Android ImageButton OnTouchListener无法正常工作

Question

Okay, there's a weird thing happening in me. I have an ImageButton named tab_btn from other layout which I imported and set onTouchListener which is working.

package com.xx

import kotlinx.android.synthetic.main.tab_btn_layout.*

import kotlinx.android.synthetic.main.btnNext_layout.*

    class EventDetails : AppCompatActivity() {
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_event_details)

        tab_btn.setOnTouchListener(object  : View.OnTouchListener {
            override fun onTouch(view: View?, event: MotionEvent?): Boolean {
                if (event!!.action ==  MotionEvent.ACTION_DOWN) {
                    val icon: Drawable = ContextCompat.getDrawable(applicationContext, R.drawable.talk_bt_tab)
                    icon.setColorFilter(Color.GRAY,PorterDuff.Mode.MULTIPLY)
                    tab_btn.setImageDrawable(icon)
                }else if (event!!.action ==  MotionEvent.ACTION_UP) {
                    tab_btn.clearColorFilter()
                }

                return true
            }
        })

        btnNext.setOnTouchListener(object : View.OnTouchListener {
            override fun onTouch(p0: View?, ev: MotionEvent?): Boolean {
                if (ev!!.action == MotionEvent.ACTION_DOWN){
                    val icon: Drawable = ContextCompat.getDrawable(applicationContext, R.drawable.layer_bt_next)
                    icon.setColorFilter(Color.GRAY,PorterDuff.Mode.MULTIPLY)
                    btnNext.setImageDrawable(icon)
                }else if(ev!!.action == MotionEvent.ACTION_UP){
                    btnNext.clearColorFilter()
                }

                return true
            }
        })
    }
}

and below that I have another ImageButton from other layout named btnNext. I set the same OnTouchListener on it. But it gives me error .

And btnNext gives me error:

Attempt to invoke virtual method 'void android.widget.ImageButton.setOnTouchListener(android.view.View$OnTouchListener)' on a null object reference

note: I have imported both layout of the Image button. tab_btn is working but btnNext is not working.

Answer 1

Okay, I solved my own problem.

The real suspect is that my btnNext is in the fragment(viewpager) which I have to inflate first the rootview in oncreateview method.

note: you cannot access the element of the fragment without inflating it.

here's ma code:

override fun onCreateView(inflater: LayoutInflater?, container: ViewGroup?, savedInstanceState: Bundle?): View {
    val rootView = inflater!!.inflate(R.layout.btnNext_layout, container, false)

    var next : ImageButton = rootView.findViewById(R.id.btnNext)
    next.setOnTouchListener(object : View.OnTouchListener {
        override fun onTouch(p0: View?, ev: MotionEvent?): Boolean {
            if (ev!!.action == MotionEvent.ACTION_DOWN){
                val icon: Drawable = ContextCompat.getDrawable(activity.applicationContext, R.drawable.layer_bt_next)
                icon.setColorFilter(Color.GRAY, PorterDuff.Mode.MULTIPLY)
                btn_next.setImageDrawable(icon)
            }else if (ev!!.action == MotionEvent.ACTION_UP){
                val icon: Drawable = ContextCompat.getDrawable(activity.applicationContext, R.drawable.layer_bt_next)
                icon.setColorFilter(Color.WHITE, PorterDuff.Mode.MULTIPLY)
                btn_next.setImageDrawable(icon)
            }

            return true
        }
    })
}