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) {
}
}
}
我想,我有ViewPager的逻辑。
如果我需要刷新一组页面并基于新的数据集显示它们,我调用notifyDataSetChanged()。
然后,ViewPager对getItemPosition()进行多次调用,将Fragment作为对象传递给那里。这个片段可以来自旧数据集(我想要丢弃的数据集),也可以来自新数据集(我想要显示的数据集)。因此,我重写了getItemPosition(),在那里我必须以某种方式确定我的片段是来自旧数据集还是来自新数据集。
In my case I have a 2-pane layout with a list of top items on the left pane and a swipe view (ViewPager) on the right. So, I store a link to my current top item inside my PagerAdapter and also inside of each instantiated page Fragment.
When the selected top item in the list changes, I store the new top item in PagerAdapter and call notifyDataSetChanged(). And in the overridden getItemPosition() I compare the top item from my adapter to the top item from my fragment.
And only if they are not equal, I return POSITION_NONE.
Then, PagerAdapter reinstantiates all the fragments that have returned POSITION_NONE.
请注意。存储顶部项id而不是引用可能是一个更好的主意。
下面的代码片段有点示意图,但我从实际工作的代码中改编了它。
public class SomeFragment extends Fragment {
private TopItem topItem;
}
public class SomePagerAdapter extends FragmentStatePagerAdapter {
private TopItem topItem;
public void changeTopItem(TopItem newTopItem) {
topItem = newTopItem;
notifyDataSetChanged();
}
@Override
public int getItemPosition(Object object) {
if (((SomeFragment) object).getTopItemId() != topItem.getId()) {
return POSITION_NONE;
}
return super.getItemPosition(object);
}
}
感谢之前所有的研究人员!
有几种方法可以实现这一点。
第一种方法更简单,但效率更低。
重写PagerAdapter中的getItemPosition,如下所示:
public int getItemPosition(Object object) {
return POSITION_NONE;
}
这样,当您调用notifyDataSetChanged()时,视图分页器将删除所有视图并重新加载它们。这样就得到了装填效果。
第二个选项是Alvaro Luis Bustamante(以前是alvarolb)建议的,在实例化一个新视图时使用instantiateItem()中的setTag()方法。然后,您可以使用findViewWithTag()来查找要更新的视图,而不是使用notifyDataSetChanged()。
结论
如果您有很多视图,或者希望支持修改任何特定的项和/或视图(在任何时候快速),那么第二种方法(标记)是非常灵活和高性能的,因为它可以防止重新创建所有未修改的视图。
(alvarolb的原创研究值得称赞。)
但如果你的应用只有“刷新”功能(甚至不允许单个条目的更改),或者只有很少的条目,请使用第一种方法,因为它节省了开发时间。
在OP提出他的问题两年半之后,这个问题仍然,嗯,仍然是一个问题。显然谷歌在这方面的优先级不是特别高,所以我没有找到解决方案,而是找到了一个变通办法。对我来说,最大的突破是找到了问题的真正原因(见本文中公认的答案)。一旦问题明显是任何活动页面都没有正确刷新,我的解决方法就很明显了:
在我的片段(几页)中:
I took all the code which populates the form out of onCreateView and put it in a function called PopulateForm which may be called from anywhere, rather than by the framework. This function attempts to get the current View using getView, and if that is null, it just returns. It's important that PopulateForm contains only the code that displays - all the other code which creates FocusChange listeners and the like is still in OnCreate
Create a boolean which can be used as a flag indicating the form must be reloaded. Mine is mbReloadForm
Override OnResume() to call PopulateForm() if mbReloadForm is set.
在我的活动中,我做页面的加载:
Go to page 0 before changing anything. I'm using FragmentStatePagerAdapter, so I know that two or three pages are affected at most. Changing to page 0 ensures I only ever have the problem on pages 0, 1 and 2.
