Android-ViewPager(翻页控件)
ViewPager(翻页控件)
ViewPager是android扩展包v4包中的类，这个类可以让用户左右切换当前的view
1.ViewPager类直接继承了ViewGroup类，所有它是一个容器类，可以在其中添加其他的view类。
2.ViewPager类需要一个PagerAdapter适配器类给它提供数据。
3.ViewPager经常和Fragment一起使用，并且提供了专门的FragmentPagerAdapter和FragmentStatePagerAdapter类供Fragment中的ViewPager使用。
ViewPager经常用来连接Fragment，它很方便管理每个页面的生命周期，使用ViewPager管理Fragment是标准的适配器实现。最常用的实现一般有FragmentPagerAdapter和FragmentStatePagerAdapte
实现一个最基本的PagerAdapter,《必须实现四个方法》，在代码里有注释
public class AdapterViewpager extends PagerAdapter {
private List mViewList;
public AdapterViewpager(List mViewList) {
this.mViewList = mViewList;
}
@Override
public int getCount() {//必须实现
return mViewList.size();
}
@Override
public boolean isViewFromObject(View view, Object object) {//必须实现
return view == object;
}
@Override
public Object instantiateItem(ViewGroup container, int position) {//必须实现，实例化
container.addView(mViewList.get(position));
return mViewList.get(position);
}
@Override
public void destroyItem(ViewGroup container, int position, Object object) {//必须实现，销毁
container.removeView(mViewList.get(position));
}
}
实现一个最基本的FragmentPagerAdapter
public class AdapterFragment extends FragmentPagerAdapter {
private List mFragments;
public AdapterFragment(FragmentManager fm, List mFragments) {
super(fm);
this.mFragments = mFragments;
}
@Override
public Fragment getItem(int position) {//必须实现
return mFragments.get(position);
}
@Override
public int getCount() {//必须实现
return mFragments.size();
}
@Override
public CharSequence getPageTitle(int position) {//选择性实现
return mFragments.get(position).getClass().getSimpleName();
}
}
两个适配器的源码
FragmentStatePagerAdapter
@Override
public Object instantiateItem(ViewGroup container, int position) {
// If we already have this item instantiated, there is nothing
// to do. This can happen when we are restoring the entire pager
// from its saved state, where the fragment manager has already
// taken care of restoring the fragments we previously had instantiated.
if (mFragments.size() > position) {
Fragment f = mFragments.get(position);//fragment被释放后这里得到的null值
if (f != null) {
return f;
}
}
if (mCurTransaction == null) {
mCurTransaction = mFragmentManager.beginTransaction();
}
Fragment fragment = getItem(position);//fragment被释放后或者是初次进入页面拿到新的Fragment实例
if (DEBUG) Log.v(TAG, "Adding item #" + position + ": f=" + fragment);
if (mSavedState.size() > position) {
Fragment.SavedState fss = mSavedState.get(position);
if (fss != null) {
fragment.setInitialSavedState(fss);
}
}
while (mFragments.size() <= position) {
mFragments.add(null);
}
fragment.setMenuVisibility(false);
fragment.setUserVisibleHint(false);
mFragments.set(position, fragment);
mCurTransaction.add(container.getId(), fragment);//新的Fragment实例 是add上去的
return fragment;
}
@Override
public void destroyItem(ViewGroup container, int position, Object object) {
Fragment fragment = (Fragment) object;
if (mCurTransaction == null) {
mCurTransaction = mFragmentManager.beginTransaction();
}
if (DEBUG) Log.v(TAG, "Removing item #" + position + ": f=" + object
+ " v=" + ((Fragment)object).getView());
while (mSavedState.size() <= position) {
mSavedState.add(null);
}
mSavedState.set(position, fragment.isAdded()
? mFragmentManager.saveFragmentInstanceState(fragment) : null);
mFragments.set(position, null);//真正释放了fragment实例
mCurTransaction.remove(fragment);
}
FragmentPagerAdapter
@Override
public Object instantiateItem(ViewGroup container, int position) {
if (mCurTransaction == null) {
mCurTransaction = mFragmentManager.beginTransaction();
}
final long itemId = getItemId(position);
// Do we already have this fragment?
String name = makeFragmentName(container.getId(), itemId);
Fragment fragment = mFragmentManager.findFragmentByTag(name);
if (fragment != null) {
if (DEBUG) Log.v(TAG, "Attaching item #" + itemId + ": f=" + fragment);
mCurTransaction.attach(fragment);//因为fragment实例没有被真正释放，所以可以直接attach效率高
} else {
fragment = getItem(position);//初始化页面的时候拿到fragment的实例
if (DEBUG) Log.v(TAG, "Adding item #" + itemId + ": f=" + fragment);
mCurTransaction.add(container.getId(), fragment,
makeFragmentName(container.getId(), itemId));//add上去
}
if (fragment != mCurrentPrimaryItem) {
fragment.setMenuVisibility(false);
fragment.setUserVisibleHint(false);
}
return fragment;
}
@Override
public void destroyItem(ViewGroup container, int position, Object object) {
if (mCurTransaction == null) {
mCurTransaction = mFragmentManager.beginTransaction();
}
if (DEBUG) Log.v(TAG, “Detaching item #” + getItemId(position) + “: f=” + object
+ " v=" + ((Fragment)object).getView());
mCurTransaction.detach((Fragment)object);//并没有真正释放fragment对象只是detach
}
FragmentPagerAdapter适用于页面比较少的情况，FragmentStatePagerAdapter适用于页面比较多的情况
ViewPager的翻页动画
public class DepthPageTransformer implements ViewPager.PageTransformer {
private static final float MIN_SCALE = 0.75f;
public void transformPage(View view, float position) {
Log.d(“DepthPageTransformer”, view.getTag() + " , " + position + “”);
int pageWidth = view.getWidth();
if (position < -1) { // [-Infinity,-1)
// This page is way off-screen to the left.
