Android 使用KOTLIN显示从Firebase Firestore到RecyclerView的数据

我有一个我工作的项目，我使用Firebase Firestore。我已经从mysql数据库向CloudFireStore添加了125个项目。我搜索Firebase online以获取信息，但出于某种原因，它对我没有帮助。我看到了web、swift、c和php，但我看不到KOTLIN的代码。但工作3天后，我在logcat中显示了项目。另一个问题是，我搜索了演示文稿，但没有指示如何在

RecyclerView

中显示数据。如何使用KOTLIN将项目显示到

RecyclerView

---

我想知道如何处理Kotlin。

我从您的问题中了解到，您已经成功地在日志中显示了项目，对吗？因此，在本例中，您还需要执行两个步骤才能在

RecyclerView

中显示数据

第一步是创建自定义适配器，或者如果需要，可以使用

FirestoreRecyclerAdapter

，第二步是为物品创建holder类。最后，只需将适配器设置为您的

RecyclerView

，即可

添加的解决方案：

对于Java delopers，建议使用

FirestoreRecyclerAdapter

从云Firestore数据库检索数据并在

RecyclerView

中显示数据

对于Kotlin开发人员，我将修改上面示例中的代码。假设您的Firestore数据库结构如下所示：

Firestore-root
    |
    --- products (collection)
           |
           --- documentIdOne (document)
           |        |
           |        --- productName: "Milk"
           |
           --- documentIdTwo (document)
           |        |
           |        --- productName: "Soy Milk"
           |
           --- documentIdThree (document)
                    |
                    --- productName: "Bacon"

class ProductModel (val productName: String = "")

<android.support.v7.widget.RecyclerView
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:id="@+id/recycler_view"/>

val rootRef = FirebaseFirestore.getInstance()
val query = rootRef!!.collection("products").orderBy("productName", Query.Direction.ASCENDING)

val options = FirestoreRecyclerOptions.Builder<ProductModel>().setQuery(query, ProductModel::class.java).build()

private inner class ProductViewHolder internal constructor(private val view: View) : RecyclerView.ViewHolder(view) {
    internal fun setProductName(productName: String) {
        val textView = view.findViewById<TextView>(R.id.text_view)
        textView.text = productName
    }
}

private inner class ProductFirestoreRecyclerAdapter internal constructor(options: FirestoreRecyclerOptions<ProductModel>) : FirestoreRecyclerAdapter<ProductModel, ProductViewHolder>(options) {
    override fun onBindViewHolder(productViewHolder: ProductViewHolder, position: Int, productModel: ProductModel) {
        productViewHolder.setProductName(productModel.productName)
    }

    override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): ProductViewHolder {
        val view = LayoutInflater.from(parent.context).inflate(R.layout.item_product, parent, false)
        return ProductViewHolder(view)
    }
}

<TextView
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:id="@+id/text_view""/>

adapter = ProductFirestoreRecyclerAdapter(options)
recycler_view.adapter = adapter

一个模型类，看起来也是这样的：

Firestore-root
    |
    --- products (collection)
           |
           --- documentIdOne (document)
           |        |
           |        --- productName: "Milk"
           |
           --- documentIdTwo (document)
           |        |
           |        --- productName: "Soy Milk"
           |
           --- documentIdThree (document)
                    |
                    --- productName: "Bacon"

class ProductModel (val productName: String = "")

<android.support.v7.widget.RecyclerView
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:id="@+id/recycler_view"/>

val rootRef = FirebaseFirestore.getInstance()
val query = rootRef!!.collection("products").orderBy("productName", Query.Direction.ASCENDING)

val options = FirestoreRecyclerOptions.Builder<ProductModel>().setQuery(query, ProductModel::class.java).build()

private inner class ProductViewHolder internal constructor(private val view: View) : RecyclerView.ViewHolder(view) {
    internal fun setProductName(productName: String) {
        val textView = view.findViewById<TextView>(R.id.text_view)
        textView.text = productName
    }
}

private inner class ProductFirestoreRecyclerAdapter internal constructor(options: FirestoreRecyclerOptions<ProductModel>) : FirestoreRecyclerAdapter<ProductModel, ProductViewHolder>(options) {
    override fun onBindViewHolder(productViewHolder: ProductViewHolder, position: Int, productModel: ProductModel) {
        productViewHolder.setProductName(productModel.productName)
    }

    override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): ProductViewHolder {
        val view = LayoutInflater.from(parent.context).inflate(R.layout.item_product, parent, false)
        return ProductViewHolder(view)
    }
}

<TextView
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:id="@+id/text_view""/>

adapter = ProductFirestoreRecyclerAdapter(options)
recycler_view.adapter = adapter

以及一个

.XML

文件，其中包含一个

RecyclerView

，该文件也如下所示：

Firestore-root
    |
    --- products (collection)
           |
           --- documentIdOne (document)
           |        |
           |        --- productName: "Milk"
           |
           --- documentIdTwo (document)
           |        |
           |        --- productName: "Soy Milk"
           |
           --- documentIdThree (document)
                    |
                    --- productName: "Bacon"

class ProductModel (val productName: String = "")