Before clearing the old list, take it's size(). This way you know how many pages are affected by the bug. If > 3, reduce it to 3 - if you're using a a different PagerAdapter, you'll have to see how many pages you have to deal with (maybe all?)
Reload the data and call pageAdapter.notifyDataSetChanged()
Now, for each of the affected pages, see if the page is active by using pager.getChildAt(i) - this tells you if you have a view. If so, call pager.PopulateView(). If not, set the ReloadForm flag.
在此之后,当您重新加载第二组页面时,该错误仍然会导致一些页面显示旧数据。但是,现在它们将被刷新,您将看到新的数据-您的用户不会知道页面是不正确的,因为这种刷新将在他们看到页面之前发生。
希望这能帮助到一些人!
我使用Tablayout与ViewPagerAdapter。为了在片段之间传递数据或在片段之间进行通信,使用下面的代码,它工作得非常好,并在片段出现时刷新它。第二段点击按钮里面写下面的代码。
b.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
String text=e1.getText().toString(); // get the text from EditText
// move from one fragment to another fragment on button click
TabLayout tablayout = (TabLayout) getActivity().findViewById(R.id.tab_layout); // here tab_layout is the id of TabLayout which is there in parent Activity/Fragment
if (tablayout.getTabAt(1).isSelected()) { // here 1 is the index number of second fragment i-e current Fragment
LocalBroadcastManager lbm = LocalBroadcastManager.getInstance(getContext());
Intent i = new Intent("EDIT_TAG_REFRESH");
i.putExtra("MyTextValue",text);
lbm.sendBroadcast(i);
}
tablayout.getTabAt(0).select(); // here 0 is the index number of first fragment i-e to which fragment it has to moeve
}
});
下面是必须在第一个片段(在我的情况下)i-e中接收片段的代码。
MyReceiver r;
Context context;
String newValue;
public void refresh() {
//your code in refresh.
Log.i("Refresh", "YES");
}
public void onPause() {
super.onPause();
LocalBroadcastManager.getInstance(context).unregisterReceiver(r);
}
public void onResume() {
super.onResume();
r = new MyReceiver();
LocalBroadcastManager.getInstance(getActivity()).registerReceiver(r,
new IntentFilter("EDIT_TAG_REFRESH"));
} // this code has to be written before onCreateview()
// below code can be written any where in the fragment
private class MyReceiver extends BroadcastReceiver {
@Override
public void onReceive(Context context, Intent intent) {
PostRequestFragment.this.refresh();
String action = intent.getAction();
newValue=intent.getStringExtra("MyTextValue");
t1.setText(newValue); // upon Referesh set the text
}
}
在我的情况下,在我的Viewpager中有一个textView,在mainActivity中单击按钮,我想改变textView的颜色并更新pagerAdapter。在按钮上单击“我在SharedPreference中保存了颜色”,并更新pagerAdapter,它可以更新从共享首选项中获取的颜色。我用下面的方式更新viewPager视图。
btn_purple.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
int color = ContextCompat.getColor(mContext, R.color.colorPrimaryDark2);
editor.putInt("sahittoFontColor", color);
editor.apply();
toNotifyDatasetChanged();
}
});
现在更新方法:
private void toNotifyDatasetChanged (){
if(viewPager!=null&& pagerAdapter!=null) {
viewPager.setAdapter(null);
viewPager.setAdapter(pagerAdapter);
}
}
我的pagerAdapter是:
pagerAdapter = new Sahitto_ViewPagerAdapter (mContext, filenameParameter, 30, lineList);
viewPager.setAdapter(pagerAdapter);
并且在instantiateItem was(在PagerAdapter中):
SharedPreferences settings = PreferenceManager.getDefaultSharedPreferences(mContext);
int bnfntcolor=settings.getInt("sahittoFontColor", 0);
if (bnfntcolor!=0){
textView.setTextColor(bnfntcolor);
}
因此,当我点击按钮,颜色立即改变在pagerAdapter的Textview。
快乐的编码。