TabLayout不正常显示标签->TabLayout和ViewPager的恩恩怨怨

问题

近日用了下android.support.design.widget.TabLayout和ViewPager发现标签不显示

tabLayout = (TabLayout) findViewById(R.id.tl_recharge);
tabLayout.addTab(tabLayout.newTab().setText("账户充值"));
tabLayout.addTab(tabLayout.newTab().setText("卡卷充值"));
tabLayout.setupWithViewPager(viewPager);

解决方案

@Override
public CharSequence getPageTitle(int position) {
return tableTitle[position];
}


删除addTab 直接在getPageTitle返回名字即可

TabLayout的代码就这样。发现无法显示，这种奇怪的问题我的解决办法是，逐行注释找问题

发现是setupWithViewPager导致问题，我把setupWithViewPager的代码注释后，发现可以正常显示标签了

但是滑动后标签不会有任何变动

我们来看看setupWithViewPager中做了什么

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;
}

代码基本无问题，最后走到setPagerAdapter中，继续追踪setPagerAdapter

private 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();
}

发现也无问题，最后转到populateFromPagerAdapter

private 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));
}
}
}
}

问题就出在这里，也就是说调用setupWithViewPager后会删除所有的tab

并且使用viewpage的adapter，自动设置tab为viewpage.getPageTitle()的字符而getPageTitle默认实现返回的是null

所以会出现不现实标签的情况

那这就好办了。也就是说TabLayout和ViewPage使用的时候不用设置tab，直接重写ViewPager的getPageTitle来设置标签的显示