今天繼續來示範文件上傳至雲端的程式碼

MainActivity的程式碼

package com.example.demogoogle;

import androidx.annotation.Nullable;
import androidx.appcompat.app.AppCompatActivity;
import androidx.core.app.ActivityCompat;

import android.Manifest;
import android.content.Intent;
import android.content.pm.PackageManager;
import android.os.Bundle;
import android.util.Log;

import com.google.android.gms.auth.api.signin.GoogleSignIn;
import com.google.android.gms.auth.api.signin.GoogleSignInClient;
import com.google.android.gms.auth.api.signin.GoogleSignInOptions;
import com.google.android.gms.common.api.Scope;
import com.google.api.client.extensions.android.http.AndroidHttp;
import com.google.api.client.googleapis.extensions.android.gms.auth.GoogleAccountCredential;
import com.google.api.client.json.gson.GsonFactory;
import com.google.api.services.drive.Drive;
import com.google.api.services.drive.DriveScopes;

import java.util.Collection;
import java.util.Collections;

public class MainActivity extends AppCompatActivity {

    private static final int REQUEST_SIGNIN_CODE = 400;
    GoogleSignInClient client;
    GoogleDriveServiceFunction googleDriveServiceFunction;

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

    }

    public void requestSignIn() {
        GoogleSignInOptions signInOptions = new GoogleSignInOptions.Builder(GoogleSignInOptions.DEFAULT_SIGN_IN)
                .requestEmail()
                .requestScopes(new Scope(DriveScopes.DRIVE_FILE),
                        new Scope(DriveScopes.DRIVE_APPDATA),
                        new Scope(DriveScopes.DRIVE))
                .build();

        client = GoogleSignIn.getClient(this, signInOptions);
        startActivityForResult(client.getSignInIntent(), REQUEST_SIGNIN_CODE);
    }

    @Override
    protected void onActivityResult(int requestCode, int resultCode, @Nullable Intent data) {
        super.onActivityResult(requestCode, resultCode, data);
        if (requestCode == REQUEST_SIGNIN_CODE && resultCode == RESULT_OK) {
            handleSignInIntent(data);
        }
    }

    private void handleSignInIntent(Intent data) {
        GoogleSignIn.getSignedInAccountFromIntent(data)
                .addOnSuccessListener(googleSignInAccount -> {
                    GoogleAccountCredential credential = GoogleAccountCredential
                            .usingOAuth2(this, Collections.singleton(DriveScopes.DRIVE_FILE));

                    credential.setSelectedAccount(googleSignInAccount.getAccount());

                    drive(credential);
                })
                .addOnFailureListener(e -> e.printStackTrace());
    }

    public void drive(GoogleAccountCredential credential) {
        Drive googleDriveService =
                new Drive.Builder(
                        AndroidHttp.newCompatibleTransport(),
                        new GsonFactory(),
                        credential)
                        .setApplicationName("Appname")
                        .build();

        googleDriveServiceFunction = new GoogleDriveServiceFunction(googleDriveService);
    }

}

上面的程式碼做完會有登入的功能，成功的話會出現以下畫面:

第二張圖片到第五張圖片對應程式碼裡面requestSignIn副程式裡面的.requestScopes,而他們的功能我們可以參考網址的解釋去對應要功能:
http://javadox.com/com.google.apis/google-api-services-drive/v3-rev12-1.18.0-rc/com/google/api/services/drive/DriveScopes.html

每一個Google帳戶的第一次登入會出現第二張~第四張圖片的畫面，如果某天不小心將程式清除儲存空間以後在登入同一支Google帳戶時就只會出現第一張圖片。

因為我們會有上傳檔案的動作，而Android 6.0以上的版本中，為了安全設計，就全面要求app要和使用者要求權限，於是我在程式碼中新增了requestStoragePremission副程式來要求使用者給app檔案存取權限，代碼如下:

public void requestStoragePremission() {
        if (ActivityCompat.checkSelfPermission(this, Manifest.permission.READ_EXTERNAL_STORAGE)
                != PackageManager.PERMISSION_GRANTED) {
            ActivityCompat.requestPermissions(this, new String[]{Manifest.permission.READ_EXTERNAL_STORAGE}, 1);
        }
    }

成功後會出現以下畫面

除了以上方法能拿到權限以外，我們也可以由"應用程式資訊"來設定權限許可。

這樣一來Google帳戶登入就完成了，我們明天開始做上傳檔案的功能。