Android resource not found exception onPageScrolled

问题

I got the following exception when trying to change the background of pages inside a ViewPager in the onPageScrolled method. I have edited the question in order to make it more clear.

android.content.res.Resources$NotFoundException: Resource ID #0x0
                                                                            at android.content.res.Resources.getValue(Resources.java:1245)
                                                                            at android.content.res.Resources.getColor(Resources.java:899)
                                                                            at android.support.v4.content.ContextCompat.getColor(ContextCompat.java:413)
                                                                            at com.noel.material_onboarding.OnboardingActivity.color(OnboardingActivity.java:113)
                                                                            at com.noel.material_onboarding.OnboardingActivity.access$200(OnboardingActivity.java:29)
                                                                            at com.noel.material_onboarding.OnboardingActivity$1.onPageScrolled(OnboardingActivity.java:86)

First I create the slider objects, this includes setting up the background color:

addSlide(new SlideFragmentBuilder()
            .description("This is a test")
            .backgroundColor(R.color.colorPrimary)
            .build());
    addSlide(new SlideFragmentBuilder()
            .description("This is a test 2")
            .backgroundColor(R.color.green)
            .build());
    addSlide(new SlideFragmentBuilder()
            .description("This is a test 3")
            .backgroundColor(R.color.orange)
            .build());
    addSlide(new SlideFragmentBuilder()
            .description("This is a test 4")
            .backgroundColor(R.color.orange)
            .build());

Here's a link to the SlideFragmentBuilder on github and the Fragment class itself

Here's my onPageScrolled method:

 mViewPager.addOnPageChangeListener(new ViewPager.OnPageChangeListener() {
        @Override
        public void onPageScrolled(int position, float positionOffset, int positionOffsetPixels) {
           int colorUpdate = (Integer) evaluator.evaluate(positionOffset,  color(mOnboardingAdapter.getItem(position).backgroundColor()), color(mOnboardingAdapter.getItem(position + 1).backgroundColor()));
            mViewPager.setBackgroundColor(colorUpdate);


            if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.LOLLIPOP) {
                Window window = getWindow();
                window.addFlags(WindowManager.LayoutParams.FLAG_DRAWS_SYSTEM_BAR_BACKGROUNDS);
                window.setStatusBarColor(colorUpdate);
            }
        }

        @Override
        public void onPageSelected(int position) {
            btnFinish.setVisibility(position == mOnboardingAdapter.getLastItemPosition() ? View.VISIBLE : View.GONE);
            btnNext.setVisibility(position == mOnboardingAdapter.getLastItemPosition() ? View.GONE : View.VISIBLE);

        }

        @Override
        public void onPageScrollStateChanged(int state) {

        }
    });

The color() method that is used

private int color(@ColorRes int color){
    return ContextCompat.getColor(this, color);

}

Basically, I just need the background of one page to fade in as the user swipes to another page.

回答1:

Ok, so I went through the docs and found an important thing I was missing out on:

int: Position index of the first page currently being displayed. Page position+1 will be visible if positionOffset is nonzero.

Basically the app was crushing on the second screen after the positionOffset went back to zero. See this is how it works: On the first screen the positionOffset is zero and the position of the page is also zero, however position + 1 is not available since the positionOffset is zero. I solved this by adding the following statement to check whether the Offset is zero or not:

positionOffset != 0.0 ? position + 1 : position

This is how the onPageScrolled method looks like:

        @Override
        public void onPageScrolled(int position, float positionOffset, int positionOffsetPixels) {

           int colorUpdate = (Integer) evaluator.evaluate(positionOffset,  color(mOnboardingAdapter.getItem(position).backgroundColor()), color(mOnboardingAdapter.getItem(positionOffset != 0.0 ? position + 1 : position).backgroundColor()));
            mViewPager.setBackgroundColor(colorUpdate);


            if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.LOLLIPOP) {
                Window window = getWindow();
                window.addFlags(WindowManager.LayoutParams.FLAG_DRAWS_SYSTEM_BAR_BACKGROUNDS);
                window.setStatusBarColor(colorUpdate);
            }
        }

回答2:

try to use this

Color.parseColor(mOnboardingAdapter.getItem(position + 1));

and don't forgot to remove integer cast

(Integer)

And i think that

mOnboardingAdapter.getItem(position + 1)

is a null value (not initialized)

来源：https://stackoverflow.com/questions/40641557/android-resource-not-found-exception-onpagescrolled