view.setAlpha(0);
} else if (position <= 0) { // [-1,0]
// Use the default slide transition when moving to the left page
view.setAlpha(1);
view.setTranslationX(0);
view.setScaleX(1);
view.setScaleY(1);
} else if (position <= 1) { // (0,1]
// Fade the page out.
view.setAlpha(1 - position);
// Counteract the default slide transition
view.setTranslationX(pageWidth * -position);
// Scale the page down (between MIN_SCALE and 1)
float scaleFactor = MIN_SCALE
+ (1 - MIN_SCALE) * (1 - Math.abs(position));
view.setScaleX(scaleFactor);
view.setScaleY(scaleFactor);
} else { // (1,+Infinity]
// This page is way off-screen to the right.
view.setAlpha(0);
}
}
}
public class ZoomOutPageTransformer implements ViewPager.PageTransformer {
private static final float MIN_SCALE = 0.85f;
private static final float MIN_ALPHA = 0.5f;
@SuppressLint(“NewApi”)
public void transformPage(View view, float position) {
int pageWidth = view.getWidth();
int pageHeight = view.getHeight();
Log.e("TAG", view + " , " + position + "");
if (position < -1) { // [-Infinity,-1)
// This page is way off-screen to the left.
view.setAlpha(0);
} else if (position <= 1)
{ // [-1,1]
// Modify the default slide transition to shrink the page as well
float scaleFactor = Math.max(MIN_SCALE, 1 - Math.abs(position));
float vertMargin = pageHeight * (1 - scaleFactor) / 2;
float horzMargin = pageWidth * (1 - scaleFactor) / 2;
if (position < 0) {
view.setTranslationX(horzMargin - vertMargin / 2);
} else {
view.setTranslationX(-horzMargin + vertMargin / 2);
}
// Scale the page down (between MIN_SCALE and 1)
view.setScaleX(scaleFactor);
view.setScaleY(scaleFactor);
// Fade the page relative to its size.
view.setAlpha(MIN_ALPHA + (scaleFactor - MIN_SCALE)
/ (1 - MIN_SCALE) * (1 - MIN_ALPHA));
} else { // (1,+Infinity]
// This page is way off-screen to the right.
view.setAlpha(0);
}
}
}
简化ViewPager的使用
PagerAdapter简化
public class QuickPageAdapter extends PagerAdapter {
private List mList;
public QuickPageAdapter(List mList) {
this.mList = mList;
}
@Override
public int getCount() {
return mList.size();
}
@Override
public boolean isViewFromObject(View view, Object object) {
return object == view;
}
@Override
public Object instantiateItem(ViewGroup container, int position) {
container.addView(mList.get(position));
return mList.get(position);
}
@Override
public void destroyItem(ViewGroup container, int position, Object object) {
container.removeView(mList.get(position));
}
}
使用它，这样不用每次都写个适配器
List views = new ArrayList<>();
…
mViewPager.setAdapter(new QuickPageAdapter(views));
- FragmentPagerAdapter简化
public class QuickFragmentPageAdapter<T extends Fragment> extends FragmentPagerAdapter {
private List<T> mList;
private String[] mStrings;
/**
* @param fm
* @param list
* @param titles PageTitles
*/
public QuickFragmentPageAdapter(FragmentManager fm, List<T> list, String[] titles) {
super(fm);
mList = list;
mStrings = titles;
}
@Override
public Fragment getItem(int position) {
return mList.get(position);
}
@Override
public int getCount() {
return mList.size();
}
@Override
public CharSequence getPageTitle(int position) {
return mStrings == null ? super.getPageTitle(position) : mStrings[position];
}
}
ViewPager结合第三方库实现小圆点指示器效果
public void setViewPager(ViewPager viewPager) {
mViewpager = viewPager;
if (mViewpager != null && mViewpager.getAdapter() != null) {
mLastPosition = -1;
createIndicators();
mViewpager.removeOnPageChangeListener(mInternalPageChangeListener);
mViewpager.addOnPageChangeListener(mInternalPageChangeListener);//绑定上内部实现的PageChangeListener
mInternalPageChangeListener.onPageSelected(mViewpager.getCurrentItem());
}
}
private final OnPageChangeListener mInternalPageChangeListener = new OnPageChangeListener() {
@Override
public void onPageScrolled(int position, float positionOffset, int positionOffsetPixels) {
}
@Override public void onPageSelected(int position) {//这里是动画的核心
if (mViewpager.getAdapter() == null || mViewpager.getAdapter().getCount() <= 0) {
return;
}
if (mAnimatorIn.isRunning()) {
mAnimatorIn.end();
mAnimatorIn.cancel();
}
if (mAnimatorOut.isRunning()) {
mAnimatorOut.end();
mAnimatorOut.cancel();
}
View currentIndicator;
if (mLastPosition >= 0 && (currentIndicator = getChildAt(mLastPosition)) != null) {//页面离开屏幕时指示器动画
currentIndicator.setBackgroundResource(mIndicatorUnselectedBackgroundResId);
mAnimatorIn.setTarget(currentIndicator);
mAnimatorIn.start();
}
View selectedIndicator = getChildAt(position);
if (selectedIndicator != null) {//页面进入屏幕时指示器动画
selectedIndicator.setBackgroundResource(mIndicatorBackgroundResId);
mAnimatorOut.setTarget(selectedIndicator);
mAnimatorOut.start();
}
mLastPosition = position;
}
@Override public void onPageScrollStateChanged(int state) {
}
};