前言：

最近的新项目使用Firebase作为app的后台,即通过Firebase的sdk来获取Firestore(数据库)的实时数据。Firebase的Firestore是一种云托管数据库，该数据库将数据存储为 JSON，并以实时方式与每个连接的客户端同步。下面我简单总结一下在MVVM架构的项目中如何获取Firebase云数据。

用到的知识点：

1.FirebaseFirestore获取动态数据 2.Recyclerview+Adapter展示列表信息

实现的代码：

1.Google官网注册应用    首先去网址：https://console.firebase.google.com/ 去注册自己的应用，并下载google-services.json的文件，把它放到项目的app/目录。

2.添加依赖

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'    //这一句一定要放在最下面，否则无效

3.在Firebase建立实时数据库

 

4.在LenderRepository里面封装FirebaseFirestore获取动态数据的方法

public class LenderRepository {    private static final String TAG = LenderRepository.class.getSimpleName();        /*     *封装一个FirebaseFirestore获取动态数据的方法     */    public void getLenderList(CompleteCallback
    
     
      > callback) {        CollectionReference loansRef = FirebaseFirestore.getInstance().collection(FIREBASE_COLLECT_LENDERS);        loansRef.get()                .addOnSuccessListener(queryDocumentSnapshots -> {                    ArrayList
      
        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的类

public class DependencyInjector {    // Repositories    private static LenderRepository sLenderRepo;    public static LenderRepository getsLenderRepository(){        if(sLenderRepo == null){            sLenderRepo = new LenderRepository();        }        return sLenderRepo;    }}

6.LenderViewModel的类

public class LenderViewModel extends PaddyViewModel {    private LenderRepository lenderRepository = DependencyInjector.getsLenderRepository();    public void getLenderList(CompleteCallback
    
     
      >  callback) {        //判断是否有网络        if (!NetworkingManager.isNetworkConnected()) {            callback.onComplete(AppError.NETWORK_CONNECTION, null);            return;        }        lenderRepository.getLenderList(callback);    }}
     
    

7.在LenderActivity调用FirebaseFirestore获取动态数据的方法

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() {        //调用FirebaseFirestore获取动态数据的方法        getLenderList();    }    /*     *调用FirebaseFirestore获取动态数据的方法     */    private void getLenderList() {        showLoading();        viewModel.getLenderList((error, lenders) -> {            if (error != null) {                hideLoading();                return;            }            setupLender(lenders);        });    }    private void setupLender(ArrayList
    
      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.适配器的代码

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

Android客户端获取Firebase云数据的功能已经实现啦，如果大家有什么疑问的话，欢迎留言联系我哦！