ViewPager2 setCurrentItem 方法抛出错误

Question

我正在使用ViewPager2，并且我有一个按钮可以将其当前页面更改为第二页，如下所示：

button_next.setOnClickListener {
            setup_view_pager.currentItem = 1
}

它在手动滑动页面之前一直有效，之后它会抛出此错误：

E/AndroidRuntime: FATAL EXCEPTION: main
    Process: rs.ac.bg.matf.risk.matfasistent, PID: 32028
    java.lang.IllegalStateException: Expected position values between -1 and 1.
        at androidx.core.util.Preconditions.checkState(Preconditions.java:96)
        at androidx.viewpager2.widget.MarginPageTransformer.transformPage(MarginPageTransformer.java:56)
        at androidx.viewpager2.widget.PageTransformerAdapter.onPageScrolled(PageTransformerAdapter.java:72)
        at androidx.viewpager2.widget.CompositeOnPageChangeCallback.onPageScrolled(CompositeOnPageChangeCallback.java:59)
        at androidx.viewpager2.widget.ScrollEventAdapter.dispatchScrolled(ScrollEventAdapter.java:407)
        at androidx.viewpager2.widget.ScrollEventAdapter.onScrolled(ScrollEventAdapter.java:188)
        at androidx.recyclerview.widget.RecyclerView.dispatchOnScrolled(RecyclerView.java:5100)
        at androidx.recyclerview.widget.RecyclerView$ViewFlinger.run(RecyclerView.java:5265)
        at android.view.Choreographer$CallbackRecord.run(Choreographer.java:1012)
        at android.view.Choreographer.doCallbacks(Choreographer.java:824)
        at android.view.Choreographer.doFrame(Choreographer.java:756)
        at android.view.Choreographer$FrameDisplayEventReceiver.run(Choreographer.java:998)
        at android.os.Handler.handleCallback(Handler.java:873)
        at android.os.Handler.dispatchMessage(Handler.java:99)
        at android.os.Looper.loop(Looper.java:193)
        at android.app.ActivityThread.main(ActivityThread.java:6745)
        at java.lang.reflect.Method.invoke(Native Method)
        at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:495)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:858)

这仅发生在这些点击上，当手动滑动片段时一切正常。错误跟踪的所有位置都没有指向我的代码:(

这是我的 ViewPager 适配器：

class SetupAdapter(fragmentManager: FragmentManager, lifecycle: Lifecycle)
    : FragmentStateAdapter(fragmentManager, lifecycle) {

    override fun getItemCount() = 3

    override fun createFragment(position: Int): Fragment {
        return when (position) {
            0, 1, 2 -> StudentSelectionFragment()
            else -> throw IllegalStateException()
        }
    }
}

这是整个Activity的相关代码：

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

        val adapter = SetupAdapter(supportFragmentManager, lifecycle)

        setup_view_pager.orientation = ViewPager2.ORIENTATION_HORIZONTAL
        setup_view_pager.adapter = adapter
        setup_view_pager.setPageTransformer(MarginPageTransformer(1500))

        button_next.setOnClickListener {
            setup_view_pager.setCurrentItem(1, true)
        }
    }

Answer 1

问题出在这一行：

setup_view_pager.setPageTransformer(MarginPageTransformer(1500))

我不确定它的作用，我仍然不确定，但我从示例实现中复制了它。删除它可以解决问题。