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) {
}
}
}
你可以动态更新所有的片段,你可以在三个步骤中看到。
在适配器中:
public class MyPagerAdapter extends FragmentPagerAdapter {
private static int NUM_ITEMS = 3;
private Map<Integer, String> mFragmentTags;
private FragmentManager mFragmentManager;
public MyPagerAdapter(FragmentManager fragmentManager) {
super(fragmentManager);
mFragmentManager = fragmentManager;
mFragmentTags = new HashMap<Integer, String>();
}
// Returns total number of pages
@Override
public int getCount() {
return NUM_ITEMS;
}
// Returns the fragment to display for that page
@Override
public Fragment getItem(int position) {
switch (position) {
case 0:
return FirstFragment.newInstance();
case 1:
return SecondFragment.newInstance();
case 2:
return ThirdFragment.newInstance();
default:
return null;
}
}
// Returns the page title for the top indicator
@Override
public CharSequence getPageTitle(int position) {
return "Page " + position;
}
@Override
public Object instantiateItem(ViewGroup container, int position) {
Object object = super.instantiateItem(container, position);
if (object instanceof Fragment) {
Fragment fragment = (Fragment) object;
String tag = fragment.getTag();
mFragmentTags.put(position, tag);
}
return object;
}
public Fragment getFragment(int position) {
Fragment fragment = null;
String tag = mFragmentTags.get(position);
if (tag != null) {
fragment = mFragmentManager.findFragmentByTag(tag);
}
return fragment;
}}
现在在你的活动中:
public class MainActivity extends AppCompatActivity implements ViewPager.OnPageChangeListener{
MyPagerAdapter mAdapterViewPager;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
ViewPager viewPager = (ViewPager) findViewById(R.id.vpPager);
mAdapterViewPager = new MyPagerAdapter(getSupportFragmentManager());
viewPager.setAdapter(mAdapterViewPager);
viewPager.addOnPageChangeListener(this);
}
@Override
public void onPageScrolled(int position, float positionOffset, int positionOffsetPixels) {
}
@Override
public void onPageSelected(int position) {
Fragment fragment = mAdapterViewPager.getFragment(position);
if (fragment != null) {
fragment.onResume();
}
}
@Override
public void onPageScrollStateChanged(int state) {
}}
最后在你的片段中,是这样的:
public class YourFragment extends Fragment {
// newInstance constructor for creating fragment with arguments
public static YourFragment newInstance() {
return new YourFragment();
}
// Store instance variables based on arguments passed
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
}
// Inflate the view for the fragment based on layout XML
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
return inflater.inflate(R.layout.fragment, container, false);
}
@Override
public void onResume() {
super.onResume();
//to refresh your view
refresh();
}}
您可以在这里看到完整的代码。
谢谢阿尔瓦罗·路易斯·布斯塔曼特。
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!
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。
1.首先,您必须在Pageradapter类中设置getItemposition方法
2.您必须阅读您的视图寻呼机的确切位置
3.然后将该位置作为新位置的数据位置发送
4.在setonPageChange监听器中写入更新按钮的点击监听器
我修改了程序代码,只设置了特定的位置元素
public class MyActivity extends Activity {
private ViewPager myViewPager;
private List<String> data;
public int location=0;
public Button updateButton;
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
data = new ArrayList<String>();
data.add("A");
data.add("B");
data.add("C");
data.add("D");
data.add("E");
data.add("F");
myViewPager = (ViewPager) findViewById(R.id.pager);
myViewPager.setAdapter(new MyViewPagerAdapter(this, data));
updateButton = (Button) findViewById(R.id.update);
myViewPager.setOnPageChangeListener(new ViewPager.OnPageChangeListener() {
@Override
public void onPageScrolled(int i, float v, int i2) {
//Toast.makeText(MyActivity.this, i+" Is Selected "+data.size(), Toast.LENGTH_SHORT).show();
}
@Override
public void onPageSelected( int i) {
// here you will get the position of selected page
final int k = i;
updateViewPager(k);
}
@Override
public void onPageScrollStateChanged(int i) {
}
});
}
private void updateViewPager(final int i) {
updateButton.setOnClickListener(new OnClickListener() {
@Override
public void onClick(View v) {
Toast.makeText(MyActivity.this, i+" Is Selected "+data.size(), Toast.LENGTH_SHORT).show();
data.set(i, "Replaced "+i);
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 int getItemPosition(Object object) {
return POSITION_NONE;
}
@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) {
}
}
}