使用 SharedPreferences 或任何其他方法在 Fragment 内的 RecyclerView 中保存复选框状态

Question

我正在尝试将复选框状态保存在 Fragment 内的 RecyclerView 中，以在退出应用程序并再次加载后恢复这些首选项。

我有一个 AppWidget 的 ConfigActivity，其中有片段。 在其中一个片段中，我有一个 RecyclerView，它从 Calendar Provider 加载可供用户使用的日历。 根据选定的日历，appwidget 将从它们加载事件。 选定的日历应传递到 appwidget。

我在滚动 RecyclerView 时保存了复选框的状态。

但我不知道如何使用 SharedPreferences 将选定的复选框保存在 Fragment 内的 RecyclerView 中（保存以重新启动应用程序）。

我的日历项目数据 class ：

data class CalendarItem(
    val idCalendar: Long,
    val displayNameCalendar: String?,
    val accountNameCalendar: String?,
    val colorCalendar: Int? 
)

xml 中带有复选框的项目：

<RelativeLayout 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="wrap_content"
android:layout_marginTop="8dp"
android:layout_marginBottom="8dp">

<ImageView
    android:id="@+id/calendar_color"
    android:layout_width="10dp"
    android:layout_height="10dp"
    android:src="@drawable/color_label_circle"
    app:tint="@color/accent_color"
    android:layout_alignParentStart="true"
    android:layout_alignTop="@+id/text_display_name_calendar"
    android:layout_alignBottom="@+id/text_display_name_calendar"/>

<com.google.android.material.checkbox.MaterialCheckBox
    android:id="@+id/text_display_name_calendar"
    style="@style/basicText"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:layout_alignParentStart="true"
    android:layout_alignParentTop="true"
    android:layout_marginStart="24dp"
    android:layout_marginEnd="4dp"
    android:maxLines="1"
    android:ellipsize="end"
    android:gravity="start|center_vertical"
    android:layoutDirection="rtl"
    android:text="Display Name" />

<TextView
    android:id="@+id/text_account_name"
    style="@style/commentText"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:text="Account Name"
    android:layout_marginEnd="4dp"
    android:maxLines="1"
    android:ellipsize="end"
    android:layout_alignStart="@+id/text_display_name_calendar"
    android:layout_below="@+id/text_display_name_calendar" /> 
</RelativeLayout>

我的片段获取日历：

class CalendarsEventsFragment : Fragment() {

// For permissions
private val PERMISSION_REQUEST_CODE = 101

// For RecyclerView - Calendars
private lateinit var calendarItemAdapter: CalendarItemAdapter
private lateinit var recyclerViewCalendars: RecyclerView

// Values for the calendars from the calendar content provider
private val EVENT_PROJECTION = arrayOf(
    CalendarContract.Calendars._ID,
    CalendarContract.Calendars.CALENDAR_DISPLAY_NAME,
    CalendarContract.Calendars.ACCOUNT_NAME,
    CalendarContract.Calendars.CALENDAR_COLOR
    )

override fun onCreateView(
    inflater: LayoutInflater,
    container: ViewGroup?,
    savedInstanceState: Bundle?
): View? {

    // Inflate the layout for this fragment
    val view =  inflater.inflate(R.layout.fragment_calendars_events, container, false)

    recyclerViewCalendars = view.findViewById(R.id.recyclerview_calendars)

    // Setup permissions + start getCalendars
    setupPermissionsGetCalendars()

    return view
}

// Function to get and show calendars
private fun getCalendars() {
    // Getting calendars from CalendarProvider
    // In practice, should be done in an asynchronous thread instead of on the main thread
    calendarItemAdapter = CalendarItemAdapter()
    calendarItemAdapter.clearData()
    val uri = CalendarContract.Calendars.CONTENT_URI
    val cur: Cursor? = context?.contentResolver?.query(
        uri,
        EVENT_PROJECTION,
        null,
        null,
        null
    )
    while (cur?.moveToNext() == true) {
        val calId = cur.getLong(PROJECTION_ID_INDEX)
        val displayName = cur.getString(PROJECTION_DISPLAY_NAME_INDEX)
        val accountName = cur.getString(PROJECTION_ACCOUNT_NAME_INDEX)
        val color = cur.getInt(PROJECTION_CALENDAR_COLOR_INDEX)
        calendarItemAdapter.pushData(
            CalendarItem(
                idCalendar = calId,
                displayNameCalendar = displayName,
                accountNameCalendar = accountName,
                colorCalendar = color
            )
        )
    }
    cur?.close()
    // Setup RecyclerView adapter
    recyclerViewCalendars.let {
        it.layoutManager = LinearLayoutManager(context)
        it.adapter = calendarItemAdapter
    }
}

// Function to check permission and make request for permission + start getCalendars
private fun setupPermissionsGetCalendars() {
    if (checkSelfPermission(requireContext(), Manifest.permission.READ_CALENDAR) !=
        PackageManager.PERMISSION_GRANTED
    ) {
        requestPermissions(
            arrayOf(Manifest.permission.READ_CALENDAR),
            PERMISSION_REQUEST_CODE
        )
    } else {
        getCalendars()
    }
}

override fun onRequestPermissionsResult(
    requestCode: Int,
    permissions: Array<out String>,
    grantResults: IntArray
) {
    super.onRequestPermissionsResult(requestCode, permissions, grantResults)
    when (requestCode) {
        PERMISSION_REQUEST_CODE -> {
            if (grantResults.isNotEmpty() && grantResults[0] == PackageManager.PERMISSION_GRANTED) {
                Toast.makeText(
                    requireActivity(),
                    getText((R.string.toast_permission_granted)),
                    Toast.LENGTH_SHORT
                ).show()
                getCalendars()
            } else {
                if (shouldShowRequestPermissionRationale(Manifest.permission.READ_CALENDAR)) {
                    Toast.makeText(
                        requireActivity(),
                        getText((R.string.toast_permission_denied)),
                        Toast.LENGTH_SHORT
                    ).show()
                    showUserRationale()
                } else {
                    askUserOpenAppInfo()
                }
            }
        }
    }
}

