为了专注于这个问题,我以下面的测试应用程序结束,它包含一个活动和两个连接到 FragmentStatePagerAdapter / ViewPager 的片段。我也有 Runnable 和 Handler 每秒打印 getView() (在生产版本中,它用于在片段的 TextView 中显示时间)。
当我启动应用程序时,getView() 可能显示几个空值(我想是由于片段生命周期),然后我得到一些非空值,这没关系...
但是,如果我暂停并唤醒我的设备 LogCat 一直显示空值。
public class MainActivity extends SherlockFragmentActivity {
private SectionsPagerAdapter sectionsPagerAdapter = new SectionsPagerAdapter(getSupportFragmentManager());
private Fragment myFragment1 = new MyFragment1();
private Fragment myFragment2 = new MyFragment2();
private Handler handler = new Handler();
private Runnable timer;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
ViewPager viewPager = (ViewPager) findViewById(R.id.pager);
viewPager.setAdapter(sectionsPagerAdapter);
}
@Override
protected void onResume() {
super.onResume();
timer = new Runnable() {
public void run() {
System.out.println(myFragment1.getView()); // HERE getView gives null
handler.postDelayed(this, 1000); // refreshing every 1 sec
}
};
handler.removeCallbacks(timer);
handler.postDelayed(timer, 0);
}
@Override
protected void onPause() {
super.onPause();
handler.removeCallbacks(timer);
}
public class SectionsPagerAdapter extends FragmentStatePagerAdapter {
public SectionsPagerAdapter(FragmentManager fm) {
super(fm);
}
@Override
public Fragment getItem(int position) {
Fragment fragment;
if (position == 0) {
fragment = myFragment1;
} else {
fragment = myFragment2;
}
return fragment;
}
@Override
public int getCount() {
return 2;
}
@Override
public CharSequence getPageTitle(int position) {
switch (position) {
case 0:
return "Fragment 1";
case 1:
return "Fragment 2";
}
return null;
}
}
}
我的片段
public class MyFragment1 extends SherlockFragment {
private TextView textView2;
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
return inflater.inflate(R.layout.fragment_layout, container, false);
}
@Override
public void onActivityCreated(Bundle savedInstanceState) {
super.onActivityCreated(savedInstanceState);
((TextView) getView().findViewById(R.id.textView1)).setText("Fragment 1");
textView2 = (TextView) this.getView().findViewById(R.id.textView2);
}
public void updateTextView2(String text) {
textView2.setText(text);
}