Question

我正在尝试使用回收者视图显示列表，但我得到了null的价值。我有三个班级Test，TestModel和TestListAdapter。以下是我的Json输出。我在一个地方遇到错误。

val catObj = response.getJSONObject(i)。

如果我将i称为int，那么我得到一个错误，因此，我需要输入i.toString()进行字符串转换。即使将i转换为字符串后，我也没有得到输出，并且错误日志中没有错误。我在代码中使用Volley和Kotlin。任何帮助表示赞赏。

Error:--Type Mismatch

 val catObj = response.getJSONObject(i)

Json输出：

[{"id":"1","name":"AAAA"},{"id":"3","name":"BBBB"}]

测试类：

class Test : AppCompatActivity() {

var volleyRequest:RequestQueue?=null
var TestList: ArrayList<TestModel>?=null
var adapter:TestListAdapter?=null
var layoutManager: RecyclerView.LayoutManager?=null
override fun onCreate(savedInstanceState: Bundle?) {
    super.onCreate(savedInstanceState)
    setContentView(R.layout.activity_Test)


 var HelloLink="https://www.abc.app"
 TestList= ArrayList<TestModel>()
 volleyRequest = Volley.newRequestQueue(this)

    getTest(HelloLink)
}

fun getTest(url: String) {

    print("Url Value is:"+url)
    val catRequest = JsonObjectRequest(Request.Method.GET,
            url, Response.Listener {
        response: JSONObject ->
        try {
            for (i in 0..response.length() - 1) {
                val Test=TestModel()
                val catObj = response.getJSONObject(i)

                var name = catObj.getString("name")

                Test.name = name
                Log.d("Name Result==>>", name)
                TestList!!.add(Test)
                adapter = TestListAdapter(TestList!!, this)
                layoutManager = LinearLayoutManager(this)
                recyclerViewTest.layoutManager = layoutManager
                recyclerViewTest.adapter = adapter
            }

            adapter!!.notifyDataSetChanged()


        }catch (e: JSONException) { e.printStackTrace()}

    },
            Response.ErrorListener {
                error: VolleyError? ->
                try {
                    Log.d("Error:", error.toString())

                }catch (e: JSONException){e.printStackTrace()}
            })
    volleyRequest!!.add(catRequest)
}

}

TestListAdapter类

    class TestListAdapter(private val list:ArrayList<TestModel>,
                              private val context: Context):RecyclerView.Adapter<TestListAdapter.ViewHolder>()

    {
        override fun getItemCount(): Int {
            return list.size
        }

        override fun onCreateViewHolder(p0: ViewGroup, p1: Int): ViewHolder {

            val view 

=LayoutInflater.from(context).inflate(R.layout.list_Test,p0,false)
        return ViewHolder(view)
    }

    override fun onBindViewHolder(p0: ViewHolder, p1: Int) {

        p0?.bindItem(list[p1])
    }


    class ViewHolder(itemView:View):RecyclerView.ViewHolder(itemView) {

        fun bindItem(Test:TestModel)
        {
            var name:TextView=itemView.findViewById<TextView>(R.id.CatName)
            name.text=Test.name

        }
    }
}

模型类

class TestModel
{
    var id:Int?=null
    var name:String?=null

}

Answer 1

将数据添加到适配器时，您会遇到一些问题，

如下更新适配器

class TestListAdapter( private val context: Context):RecyclerView.Adapter<TestListAdapter.ViewHolder>()

    private val list = arrayListOf<TestModel> 

    public fun injectData(list : ArrayList<TestModel>){
    this.list.addAll(list)
    notifyDataSetChanged() 
} 

    {
        override fun getItemCount(): Int {
            return list.size
        }

        override fun onCreateViewHolder(p0: ViewGroup, p1: Int): ViewHolder {

            val view 

=LayoutInflater.from(context).inflate(R.layout.list_Test,p0,false)
        return ViewHolder(view)
    }

    override fun onBindViewHolder(p0: ViewHolder, p1: Int) {

        p0?.bindItem(list[p1])
    }


    class ViewHolder(itemView:View):RecyclerView.ViewHolder(itemView) {

        fun bindItem(Test:TestModel)
        {
            var name:TextView=itemView.findViewById<TextView>(R.id.CatName)
            name.text=Test.name

        }
    }
}

并在您的TestClass中：

            adapter = TestListAdapter(this)
            layoutManager = LinearLayoutManager(this)
            recyclerViewTest.layoutManager = layoutManager
            recyclerViewTest.adapter = adapter

         try {
            for (i in 0..response.length() - 1) {
                val Test=TestModel()
                val catObj = response.getJSONObject(i)

                var name = catObj.getString("name")

                Test.name = name
                Log.d("Name Result==>>", name)
                TestList!!.add(Test)
            }

            adapter.injectData(TestList);


        }catch (e: JSONException) { e.printStackTrace()}

还有一件小事，请考虑在使用!!时，使用前应检查null

示例，而不是

TestList!!.add(Test)

尝试

TestList?.let {
  it.add(Test)
}

Answer 2

正如我在评论中提到的那样-我不太熟悉kotlin语言，但是您发布的JSON示例：

[{“ id”：“ 1”，“名称”：“ AAAA”}，{“ id”：“ 3”，“名称”：“ BBBB”}]

实际上是JSONArray而不是JSONObject，所以我认为您应该使用如下代码：

fun getTest(url: String) {

    print("Url Value is:"+url)
    val catRequest = JsonArrayRequest(Request.Method.GET,
            url, Response.Listener {
        response: JSONArray ->
        try {
            for (i in 0..response.length() - 1) {
                val Test=TestModel()
                val catObj = response.getJSONObject(i)

                var name = catObj.getString("name")

                Test.name = name
                Log.d("Name Result==>>", name)
                TestList!!.add(Test)
                adapter = TestListAdapter(TestList!!, this)
                layoutManager = LinearLayoutManager(this)
                recyclerViewTest.layoutManager = layoutManager
                recyclerViewTest.adapter = adapter
            }

            adapter!!.notifyDataSetChanged()


        }catch (e: JSONException) { e.printStackTrace()}

    },
            Response.ErrorListener {
                error: VolleyError? ->
                try {
                    Log.d("Error:", error.toString())

                }catch (e: JSONException){e.printStackTrace()}
            })
    volleyRequest!!.add(catRequest)
}

请注意，JsonArrayRequest代替了JsonObjectRequest，响应是JSONArray而不是JSONObject。

RecyclerView在日志中显示空值，但没有错误

2 个答案: