Android 我使用Firebase UI Recyclerview获得空屏幕

我无法在我的Recyclerview上显示firebase项目。数据库连接正常

编辑：根据链接问题的答案，我添加了startListening（）方法。但现在我的应用程序崩溃了。看起来像这样

  @Override
    protected void onStart() {
        super.onStart();

        FirebaseRecyclerOptions<Coupon> options =
                new FirebaseRecyclerOptions.Builder<Coupon>()
                        .setQuery(mDatabase, Coupon.class)
                        .build();

        FirebaseRecyclerAdapter<Coupon, CouponViewHolder> firebaseRecyclerAdapter = new FirebaseRecyclerAdapter<Coupon, CouponsActivity.CouponViewHolder>
                (options) {

            @Override
            protected void onBindViewHolder(@NonNull CouponsActivity.CouponViewHolder holder, int position, @NonNull Coupon model) {

                holder.setTitle(model.getTitle());
                holder.setDesc(model.getDesc());

            }

            @Override
            public CouponsActivity.CouponViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
                View view = LayoutInflater.from(parent.getContext())
                        .inflate(R.layout.item_coupon_row, parent, false);

                return new CouponsActivity.CouponViewHolder(view);
            }
        };

        firebaseRecyclerAdapter.startListening();
        mRecyclerview.setAdapter(firebaseRecyclerAdapter);


    }

    @Override
    protected void onStop() {
        super.onStop();
        firebaseRecyclerAdapter.stopListening();
    }

---

这是我的身材，格雷德尔

apply plugin: 'com.android.application'

android {
    compileSdkVersion 27
    defaultConfig {
        applicationId "com.myapp"
        minSdkVersion 19
        targetSdkVersion 27
        versionCode 1
        versionName "1.0"
        testInstrumentationRunner "android.support.test.runner.AndroidJUnitRunner"
    }
    buildTypes {
        release {
            minifyEnabled false
            proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard-rules.pro'
        }
    }
}

dependencies {
    implementation fileTree(dir: 'libs', include: ['*.jar'])
    implementation 'com.android.support:appcompat-v7:27.0.2'
    implementation 'com.android.support.constraint:constraint-layout:1.0.2'

    // firebase
    implementation 'com.google.firebase:firebase-core:11.8.0'
    implementation 'com.google.firebase:firebase-database:11.8.0'
    implementation 'com.firebaseui:firebase-ui-database:3.1.3'

    testImplementation 'junit:junit:4.12'
    androidTestImplementation 'com.android.support.test:runner:1.0.1'
    androidTestImplementation 'com.android.support.test.espresso:espresso-core:3.0.1'

    compile 'com.android.support:cardview-v7:27.0.2'
    compile 'com.android.support:recyclerview-v7:27.0.2'
    compile 'com.android.support:design:27.0.2'

}
apply plugin: 'com.google.gms.google-services'

这是我的活动：

public class CouponsActivity extends AppCompatActivity {
    private DatabaseReference mDatabase;
    private RecyclerView mRecyclerview;


    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_coupons);

        mDatabase = FirebaseDatabase.getInstance().getReference().child("coupon");
        mDatabase.keepSynced(true);

        mRecyclerview = (RecyclerView) findViewById(R.id.coupon_recyclerView_list);
        mRecyclerview.setHasFixedSize(true);
        mRecyclerview.setLayoutManager(new LinearLayoutManager(this));
    }

    @Override
    protected void onStart() {
        super.onStart();


        FirebaseRecyclerOptions<Coupon> options =
                new FirebaseRecyclerOptions.Builder<Coupon>()
                        .setQuery(mDatabase, Coupon.class)
                        .build();

        FirebaseRecyclerAdapter<Coupon, CouponViewHolder> firebaseRecyclerAdapter = new FirebaseRecyclerAdapter<Coupon, CouponsActivity.CouponViewHolder>
                (options) {

            @Override
            protected void onBindViewHolder(@NonNull CouponsActivity.CouponViewHolder holder, int position, @NonNull Coupon model) {

                holder.setTitle(model.getTitle());
                holder.setDesc(model.getDesc());

            }

            @Override
            public CouponsActivity.CouponViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
                View view = LayoutInflater.from(parent.getContext())
                        .inflate(R.layout.item_coupon_row, parent, false);

                return new CouponsActivity.CouponViewHolder(view);
            }
        };

        mRecyclerview.setAdapter(firebaseRecyclerAdapter);

    }

    public static class CouponViewHolder extends RecyclerView.ViewHolder{

        TextView postTitle;
        TextView postDescription;

        public CouponViewHolder(View itemView) {
            super(itemView);
            postTitle = (TextView)itemView.findViewById(R.id.post_title);
            postDescription = (TextView)itemView.findViewById(R.id.post_description);

        }

        public void setTitle(String title) {
            postTitle.setText(title);
        }

        public void setDesc(String desc) {
            postDescription.setText(desc);
        }
    }

}

这是活动的布局：

<?xml version="1.0" encoding="utf-8"?>
<android.support.constraint.ConstraintLayout 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"
    tools:context="com.myapp.coupons.CouponsActivity">


    <android.support.v7.widget.RecyclerView
        android:id="@+id/coupon_recyclerView_list"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:background="@color/YELLOW">


    </android.support.v7.widget.RecyclerView>

</android.support.constraint.ConstraintLayout>

这是卡片项目布局：

<?xml version="1.0" encoding="utf-8"?>
<android.support.v7.widget.CardView xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    android:layout_margin="8dp"
    android:orientation="vertical"
    android:background="@color/GREEN"
    app:cardCornerRadius="5dp"
    android:elevation="90dp">

    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:orientation="vertical">


        <TextView
            android:id="@+id/post_title"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:padding="10dp"

            />

        <TextView
            android:id="@+id/post_description"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:paddingBottom="10dp"
            android:paddingLeft="10dp"
            android:paddingRight="10dp"
            />

    </LinearLayout>


</android.support.v7.widget.CardView>

---

这是因为数据库中只存储了一个优惠券对象，而不是列表

如果您想创建优惠券列表，我建议添加一个带有键

优惠券

的节点，并将每个优惠券存储在该节点下。因此，您的结构将如下所示：

Root
  |
  |__Coupons
       |____coupon
               |_____title: "This is title"
               |_____desc: "This is description"

然后您的

数据库引用将是：

mDatabase = FirebaseDatabase.getInstance().getReference().child("Coupons");

检查数据库中字段的名称是否与模型类中的字段匹配。可能是@PeterHaddad No的重复项，它无法解决。在我的适配器上调用startListening（）方法会导致应用程序崩溃。“导致应用程序崩溃”。。。您的问题中没有崩溃日志。请包括them@PeterHaddad它们在同一范围内。我在onStart（）的末尾，在适配器之后调用startListening（）。您的意思是将其初始化为活动类顶部的全局变量吗？或者：如果您只想在数据库中存储优惠券，而不想存储其他内容，那么您可能只需要将DatabaseReference更改为
mDatabase=FirebaseDatabase.getInstance（）.getReference（）
，而无需重新构建数据库。
Root
  |
  |__Coupons
       |____coupon
               |_____title: "This is title"
               |_____desc: "This is description"

mDatabase = FirebaseDatabase.getInstance().getReference().child("Coupons");