如何使用Kotlin中的按钮单击按钮切换ViewPager选项卡

Question

我想通过按钮单击片段本身来切换片段。我已经创建了ViewPager TablayOut，一切都可以使用，直到我进行了一个接口来与我的活动进行通信，在那里我可以为ViewPager设置不同的页面。我对Kotlin非常陌生，我不明白为什么要抓住Nullpointer :(我可能也很初始化我的按钮，但我不确定

这是我的MainActivity代码

class MainActivity : AppCompatActivity()
, MyFragment1.buttonClick {
override fun onCreate(savedInstanceState: Bundle?) {
    super.onCreate(savedInstanceState)
    setContentView(R.layout.activity_main)
    tablayout.addTab(tablayout.newTab().setIcon(R.drawable.ic_fragment1))
    tablayout.addTab(tablayout.newTab().setIcon(R.drawable.ic_fragment_2))
    tablayout.addTab(tablayout.newTab().setIcon(R.drawable.ic_fragment3))
    tablayout.tabGravity = TabLayout.GRAVITY_FILL
    val adapter = MyAdapter(this, supportFragmentManager, tablayout.tabCount)
    viewpager!!.adapter = adapter
    viewpager.addOnPageChangeListener(TabLayout.TabLayoutOnPageChangeListener(tablayout))

    val tabStrip = tablayout.getChildAt(0) as LinearLayout
    for (i in 0 until tabStrip.childCount) {
        tabStrip.getChildAt(i).setOnTouchListener { v, event -> true }
    }
}

override fun buttonClicked(view: View) {
    viewpager.currentItem = 2
}
fun selectIndex(index: Int) {
    viewpager.currentItem = index
}
override fun onBackPressed() {
    val currentPos = viewpager.currentItem
    if (currentPos != 0) {
        viewpager.currentItem = 0
    } else {
        super.onBackPressed()
    }
}
}

**And a code for my Fragment**

 class MyFragment1 : Fragment() {
private  var click: buttonClick? = null
interface buttonClick {
    fun buttonClicked(view: View)
}
var currentPage: Int = 0

override fun onCreateView(inflater: LayoutInflater, container: ViewGroup?, savedInstanceState: Bundle?): View? {
    val view: View = inflater.inflate(R.layout.fragment_my_fragment1, container, false)
    val btn: Button = view?.findViewById(R.id.btn_next)
    btn.setOnClickListener {
        Toast.makeText(context, "test", Toast.LENGTH_LONG).show()
        click?.buttonClicked(it)
    }
    return view
}

}

Answer 1

您是否初始化了click变量？

private var click: buttonClick? = null
override fun onAttach(context: Context?) {
    super.onAttach(context)
    click = context as? buttonClick
}
override fun onDetach() {
    super.onDetach()
    click = null
}