(我想出了一个解决方案--请看下面答案部分我的帖子。)
在我的应用程序中,用户将从他的数据的单一视图开始。我想添加一个ViewPager并允许用户添加更多视图。我该怎么做?(我不想使用FragmentPagerAdapter.)
我已经读了无数的帖子和综述,但仍然遗漏了一些东西。我想我明白的是:
MainActivity创建ViewPager和PagerAdapter:
ViewPager pager = null;
MainPagerAdapter adapter = null;
public void onCreate (Bundle savedInstanceState)
{
super.onCreate (savedInstanceState);
pager = new ViewPager (this);
setContentView (pager);
adapter = new MainPagerAdapter();
pager.setAdapter (adapter);
View v0 = code_to_create_initial_view();
adapter.add (v0, 0);
}
使用PagerAdapter提供视图集。为此,我似乎需要添加和删除视图的方法,类似于这样的方法;显然,要告诉ViewPager的内容发生了变化,以及如何显示这些变化,还需要更多的内容:
class MainPagerAdapter extends PagerAdapter
{
// This holds all the currently displayable views, in order from left to right.
private ArrayList<View> views = new ArrayList<View>();
public void addView (View v, int position)
{
views.add (position, v);
}
public void removeView (int position)
{
views.remove (position);
}
}
此外,我需要实现以下vitual方法。我在这里迷路了--什么叫它们,它们应该做什么(好吧,getCount是显而易见的)?
public object instantiateItem (ViewGroup pager, int position);
public void destroyItem (ViewGroup, int, Object);
public int getCount ();
public boolean isViewFromObject (View, Object);
谢了。
在搞清楚哪些ViewPager方法是由ViewPager调用的,哪些是用于其他目的之后,我想出了一个解决方案。我在这里介绍它,因为我看到很多人都在纠结这个问题,而我没有看到任何其他相关的答案。
首先,这里是我的适配器;希望代码中的注释就足够了:
public class MainPagerAdapter extends PagerAdapter
{
// This holds all the currently displayable views, in order from left to right.
private ArrayList<View> views = new ArrayList<View>();
//-----------------------------------------------------------------------------
// Used by ViewPager. "Object" represents the page; tell the ViewPager where the
// page should be displayed, from left-to-right. If the page no longer exists,
// return POSITION_NONE.
@Override
public int getItemPosition (Object object)
{
int index = views.indexOf (object);
if (index == -1)
return POSITION_NONE;
else
return index;
}
//-----------------------------------------------------------------------------
// Used by ViewPager. Called when ViewPager needs a page to display; it is our job
// to add the page to the container, which is normally the ViewPager itself. Since
// all our pages are persistent, we simply retrieve it from our "views" ArrayList.
@Override
public Object instantiateItem (ViewGroup container, int position)
{
View v = views.get (position);
container.addView (v);
return v;
}
//-----------------------------------------------------------------------------
// Used by ViewPager. Called when ViewPager no longer needs a page to display; it
// is our job to remove the page from the container, which is normally the
// ViewPager itself. Since all our pages are persistent, we do nothing to the
// contents of our "views" ArrayList.
@Override
public void destroyItem (ViewGroup container, int position, Object object)
{
container.removeView (views.get (position));
}
//-----------------------------------------------------------------------------
// Used by ViewPager; can be used by app as well.
// Returns the total number of pages that the ViewPage can display. This must
// never be 0.
@Override
public int getCount ()
{
return views.size();
}
//-----------------------------------------------------------------------------
// Used by ViewPager.
@Override
public boolean isViewFromObject (View view, Object object)
{
return view == object;
}
//-----------------------------------------------------------------------------
// Add "view" to right end of "views".
// Returns the position of the new view.
// The app should call this to add pages; not used by ViewPager.
public int addView (View v)
{
return addView (v, views.size());
}
//-----------------------------------------------------------------------------
// Add "view" at "position" to "views".
// Returns position of new view.
// The app should call this to add pages; not used by ViewPager.
public int addView (View v, int position)
{
views.add (position, v);
return position;
}
//-----------------------------------------------------------------------------
// Removes "view" from "views".
// Retuns position of removed view.
// The app should call this to remove pages; not used by ViewPager.
public int removeView (ViewPager pager, View v)
{
return removeView (pager, views.indexOf (v));
}
//-----------------------------------------------------------------------------
// Removes the "view" at "position" from "views".
// Retuns position of removed view.
