Android客戶端獲取Firebase雲數據

前言：
最近的新項目使用Firebase做爲app的後臺,即經過Firebase的sdk來獲取Firestore(數據庫)的實時數據。Firebase的Firestore是一種雲託管數據庫，該數據庫將數據存儲爲 JSON，並以實時方式與每一個鏈接的客戶端同步。下面我簡單總結一下在MVVM架構的項目中如何獲取Firebase雲數據。

用到的知識點：
1.FirebaseFirestore獲取動態數據
2.Recyclerview+Adapter展現列表信息

實現的代碼：
1.Google官網註冊應用
   首先去網址：https://console.firebase.google.com/ 去註冊本身的應用，並下載google-services.json的文件，把它放到項目的app/目錄。

2.添加依賴

2.1 Project的build.gradle
        classpath 'com.google.gms:google-services:4.1.0'    
  2.2  Module的build.gradle
        dependencies {
        compile 'com.google.firebase:firebase-database:15.0.1'
        }
        apply plugin: 'com.google.gms.google-services'    //這一句必定要放在最下面，不然無效

3.在Firebase創建實時數據庫

 

4.在LenderRepository裏面封裝FirebaseFirestore獲取動態數據的方法

public class LenderRepository {
    private static final String TAG = LenderRepository.class.getSimpleName();
    
    /*
     *封裝一個FirebaseFirestore獲取動態數據的方法
     */
    public void getLenderList(CompleteCallback<ArrayList<Lender>> callback) {
        CollectionReference loansRef = FirebaseFirestore.getInstance().collection(FIREBASE_COLLECT_LENDERS);
        loansRef.get()
                .addOnSuccessListener(queryDocumentSnapshots -> {
                    ArrayList<Lender> lenders = new ArrayList<>();
                    if (!queryDocumentSnapshots.isEmpty()) {
                        lenders.addAll(queryDocumentSnapshots.toObjects(Lender.class));
                    }
                    callback.onComplete(null, lenders);
                })
                .addOnFailureListener(e -> {
                    callback.onComplete(AppError.parse(e.getCause()), null);
                });
    }

}

5.DependencyInjector的類

public class DependencyInjector {
    // Repositories
    private static LenderRepository sLenderRepo;

    public static LenderRepository getsLenderRepository(){
        if(sLenderRepo == null){
            sLenderRepo = new LenderRepository();
        }
        return sLenderRepo;
    }

}

6.LenderViewModel的類

public class LenderViewModel extends PaddyViewModel {
    private LenderRepository lenderRepository = DependencyInjector.getsLenderRepository();

    public void getLenderList(CompleteCallback<ArrayList<Lender>>  callback) {
        //判斷是否有網絡
        if (!NetworkingManager.isNetworkConnected()) {
            callback.onComplete(AppError.NETWORK_CONNECTION, null);
            return;
        }
        lenderRepository.getLenderList(callback);
    }
}

7.在LenderActivity調用FirebaseFirestore獲取動態數據的方法

public class LenderActivity extends PaddyActivity {
    private ActivityLenderBinding mBinding;
    private LenderViewModel viewModel;
    private LenderAdapter adapter;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        mBinding = DataBindingUtil.setContentView(this, R.layout.activity_lender);
        viewModel = obtainViewModel(LenderViewModel.class);
        setupViews();
    }

    private void setupViews() {
        //調用FirebaseFirestore獲取動態數據的方法
        getLenderList();
    }

    /*
     *調用FirebaseFirestore獲取動態數據的方法
     */
    private void getLenderList() {
        showLoading();
        viewModel.getLenderList((error, lenders) -> {
            if (error != null) {
                hideLoading();
                return;
            }
            setupLender(lenders);
        });
    }

    private void setupLender(ArrayList<Lender> lenders) {
        adapter = new LenderAdapter(this, lenders);
        mBinding.rcvLenders.setLayoutManager(new GridLayoutManager(this, 2));
        mBinding.rcvLenders.setAdapter(adapter);
        hideLoading();
    }
  

    @Override
    protected PaddyViewModel getViewModel() {
        if (viewModel == null) {
            viewModel = obtainViewModel(LenderViewModel.class);
        }
        return viewModel;
    }

}

8.適配器的代碼

public class LenderAdapter extends RecyclerView.Adapter<LenderAdapter.ViewHolder> {
    private LayoutInflater mInflater;
    private ArrayList<Lender> lenderList = new ArrayList<>();
    private Context context;

    public LenderAdapter(Context context,ArrayList<Lender> lenderList) {
        this.context=context;
        this.lenderList.addAll(lenderList);
    }

    @NonNull
    @Override
    public ViewHolder onCreateViewHolder(@NonNull ViewGroup parent, int viewType) {
        if (mInflater == null) {
            mInflater = LayoutInflater.from(parent.getContext());
        }
        View itemView = mInflater.inflate(R.layout.item_lenders, parent, false);
        return new LenderAdapter.ViewHolder(itemView);
    }

    @Override
    public void onBindViewHolder(@NonNull LenderAdapter.ViewHolder holder, int position) {
        String logo_url = lenderList.get(position).getLogo();
        setLenderImage(logo_url, holder.imvLender);
        String name = lenderList.get(position).getName();
        holder.tvLender.setText(name);
    }

    private void setLenderImage(@NonNull String url, @NonNull ImageView imageView) {
        ImageUtil.load(context, imageView, url);
    }

    @Override
    public int getItemCount() {
        return lenderList.size();
    }

    class ViewHolder extends RecyclerView.ViewHolder {
        @BindView(R.id.imv_lender)
        ImageView imvLender;
        @BindView(R.id.tv_lender)
        TextView tvLender;

        ViewHolder(View itemView) {
            super(itemView);
            ButterKnife.bind(this, itemView);
        }
    }

}

9.總結：

Android客戶端獲取Firebase雲數據的功能已經實現啦，若是你們有什麼疑問的話，歡迎留言聯繫我哦！