我正在按照本教程創建一個帶有空間影片內容的 android 應用程式。在標題為“Transition Manager”的步驟中，系統會指示您將以下代碼添加到 MainActivity.kt 檔案中：`
constraintSet1.clone(constraintLayout) //1
constraintSet2.clone(this, R.layout.activity_main) //2
departButton.setOnClickListener { //3
//apply the transition
TransitionManager.beginDelayedTransition(constraintLayout) //4
val constraint = if (!isOffscreen) constraintSet1 else constraintSet2
isOffscreen = !isOffscreen
constraint.applyTo(constraintLayout) //5
}
` 添加此代碼時，變數“constraintLayout”會引發未解決的參考錯誤
我認為 constraintLayout 應該指向 xml 中的某些東西，而某些東西未能實作這一點，我只是不知道是什么。
添加上述塊后的kotlin代碼為：`
package com.raywenderlich.android.razegalactic
import android.os.Bundle
import android.support.constraint.*
import android.support.v7.app.AppCompatActivity
import android.transition.TransitionManager
import kotlinx.android.synthetic.main.keyframe1.*
/**
* Main Screen
*/
class MainActivity : AppCompatActivity() {
private val constraintSet1 = ConstraintSet()
private val constraintSet2 = ConstraintSet()
private var isOffscreen = true
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
setContentView(R.layout.keyframe1)
switch1.setOnCheckedChangeListener { _, isChecked ->
switch1.setText(if (isChecked) R.string.round_trip else R.string.one_way)
constraintSet1.clone(constraintLayout) //1
constraintSet2.clone(this, R.layout.activity_main) //2
departButton.setOnClickListener { //3
//apply the transition
TransitionManager.beginDelayedTransition(constraintLayout) //4
val constraint = if (!isOffscreen) constraintSet1 else constraintSet2
isOffscreen = !isOffscreen
constraint.applyTo(constraintLayout) //5
}
}
}
}
`
主要xml如下：`
<android.support.constraint.ConstraintLayout 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:id="@ id/ConstraintLayout"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:gravity="center_horizontal"
android:orientation="vertical"
tools:context=".MainActivity">
<ImageView
android:id="@ id/flightsIcon"
android:layout_width="30dp"
android:layout_height="30dp"
android:src="@drawable/rocket_icon"
app:layout_constraintBottom_toBottomOf="@ id/spaceStationIcon"
app:layout_constraintEnd_toStartOf="@ id/roverIcon"
app:layout_constraintStart_toEndOf="@ id/spaceStationIcon"
app:layout_constraintTop_toTopOf="@ id/spaceStationIcon" />
<ImageView
android:id="@ id/spaceStationIcon"
android:layout_width="30dp"
android:layout_height="30dp"
android:layout_marginTop="15dp"
android:src="@drawable/space_station_icon"
app:layout_constraintEnd_toStartOf="@ id/flightsIcon"
app:layout_constraintHorizontal_chainStyle="spread"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toTopOf="parent" />
<ImageView
android:id="@ id/roverIcon"
android:layout_width="30dp"
android:layout_height="30dp"
android:src="@drawable/rover_icon"
app:layout_constraintBottom_toBottomOf="@ id/flightsIcon"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintStart_toEndOf="@ id/flightsIcon"
app:layout_constraintTop_toTopOf="@ id/flightsIcon" />
<TextView
android:id="@ id/spaceStationLabel"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_marginTop="15dp"
android:text="@string/space_stations"
app:layout_constraintEnd_toEndOf="@ id/spaceStationIcon"
app:layout_constraintStart_toStartOf="@ id/spaceStationIcon"
app:layout_constraintTop_toBottomOf="@ id/spaceStationIcon" />
<TextView
android:id="@ id/textView1"
android:layout_width="124dp"
android:layout_height="98dp"
android:layout_marginEnd="40dp"
android:background="@color/colorPrimary"
android:gravity="center"
android:paddingEnd="20dp"
android:text="@string/dca"
android:textColor="@android:color/white"
app:layout_constraintBottom_toBottomOf="@ id/doubleArrowsIcon"
app:layout_constraintEnd_toEndOf="@ id/doubleArrowsIcon"
app:layout_constraintTop_toTopOf="@ id/doubleArrowsIcon" />
<TextView
android:id="@ id/roverLabel"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_marginTop="15dp"
android:text="@string/rovers"
app:layout_constraintEnd_toEndOf="@ id/roverIcon"
