我正在使用兼容性库中的ViewPager。我已经成功地让它显示几个视图，我可以通过页面。
但是，我很难弄清楚如何用一组新的视图更新ViewPager。
我已经尝试了各种各样的事情，比如调用mAdapter.notifyDataSetChanged()， mviewpage .invalidate()，甚至在每次我想使用新的数据列表时创建一个全新的适配器。
没有任何帮助，textviews保持不变，从原始数据。
更新:
我做了一个小测试项目，我几乎能够更新视图。我将在下面粘贴这个类。
然而，似乎没有更新的是第二个视图，“B”仍然存在，它应该在按下更新按钮后显示“Y”。
public class ViewPagerBugActivity extends Activity {
private ViewPager myViewPager;
private List<String> data;
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
data = new ArrayList<String>();
data.add("A");
data.add("B");
data.add("C");
myViewPager = (ViewPager) findViewById(R.id.my_view_pager);
myViewPager.setAdapter(new MyViewPagerAdapter(this, data));
Button updateButton = (Button) findViewById(R.id.update_button);
updateButton.setOnClickListener(new OnClickListener() {
@Override
public void onClick(View v) {
updateViewPager();
}
});
}
private void updateViewPager() {
data.clear();
data.add("X");
data.add("Y");
data.add("Z");
myViewPager.getAdapter().notifyDataSetChanged();
}
private class MyViewPagerAdapter extends PagerAdapter {
private List<String> data;
private Context ctx;
public MyViewPagerAdapter(Context ctx, List<String> data) {
this.ctx = ctx;
this.data = data;
}
@Override
public int getCount() {
return data.size();
}
@Override
public Object instantiateItem(View collection, int position) {
TextView view = new TextView(ctx);
view.setText(data.get(position));
((ViewPager)collection).addView(view);
return view;
}
@Override
public void destroyItem(View collection, int position, Object view) {
((ViewPager) collection).removeView((View) view);
}
@Override
public boolean isViewFromObject(View view, Object object) {
return view == object;
}
@Override
public Parcelable saveState() {
return null;
}
@Override
public void restoreState(Parcelable arg0, ClassLoader arg1) {
}
@Override
public void startUpdate(View arg0) {
}
@Override
public void finishUpdate(View arg0) {
}
}
}
你只需要这段简单的代码:
代码:
private void updateAdapter() {
if (adapterViewPager != null) {
int from = vpMyViewPager.getCurrentItem() - vpMyViewPager.getOffscreenPageLimit();
int to = vpMyViewPager.getCurrentItem() + vpMyViewPager.getOffscreenPageLimit();
vpMyViewPager.removeAllViews();
for (int i = from; i <= to; i++) {
if (i < 0) {
continue;
}
adapterViewPager.instantiateItem(vpMyViewPager, i);
}
}
}
解释:
If you haven't changed offscreenPageLimit of the ViewPager, it always has 3 to 4 children depending on which direction you are going. And in order to show the correct content inside its children, it uses the adapter to get the right content.
now when you call removeAllViews() on your ViewPager, only 3 to 4 Views are actually being removed from the Window's hierarchy, and by calling instantiateItem(ViewGroup viewPager, int index), you are only recreating 3 to 4 Views. Then everything is back to normal, you swipe and scroll, the ViewPager shows contents using its adapter. The number of its children is not the same on all devices in all situations, for example if you set the offscreenPageLimit to 5, it will probably have around 11 to 12 children, but that's all, it's not much. it's fast.
感谢瑞。阿劳霍和阿尔瓦罗路易斯布斯塔曼特。首先，我尝试使用rui。阿劳霍的方法，因为很简单。它可以工作，但当数据发生变化时，页面会明显重绘。这很糟糕，所以我试着用布斯塔曼特的方法。它是完美的。代码如下:
@Override
protected void onStart() {
super.onStart();
}
private class TabPagerAdapter extends PagerAdapter {
@Override
public int getCount() {
return 4;
}
@Override
public boolean isViewFromObject(final View view, final Object object) {
return view.equals(object);
}
@Override
public void destroyItem(final View container, final int position, final Object object) {
((ViewPager) container).removeView((View) object);
}
@Override
public Object instantiateItem(final ViewGroup container, final int position) {
final View view = LayoutInflater.from(
getBaseContext()).inflate(R.layout.activity_approval, null, false);
container.addView(view);
ListView listView = (ListView) view.findViewById(R.id.list_view);
view.setTag(position);
new ShowContentListTask(listView, position).execute();
return view;
}
}
当数据发生变化时:
for (int i = 0; i < 4; i++) {
View view = contentViewPager.findViewWithTag(i);
if (view != null) {
ListView listView = (ListView) view.findViewById(R.id.list_view);
new ShowContentListTask(listView, i).execute();
}
}
我认为PagerAdapter中没有任何类型的错误。问题是，理解它是如何工作的有点复杂。看看这里解释的解决方案，从我的角度来看，有一个误解，因此实例化视图的使用很差。
在过去的几天里，我一直在使用PagerAdapter和ViewPager，我发现了以下内容:
PagerAdapter上的notifyDataSetChanged()方法只会通知ViewPager底层页面已经更改。例如，如果您动态地创建/删除页面(从列表中添加或删除项目)，ViewPager应该负责这些。在这种情况下，我认为ViewPager决定是否应该使用getItemPosition()和getCount()方法删除或实例化一个新视图。
我认为ViewPager，在notifyDataSetChanged()调用后，它的子视图和检查他们的位置与getItemPosition()。如果对于子视图，该方法返回POSITION_NONE, ViewPager会认为该视图已被删除，并调用destroyItem()方法删除该视图。
通过这种方式，如果您只想更新页面的内容，覆盖getItemPosition()以总是返回POSITION_NONE是完全错误的，因为每次调用notifyDatasetChanged()时，以前创建的视图将被销毁，而新的视图将被创建。对于一些textview来说，这似乎没有什么问题，但是当你有复杂的视图时，比如从数据库中填充的listview，这可能是一个真正的问题和资源浪费。
So there are several approaches to efficiently change the content of a view without having to remove and instantiate the view again. It depends on the problem you want to solve. My approach is to use the setTag() method for any instantiated view in the instantiateItem() method. So when you want to change the data or invalidate the view that you need, you can call the findViewWithTag() method on the ViewPager to retrieve the previously instantiated view and modify/use it as you want without having to delete/create a new view each time you want to update some value.
例如，假设您有100个带有100个textview的页面，并且您只想定期更新一个值。使用前面解释的方法，这意味着您在每次更新时删除并实例化100个textview。这没有道理……
