为 ViewPager 的特定页面设置动画

Question

I used the following code to give the ViewPager a fade in and fade out effect:

//define view pager and set adapter:  
... 
  @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        setContentView(R.layout.activity_startup_preference);
        //we're not using the layout natively, but using Fragment's layout
        //but setContentView is required -> it is accessed by : R.id.startPref_pager


        StartPrefPagerAdapter prefPagerAdapter =
                new StartPrefPagerAdapter(getSupportFragmentManager());

        final ViewPager StartPref_Viewpager = findViewById(R.id.startPref_pager);
        StartPref_Viewpager.setAdapter(prefPagerAdapter);  
...
... 




//set the animation with:  
StartPref_Viewpager.setPageTransformer(false, new ViewPager.PageTransformer() {
            @Override
            public void transformPage(@NonNull View page, float position) {

            DisplayMetrics displayMetrics = new DisplayMetrics();
            getWindowManager().getDefaultDisplay().getMetrics(displayMetrics);

            page.setScaleX(0.5f);
            page.setScaleY(0.5f);
            page.setAlpha(0f);
            page.setVisibility(View.VISIBLE);

            page.animate().alpha(1f).setDuration(1000);
            page.animate().scaleX(1f).setDuration(500);
            page.animate().scaleY(1f).setDuration(500);

        }
    });  

...

But, I'd like the animation to be applied starting from the second page of the ViewPager and not from the first page itself. How can I achieve this?

Answer 1

I have not done it practically but it seems from your code that applying condition on base of position , it should be possible, like below.

StartPref_Viewpager.setPageTransformer(false, new ViewPager.PageTransformer() {
            @Override
            public void transformPage(@NonNull View page, float position) {

            //this is the viewpager page position
            if(position!=0)
            {

            DisplayMetrics displayMetrics = new DisplayMetrics();
            getWindowManager().getDefaultDisplay().getMetrics(displayMetrics);

            page.setScaleX(0.5f);
            page.setScaleY(0.5f);
            page.setAlpha(0f);
            page.setVisibility(View.VISIBLE);

            page.animate().alpha(1f).setDuration(1000);
            page.animate().scaleX(1f).setDuration(500);
            page.animate().scaleY(1f).setDuration(500);

            }
        }
    });  

Answer 2

You can use a OnPageChangeListener to check the page number while scrolling, and act with the default PageTransformer for page 0, and your custom PageTransformer with other pages

StartPref_Viewpager.addOnPageChangeListener(new ViewPager.OnPageChangeListener() {
    @Override
    public void onPageScrolled(int position, float positionOffset, int positionOffsetPixels) {
        if (position == 0)
            StartPref_Viewpager.setPageTransformer(false, mDefaultPageTransformer);
        else
            StartPref_Viewpager.setPageTransformer(false, mPageTransformer);
    }

    @Override
    public void onPageSelected(int position) {
    }

    @Override
    public void onPageScrollStateChanged(int state) {
    }
});


ViewPager.PageTransformer mPageTransformer = new ViewPager.PageTransformer() {
    @Override
    public void transformPage(@NonNull View page, float position) {

        DisplayMetrics displayMetrics = new DisplayMetrics();
        getWindowManager().getDefaultDisplay().getMetrics(displayMetrics);

        page.setScaleX(0.5f);
        page.setScaleY(0.5f);
        page.setAlpha(0f);
        page.setVisibility(View.VISIBLE);

        page.animate().alpha(1f).setDuration(1000);
        page.animate().scaleX(1f).setDuration(500);
        page.animate().scaleY(1f).setDuration(500);

    }
};

ViewPager.PageTransformer mDefaultPageTransformer = new ViewPager.PageTransformer() {
    @Override
    public void transformPage(@NonNull View page, float position) {

    }
};