对于问题的逻辑，您可以参考这个问题：- question Logic
经过很多努力，我走到了这一步。请帮我解决这个问题。
这是活动代码：-
class CheckboxesActivity : AppCompatActivity() {
lateinit var recyclerView: RecyclerView
lateinit var adapter: CheckboxAdapter
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
setContentView(R.layout.activity_trail)
recyclerView =findViewById(R.id.trail_rv)
val list = listOf(
RowModel(RowType.TopHeader, "", "", false),
RowModel(RowType.Course, "", "Science", false),
RowModel(RowType.SubjectRow, "Physics", "Science", false),
RowModel(RowType.SubjectRow, "Math", "Science", false),
RowModel(RowType.SubjectRow, "Chemistry", "Science", false),
RowModel(RowType.Course, "", "Arts", false),
RowModel(RowType.SubjectRow, "Economics", "Arts", false),
RowModel(RowType.SubjectRow, "History", "Arts", false),
RowModel(RowType.SubjectRow, "Political Science", "Arts", false),
RowModel(RowType.Course, "", "Commerce", false),
RowModel(RowType.SubjectRow, "Accountancy", "Commerce", false),
RowModel(RowType.SubjectRow, "Business Studies", "Commerce", false),
RowModel(RowType.SubjectRow, "Physical Education", "Commerce", false)
)
adapter = CheckboxAdapter(this, list)
adapter.setList(list)
recyclerView.adapter = adapter
recyclerView.layoutManager = LinearLayoutManager(this)
findViewById<Button>(R.id.showTextBtn).setOnClickListener {
selectedCheckboxes!!.clear()
val checkboxesValue: String = selectedCheckboxes!!.joinToString(separator = ";")
findViewById<TextView>(R.id.ShowTextView).text = checkboxesValue
}
}
}
这是我的适配器代码：-
class CheckboxAdapter(
private val context: Context,
var productList: List<RowModel>,
) : RecyclerView.Adapter<CheckboxAdapter.TableViewHolder>() {
override fun onBindViewHolder(holder: TableViewHolder, position: Int) {
val item = productList[position]
holder.checkBox.setOnCheckedChangeListener(null)
holder.checkBox.isChecked = item.isChecked
val params: ViewGroup.MarginLayoutParams =
holder.checkBox.layoutParams as ViewGroup.MarginLayoutParams
when (item.rowType) {
RowType.TopHeader -> {
holder.checkBox.text = "All Courses"
holder.checkBox.visibility = View.VISIBLE
holder.checkBox.typeface = Typeface.DEFAULT_BOLD
params.setMargins(0, 0, 0, 0)
holder.checkBox.layoutParams = params
}
RowType.Course -> {
holder.checkBox.visibility = View.VISIBLE
holder.checkBox.text = item.category
holder.checkBox.typeface = Typeface.DEFAULT_BOLD
params.setMargins(0, 0, 0, 0)
holder.checkBox.layoutParams = params
}
RowType.SubjectRow -> {
holder.checkBox.visibility = View.VISIBLE
holder.checkBox.text = item.subjectName
holder.checkBox.typeface = Typeface.DEFAULT
params.setMargins(convertDpToPixel(20f, context).toInt(), 0, 0, 0)
holder.checkBox.layoutParams = params
}
}
holder.checkBox.setOnCheckedChangeListener { _, isChecked ->
if (item.isChecked != isChecked) {
item.isChecked = isChecked
when (item.rowType) {
RowType.TopHeader -> {
val indexList = mutableListOf<Int>()
productList.filter { it.rowType != RowType.TopHeader }.forEach {
it.isChecked = isChecked
indexList.add(productList.indexOf(it))
}
indexList.forEach {
notifyItemChanged(it)
}
}
RowType.Course -> {
val indexList = mutableListOf<Int>()
productList.filter { it.rowType == RowType.SubjectRow && it.category == item.category }
.forEach {
it.isChecked = isChecked
indexList.add(productList.indexOf(it))
}
indexList.forEach {
notifyItemChanged(it)
}
isAllItemsSameStatus() //for header
}
RowType.SubjectRow -> {
isAllItemsSameStatus(item.category) //set prep area accordingly
isAllItemsSameStatus() //set top header
}
}
}
}
when (item.rowType) {
RowType.SubjectRow -> {
if (holder.checkBox.isChecked)
selectedCheckboxes?.add(holder.checkBox.text.toString())
if (!holder.checkBox.isChecked) {
Toast.makeText(context, holder.checkBox.text, Toast.LENGTH_SHORT).show()
selectedCheckboxes?.remove(holder.checkBox.text.toString())
}
}
}
}