<android.support.v7.widget.RecyclerView
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:id="@+id/recycler_view"/>

val rootRef = FirebaseFirestore.getInstance()
val query = rootRef!!.collection("products").orderBy("productName", Query.Direction.ASCENDING)

val options = FirestoreRecyclerOptions.Builder<ProductModel>().setQuery(query, ProductModel::class.java).build()

private inner class ProductViewHolder internal constructor(private val view: View) : RecyclerView.ViewHolder(view) {
    internal fun setProductName(productName: String) {
        val textView = view.findViewById<TextView>(R.id.text_view)
        textView.text = productName
    }
}

private inner class ProductFirestoreRecyclerAdapter internal constructor(options: FirestoreRecyclerOptions<ProductModel>) : FirestoreRecyclerAdapter<ProductModel, ProductViewHolder>(options) {
    override fun onBindViewHolder(productViewHolder: ProductViewHolder, position: Int, productModel: ProductModel) {
        productViewHolder.setProductName(productModel.productName)
    }

    override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): ProductViewHolder {
        val view = LayoutInflater.from(parent.context).inflate(R.layout.item_product, parent, false)
        return ProductViewHolder(view)
    }
}

<TextView
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:id="@+id/text_view""/>

adapter = ProductFirestoreRecyclerAdapter(options)
recycler_view.adapter = adapter

然后只需使用以下代码行：

recycler_view.layoutManager = LinearLayoutManager(this)

其中，

recycler\u视图

实际上是

RecyclerView

的id，如上面的.XML文件所示

然后，您需要创建Firestore数据库的根引用和如下所示的

Query

对象：

Firestore-root
    |
    --- products (collection)
           |
           --- documentIdOne (document)
           |        |
           |        --- productName: "Milk"
           |
           --- documentIdTwo (document)
           |        |
           |        --- productName: "Soy Milk"
           |
           --- documentIdThree (document)
                    |
                    --- productName: "Bacon"

class ProductModel (val productName: String = "")

<android.support.v7.widget.RecyclerView
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:id="@+id/recycler_view"/>

val rootRef = FirebaseFirestore.getInstance()
val query = rootRef!!.collection("products").orderBy("productName", Query.Direction.ASCENDING)

val options = FirestoreRecyclerOptions.Builder<ProductModel>().setQuery(query, ProductModel::class.java).build()

private inner class ProductViewHolder internal constructor(private val view: View) : RecyclerView.ViewHolder(view) {
    internal fun setProductName(productName: String) {
        val textView = view.findViewById<TextView>(R.id.text_view)
        textView.text = productName
    }
}

private inner class ProductFirestoreRecyclerAdapter internal constructor(options: FirestoreRecyclerOptions<ProductModel>) : FirestoreRecyclerAdapter<ProductModel, ProductViewHolder>(options) {
    override fun onBindViewHolder(productViewHolder: ProductViewHolder, position: Int, productModel: ProductModel) {
        productViewHolder.setProductName(productModel.productName)
    }

    override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): ProductViewHolder {
        val view = LayoutInflater.from(parent.context).inflate(R.layout.item_product, parent, false)
        return ProductViewHolder(view)
    }
}

<TextView
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:id="@+id/text_view""/>

adapter = ProductFirestoreRecyclerAdapter(options)
recycler_view.adapter = adapter

然后您必须创建一个

FirestoreRecyclerOptions

对象，如下所示：

Firestore-root
    |
    --- products (collection)
           |
           --- documentIdOne (document)
           |        |
           |        --- productName: "Milk"
           |
           --- documentIdTwo (document)
           |        |
           |        --- productName: "Soy Milk"
           |
           --- documentIdThree (document)
                    |
                    --- productName: "Bacon"

class ProductModel (val productName: String = "")

<android.support.v7.widget.RecyclerView
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:id="@+id/recycler_view"/>

val rootRef = FirebaseFirestore.getInstance()
val query = rootRef!!.collection("products").orderBy("productName", Query.Direction.ASCENDING)

val options = FirestoreRecyclerOptions.Builder<ProductModel>().setQuery(query, ProductModel::class.java).build()

private inner class ProductViewHolder internal constructor(private val view: View) : RecyclerView.ViewHolder(view) {
    internal fun setProductName(productName: String) {
        val textView = view.findViewById<TextView>(R.id.text_view)
        textView.text = productName
    }
}

private inner class ProductFirestoreRecyclerAdapter internal constructor(options: FirestoreRecyclerOptions<ProductModel>) : FirestoreRecyclerAdapter<ProductModel, ProductViewHolder>(options) {
    override fun onBindViewHolder(productViewHolder: ProductViewHolder, position: Int, productModel: ProductModel) {
        productViewHolder.setProductName(productModel.productName)
    }

    override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): ProductViewHolder {
        val view = LayoutInflater.from(parent.context).inflate(R.layout.item_product, parent, false)
        return ProductViewHolder(view)
    }
}

