method with Retrofit API setup) 
}

Step 3: Create Your Retrofit Interface

Define an interface for your API interaction:

// File: ApiService.java 
import retrofit2.Call;
import retrofit2.http.Multipart;
import retrofit2.http.POST;
import retrofit2.http.Part;
import retrofit2.http.Header;

interface ApiService {
    @Multipart
    @POST("your_upload_endpoint") // Replace with your API endpoint
    Call<PodUploadResponse> uploadPOD(@Header("Authorization") String authorization,
                                      @Part MultipartBody.Part file,
                                      @Part("docketNo") RequestBody docketNo,

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