private fun showUserRationale() {
    AlertDialog.Builder(requireContext())
        .setTitle(getString(R.string.request_permission_rationale_title))
        .setMessage(getString(R.string.request_permission_rationale_message))
        .setPositiveButton("OK") { dialog, id ->
            requestPermissions(
                arrayOf(Manifest.permission.READ_CALENDAR),
                PERMISSION_REQUEST_CODE
            )
        }
        .create()
        .show()
}

private fun askUserOpenAppInfo() {
    val appSettingsIntent = Intent(
        Settings.ACTION_APPLICATION_DETAILS_SETTINGS,
        Uri.fromParts("package", activity?.packageName, null)
    )
    if (activity?.packageManager?.resolveActivity(
            appSettingsIntent,
            PackageManager.MATCH_DEFAULT_ONLY
        ) == null
    ) {
        Toast.makeText(
            requireContext(),
            getText(R.string.toast_permission_denied_forever),
            Toast.LENGTH_SHORT
        ).show()
    } else {
        AlertDialog.Builder(requireContext())
            .setTitle(getString(R.string.request_permission_denied_forever_title))
            .setMessage(getString(R.string.request_permission_denied_forever_message))
            .setPositiveButton(getString(R.string.open_app_info_dialog_positive_button_text)) { dialog, id ->
                startActivity(appSettingsIntent)
                requireActivity().finish()
            }
            .setNegativeButton(getString(R.string.open_app_info_dialog_negative_button_text)) { dialog, id ->
                requireActivity().finish()
            }
            .create()
            .show()
    }
} 
}

我的RecyclerView 适配器：

class CalendarItemAdapter() : RecyclerView.Adapter<CalendarItemAdapter.ViewHolder>() {

var data: MutableList<CalendarItem> = mutableListOf()
var checkedCalendarItems = SparseBooleanArray()

fun clearData() {
    data.clear()
    notifyDataSetChanged()
}

fun pushData(calendarItem: CalendarItem) {
    data.add(calendarItem)
    notifyDataSetChanged()
}

inner class ViewHolder(view: View) : RecyclerView.ViewHolder(view) {
    val imageViewColor: ImageView = view.findViewById(R.id.calendar_color)
    val displayNameOfCalendar: CheckBox = view.findViewById(R.id.text_display_name_calendar)
    val accountName: TextView = view.findViewById(R.id.text_account_name)

    init {
        displayNameOfCalendar.setOnClickListener {
            if(!checkedCalendarItems.get(adapterPosition, false)) {
                displayNameOfCalendar.isChecked = true
                checkedCalendarItems.put(adapterPosition, true)
            } else {
                displayNameOfCalendar.isChecked = false
                checkedCalendarItems.put(adapterPosition, false)
            }
        }
    }
}

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

override fun onBindViewHolder(holder: ViewHolder, position: Int) {
    val datum = data[position]
    datum.colorCalendar?.let {
        holder.imageViewColor.setColorFilter(it)
    }
    holder.displayNameOfCalendar.text = datum.displayNameCalendar
    holder.displayNameOfCalendar.isChecked = checkedCalendarItems.get(position, false)
    holder.accountName.text = datum.accountNameCalendar
}

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

请问你能帮帮我吗？

Answer 1

SharedPreferences 只能存储原语和String arrays所以你必须以某种方式序列化你的数组。 可能最简单的方法是获取检查项目的所有索引并将它们放入字符串中。 当你把它拉回来时，把它们分开并将它们设置为真。

您可能应该在适配器中处理这个问题，因为它实际上是只有适配器需要知道的内部实现细节。 可能是这样的：

class CalendarItemAdapter() : RecyclerView.Adapter<CalendarItemAdapter.ViewHolder>() {
    var checkedCalendarItems = SparseBooleanArray()

    fun saveState(prefs: SharedPreferences) {
        // make a list of all the indices that are set to true, join them as a string
        val checkedIndices = checkedCalendarItems
            .mapIndexedNotNull {index, checked -> if (checked) index else null }
            .joinToString(SEPARATOR)
        prefs.edit { putString(KEY_CHECKED_INDICES, checkedIndices) }
    }
    
    fun restoreState(prefs: SharedPreferences) {
        // reset the array - we're clearing the current state
        // whether there's anything stored or not
        checkedCalendarItems = SparseBooleanArray()

        // grab the checked indices and set them - using null as a "do nothing" fallback
        val checkedIndices = prefs.getString(KEY_CHECKED_INDICES, null)
            ?.split(SEPARATOR)
            ?.map(String::toInt) // or mapNotNull(String::toIntOrNull) to be super safe
            ?.forEach { checkedCalendarItems[it] = true }
        
        // update the display - onBindViewHolder should be setting/clearing checkboxes
        // by referring to the checked array
        notifyDataSetChanged()
    }

    ...

    companion object {
        // making these constants that both functions refer to avoids future bugs
        // e.g. someone changing the separator in one function but not the other
        const val SEPARATOR = ","
        const val KEY_CHECKED_INDICES = "checked indices"
    }
}

然后您可以在适配器上酌情调用这些保存/恢复 state 函数，例如在onStop和onStart中，传入您的SharedPreferences state object