<TextView
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:id="@+id/text_view""/>

adapter = ProductFirestoreRecyclerAdapter(options)
recycler_view.adapter = adapter

现在我们需要创建一个适配器类，在本例中，该类应如下所示：

Firestore-root
    |
    --- products (collection)
           |
           --- documentIdOne (document)
           |        |
           |        --- productName: "Milk"
           |
           --- documentIdTwo (document)
           |        |
           |        --- productName: "Soy Milk"
           |
           --- documentIdThree (document)
                    |
                    --- productName: "Bacon"

class ProductModel (val productName: String = "")

<android.support.v7.widget.RecyclerView
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:id="@+id/recycler_view"/>

val rootRef = FirebaseFirestore.getInstance()
val query = rootRef!!.collection("products").orderBy("productName", Query.Direction.ASCENDING)

val options = FirestoreRecyclerOptions.Builder<ProductModel>().setQuery(query, ProductModel::class.java).build()

private inner class ProductViewHolder internal constructor(private val view: View) : RecyclerView.ViewHolder(view) {
    internal fun setProductName(productName: String) {
        val textView = view.findViewById<TextView>(R.id.text_view)
        textView.text = productName
    }
}

private inner class ProductFirestoreRecyclerAdapter internal constructor(options: FirestoreRecyclerOptions<ProductModel>) : FirestoreRecyclerAdapter<ProductModel, ProductViewHolder>(options) {
    override fun onBindViewHolder(productViewHolder: ProductViewHolder, position: Int, productModel: ProductModel) {
        productViewHolder.setProductName(productModel.productName)
    }

    override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): ProductViewHolder {
        val view = LayoutInflater.from(parent.context).inflate(R.layout.item_product, parent, false)
        return ProductViewHolder(view)
    }
}

<TextView
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:id="@+id/text_view""/>

adapter = ProductFirestoreRecyclerAdapter(options)
recycler_view.adapter = adapter

然后创建一个声明为全局的

适配器
字段：

private var adapter: ProductFirestoreRecyclerAdapter? = null

并在您的活动中实例化它，如下所示：

Firestore-root
    |
    --- products (collection)
           |
           --- documentIdOne (document)
           |        |
           |        --- productName: "Milk"
           |
           --- documentIdTwo (document)
           |        |
           |        --- productName: "Soy Milk"
           |
           --- documentIdThree (document)
                    |
                    --- productName: "Bacon"

class ProductModel (val productName: String = "")

<android.support.v7.widget.RecyclerView
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:id="@+id/recycler_view"/>

val rootRef = FirebaseFirestore.getInstance()
val query = rootRef!!.collection("products").orderBy("productName", Query.Direction.ASCENDING)

val options = FirestoreRecyclerOptions.Builder<ProductModel>().setQuery(query, ProductModel::class.java).build()

private inner class ProductViewHolder internal constructor(private val view: View) : RecyclerView.ViewHolder(view) {
    internal fun setProductName(productName: String) {
        val textView = view.findViewById<TextView>(R.id.text_view)
        textView.text = productName
    }
}

private inner class ProductFirestoreRecyclerAdapter internal constructor(options: FirestoreRecyclerOptions<ProductModel>) : FirestoreRecyclerAdapter<ProductModel, ProductViewHolder>(options) {
    override fun onBindViewHolder(productViewHolder: ProductViewHolder, position: Int, productModel: ProductModel) {
        productViewHolder.setProductName(productModel.productName)
    }

    override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): ProductViewHolder {
        val view = LayoutInflater.from(parent.context).inflate(R.layout.item_product, parent, false)
        return ProductViewHolder(view)
    }
}

<TextView
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:id="@+id/text_view""/>

adapter = ProductFirestoreRecyclerAdapter(options)
recycler_view.adapter = adapter

最后，不要忘记覆盖以下两个函数并开始侦听更改：

override fun onStart() {
    super.onStart()
    adapter!!.startListening()
}

override fun onStop() {
    super.onStop()

    if (adapter != null) {
        adapter!!.stopListening()
    }
}

结果是：


正如您在使用Kotlin时所看到的，代码更简单，代码行数更少，但请记住，官方文档永远不会为您提供特定的代码，您必须创建自己的代码。
谢谢，但这是java中的信息，我在Kotlin中搜索。你能帮我处理KOTLIN吗？你可以简单地复制Java代码并粘贴到你的IDE中，然后在KOTLIN代码中进行转换，对吗？我尝试过这样做，但没有成功。请帮助我了解KOTLIN。如果你没有看到你的一些代码，如果你不提供你所得到的行为或错误，我就帮不了你什么忙。但我将尝试为您提供该示例的快速改编。@Dika您只需将产品id作为属性存储在文档中，然后像这样使用：
productViewHolder.setProductId（productModel.productId）