Android-ViewPager+Fragment数据更新问题 _Viewpager

案头见蠹鱼，犹胜凡俦侣。这篇文章主要讲述Android-ViewPager+Fragment数据更新问题相关的知识，希望能为你提供帮助。
由于FragmentPagerAdapter内部存在缓存。因此调用notifyDataSetChanged()并不可以去更新Fragment的内容。
參考：http://www.devba.com/index.php/archives/5826.html
http://stackoverflow.com/questions/7263291/viewpager-pageradapter-not-updating-the-view/7287121#7287121

能够有两种解决的方法：
（1）重写Adapter的getItemPosition()：

public int getItemPosition(Object object) { return POSITION_NONE; }

当调用notifyDataSetChanged()的时候。ViewPager会remove掉全部的view，然后又一次去载入。可行，可是效率低。

【Android-ViewPager+Fragment数据更新问题】（2）在view上调用SetTag。然后用ViewPager.findViewWithTag()来找到要更新的view，然后做更新。
由于FragmentPagerAdapter内部缓存Fragment的时候，已经是依照tag的方式缓存的，因此。在更新的时候，我们仅仅要依据tag，拿到fragment，然后去更新fragment就能够了。
看下FragmentPagerAdapter的instantiateItem()方法：

public Object instantiateItem(ViewGroup container, int position) { if (this.mCurTransaction == null) { this.mCurTransaction = this.mFragmentManager.beginTransaction(); }long itemId = getItemId(position); String name = makeFragmentName(container.getId(), itemId); //这里就是在生成fragment的tag Fragment fragment = this.mFragmentManager.findFragmentByTag(name); //这里是依据tag查找 if (fragment != null) { this.mCurTransaction.attach(fragment); //找到直接attch } else { fragment = getItem(position); //找不到的时候。才会调用getItemthis.mCurTransaction.add(container.getId(), fragment, makeFragmentName(container.getId(), itemId)); }if (fragment != this.mCurrentPrimaryItem) { fragment.setMenuVisibility(false); fragment.setUserVisibleHint(false); }return fragment; }

依据原代码我们能够知道系统给每个Fragment都打上了一个标签，通过标签来寻找对应的fragment，所以当我们第二次进入fragment的时候。fragment的oncreate,oncreateView方法都不会被调用的。由于FragmentPageAdapter中的getitem()方法根本不会被调用，由于系统会依据标签找到对应的fragment。假设已经存在，就不会被调用，fragment有一个缓存机制在这里。

如今的问题是必需要做更新，那么能够这么弄：

public class FragmentViewPagerAdapter extends FragmentPagerAdapter { private FragmentManager mFragmentManager; private List< String> mDatas; private List< String> tagList = new ArrayList< String> (); public FragmentViewPagerAdapter(FragmentManager fm, List< String> datas) { super(fm); this.mFragmentManager = fm; this.mDatas = datas; } @Override public Object instantiateItem(ViewGroup container, int position) { tagList.add(makeFragmentName(container.getId(), getItemId(position))); //把tag存起来 return super.instantiateItem(container, position); } @Override public void destroyItem(ViewGroup container, int position, Object object){ super.destroyItem(container, position, object); tagList.remove(makeFragmentName(container.getId(), getItemId(position))); //把tag删掉 } @Override public Fragment getItem(int position) { String url = mDatas.get(position); WebViewFragmentV4 webview = new WebViewFragmentV4(url); //本文測试的Fragment是一个WebViewFragment

return webview; } @Override public int getCount() { if (mDatas == null) { return 0; } else { return mDatas.size(); } } public void update(List< String> datas){ this.mDatas = datas; notifyDataSetChanged(); //并不能起到更新Fragment内容的作用。
} public void update(int position){//这个事真正的更新Fragment的内容 WebViewFragmentV4 fragment = (WebViewFragmentV4)mFragmentManager.findFragmentByTag(tagList.get(position)); if(fragment == null){ return; } fragment.update(); } private static String makeFragmentName(int viewId, long id) { return " android:switcher:" + viewId + " :" + id; } }

