使用 Firebase 实时数据库引用填充 RecyclerView
Populate RecyclerView with Firebase Realtime Database References
我正在尝试为 HomeFragment 创建类别 RecyclerView，但在 addValueEventListener 的 onDataChange() 函数中设置类别和类别图像时遇到问题。我怎样才能做一个 for 循环来获取我的 job-category 引用下的所有引用？谢谢！
数据库参考
Category.kt
data class Category constructor(val category: String, val categoryImage: String)
CategoryAdapter.kt
class CategoriesAdapter(val category: ArrayList<Category>) : RecyclerView.Adapter<CategoriesAdapter.ViewHolder>() {
override fun onBindViewHolder(holder: ViewHolder, position: Int) {
holder?.bindCategory(category[position])
}
override fun getItemCount(): Int {
return category.count()
}
override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): ViewHolder {
val view = LayoutInflater.from(parent?.context).inflate(R.layout.category, parent, false)
return ViewHolder(view)
}
inner class ViewHolder(itemView: View) : RecyclerView.ViewHolder(itemView) {
val categoryName = itemView?.findViewById<TextView>(R.id.categoryNameTextView)
val categoryImage = itemView?.findViewById<ImageView>(R.id.categoryImageView)
fun bindCategory(category: Category) {
categoryName?.text = category.category
categoryImage?.setImageURI(category.categoryImage.toUri())
}
}
}
category.xml
<ImageView
android:id="@+id/categoryImageView"
android:layout_width="420dp"
android:layout_height="676dp"
android:background="@drawable/image_rounded_top_corners"
android:scaleType="fitXY"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toTopOf="parent"
app:srcCompat="@drawable/profile_photo_"
android:contentDescription="@string/category_image" />
<TextView
android:id="@+id/categoryNameTextView"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="@string/category_name"
android:textAlignment="center"
android:textColor="@color/black"
android:textSize="14sp"
android:textStyle="bold"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toBottomOf="@+id/categoryImageView" />
HomeFragment.kt
lateinit var categoriesAdapter: CategoriesAdapter
val categories = ArrayList Category ()
val categoriesDatabaseRef = FirebaseDatabase.getInstance().reference.child(REF_JOB_CATEGORIES)
override fun onCreateView(inflater: LayoutInflater, container: ViewGroup?, savedInstanceState: Bundle?): View? {
val view: View = inflater.inflate(R.layout.fragment_home, container, false)
categoriesAdapter = CategoriesAdapter(categories)
val popularCategoriesRecyclerView = view.findViewById<RecyclerView>(R.id.popularCategoriesRecyclerView)
val layoutManager = GridLayoutManager(view.context, 3, GridLayoutManager.HORIZONTAL, false)
popularCategoriesRecyclerView.layoutManager = layoutManager
categoriesDatabaseRef.addValueEventListener(object: ValueEventListener {
@SuppressLint("NotifyDataSetChanged")
override fun onDataChange(snapshot: DataSnapshot) {
categories.clear()
for (snap in snapshot.children) {
val category = Category(snap.child("category").getValue(String::class.java)!!,snap.child("categoryImage").getValue(String::class.java)!!)
categories.add(category)
}
categoriesAdapter.notifyDataSetChanged()
}
override fun onCancelled(error: DatabaseError) {
Log.d("HomeFragment", "LoadPost:onCancelled", error.toException())
}
})
return view
}
Logcat 错误
Process: com.zwdalpha.skedaddle, PID: 19898
java.lang.IllegalArgumentException: Span count should be at least 1. Provided 0
at androidx.recyclerview.widget.GridLayoutManager.setSpanCount(GridLayoutManager.java:829)
at androidx.recyclerview.widget.GridLayoutManager.<init>(GridLayoutManager.java:86)
at com.zwdalpha.skedaddle.Fragments.HomeFragment.onCreateView(HomeFragment.kt:74)
at androidx.fragment.app.Fragment.performCreateView(Fragment.java:2963)
at androidx.fragment.app.FragmentStateManager.createView(FragmentStateManager.java:518)
at androidx.fragment.app.FragmentStateManager.moveToExpectedState(FragmentStateManager.java:282)
at androidx.fragment.app.FragmentStore.moveToExpectedState(FragmentStore.java:112)
at androidx.fragment.app.FragmentManager.moveToState(FragmentManager.java:1647)
at androidx.fragment.app.FragmentManager.dispatchStateChange(FragmentManager.java:3128)
at androidx.fragment.app.FragmentManager.dispatchViewCreated(FragmentManager.java:3065)
at androidx.fragment.app.Fragment.performViewCreated(Fragment.java:2988)
at androidx.fragment.app.FragmentStateManager.createView(FragmentStateManager.java:546)
at androidx.fragment.app.FragmentStateManager.moveToExpectedState(FragmentStateManager.java:282)
at androidx.fragment.app.FragmentStore.moveToExpectedState(FragmentStore.java:112)
at androidx.fragment.app.FragmentManager.moveToState(FragmentManager.java:1647)
at androidx.fragment.app.FragmentManager.dispatchStateChange(FragmentManager.java:3128)
at androidx.fragment.app.FragmentManager.dispatchActivityCreated(FragmentManager.java:3072)
at androidx.fragment.app.FragmentController.dispatchActivityCreated(FragmentController.java:251)
at androidx.fragment.app.FragmentActivity.onStart(FragmentActivity.java:502)
at androidx.appcompat.app.AppCompatActivity.onStart(AppCompatActivity.java:246)
