我试图实现一个四选项卡ViewPager作为TabHost不支持滑动。这里的问题是,我在每个片段的OnCreateView和下一个片段的调用中都有一些异步调用,除了我在使用ViewPager时滑动到的调用。
然而,对于TabHost,情况并非如此。只从选定的选项卡进行调用。这是一个问题与ViewPager,我应该解决还是我使用错误的回调方法片段?下面是项目的部分代码:
public class MainActivity extends FragmentActivity implements TabHost.OnTabChangeListener, ViewPager.OnPageChangeListener {
private TabHost mTabHost;
private ViewPager mViewPager;
private HashMap<String, TabInfo> mapTabInfo = new HashMap<String, MainActivity.TabInfo>();
private PagerAdapter mPagerAdapter;
private class TabInfo {
private String tag;
private Class<?> clss;
private Bundle args;
private Fragment fragment;
TabInfo(String tag, Class<?> clazz, Bundle args) {
this.tag = tag;
this.clss = clazz;
this.args = args;
}
}
class TabFactory implements TabContentFactory {
private final Context mContext;
/**
* @param context
*/
public TabFactory(Context context) {
mContext = context;
}
public View createTabContent(String tag) {
View v = new View(mContext);
v.setMinimumWidth(0);
v.setMinimumHeight(0);
return v;
}
}
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
// Inflate the layout
setContentView(R.layout.activity_main);
// Initialise the TabHost
this.initialiseTabHost(savedInstanceState);
if (savedInstanceState != null) {
mTabHost.setCurrentTabByTag(savedInstanceState.getString("tab"));
}
// Intialise ViewPager
this.intialiseViewPager();
}
protected void onSaveInstanceState(Bundle outState) {
outState.putString("tab", mTabHost.getCurrentTabTag()); //save the tab selected
super.onSaveInstanceState(outState);
}
private void intialiseViewPager() {
List<Fragment> fragments = new Vector<Fragment>();
fragments.add(new ActivityFeedFragment());
fragments.add(new InboxFragment());
fragments.add(new TaskFragment());
fragments.add(new CalendarEventFragment());
this.mPagerAdapter = new PagerAdapter(super.getSupportFragmentManager(), fragments);
this.mViewPager = (ViewPager)super.findViewById(R.id.viewpager);
this.mViewPager.setAdapter(this.mPagerAdapter);
this.mViewPager.setOnPageChangeListener(this);
}
private void initialiseTabHost(Bundle args) {
mTabHost = (TabHost)findViewById(android.R.id.tabhost);
mTabHost.setup();
TabInfo tabInfo = null;
MainActivity.AddTab(this, this.mTabHost, this.mTabHost.newTabSpec("Tab1").setIndicator("Tab 1"), ( tabInfo = new TabInfo("Tab1", ActivityFeedFragment.class, args)));
this.mapTabInfo.put(tabInfo.tag, tabInfo);
MainActivity.AddTab(this, this.mTabHost, this.mTabHost.newTabSpec("Tab2").setIndicator("Tab 2"), ( tabInfo = new TabInfo("Tab2", InboxFragment.class, args)));
this.mapTabInfo.put(tabInfo.tag, tabInfo);
MainActivity.AddTab(this, this.mTabHost, this.mTabHost.newTabSpec("Tab3").setIndicator("Tab 3"), ( tabInfo = new TabInfo("Tab3", TaskFragment.class, args)));
this.mapTabInfo.put(tabInfo.tag, tabInfo);
MainActivity.AddTab(this, this.mTabHost, this.mTabHost.newTabSpec("Tab4").setIndicator("Tab 4"), ( tabInfo = new TabInfo("Tab4", CalendarEventFragment.class, args)));
this.mapTabInfo.put(tabInfo.tag, tabInfo);
mTabHost.setOnTabChangedListener(this);
}
private static void AddTab(MainActivity activity, TabHost tabHost, TabHost.TabSpec tabSpec, TabInfo tabInfo) {
// Attach a Tab view factory to the spec
tabSpec.setContent(activity.new TabFactory(activity));
tabHost.addTab(tabSpec);
}
public void onTabChanged(String tag) {
int pos = this.mTabHost.getCurrentTab();
this.mViewPager.setCurrentItem(pos, true);
}
@Override
public void onPageScrolled(int position, float positionOffset,
int positionOffsetPixels) {
// TODO Auto-generated method stub
}
@Override
public void onPageSelected(int position) {
// TODO Auto-generated method stub
this.mTabHost.setCurrentTab(position);
}
@Override
public void onPageScrollStateChanged(int state) {
// TODO Auto-generated method stub
}
}
还有,这是我使用的适配器
public class PagerAdapter extends FragmentStatePagerAdapter {
private List<Fragment> fragments;
public PagerAdapter(FragmentManager fm, List<Fragment> fragments) {
super(fm);
this.fragments = fragments;
}
@Override
public Fragment getItem(int position) {
return this.fragments.get(position);
}
@Override
public int getCount() {
return this.fragments.size();
}
}
如果有任何关于在TabHost中启用滑动手势的建议,我也愿意尝试。
默认情况下,ViewPager
在当前页面之外创建并保留一个页面,如果您不希望,您可以将ViewPager
的setOffscreenPageLimit
改为0
viewPager.setOffscreenPageLimit(0);
,
另一种解决方案是setOnPageChangeListener
到viewpage,并在片段选择
private static class CustomOnPageChangeListener extends SimpleOnPageChangeListener
{
@Override
public void onPageSelected(int position)
{
switch(position){
case 1:
FirstFragment fragment1 = (FirstFragment) = FirstFragment.getInstance();
fragment1.startAsyncProcess();
break;
case 2:
SecondFragment fragment2 = (SecondFragment) = SecondFragment.getInstance();
fragment2.startAsyncProcess();
break;
}
super.onPageSelected(position);
}
}
...
viewPager.setOnPageChangeListener(new CustomOnPageChangeListener());
ViewPager除了加载当前片段外,还加载上一个和下一个片段,以提供流畅的用户体验。因此,我们的异步任务从其他片段被调用。
我建议你做的是在每个片段中保持公共静态布尔变量,在你的OnPageSelected方法中你可以设置这些变量。
然后在每个方法的onResume方法中检查该变量的值是否为真,然后只执行asynctask。
如果你不喜欢静态变量,那么使用片段管理器访问你的片段,并设置布尔值