标签：android fragment viewpager 源码 缓存机制
在一个 Android 应用中，我们可以使用 FragmentPageAdapter 来处理多 Fragment 页面的横向滑动。但是当 Fragment 对应的数据集发生改变时，我们都希望能够通过调用 mAdapter.notifyDataSetChanged() 来触发 Fragment 页面使用新的数据调整或重新生成其内容，可是当我们使用 notifyDataSetChanged() 后，我们会发现这个方法不会生效。那为什么会这样呢，之前遇到了相同的问题一直没法解决，在网上给出的乱七八糟的答案感觉也不是正解，终于在今早彻底解决了这个问题。我们先来了解下FragmentPagerAdapter的源代码。 @Override
public Object instantiateItem(ViewGroup container, int position) {
if (mCurTransaction == null) {
mCurTransaction = mFragmentManager.beginTransaction();
}
final long itemId = getItemId(position);
// Do we already have this fragment?
String name = makeFragmentName(container.getId(), itemId);
Fragment fragment = mFragmentManager.findFragmentByTag(name);
if (fragment != null) {
if (DEBUG) Log.v(TAG, "Attaching item #" + itemId + ": f=" + fragment);
mCurTransaction.attach(fragment);
} else {
fragment = getItem(position);
if (DEBUG) Log.v(TAG, "Adding item #" + itemId + ": f=" + fragment);
mCurTransaction.add(container.getId(), fragment,
makeFragmentName(container.getId(), itemId));
}
if (fragment != mCurrentPrimaryItem) {
fragment.setMenuVisibility(false);
fragment.setUserVisibleHint(false);
}
return fragment;
} String name = makeFragmentName(container.getId(), itemId);
Fragment fragment = mFragmentManager.findFragmentByTag(name); 我们先来定义一个list<String> tagList 来存储一下tag
private List<String> tagList;第二部重写instantiateItem方法，把fragment对应的标签存储在taglist集合里
public Object instantiateItem(ViewGroup container, int position) {
tagList.add(makeFragmentName(container.getId(), getItemId(position)));
return super.instantiateItem(container, position);
} makeFragmentName（）是FragmentPageAdapter源码里打fragment标签的方法public static String makeFragmentName(int viewId, int index) {
return "android:switcher:" + viewId + ":" + index;
}
第三步我们再adapter里自己写一个update（）方法
public void update(int item) {
Fragment fragment = fm.findFragmentByTag(tagList.get(item));
if (fragment != null) {
switch (item) {
case 0:
break;
case 1:
((QueryFragment) fragment).update();
break;
case 2:
break;
default:
break;
}
}
}好的现在万事具备只要实现fragment的数据更新问题就可以了，通过接口回掉机制来实现。
首先我们定义一个接口，让我们的主Activity来实现
public interface FragmentListener {
public void onFragmentClickListener(int item);
} public void onAttach(Activity activity) {
super.onAttach(activity);
try {
listener = (FragmentListener)activity;
} catch (Exception e) {
e.printStackTrace();
}
} 然后对数据更新的时候，我们就在Afragment调用这个接口if (listener != null) {
listener.onFragmentClickListener(1);
}public void onFragmentClickListener(int item) {
adapter.update(item);
adapter.update(item);
}package com.example.account.main;
import java.util.ArrayList;
import java.util.List;
import com.example.account.add.AddFragment;
import com.example.account.query.QueryFragment;
import com.example.account.setting.SettingFragment;
import com.example.account.utils.PagerSlidingTabStrip;
import com.melhc.xiji.R;
import android.annotation.SuppressLint;
import android.content.Intent;
import android.graphics.Color;
import android.os.Bundle;
import android.os.Handler;
import android.os.Message;
import android.support.v4.app.Fragment;
import android.support.v4.app.FragmentActivity;
import android.support.v4.app.FragmentManager;
import android.support.v4.app.FragmentPagerAdapter;
import android.support.v4.view.ViewPager;
import android.util.DisplayMetrics;
import android.util.TypedValue;
import android.view.KeyEvent;
import android.view.ViewGroup;
import android.widget.Toast;
public class MainActivity extends FragmentActivity implements FragmentListener{
private MyPagerAdapter adapter;
private AddFragment addFragment;
private List<String> tagList;
private SettingFragment settingFragment;
private boolean isExit;
private QueryFragment queryFragment;
private ViewPager pager;
private PagerSlidingTabStrip tabs;
private FragmentManager fm;
private DisplayMetrics dm;
private List<Fragment> list;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
pager = (ViewPager) findViewById(R.id.pager);
tabs = (PagerSlidingTabStrip) findViewById(R.id.tabs);
initFragment();
fm = getSupportFragmentManager();
tagList = new ArrayList<String>();
adapter = new MyPagerAdapter(fm);
pager.setAdapter(adapter);
tabs.setViewPager(pager);
}
public void initFragment() {
list = new ArrayList<Fragment>();
addFragment = new AddFragment();
queryFragment = new QueryFragment();
settingFragment = new SettingFragment();
list.add(addFragment);
list.add(queryFragment);
list.add(settingFragment);
}
public class MyPagerAdapter extends FragmentPagerAdapter {
public MyPagerAdapter(FragmentManager fm) {
super(fm);
}
private final String[] titles = { "1", "2", "3" };
@Override
public CharSequence getPageTitle(int position) {
return titles[position];
}
@Override
public int getCount() {
return titles.length;
}
@Override
public Fragment getItem(int position) {
return list.get(position);
}
public Object instantiateItem(ViewGroup container, int position) {
tagList.add(makeFragmentName(container.getId(),
(int) getItemId(position)));
return super.instantiateItem(container, position);
}
public void update(int item) {
Fragment fragment = fm.findFragmentByTag(tagList.get(item));
if (fragment != null) {
switch (item) {
case 0:
break;
case 1:
((QueryFragment) fragment).update();
break;
case 2:
break;
default:
break;
}
}
}
}
public static String makeFragmentName(int viewId, int index) {
return "android:switcher:" + viewId + ":" + index;
}
public void onFragmentClickListener(int item) {
adapter.update(item);
adapter.update(item);
}
}FragmentPageAdapter切换时无法更新数据问题解析,布布扣,bubuko.com
FragmentPageAdapter切换时无法更新数据问题解析
标签：android fragment viewpager 源码 缓存机制
原文地址：http://blog.csdn.net/gerogelin/article/details/38232359
