The generated apk.debug does not work on a cell phone [closed]

I am new to the group, I have a problem with making a slider functional (intro) on the cell phone. everything comes out ok when I give it Run, but when I install the application to verify, a warning comes out "unfortunately, test1 has stopped". Thank you very much

I attached the sync here is the gradle, I do not know if it will be the problem for the sdk.

It's the code of the intro. If any information you want, I can provide it. Thanks

 private ViewPager viewPager;
private LinearLayout layoutDot;
private TextView[]dotstv;
private int [] layouts;
private Button btnSkip;
private Button btnNext;
private MyPagerAdapter pagerAdapter;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    //aqui conecta con el xml



  setContentView(R.layout.activity_main);

    viewPager= findViewById(R.id.view_pager);
    layoutDot=findViewById(R.id.dotLayout);
    btnNext=findViewById(R.id.btn_next);
    btnSkip=findViewById(R.id.btn_skip);

    //when user press skip, start main activity
    btnSkip.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View view) {

            startMainActivity ();

        }
    });

    btnSkip.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View view) {
            int currentPage = viewPager.getCurrentItem()+1;
            if (currentPage < layouts.length){
                //move to next page

                viewPager.setCurrentItem(currentPage);
            }else {
                startMainActivity();
            }

        }
    });







    layouts = new int[] {R.layout.slide_1, R.layout.slide_2, R.layout.slide_3, R.layout.slide_4};
    pagerAdapter = new MyPagerAdapter(layouts,getApplicationContext());
    viewPager.setAdapter(pagerAdapter);


    viewPager.addOnPageChangeListener(new ViewPager.OnPageChangeListener() {
        @Override
        public void onPageScrolled(int i, float v, int i1) {

        }

        @Override
        public void onPageSelected(int position) {
            if (position == layouts.length - 1) {
                btnNext.setText("START");
                btnSkip.setVisibility(View.GONE);
            }else {
                btnNext.setText("NEXT");
                btnSkip.setVisibility(View.VISIBLE);
            }

            setDotStatus(position);
        }

        @Override
        public void onPageScrollStateChanged(int i) {

        }
    });
    setDotStatus(0);

}

private boolean isFirstTimeStartApp (){
    SharedPreferences ref = getApplicationContext().getSharedPreferences("IntroSlider", Context.MODE_PRIVATE );
    return ref.getBoolean( "FirstTimeStartFlag",true );

}
private void setFirstTimeStatus (boolean stt) {
    SharedPreferences ref = getApplicationContext().getSharedPreferences("IntroSlider", Context.MODE_PRIVATE);
    SharedPreferences.Editor editor = ref.edit();
    editor.putBoolean("FirstTimeStarting", stt);
    editor.commit();
}
private void setDotStatus (int page){
    layoutDot.removeAllViews();
    dotstv=new TextView[layouts.length];
    for (int i = 0; i < dotstv.length; i++){
        dotstv[i] = new TextView(this);
        dotstv[i].setText(Html.fromHtml("&#8226;"));
        dotstv[i].setTextSize(30);
        dotstv[i].setTextColor(Color.parseColor("#a9b4bb"));
        layoutDot.addView(dotstv[i]);
    }

    //set current to Dot

    if (dotstv.length > 0){
        dotstv[page].setTextColor(Color.parseColor("#ffffff"));
    }
}

private void startMainActivity () {
    //true when mainactivity start
    setFirstTimeStatus (false);
    startActivity(new Intent(WelcomeActivity.this, MainActivity.class));
    finish();

}

private void SetStatusBarTransparent () {

    if(Build.VERSION.SDK_INT >=21){
        getWindow().getDecorView().setSystemUiVisibility(View.SYSTEM_UI_FLAG_LAYOUT_STABLE|View.SYSTEM_UI_FLAG_LAYOUT_FULLSCREEN);
       Window window = getWindow();
        window.addFlags(WindowManager.LayoutParams.FLAG_DRAWS_SYSTEM_BAR_BACKGROUNDS);
        window.setStatusBarColor(Color.TRANSPARENT);


    }



}

}