TabLayout踩坑傳奇
今天中午休息的時候鸟款，同事研究起了MD顿乒，對!就是傳說中的Material design刷允。他想要寫一個MD主題的app，可是遇到個關于TabLayout的問題恩掷。本來想做出的效果是這個樣子的倡鲸。
想象中的效果
img
title不見了！！
我好奇的過去瞅瞅病袄，看了看凌外。沒有問題啊佑女。
private void initViews() {
tabLayout.addTab(tabLayout.newTab().setText("ftm1"));
tabLayout.addTab(tabLayout.newTab().setText("ftm2"));
viewPager.setAdapter(new FragmentStatePagerAdapter(getSupportFragmentManager()) {
@Override
public Fragment getItem(int position) {
return fragments.get(position);
}
@Override
public int getCount() {
return fragments == null ? 0 : fragments.size();
}
});
tabLayout.setupWithViewPager(viewPager);
}
設置了tab也加上了setupWithViewPager方法啊奥秆。查閱了一番資料，是調用setupWithViewPager方法將所有tab清除了傅是。不說廢話了上代碼匪燕，看下是怎么移除tab的：
public void setupWithViewPager(@Nullable final ViewPager viewPager, boolean autoRefresh) {
setupWithViewPager(viewPager, autoRefresh, false);
}
private void setupWithViewPager(@Nullable final ViewPager viewPager, boolean autoRefresh,
boolean implicitSetup) {
if (mViewPager != null) {
// If we've already been setup with a ViewPager, remove us from it
if (mPageChangeListener != null) {
mViewPager.removeOnPageChangeListener(mPageChangeListener);
}
if (mAdapterChangeListener != null) {
mViewPager.removeOnAdapterChangeListener(mAdapterChangeListener);
}
}
if (mCurrentVpSelectedListener != null) {
// If we already have a tab selected listener for the ViewPager, remove it
removeOnTabSelectedListener(mCurrentVpSelectedListener);
mCurrentVpSelectedListener = null;
}
if (viewPager != null) {
mViewPager = viewPager;
// Add our custom OnPageChangeListener to the ViewPager
if (mPageChangeListener == null) {
mPageChangeListener = new TabLayoutOnPageChangeListener(this);
}
mPageChangeListener.reset();
viewPager.addOnPageChangeListener(mPageChangeListener);
// Now we'll add a tab selected listener to set ViewPager's current item
mCurrentVpSelectedListener = new ViewPagerOnTabSelectedListener(viewPager);
addOnTabSelectedListener(mCurrentVpSelectedListener);
final PagerAdapter adapter = viewPager.getAdapter();
if (adapter != null) {
// Now we'll populate ourselves from the pager adapter, adding an observer if
// autoRefresh is enabled
setPagerAdapter(adapter, autoRefresh);
}
// Add a listener so that we're notified of any adapter changes
if (mAdapterChangeListener == null) {
mAdapterChangeListener = new AdapterChangeListener();
}
mAdapterChangeListener.setAutoRefresh(autoRefresh);
viewPager.addOnAdapterChangeListener(mAdapterChangeListener);
// Now update the scroll position to match the ViewPager's current item
setScrollPosition(viewPager.getCurrentItem(), 0f, true);
} else {
// We've been given a null ViewPager so we need to clear out the internal state,
// listeners and observers
mViewPager = null;
setPagerAdapter(null, false);
}
mSetupViewPagerImplicitly = implicitSetup;
}
在調用setupWithViewPager會調用到setPagerAdapter(null, false)看下這個方法里發(fā)生了什么吧。
void setPagerAdapter(@Nullable final PagerAdapter adapter, final boolean addObserver) {
if (mPagerAdapter != null && mPagerAdapterObserver != null) {
// If we already have a PagerAdapter, unregister our observer
mPagerAdapter.unregisterDataSetObserver(mPagerAdapterObserver);
}
mPagerAdapter = adapter;
if (addObserver && adapter != null) {
// Register our observer on the new adapter
if (mPagerAdapterObserver == null) {
mPagerAdapterObserver = new PagerAdapterObserver();
}
adapter.registerDataSetObserver(mPagerAdapterObserver);
}
// Finally make sure we reflect the new adapter
populateFromPagerAdapter();
}
在setPagerAdapter里又調用了populateFromPagerAdapter（）,點開這個方法：
void populateFromPagerAdapter() {
removeAllTabs();
if (mPagerAdapter != null) {
final int adapterCount = mPagerAdapter.getCount();
for (int i = 0; i < adapterCount; i++) {
addTab(newTab().setText(mPagerAdapter.getPageTitle(i)), false);
}
// Make sure we reflect the currently set ViewPager item
if (mViewPager != null && adapterCount > 0) {
final int curItem = mViewPager.getCurrentItem();
if (curItem != getSelectedTabPosition() && curItem < getTabCount()) {
selectTab(getTabAt(curItem));
}
}
}
}
這個populateFromPagerAdapter（）方法里將tabLayout里所有的tab移除了喧笔，又重新new了tab帽驯。所以原來add的tab沒有顯示，那怎么解決呢书闸？再仔細看這個方法尼变，對沒錯，addTab(newTab().setText(mPagerAdapter.getPageTitle(i)), false);在重新new tab的過程中有重新傳title浆劲，這個值是通過mPagerAdapter.getPageTitle(i))獲取的嫌术，那么我們在ViewPager的FragmentPagerAdapter重寫getPageTitle方法哀澈，默認的PagerAdapter返回的是null。
public CharSequence getPageTitle(int position) {
return null;
}
現(xiàn)在我們把代碼修改成下面的樣子：
private void initViews() {
viewPager.setAdapter(new FragmentPagerAdapter(getSupportFragmentManager()) {
@Override
public Fragment getItem(int position) {
return fragments.get(position);
}
@Override
public int getCount() {
return fragments == null ? 0 : fragments.size();
}
@Override
public CharSequence getPageTitle(int position) {
return titles.get(position);
}
});
tabLayout.setupWithViewPager(viewPager);
}
O(∩_∩)O哈哈~現(xiàn)在就是我們想要的樣子啦度气。割按。。我寫的Demo源碼