at com.zwdalpha.skedaddle.MainActivity.onStart(MainActivity.kt:36)
at android.app.Instrumentation.callActivityOnStart(Instrumentation.java:1391)
at android.app.Activity.performStart(Activity.java:7157)
at android.app.ActivityThread.handleStartActivity(ActivityThread.java:2937)
at android.app.servertransaction.TransactionExecutor.performLifecycleSequence(TransactionExecutor.java:180)
at android.app.servertransaction.TransactionExecutor.cycleToPath(TransactionExecutor.java:165)
at android.app.servertransaction.TransactionExecutor.executeLifecycleState(TransactionExecutor.java:142)
at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:70)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1808)
at android.os.Handler.dispatchMessage(Handler.java:106)
at android.os.Looper.loop(Looper.java:193)
at android.app.ActivityThread.main(ActivityThread.java:6669)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:493)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:858)
你很接近。在您的 onDataChange 中，您需要遍历 snapshot.children，然后为每个属性获取所需的属性值。
Kotlin 不是我的强项，但应该是这样的：
categoriesDatabaseRef.addValueEventListener(object: ValueEventListener {
@SuppressLint("NotifyDataSetChanged")
override fun onDataChange(snapshot: DataSnapshot) {
categories.clear()
for (snapshot in dataSnapshot.children) { // loop over children
categories.add(snapshot.child("category").getValue<String>(); // get value
}
categoriesAdapter.notifyDataSetChanged()
}
override fun onCancelled(error: DatabaseError) {
Log.w(TAG, "loadPost:onCancelled", databaseError.toException()) // never ignore errors
}
})
如果 getValue<String>() 无法编译，您可能需要将 Firebase 实时数据库的 ktx 扩展添加到 Gradle 文件，或使用 snapshot.child("category").getValue(String::class.java)。
另请参阅 listening for children through a value event and on reading a value 上的 Firebase 文档。
只需将此代码放在 categories.clear()
之后
for (snap in snapshot.children){
val category = snap.getValue(Category::class.java)
//Here is Other Option To create category object without creating no-arg con
//val category = Category(snap.child("category").getValue(String::class.java)!!,snap.child("categoryImage").getValue(String::class.java)!!)
categories.add(category)
}
你可以这样列单
我正在尝试为 HomeFragment 创建类别 RecyclerView，但在 addValueEventListener 的 onDataChange() 函数中设置类别和类别图像时遇到问题。我怎样才能做一个 for 循环来获取我的 job-category 引用下的所有引用？谢谢！
数据库参考
Category.kt
data class Category constructor(val category: String, val categoryImage: String)
CategoryAdapter.kt
class CategoriesAdapter(val category: ArrayList<Category>) : RecyclerView.Adapter<CategoriesAdapter.ViewHolder>() {
override fun onBindViewHolder(holder: ViewHolder, position: Int) {
holder?.bindCategory(category[position])
}
override fun getItemCount(): Int {
return category.count()
}
override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): ViewHolder {
val view = LayoutInflater.from(parent?.context).inflate(R.layout.category, parent, false)
return ViewHolder(view)
}
inner class ViewHolder(itemView: View) : RecyclerView.ViewHolder(itemView) {
val categoryName = itemView?.findViewById<TextView>(R.id.categoryNameTextView)
val categoryImage = itemView?.findViewById<ImageView>(R.id.categoryImageView)
fun bindCategory(category: Category) {
categoryName?.text = category.category
categoryImage?.setImageURI(category.categoryImage.toUri())
}
}
}
category.xml
<ImageView
android:id="@+id/categoryImageView"
android:layout_width="420dp"
android:layout_height="676dp"
android:background="@drawable/image_rounded_top_corners"
android:scaleType="fitXY"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toTopOf="parent"
app:srcCompat="@drawable/profile_photo_"
android:contentDescription="@string/category_image" />
<TextView
android:id="@+id/categoryNameTextView"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="@string/category_name"
android:textAlignment="center"
android:textColor="@color/black"
android:textSize="14sp"
android:textStyle="bold"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toBottomOf="@+id/categoryImageView" />
HomeFragment.kt
lateinit var categoriesAdapter: CategoriesAdapter
val categories = ArrayList Category ()
val categoriesDatabaseRef = FirebaseDatabase.getInstance().reference.child(REF_JOB_CATEGORIES)
override fun onCreateView(inflater: LayoutInflater, container: ViewGroup?, savedInstanceState: Bundle?): View? {
val view: View = inflater.inflate(R.layout.fragment_home, container, false)
categoriesAdapter = CategoriesAdapter(categories)
val popularCategoriesRecyclerView = view.findViewById<RecyclerView>(R.id.popularCategoriesRecyclerView)
val layoutManager = GridLayoutManager(view.context, 3, GridLayoutManager.HORIZONTAL, false)
popularCategoriesRecyclerView.layoutManager = layoutManager
categoriesDatabaseRef.addValueEventListener(object: ValueEventListener {
@SuppressLint("NotifyDataSetChanged")
override fun onDataChange(snapshot: DataSnapshot) {
categories.clear()
for (snap in snapshot.children) {
val category = Category(snap.child("category").getValue(String::class.java)!!,snap.child("categoryImage").getValue(String::class.java)!!)
