android - 删除有条件的片段

Question

如果我添加片段，我可以删除片段。但是我在没有片段的情况下单击了删除片段按钮，问题崩溃了。但它应该给我祝酒词。我在 Logcat 中收到此错误消息：

019-08-23 16:38:14.239 3951-3951/com.example.fragment E/AndroidRuntime: FATAL EXCEPTION: main
    Process: com.example.fragment, PID: 3951
    java.lang.IllegalStateException: Could not execute method for android:onClick
        at androidx.appcompat.app.AppCompatViewInflater$DeclaredOnClickListener.onClick(AppCompatViewInflater.java:390)
        at android.view.View.performClick(View.java:6597)
        at android.view.View.performClickInternal(View.java:6574)
        at android.view.View.access$3100(View.java:778)
        at android.view.View$PerformClick.run(View.java:25885)
        at android.os.Handler.handleCallback(Handler.java:873)
        at android.os.Handler.dispatchMessage(Handler.java:99)
        at android.os.Looper.loop(Looper.java:193)
        at android.app.ActivityThread.main(ActivityThread.java:6680)
        at java.lang.reflect.Method.invoke(Native Method)
        at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:493)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:858)
     Caused by: java.lang.reflect.InvocationTargetException
        at java.lang.reflect.Method.invoke(Native Method)
        at androidx.appcompat.app.AppCompatViewInflater$DeclaredOnClickListener.onClick(AppCompatViewInflater.java:385)
        at android.view.View.performClick(View.java:6597) 
        at android.view.View.performClickInternal(View.java:6574) 
        at android.view.View.access$3100(View.java:778) 
        at android.view.View$PerformClick.run(View.java:25885) 
        at android.os.Handler.handleCallback(Handler.java:873) 
        at android.os.Handler.dispatchMessage(Handler.java:99) 
        at android.os.Looper.loop(Looper.java:193) 
        at android.app.ActivityThread.main(ActivityThread.java:6680) 
        at java.lang.reflect.Method.invoke(Native Method) 
        at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:493) 
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:858) 
     Caused by: kotlin.TypeCastException: null cannot be cast to non-null type com.example.fragment.FragmentA
        at com.example.fragment.MainActivity.removeFragmentA(MainActivity.kt:47)
        at java.lang.reflect.Method.invoke(Native Method) 
        at androidx.appcompat.app.AppCompatViewInflater$DeclaredOnClickListener.onClick(AppCompatViewInflater.java:385) 
        at android.view.View.performClick(View.java:6597) 
        at android.view.View.performClickInternal(View.java:6574) 
        at android.view.View.access$3100(View.java:778) 
        at android.view.View$PerformClick.run(View.java:25885) 
        at android.os.Handler.handleCallback(Handler.java:873) 
        at android.os.Handler.dispatchMessage(Handler.java:99) 
        at android.os.Looper.loop(Looper.java:193) 
        at android.app.ActivityThread.main(ActivityThread.java:6680) 
        at java.lang.reflect.Method.invoke(Native Method) 
        at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:493) 
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:858) 


fun removeFragmentA(v: View) {

        val fragmentA = manager.findFragmentByTag("FragA") as FragmentA
        val transaction = manager.beginTransaction()
        if (fragmentA != null) {
            transaction.remove(fragmentA)
            transaction.commit()
        } else {
            Toast.makeText(this, "Fragment A bulunamadı", Toast.LENGTH_LONG).show()
        }

    }

这是我的删除片段功能：

   fun removeFragmentA(v: View) {
   val fragmentA = manager.findFragmentByTag("FragA") as FragmentA
    val transaction = manager.beginTransaction()
    if (fragmentA != null) {
        transaction.remove(fragmentA)
        transaction.commit()
    } else {
        Toast.makeText(this, "Fragment A bulunamadı", Toast.LENGTH_LONG).show()
    }

}

这是我的xml：

            <Button
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="ÇIKAR A"
            android:onClick="removeFragmentA"/>

我认为问题在于该错误：

原因kotlin.TypeCastException：：null 不能转换为非 null 类型com.example.fragment.FragmentA

但我找不到任何解决方案。

标签： androidandroid-fragmentskotlin

Answer 1

好的，我解决了我猜的问题。:)

它应该是：

val fragmentA = manager.findFragmentByTag("FragA") as FragmentA?

而不是

val fragmentA = manager.findFragmentByTag("FragA") as FragmentA