app:layout_constraintStart_toStartOf="@ id/roverIcon"
app:layout_constraintTop_toBottomOf="@ id/roverIcon" />
<TextView
android:id="@ id/textView2"
android:layout_width="124dp"
android:layout_height="98dp"
android:layout_marginStart="40dp"
android:background="@color/colorPrimary"
android:gravity="center"
android:paddingStart="20dp"
android:text="@string/mars"
android:textColor="@android:color/white"
app:layout_constraintBottom_toBottomOf="@ id/doubleArrowsIcon"
app:layout_constraintStart_toStartOf="@ id/doubleArrowsIcon"
app:layout_constraintTop_toTopOf="@ id/doubleArrowsIcon" />
<TextView
android:id="@ id/flightsLabel"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_marginTop="15dp"
android:text="@string/flights"
app:layout_constraintEnd_toEndOf="@ id/flightsIcon"
app:layout_constraintStart_toStartOf="@ id/flightsIcon"
app:layout_constraintTop_toBottomOf="@ id/flightsIcon" />
<ImageView
android:id="@ id/doubleArrowsIcon"
android:layout_width="60dp"
android:layout_height="60dp"
android:layout_marginBottom="40dp"
android:src="@drawable/double_arrows"
app:layout_constraintBottom_toTopOf="@ id/guideline1"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintStart_toStartOf="parent" />
<Switch
android:id="@ id/switch1"
android:layout_width="160dp"
android:layout_height="wrap_content"
android:layout_marginStart="8dp"
android:layout_marginTop="200dp"
android:background="@color/colorAccent"
android:checked="false"
android:padding="8dp"
android:switchPadding="24dp"
android:text="@string/one_way"
android:textColor="@android:color/white"
app:layout_constraintStart_toStartOf="@ id/guideline2"
app:layout_constraintTop_toTopOf="parent" />
<TextView
android:id="@ id/textView3"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_marginStart="8dp"
android:layout_marginTop="8dp"
android:background="@color/colorAccent"
android:padding="8dp"
android:text="@string/traveller"
android:textColor="@android:color/white"
app:layout_constraintStart_toStartOf="@ id/guideline2"
app:layout_constraintTop_toBottomOf="@ id/switch1" />
<ImageView
android:id="@ id/rocketIcon"
android:layout_width="30dp"
android:layout_height="30dp"
android:layout_marginEnd="8dp"
android:src="@drawable/rocket_icon"
app:layout_constraintCircle="@id/galaxyIcon"
app:layout_constraintCircleAngle="270"
app:layout_constraintCircleRadius="100dp" />
<ImageView
android:id="@ id/galaxyIcon"
android:layout_width="90dp"
android:layout_height="90dp"
android:src="@drawable/galaxy"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintHorizontal_bias="0.498"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toTopOf="@ id/guideline1"
app:layout_constraintVertical_bias="0.495" />
<Button
android:id="@ id/departButton"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:text="@string/depart"
android:textColor="@android:color/white"
app:backgroundTint="@color/colorPrimary"
app:layout_constraintBottom_toBottomOf="parent"
tools:layout_editor_absoluteX="158dp" />
<android.support.constraint.Guideline
android:id="@ id/guideline1"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:orientation="horizontal"
app:layout_constraintGuide_begin="0dp" />
<android.support.constraint.Guideline
android:id="@ id/guideline2"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:orientation="vertical"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintGuide_percent="1" />
</android.support.constraint.ConstraintLayout>
` 誰能告訴我我可能缺少什么或如何解決這個問題？提前致謝。
uj5u.com熱心網友回復：
您應該在使用它之前參考 a view。xml
這樣做，如果假設使用的布局名稱MainActivity是main.xml，它應該是您setContentView使用的，而不是其他布局。
lateinit var cosntraintLayout: ConstraintLayout
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
setContentView(R.layout.main) // <- main.xml
cosntraintLayout = findViewById<ConstraintLayout>(R.id.ConstraintLayout) // <- add this line
...
...
}
switch1并且departButton也會拋出相同的錯誤，但我將根據我提供的代碼將其留給您解決。
轉載請註明出處，本文鏈接：https://www.uj5u.com/houduan/525009.html