Question

问题是我看不到ViewPager的内容。我什至试图用Java查找合适的项目并重写为Kotlin。 Java中的所有项目都可以完美显示ViewPager，而Kotlin则不起作用。

主要活动的布局：

<RelativeLayoutxmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".MainActivity">

    <android.support.v4.view.ViewPager
        android:id="@+id/viewPager"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:layout_above="@+id/viewPagerDots" />

view_pager_item的布局：

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical">

    <ImageView
        android:id="@+id/imageView"
        android:layout_marginTop="50dp"
        android:layout_marginLeft="@dimen/activity_horizontal_margin"
        android:layout_marginRight="@dimen/activity_horizontal_margin"
        android:paddingTop="8dp"
        android:paddingBottom="8dp"
        android:layout_width="match_parent"
        android:layout_height="@dimen/ob_banner_height"
        android:gravity="center"
        android:scaleType="fitXY"
        android:src="@drawable/first_image_item"
        android:contentDescription="@string/app_name"/>

        <LinearLayout
            android:orientation="vertical"
            android:layout_width="match_parent"
            android:layout_height="wrap_content">

            <TextView
                android:id="@+id/textViewTitle"
                android:layout_width="match_parent"
                android:layout_height="wrap_content"
                android:gravity="center"
                android:paddingLeft="@dimen/ob_desc_padding"
                android:paddingRight="@dimen/ob_desc_padding"
                android:text="@string/app_name"
                android:textAllCaps="true"
                android:textColor="@color/colorAccent"
                android:textSize="@dimen/ob_header_text_size" />

            <TextView
                android:id="@+id/textViewDescription"
                android:layout_width="match_parent"
                android:layout_height="wrap_content"
                android:layout_marginTop="20dp"
                android:gravity="center"
                android:paddingLeft="@dimen/ob_desc_padding"
                android:paddingRight="@dimen/ob_desc_padding"
                android:text="@string/app_name"
                android:textColor="@color/colorAccent"
                android:textSize="@dimen/ob_desc_text_size" />
        </LinearLayout>
</LinearLayout>

ViewPagerAdapter的代码：

   class ViewPagerAdapter(private var context: Context, private var viewPagerItems: ArrayList<ViewPagerItem>): PagerAdapter() {

    override fun getCount() = viewPagerItems.size

    override fun isViewFromObject(view: View, `object`: Any) = `object` === Any()

    override fun instantiateItem(container: ViewGroup, position: Int): Any {
        val view = LayoutInflater.from(context).inflate(R.layout.view_pager_item, container, false)

        val item = viewPagerItems[position]

        val imageView = view.findViewById<ImageView>(R.id.imageView)
        imageView.setImageResource(item.imageId)

        val textViewTitle = view.findViewById<TextView>(R.id.textViewTitle)
        textViewTitle.text = item.title

        val textViewDescription = view.findViewById<TextView>(R.id.textViewDescription)
        textViewDescription.text = item.description

        container.addView(view)

        return view
    }

    override fun destroyItem(container: ViewGroup, position: Int, `object`: Any) {
        container.removeView(`object` as LinearLayout)
    }
}

ViewPagerItem是通常的数据类：

    data class ViewPagerItem(
    val imageId: Int,
    val title: String,
    val description: String)

MainActivity类：

class MainActivity : AppCompatActivity() {

private lateinit var viewPagerAdapter: ViewPagerAdapter
private lateinit var viewPager: ViewPager
private lateinit var buttonNext: Button

private lateinit var pagerIndicator: LinearLayout
private lateinit var dots: Array<ImageView?>

private var previousPosition = 0
private var dotsCount: Int = 3

private var viewPagerItems: ArrayList<ViewPagerItem> = arrayListOf()


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

    buttonNext = findViewById(R.id.buttonNext)
    viewPager = findViewById(R.id.viewPager)
    pagerIndicator = findViewById(R.id.viewPagerDots)

    initializeData()

    viewPagerAdapter = ViewPagerAdapter(this, viewPagerItems)
    viewPager.adapter = viewPagerAdapter

    setUiViewPagerController()

    viewPager.currentItem = 0
    viewPager.addOnPageChangeListener(object : ViewPager.OnPageChangeListener {
        override fun onPageScrolled(position: Int, positionOffset: Float, positionOffsetPixels: Int) {}

        override fun onPageSelected(position: Int) {
            for (i in 0 until dotsCount) {
                dots[i]?.setImageDrawable(ContextCompat.getDrawable(this@MainActivity, R.drawable.non_selected_view_pager_item))
            }

            dots[position]?.setImageDrawable(ContextCompat.getDrawable(this@MainActivity, R.drawable.selected_view_pager_item))


            val pos = position + 1

            if (pos == dotsCount && previousPosition == dotsCount - 1)
                showAnimation()
            else if (pos == dotsCount - 1 && previousPosition == dotsCount)
                hideAnimation()

            previousPosition = pos
        }

        override fun onPageScrollStateChanged(state: Int) {}
    })

    buttonNext.setOnClickListener {
        Toast.makeText(this@MainActivity, "Redirect to wherever you want", Toast.LENGTH_LONG).show()
    }
}

private fun initializeData() {
    val titles = intArrayOf(R.string.app_name, R.string.app_name, R.string.app_name)
    val descriptions = intArrayOf(R.string.app_name, R.string.app_name, R.string.app_name)
    val images = intArrayOf(R.drawable.first_image_item, R.drawable.onboard_page2, R.drawable.onboard_page3)

    for (i in images.indices) {
        val item = ViewPagerItem(
                images[i],
                resources.getString(titles[i]),
                resources.getString(descriptions[i]))

        viewPagerItems.add(item)
    }
}

fun showAnimation() {
    ...
}

fun hideAnimation() {
    ...
}

private fun setUiViewPagerController() {
    dotsCount = viewPagerAdapter.count
    dots = arrayOfNulls(dotsCount)

    for (i in 0 until dotsCount) {
        dots[i] = ImageView(this)
        dots[i]?.setImageDrawable(ContextCompat.getDrawable(this@MainActivity, R.drawable.non_selected_view_pager_item))

        val params = LinearLayout.LayoutParams(
                LinearLayout.LayoutParams.WRAP_CONTENT,
                LinearLayout.LayoutParams.WRAP_CONTENT
        )

        params.setMargins(6, 0, 6, 0)

        pagerIndicator.addView(dots[i], params)
    }

    dots[0]?.setImageDrawable(ContextCompat.getDrawable(this@MainActivity, R.drawable.selected_view_pager_item))
}
}

Answer 1

您应按以下方式更改ViewPagerAdapter中的代码：

override fun isViewFromObject(view: View, any: Any) = any == view

不显示ViewPager内容

1 个答案: