Question

<ScrollView xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:id="@+id/scrollMenu"
    android:layout_height="wrap_content">



 @RequiresApi(api = Build.VERSION_CODES.P)
    private void initViews() {
        scrollMenu = findViewById(R.id.scrollMenu);
        scrollMenu.setOnScrollChangeListener(new View.OnScrollChangeListener() {
            @Override
            public void onScrollChange(View v, int scrollX, int scrollY, int oldScrollX, int oldScrollY) {

            }
        });
//        }

E / Android运行时：致命异常：主要流程：com.dsmsoft.traccia.sampleui，PID：12790 java.lang.RuntimeException：无法启动活动ComponentInfo {com.dsmsoft.traccia.sampleui / com.dsmsoft.traccia.sampleui.MainActivity}：java.lang.NullPointerException：尝试调用虚拟方法'void android.widget.ScrollView。在空对象引用上的setOnScrollChangeListener（android.view.View $ OnScrollChangeListener）' 在android.app.ActivityThread.performLaunchActivity（ActivityThread.java:2778）在android.app.ActivityThread.handleLaunchActivity（ActivityThread.java:2856）在android.app.ActivityThread.-wrap11（未知来源：0）在ndroid.app.ActivityThread $ H.handleMessage（ActivityThread.java:1589）在android.os.Handler.dispatchMessage（Handler.java:106）在android.os.Looper.loop（Looper.java:164）在android.app.ActivityThread.main（ActivityThread.java:6494）在java.lang.reflect.Method.invoke（本机方法）在com.android.internal.os.RuntimeInit $ MethodAndArgsCaller.run（RuntimeInit.java:438）在com.android.internal.os.ZygoteInit.main（ZygoteInit.java:807）原因：java.lang.NullPointerException：尝试在空对象引用上调用虚拟方法'void android.widget.ScrollView.setOnScrollChangeListener（android.view.View $ OnScrollChangeListener）' 在com.dsmsoft.traccia.sampleui.MainActivity.initViews（MainActivity.java:25）在com.dsmsoft.traccia.sampleui.MainActivity.onCreate（MainActivity.java:19）在android.app.Activity.performCreate（Activity.java:7009）在android.app.Activity.performCreate（Activity.java:7000）在android.app.Instrumentation.callActivityOnCreate（Instrumentation.java:1214）在android.app.ActivityThread.performLaunchActivity（ActivityThread.java:2731）在android.app.ActivityThread.handleLaunchActivity（ActivityThread.java:2856）在android.app.ActivityThread.-wrap11（未知来源：0）在android.app.ActivityThread $ H.handleMessage（ActivityThread.java:1589）在android.os.Handler.dispatchMessage（Handler.java:106）在android.os.Looper.loop（Looper.java:164）在android.app.ActivityThread.main（ActivityThread.java:6494）在java.lang.reflect.Method.invoke（本机方法）在com.android.internal.os.RuntimeInit $ MethodAndArgsCaller.run（RuntimeInit.java:438）在com.android.internal.os.ZygoteInit.main（ZygoteInit.java:807）进程12790终止。

Answer 1

您的窗口小部件setOnScrollListener为null。您忘记了findViewById（）吗？

Answer 2

您可以在滚动视图中添加其他任何布局，例如约束布局和内部布局

<androidx.constraintlayout.widget.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:layout_width="match_parent"
android:layout_height="match_parent">

<ScrollView
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    app:layout_constraintBottom_toBottomOf="parent"
    app:layout_constraintEnd_toEndOf="parent"
    app:layout_constraintHorizontal_bias="0.0"
    app:layout_constraintStart_toStartOf="parent"
    app:layout_constraintTop_toTopOf="parent">

    <androidx.constraintlayout.widget.ConstraintLayout
        android:layout_width="match_parent"
        android:layout_height="wrap_content">


        <ImageView
            android:id="@+id/imageView4"
            android:layout_width="104dp"
            android:layout_height="109dp"
            android:layout_marginTop="32dp"
            app:layout_constraintEnd_toEndOf="parent"
            app:layout_constraintHorizontal_bias="0.498"
            app:layout_constraintStart_toStartOf="parent"
            app:layout_constraintTop_toTopOf="parent"
            app:srcCompat="@android:drawable/screen_background_light" />

        <TextView
            android:id="@+id/firstname"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_marginTop="32dp"
            android:text="First Name :"
            android:textColor="@android:color/black"
            app:layout_constraintEnd_toStartOf="@+id/textView14"
            app:layout_constraintHorizontal_bias="0.217"
            app:layout_constraintStart_toStartOf="parent"
            app:layout_constraintTop_toBottomOf="@+id/imageView4" />
 </androidx.constraintlayout.widget.ConstraintLayout>
    </ScrollView>
</androidx.constraintlayout.widget.ConstraintLayout>

如何解决AS ..中的问题？ ScrollView.setOnScrollChangeListener

2 个答案: