为什么FindViewById（）返回null

Question

我正在尝试制作一个绘图应用程序，但是当我设置刷子尺寸并尝试进行文本视图以显示其尺寸时，它总是返回null，我尝试了多种方法，但它没有成功，所以请任何方法一个帮助我修复了此代码中的台词，因此文本显示了Seekbar Progress Text

class MainActivity : AppCompatActivity() {
        private var ibBrush: ImageView? = null
        private var tvBrushSize: TextView? = null
        private var sbBrushSize: SeekBar?= null
    
        override fun onCreate(savedInstanceState: Bundle?) {
            AppCompatDelegate.setDefaultNightMode(AppCompatDelegate.MODE_NIGHT_NO)
            super.onCreate(savedInstanceState)
            setContentView(R.layout.activity_main)
            ibBrush = findViewById(R.id.ib_brush)
            ibBrush?.setOnClickListener{
                changeBrushSize()
            }
    
    
        }
        private fun changeBrushSize(){
            AppCompatDelegate.setDefaultNightMode(AppCompatDelegate.MODE_NIGHT_NO)
            val brushDialog = Dialog(this)
            brushDialog.setContentView(R.layout.brush_size_dialog)
            tvBrushSize = findViewById(R.id.tv_brush_size)
            sbBrushSize = findViewById(R.id.sb_brush_size)
    
            tvBrushSize?.text = sbBrushSize?.progress.toString()
    
    
            brushDialog.show()
    
    
        }
    }

为什么TVBrushSize在我将其设置为FindViewById（）中返回null的原因是XML

* *这是XML *

<?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="wrap_content"
    android:layout_height="match_parent"
    android:padding="10dp"
    android:orientation="vertical"

    >

    <TextView
        android:id="@+id/textView"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="@string/brush_size"
        android:gravity="center"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent"
        app:layout_constraintBottom_toTopOf="@+id/linear"/>

    <LinearLayout
        android:layout_width="350dp"
        android:layout_height="wrap_content"
        android:layout_margin="10dp"
        android:orientation="horizontal"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toBottomOf="@+id/textView">

        <SeekBar
            android:id="@+id/sb_brush_size"
            android:layout_width="0dp"
            android:layout_height="match_parent"
            android:layout_weight="10"
            android:max="30"
            />

        <TextView
            android:id="@+id/tv_brush_size"
            android:layout_width="0dp"
            android:layout_height="match_parent"
            android:layout_weight="1"
            android:gravity="center"
            android:text="@string/_0" />
    </LinearLayout>
</LinearLayout>

Answer 1

您应该首先使用layoutinflater.inflate（layoutID）首先夸大对话框视图，然后使用view.findviewbyid（id）像此片段：

   private fun changeBrushSize(){
        AppCompatDelegate.setDefaultNightMode(AppCompatDelegate.MODE_NIGHT_NO)
        val brushDialog = Dialog(this)
        val dialogView = LayoutInflater.inflate(R.layout.brush_size_dialog, null)
        brushDialog.setContentView(dialogView)
        tvBrushSize = dialogView.findViewById(R.id.tv_brush_size)
        sbBrushSize = dialogView.findViewById(R.id.sb_brush_size)

        tvBrushSize?.text = sbBrushSize?.progress.toString()


        brushDialog.show()


    }

Answer 2

您需要从对话框中绑定视图，因此请这样管理；

  brushDialog.setContentView(R.layout.brush_size_dialog)
  val dialogView = layoutInflater.inflate(R.layout.brush_size_dialog, null) 
  brushDialog.setContentView(dialogView)
  tvBrushSize = dialogView.findViewById(R.id.tv_brush_size)

Answer 3

当您尝试使用FindViewById（）引用它时，与您的视图的对话框尚不存在
您可以首先夸大视图，然后按以下方式访问

        val brushDialog = Dialog(this)
        val view = layoutInflater.inflate(R.layout.brush_size_dialog, null) 
        brushDialog.setContentView(view)
        tvBrushSize = view.findViewById(R.id.tv_brush_size)
        sbBrushSize = view.findViewById(R.id.sb_brush_size)
        tvBrushSize?.text = sbBrushSize?.progress.toString()
        brushDialog.show()

或调用brushdialog.show（）首先，然后使用findViewById（）访问视图，

该视图也应该有效

Answer 4

您应该先夸大视图

val dialogView = LayoutInflater.inflate(R.layout.brush_size_dialog, null)
brushDialog.setContentView(dialogView)

，然后尝试使用

dialogView.findViewById(...)