Android Studio / Kotlin-findViewById使我的应用程序崩溃

Question

程序到达findViewById时停止，我不知道为什么：

    override fun onCreate(savedInstanceState: Bundle?) {
    super.onCreate(savedInstanceState)
    setContentView(R.layout.splash_screen)

    handler.postDelayed({ setContentView(R.layout.activity_main) }, 500) // 5 seconds
    val imageView: ImageView = findViewById(R.id.splashScreenIMG)
    Glide.with(this).load(R.drawable.sligames_waiting).into(imageView)
}

    fun showButtons()
{
    val view: View = findViewById(R.id.boutonOui)
    val cx = view.width / 2
    val cy = view.height / 2
    val finalRadius = hypot(cx.toDouble(), cy.toDouble()).toFloat()
    val anim = ViewAnimationUtils.createCircularReveal(view, cx, cy, 0f, finalRadius)
    // make the view visible and start the animation
    view.visibility = View.VISIBLE
    anim.duration = 1500
    anim.start()
}

我从另一个文件的这一行执行此功能：

MainActivity().showButtons()

这是堆栈跟踪：

2020-06-01 12:55:02.783 22557-22557/com.example.yourmajesty E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.example.yourmajesty, PID: 22557
java.lang.NullPointerException: Attempt to invoke virtual method 'android.content.pm.ApplicationInfo android.content.Context.getApplicationInfo()' on a null object reference
    at android.content.ContextWrapper.getApplicationInfo(ContextWrapper.java:163)
    at android.view.ContextThemeWrapper.getTheme(ContextThemeWrapper.java:174)
    at android.content.Context.obtainStyledAttributes(Context.java:738)
    at androidx.appcompat.app.AppCompatDelegateImpl.createSubDecor(AppCompatDelegateImpl.java:692)
    at androidx.appcompat.app.AppCompatDelegateImpl.ensureSubDecor(AppCompatDelegateImpl.java:659)
    at androidx.appcompat.app.AppCompatDelegateImpl.findViewById(AppCompatDelegateImpl.java:479)
    at androidx.appcompat.app.AppCompatActivity.findViewById(AppCompatActivity.java:214)
    at com.example.yourmajesty.MainActivity.showButtons(MainActivity.kt:122)
    at com.example.yourmajesty.Dialog.dialogChanger(Dialog.kt:26)
    at com.example.yourmajesty.MainActivity$dialogBoxDiseappear$2.run(MainActivity.kt:190)
    at android.os.Handler.handleCallback(Handler.java:883)
    at android.os.Handler.dispatchMessage(Handler.java:100)
    at android.os.Looper.loop(Looper.java:214)
    at android.app.ActivityThread.main(ActivityThread.java:7695)
    at java.lang.reflect.Method.invoke(Native Method)
    at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:516)
    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:950)

提前感谢

Answer 1

MainActivity().showButtons()

Answer 2

解决方案1：您应该将该函数设为公共静态，以便可以使用Main Class名称直接调用文件，即MainActivity（）。showButtons（）