问题
i am successfull in showing and hiding of appbar when swiping between tabs in tablayout. but now i want to animate this hiding and appearing of tab smoothly like we do in switching for the camera tab in whatsapp.
回答1:
The way to go about it is to translate the AppbarLayout using its translationY attribute in onPageScrolled() callback of the ViewPager's OnPageChangeListener interface using the AppbarLayout's bottom value.
mViewPager.addOnPageChangeListener(new OnPageChangeListener(){
@Override
public void onPageScrolled(int position, float positionOffset, int positionOffsetPixels) {
// get an instance of the appBarLayout This should probably be done at the activity level in its oncreate() method
/* example:
public ViewPager mViewPager;
public AppBarLayout appBar;
onCreate(...){
...
mViewPager = (ViewPager) findViewById(R.id.viewpager);
appBar = (AppBarLayout) findViewById(R.id.appbar);
mViewPager.addOnPageChangeListener(...);
...
}
*/
// set the position you want the app bar to be hidden on the ViewPager
int hideAppBarAtPosition = 0;
if (appBar != null) {
// get an instance of the bottom value of the appBar
float mBottom = (float) appBar.getBottom();
// going right offset changes from zero to one
if (position == hideAppBarAtPosition) {
// Translate the appBar up as the resideReveal slides into view
float y = (positionOffset * mBottom) - mBottom;
// Raise the appBar a little bit higher when it is no longer visible
if (y == -mBottom) {
float h = (float) appBar.getHeight();
if (mBottom < h) mBottom = h;
y = -mBottom - mBottom / 8f;
}
appBar.setTranslationY(y);
} else if (position == hideAppBarAtPosition - 1) {
// Translate the appBar up as the resideReveal slides into view
appBar.setTranslationY(-(positionOffset * mBottom));
} else if (appBar.getTranslationY() != 0f) {
// Reset translation of the appBar
appBar.setTranslationY(0f);
}
}
}
@Override
public void onPageSelected(int position) {
}
@Override
public void onPageScrollStateChanged(int state) {
}
});
If you need more ideas on how to implement it, view this open source project https://github.com/goody-h/ResidingTab
来源：https://stackoverflow.com/questions/49386012/android-animate-the-hiding-showing-of-toolbar-on-swiping-between-tabs-like-in-wh