我无法在Recyclerview上显示firebase项目。数据库连接没问题。
编辑：我添加了startListening（）方法作为建议的链接问题的答案。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();
}
Logcat中的崩溃信息： coupons.Coupon是模特。
01-15 15:16:26.381 16526-16526/com.myapp E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.myapp, PID: 16526
com.google.firebase.database.DatabaseException: Can't convert object of type java.lang.String to type com.myapp.coupons.Coupon
at com.google.android.gms.internal.zzelw.zzb(Unknown Source)
at com.google.android.gms.internal.zzelw.zza(Unknown Source)
at com.google.firebase.database.DataSnapshot.getValue(Unknown Source)
at com.firebase.ui.database.ClassSnapshotParser.parseSnapshot(ClassSnapshotParser.java:29)
at com.firebase.ui.database.ClassSnapshotParser.parseSnapshot(ClassSnapshotParser.java:15)
at com.firebase.ui.common.BaseCachingSnapshotParser.parseSnapshot(BaseCachingSnapshotParser.java:35)
at com.firebase.ui.common.BaseObservableSnapshotArray.get(BaseObservableSnapshotArray.java:52)
at com.firebase.ui.database.FirebaseRecyclerAdapter.getItem(FirebaseRecyclerAdapter.java:106)
at com.firebase.ui.database.FirebaseRecyclerAdapter.onBindViewHolder(FirebaseRecyclerAdapter.java:122)
at android.support.v7.widget.RecyclerView$Adapter.onBindViewHolder(RecyclerView.java:6508)
at android.support.v7.widget.RecyclerView$Adapter.bindViewHolder(RecyclerView.java:6541)
at android.support.v7.widget.RecyclerView$Recycler.tryBindViewHolderByDeadline(RecyclerView.java:5484)
at android.support.v7.widget.RecyclerView$Recycler.tryGetViewHolderForPositionByDeadline(RecyclerView.java:5750)
at android.support.v7.widget.RecyclerView$Recycler.getViewForPosition(RecyclerView.java:5589)
at android.support.v7.widget.RecyclerView$Recycler.getViewForPosition(RecyclerView.java:5585)
at android.support.v7.widget.LinearLayoutManager$LayoutState.next(LinearLayoutManager.java:2231)
at android.support.v7.widget.LinearLayoutManager.layoutChunk(LinearLayoutManager.java:1558)
at android.support.v7.widget.LinearLayoutManager.fill(LinearLayoutManager.java:1518)
at android.support.v7.widget.LinearLayoutManager.onLayoutChildren(LinearLayoutManager.java:610)
at android.support.v7.widget.RecyclerView.dispatchLayoutStep2(RecyclerView.java:3719)
at android.support.v7.widget.RecyclerView.dispatchLayout(RecyclerView.java:3436)
at android.support.v7.widget.RecyclerView.consumePendingUpdateOperations(RecyclerView.java:1742)
at android.support.v7.widget.RecyclerView$1.run(RecyclerView.java:354)
at android.view.Choreographer$CallbackRecord.run(Choreographer.java:874)
at android.view.Choreographer.doCallbacks(Choreographer.java:686)
at android.view.Choreographer.doFrame(Choreographer.java:618)
at android.view.Choreographer$FrameDisplayEventReceiver.run(Choreographer.java:860)
at android.os.Handler.handleCallback(Handler.java:751)
at android.os.Handler.dispatchMessage(Handler.java:95)
at android.os.Looper.loop(Looper.java:154)
at android.app.ActivityThread.main(ActivityThread.java:6119)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:886)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:776)
这是我的build.gradle
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);
}
}
}
这就是我的Firebase数据库的样子
Root
|
|__coupon
|_____title: "This is title"
|_____desc: "This is description"
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>
这就是卡片项目布局：
<?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>
答案 0 :(得分：1)
那是因为您的数据库中只存储了一个优惠券对象，而不是列表。
如果您要创建优惠券列表，我建议您添加一个包含密钥Coupons的节点，并将每个优惠券存储在其下。所以你的结构看起来像这样：
Root
|
|__Coupons
|____coupon
|_____title: "This is title"
|_____desc: "This is description"
然后你的DatabaseReference会是：
mDatabase = FirebaseDatabase.getInstance().getReference().child("Coupons");