override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): TableViewHolder {
return TableViewHolder(
LayoutInflater.from(context).inflate(
R.layout.rv_trail,
parent,
false
)
)
}
class TableViewHolder(itemView: View) : RecyclerView.ViewHolder(itemView) {
val checkBox: CheckBox = itemView.findViewById(R.id.trailCheckbox)
}
override fun getItemCount() = productList.size
fun setList(profiles: List<RowModel>) {
productList = profiles
notifyDataSetChanged()
}
private fun isAllItemsSameStatus(cat: String? = null) {
val row: RowModel
var isChecked: Boolean = true
var position: Int = 0
if (cat != null) {
val catRow = productList.find { it.rowType == RowType.Course && it.category == cat }
catRow?.let {
val subList =
productList.filter { it.category == it.category && it.rowType == RowType.SubjectRow }
isChecked = subList.filter { it.isChecked }.size == subList.size
position = productList.indexOf(catRow)
}
if (catRow == null)
return
else
row = catRow
} else {
row = productList[0]
isChecked =
productList.filter { it.rowType != RowType.TopHeader && it.isChecked }.size == productList.size - 1
position = 0
}
updateHeader(row, isChecked, position)
}
private fun updateHeader(item: RowModel, isChecked: Boolean, position: Int) {
if (item.isChecked != isChecked) // no need to update if no change
{
item.isChecked = isChecked
notifyItemChanged(position)
}
}
private fun convertDpToPixel(dp: Float, context: Context): Float {
return dp * (context.resources
.displayMetrics.densityDpi.toFloat() / DisplayMetrics.DENSITY_DEFAULT)
}
companion object {
var selectedCheckboxes: MutableList<String>? = null
}
}
这是我的模型代码：-
data class RowModel (
val rowType: RowType,
val subjectName: String,
val category: String,
var isChecked: Boolean = true)
enum class RowType(val id : Int) {
TopHeader(1),
Course(2),
SubjectRow(3);
}
这是 activity_trail 布局代码：-
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout 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="match_parent"
android:orientation="vertical"
tools:context=".CheckboxesActivity">
<androidx.recyclerview.widget.RecyclerView
android:id="@+id/trail_rv"
android:layout_width="match_parent"
android:layout_height="wrap_content"/>
<Button
android:id="@+id/showTextBtn"
style="@style/ButtonTransparent"
android:text="@string/save"/>
<TextView
android:id="@+id/ShowTextView"
android:layout_width="match_parent"
android:layout_height="wrap_content"/>
</LinearLayout>
问题的逻辑是：-
我正在尝试进行活动，如果：- 1）选中所有课程复选框，则应选中所有其他复选框，反之亦然。
2）选中所有科学按钮，然后应选择所有其他主题按钮，反之亦然。所有其他科目也一样。
3）如果任何课程按钮没有被选中，那么所有课程按钮也不应该被选中。所有科目也一样。
单击 showTextBtn（按钮）后。该应用程序正在崩溃。这是崩溃报告：-
java.lang.NullPointerException
at com.trail.CheckboxesActivity.onCreate$lambda-0(CheckboxesActivity.kt:45)
at com.trail.CheckboxesActivity.$r8$lambda$Q7Wv2MEY_mNrpZmgjbfsuGABR0o(Unknown Source:0)
at com.trail.CheckboxesActivity$$ExternalSyntheticLambda0.onClick(Unknown Source:2)
at android.view.View.performClick(View.java:8160)
at android.widget.TextView.performClick(TextView.java:16222)
at com.google.android.material.button.MaterialButton.performClick(MaterialButton.java:1194)
at android.view.View.performClickInternal(View.java:8137)
at android.view.View.access$3700(View.java:888)
at android.view.View$PerformClick.run(View.java:30236)
at android.os.Handler.handleCallback(Handler.java:938)
at android.os.Handler.dispatchMessage(Handler.java:99)
at android.os.Looper.loop(Looper.java:246)
at android.app.ActivityThread.main(ActivityThread.java:8653)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:602)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1130)
在这里，我试图获取所有选定复选框的文本。在 textView 中显示该文本。其他一切工作正常，但问题仅在于获取选定复选框文本应用程序崩溃的值时。如果可能的话，你能告诉我如何使用字符串数组而不是输入所有这些列表吗？
而不是使用：-
var selectedCheckboxes: MutableList<String>? = null
利用：-
var selectedCheckboxes: ArrayList<String> = ArrayList()
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