categories.add(category)
}
categoriesAdapter.notifyDataSetChanged()
}
override fun onCancelled(error: DatabaseError) {
Log.d("HomeFragment", "LoadPost:onCancelled", error.toException())
}
})
return view
}
Logcat 错误
Process: com.zwdalpha.skedaddle, PID: 19898
java.lang.IllegalArgumentException: Span count should be at least 1. Provided 0
at androidx.recyclerview.widget.GridLayoutManager.setSpanCount(GridLayoutManager.java:829)
at androidx.recyclerview.widget.GridLayoutManager.<init>(GridLayoutManager.java:86)
at com.zwdalpha.skedaddle.Fragments.HomeFragment.onCreateView(HomeFragment.kt:74)
at androidx.fragment.app.Fragment.performCreateView(Fragment.java:2963)
at androidx.fragment.app.FragmentStateManager.createView(FragmentStateManager.java:518)
at androidx.fragment.app.FragmentStateManager.moveToExpectedState(FragmentStateManager.java:282)
at androidx.fragment.app.FragmentStore.moveToExpectedState(FragmentStore.java:112)
at androidx.fragment.app.FragmentManager.moveToState(FragmentManager.java:1647)
at androidx.fragment.app.FragmentManager.dispatchStateChange(FragmentManager.java:3128)
at androidx.fragment.app.FragmentManager.dispatchViewCreated(FragmentManager.java:3065)
at androidx.fragment.app.Fragment.performViewCreated(Fragment.java:2988)
at androidx.fragment.app.FragmentStateManager.createView(FragmentStateManager.java:546)
at androidx.fragment.app.FragmentStateManager.moveToExpectedState(FragmentStateManager.java:282)
at androidx.fragment.app.FragmentStore.moveToExpectedState(FragmentStore.java:112)
at androidx.fragment.app.FragmentManager.moveToState(FragmentManager.java:1647)
at androidx.fragment.app.FragmentManager.dispatchStateChange(FragmentManager.java:3128)
at androidx.fragment.app.FragmentManager.dispatchActivityCreated(FragmentManager.java:3072)
at androidx.fragment.app.FragmentController.dispatchActivityCreated(FragmentController.java:251)
at androidx.fragment.app.FragmentActivity.onStart(FragmentActivity.java:502)
at androidx.appcompat.app.AppCompatActivity.onStart(AppCompatActivity.java:246)
at com.zwdalpha.skedaddle.MainActivity.onStart(MainActivity.kt:36)
at android.app.Instrumentation.callActivityOnStart(Instrumentation.java:1391)
at android.app.Activity.performStart(Activity.java:7157)
at android.app.ActivityThread.handleStartActivity(ActivityThread.java:2937)
at android.app.servertransaction.TransactionExecutor.performLifecycleSequence(TransactionExecutor.java:180)
at android.app.servertransaction.TransactionExecutor.cycleToPath(TransactionExecutor.java:165)
at android.app.servertransaction.TransactionExecutor.executeLifecycleState(TransactionExecutor.java:142)
at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:70)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1808)
at android.os.Handler.dispatchMessage(Handler.java:106)
at android.os.Looper.loop(Looper.java:193)
at android.app.ActivityThread.main(ActivityThread.java:6669)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:493)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:858)
你很接近。在您的 onDataChange 中，您需要遍历 snapshot.children，然后为每个属性获取所需的属性值。
Kotlin 不是我的强项，但应该是这样的：
categoriesDatabaseRef.addValueEventListener(object: ValueEventListener {
@SuppressLint("NotifyDataSetChanged")
override fun onDataChange(snapshot: DataSnapshot) {
categories.clear()
for (snapshot in dataSnapshot.children) { // loop over children
categories.add(snapshot.child("category").getValue<String>(); // get value
}
categoriesAdapter.notifyDataSetChanged()
}
override fun onCancelled(error: DatabaseError) {
Log.w(TAG, "loadPost:onCancelled", databaseError.toException()) // never ignore errors
}
})
如果 getValue<String>() 无法编译，您可能需要将 Firebase 实时数据库的 ktx 扩展添加到 Gradle 文件，或使用 snapshot.child("category").getValue(String::class.java)。
另请参阅 listening for children through a value event and on reading a value 上的 Firebase 文档。
只需将此代码放在 categories.clear()
之后for (snap in snapshot.children){
val category = snap.getValue(Category::class.java)
//Here is Other Option To create category object without creating no-arg con
//val category = Category(snap.child("category").getValue(String::class.java)!!,snap.child("categoryImage").getValue(String::class.java)!!)
categories.add(category)
}
你可以这样列单