如何使用Retrofit2 API在RecyclerView中显示数据？
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首先，我是android / Java / Kotlin开发的新手。我正在使用Retrofit2从Udacity API检索数据。我可以在Logcat中看到响应，但是当我尝试在RecyclerView中显示它时，只有一个空白屏幕。我认为错误在MainActivity中，但我仍然无能为力，需要帮助。
我的模型类
class Course(var title: String,
var subtitle: String,
var key: String,
var instructors: List<Instructor>,
var expected_learning: String,
var required_knowledge: String)
class Instructor(var name: String,
var bio: String)
我的界面
interface ApiServiceInterface {
@GET("courses")
fun list() : Call<UdacityCatalog>
}
我的适配器
class CourseAdapter(val listCourses: ArrayList<Course?>, val context: Context) : RecyclerView.Adapter<CourseAdapter.CourseViewHolder>() {
class CourseViewHolder(viewItem: View) : RecyclerView.ViewHolder(viewItem) {
val courseTitle = viewItem.findViewById<TextView?>(R.id.tv_title) as TextView
val courseSubtitle = viewItem.findViewById<TextView?>(R.id.tv_subtitle) as TextView
val courseKey = viewItem.findViewById<TextView?>(R.id.tv_course_key) as TextView
val instructorName = viewItem.findViewById<TextView?>(R.id.tv_instructor_name) as TextView
}
override fun onCreateViewHolder(parent: ViewGroup?, viewType: Int): CourseViewHolder {
val viewHolder = LayoutInflater.from(parent?.context).inflate(R.layout.activity_item_list, parent, false)
val itemViewHolder = CourseViewHolder(viewHolder)
return itemViewHolder
}
override fun onBindViewHolder(holder: CourseViewHolder?, position: Int) {
holder?.courseTitle?.text = listCourses[position].title
holder?.courseSubtitle?.text = listCourses[position].subtitle
holder?.courseKey?.text = listCourses[position].key
holder?.instructorName?.text = listCourses[position].instructors.toString()
}
override fun getItemCount(): Int = listCourses.size
}
我的MainActivity - 我认为错误就在这里，但我还没想到它
class MainActivity : AppCompatActivity() {
internal val TAG = "Testing Retrofit2 API"
lateinit var mRecyclerView: RecyclerView
lateinit var mCourseAdapter: RecyclerView.Adapter<CourseAdapter.CourseViewHolder>
val listCourse = arrayListOf<Course?>()
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
setContentView(R.layout.activity_main_recyclerview)
mRecyclerView = findViewById<RecyclerView?>(R.id.id_recycler_view) as RecyclerView
val mLayoutManager = LinearLayoutManager(this, LinearLayoutManager.VERTICAL, false)
mRecyclerView.layoutManager = mLayoutManager
mRecyclerView.setHasFixedSize(true)
mCourseAdapter = CourseAdapter(listCourse, applicationContext)
mRecyclerView.adapter = mCourseAdapter
mCourseAdapter.notifyDataSetChanged()
val call = RetrofitInitializer().createService().list()
call.enqueue(object : Callback<UdacityCatalog> {
override fun onResponse(call: Call<UdacityCatalog>, response: Response<UdacityCatalog>) {
response.body()
if (!response.isSuccessful) {
Log.i(TAG, "[ ERROR ] " + response.code())
} else {
if (listCourse.isEmpty()) {
Toast.makeText(applicationContext, "Empty list!", Toast.LENGTH_LONG).show()
} else {
Toast.makeText(applicationContext, "Full list!", Toast.LENGTH_LONG).show()
}
val catalog = response.body()
for (c in catalog!!.courses!!) {
Log.i(TAG, String.format("%s: %s", c.title, c.subtitle, c.key, c.required_knowledge, c.expected_learning))
for (i in c.instructors!!) {
Log.i(TAG, i.name)
}
Log.i(TAG, "
****************************************************************************************************
")
}
}
}
override fun onFailure(call: Call<UdacityCatalog>?, t: Throwable?) {
Log.d(TAG, "onFailure() : " + t?.message)
}
})
}
}
Retrofit实例的初始化类
class RetrofitInitializer {
companion object Factory {
val BASE_URL = "https://www.udacity.com/public-api/v0/"
}
private val retrofit = Retrofit.Builder()
.baseUrl(BASE_URL)
.addConverterFactory(GsonConverterFactory.create())
.build()
fun createService(): ApiServiceInterface = retrofit.create(ApiServiceInterface::class.java)
}
我的RecyclerView xml文件
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:orientation="vertical"
android:paddingBottom="16dp"
android:paddingLeft="16dp"
android:paddingRight="16dp"
android:paddingTop="16dp"
tools:context="activities.MainActivity">
<android.support.v7.widget.RecyclerView
android:id="@+id/id_recycler_view"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:orientation="vertical">
</android.support.v7.widget.RecyclerView>
</LinearLayout>
我的CardView xml文件
<?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="match_parent"
android:layout_margin="16dp"
android:orientation="vertical">
<LinearLayout
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical"
android:paddingBottom="16dp"
android:paddingLeft="16dp"
android:paddingRight="16dp"
android:paddingTop="16dp">
<TextView
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:gravity="center"
android:text="@string/udacity_catalog"
android:textAppearance="?android:textAppearanceLarge"
android:textColor="#9C27B0"
android:textStyle="bold" />
<TextView
android:id="@+id/tv_title"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_marginTop="20dp"
android:gravity="start"
android:hint="@string/hint_title"
android:textAppearance="?android:textAppearanceMedium"
android:textColor="#000000" />
<TextView
android:id="@+id/tv_subtitle"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_marginTop="20dp"
android:gravity="start"
android:hint="@string/hint_subtitle"
android:textAppearance="?android:textAppearanceMedium"
android:textColor="#000000" />
<TextView
android:id="@+id/tv_course_key"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_marginTop="20dp"
android:gravity="start"
android:hint="@string/hint_key"
android:textAppearance="?android:textAppearanceMedium"
android:textColor="#000000" />
<TextView
android:id="@+id/tv_instructor_name"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_marginTop="20dp"
android:gravity="start"
android:hint="@string/hint_name"
android:textAppearance="?android:textAppearanceMedium"
android:textColor="#000000" />
</LinearLayout>
</android.support.v7.widget.CardView>
答案
你的listCourse有一个空的课程列表（Activity）。您通过它的构造函数将该空列表传递给适配器。即使你拿到了课程，该列表仍然是空的。所以适配器/ RecyclerView保持空白。
使用后，尝试在获取课程后创建适配器
mCourseAdapter = CourseAdapter(catalog!!.courses!!, applicationContext)
或者在适配器里面有一个课程属性
YourAdapter(...) {
var courses = listOf(Course)
}
然后在你的Activity（获取课程后）：
adapter.courses = catalog!!.courses!!
adapter.notifyDataSetChanged()
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