WebViewFragmentV4.java:

public class WebViewFragmentV4 extends Fragment { private WebView mWebView; private boolean mIsWebViewAvailable; private String mUrl; public WebViewFragmentV4(String url) { this.mUrl = url; } /** * Called to instantiate the view. Creates and returns the WebView. */ @Override public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) { if (mWebView != null) { mWebView.destroy(); } mWebView = new WebView(getActivity()); mWebView.getSettings().setUseWideViewPort(true); mWebView.getSettings().setLoadWithOverviewMode(true); mWebView.setWebViewClient(new MyWebViewClient()); mWebView.loadUrl(mUrl); mIsWebViewAvailable = true; return mWebView; } /** * Called when the fragment is visible to the user and actively running. * Resumes the WebView. */ @Override public void onPause() { super.onPause(); mWebView.onPause(); } /** * Called when the fragment is no longer resumed. Pauses the WebView. */ @Override public void onResume() { mWebView.onResume(); super.onResume(); } /** * Called when the WebView has been detached from the fragment. The WebView * is no longer available after this time. */ @Override public void onDestroyView() { mIsWebViewAvailable = false; super.onDestroyView(); } /** * Called when the fragment is no longer in use. Destroys the internal state * of the WebView. */ @Override public void onDestroy() { if (mWebView != null) { mWebView.destroy(); mWebView = null; } super.onDestroy(); } public void update(){ if (mWebView != null) { mWebView.reload(); } } /** * Gets the WebView. */ public WebView getWebView() { return mIsWebViewAvailable ? mWebView : null; } private static class MyWebViewClient extends WebViewClient {@Override public boolean shouldOverrideUrlLoading(WebView view, String url) { view.loadUrl(url); return true; }@Override public void onPageStarted(WebView view, String url, Bitmap favicon) { super.onPageStarted(view, url, favicon); }@Override public void onPageFinished(WebView view, String url) { super.onPageFinished(view, url); }@Override public void onReceivedError(WebView view, int errorCode, String description, String failingUrl) { super.onReceivedError(view, errorCode, description, failingUrl); } } }

转载请标明出处：http://blog.csdn.net/goldenfish1919/article/details/47661443
測试代码：

//1. 初始化 viewpager = (ViewPager)this.findViewById(R.id.viewpager); adapter = new FragmentViewPagerAdapter(getSupportFragmentManager(), null); viewpager.setAdapter(adapter); //2. 载入数据 List< String> urls = new ArrayList< String> (); urls.add(" http://172.16.28.253:8080/web/1.jsp" ); urls.add(" http://172.16.28.253:8080/web/2.jsp" ); urls.add(" http://172.16.28.253:8080/web/3.jsp" ); urls.add(" http://172.16.28.253:8080/web/4.jsp" ); adapter.update(urls); //3. 做更新 Button update = (Button) this.findViewById(R.id.update); update.setOnClickListener(new View.OnClickListener() { @Override public void onClick(View v) { if(viewpager != null & & adapter != null){ viewpager.setCurrentItem(3, true); adapter.update(3); //又一次载入position是3的页面 } } });

重构一下：
（1）BaseFragmentPagerAdapter.java

public abstract class BaseFragmentPagerAdapter extends FragmentPagerAdapter{ private FragmentManager mFragmentManager; private List< String> tagList = new ArrayList< String> (); public BaseFragmentPagerAdapter(FragmentManager fm) { super(fm); this.mFragmentManager = fm; } @Override public Object instantiateItem(ViewGroup container, int position) { tagList.add(makeFragmentName(container.getId(), getItemId(position))); return super.instantiateItem(container, position); } @Override public void destroyItem(ViewGroup container, int position, Object object){ super.destroyItem(container, position, object); tagList.remove(makeFragmentName(container.getId(), getItemId(position))); } private static String makeFragmentName(int viewId, long id) { return " android:switcher:" + viewId + " :" + id; } public void update(int position){ Fragment fragment = (Fragment)mFragmentManager.findFragmentByTag(tagList.get(position)); if(fragment == null){ return; } if(fragment instanceof UpdateAble){//这里唯一的要求是Fragment要实现UpdateAble接口 ((UpdateAble)fragment).update(); } } public interface UpdateAble { public void update(); } }

以后我们的Adapter仅仅要继承BaseFragmentPagerAdapter就能够了。比方：
（2）FragmentViewPagerAdapter.java

public class FragmentViewPagerAdapter extends BaseFragmentPagerAdapter { private List< String> mDatas; public FragmentViewPagerAdapter(FragmentManager fm, List< String> datas) { super(fm); this.mDatas = datas; } @Override public Fragment getItem(int position) { String url = mDatas.get(position); WebViewFragmentV4 webview = new WebViewFragmentV4(url); return webview; } @Override public int getCount() { if (mDatas == null) { return 0; } else { return mDatas.size(); } } public void update(List< String> datas){ this.mDatas = datas; notifyDataSetChanged(); } }

跟普通的使用方法一样。唯一的要求是。Fragment必需要实现UpdateAble接口，perfect！