// The app should call this to remove pages; not used by ViewPager.
public int removeView (ViewPager pager, int position)
{
// ViewPager doesn't have a delete method; the closest is to set the adapter
// again. When doing so, it deletes all its views. Then we can delete the view
// from from the adapter and finally set the adapter to the pager again. Note
// that we set the adapter to null before removing the view from "views" - that's
// because while ViewPager deletes all its views, it will call destroyItem which
// will in turn cause a null pointer ref.
pager.setAdapter (null);
views.remove (position);
pager.setAdapter (this);
return position;
}
//-----------------------------------------------------------------------------
// Returns the "view" at "position".
// The app should call this to retrieve a view; not used by ViewPager.
public View getView (int position)
{
return views.get (position);
}
// Other relevant methods:
// finishUpdate - called by the ViewPager - we don't care about what pages the
// pager is displaying so we don't use this method.
}
下面是一些展示如何使用适配器的代码片段。
class MainActivity extends Activity
{
private ViewPager pager = null;
private MainPagerAdapter pagerAdapter = null;
//-----------------------------------------------------------------------------
@Override
public void onCreate (Bundle savedInstanceState)
{
super.onCreate(savedInstanceState);
setContentView (R.layout.main_activity);
... do other initialization, such as create an ActionBar ...
pagerAdapter = new MainPagerAdapter();
pager = (ViewPager) findViewById (R.id.view_pager);
pager.setAdapter (pagerAdapter);
// Create an initial view to display; must be a subclass of FrameLayout.
LayoutInflater inflater = context.getLayoutInflater();
FrameLayout v0 = (FrameLayout) inflater.inflate (R.layout.one_of_my_page_layouts, null);
pagerAdapter.addView (v0, 0);
pagerAdapter.notifyDataSetChanged();
}
//-----------------------------------------------------------------------------
// Here's what the app should do to add a view to the ViewPager.
public void addView (View newPage)
{
int pageIndex = pagerAdapter.addView (newPage);
// You might want to make "newPage" the currently displayed page:
pager.setCurrentItem (pageIndex, true);
}
//-----------------------------------------------------------------------------
// Here's what the app should do to remove a view from the ViewPager.
public void removeView (View defunctPage)
{
int pageIndex = pagerAdapter.removeView (pager, defunctPage);
// You might want to choose what page to display, if the current page was "defunctPage".
if (pageIndex == pagerAdapter.getCount())
pageIndex--;
pager.setCurrentItem (pageIndex);
}
//-----------------------------------------------------------------------------
// Here's what the app should do to get the currently displayed page.
public View getCurrentPage ()
{
return pagerAdapter.getView (pager.getCurrentItem());
}
//-----------------------------------------------------------------------------
// Here's what the app should do to set the currently displayed page. "pageToShow" must
// currently be in the adapter, or this will crash.
public void setCurrentPage (View pageToShow)
{
pager.setCurrentItem (pagerAdapter.getItemPosition (pageToShow), true);
}
}
最后,您可以将以下内容用于activity_main.xml
布局:
<?xml version="1.0" encoding="utf-8"?>
<android.support.v4.view.ViewPager
xmlns:android="http://schemas.android.com/apk/res/android"
android:id="@+id/view_pager"
android:layout_width="match_parent"
android:layout_height="match_parent" >
</android.support.v4.view.ViewPager>
我正在寻找简单的解决方案,以删除视图从viewpager(没有碎片)动态。因此,如果您有一些信息,您的页面属于,您可以将它设置为视图作为标记。就像那样(适配器代码):
@Override
public Object instantiateItem(ViewGroup collection, int position)
{
ImageView iv = new ImageView(mContext);
MediaMessage msg = mMessages.get(position);
...
iv.setTag(media);
return iv;
}
@Override
public int getItemPosition (Object object)
{
View o = (View) object;
int index = mMessages.indexOf(o.getTag());
if (index == -1)
return POSITION_NONE;
else
return index;
}
您只需要从mMessages中删除您的信息,然后为您的适配器调用NotifyDataSetChanged()
。坏消息在这种情况下没有动画。
围绕这个话题有不少讨论
虽然我们经常看到,但使用position_none
似乎并不是一种可行的方法,因为它在内存方面效率非常低。
在这个问题中,我们应该考虑使用Alvaro的方法:
。。。是在实例化新视图时执行InstantiateItem()
中的SetTag()
方法。则可以使用FindViewWithTag()
查找要更新的视图,而不是使用NotifyDataSetChanged()
。
下面是基于此思想的SO答案和代码