FragmentPagerAdapter刷新fragment最完美解决方案

时间:2023-12-25 19:40:31

FragmentPagerAdapter刷新fragment最完美解决方案

先感谢kingjxl2006的博客文章《Android FragmentPagerAdapter数据刷新notifyDataSetChanged没效果研究》http://blog.sina.com.cn/s/blog_783ede03010173b4.html,没有他的抛砖引玉,就没有这篇博文。

    好,切入正题,正如上文所说的那样,在fragmentpageadapter的instantiateItem方法里,他会先去FragmentManager里面去查找有没有相关的fragment如果有就直接使用如果没有才会触发fragmentpageadapter的getItem方法获取一个fragment。所以你更新fragments集合是没有作用的。引用kingjxl2006的文章里的代码如下:
        // Do we already have this fragment?
        String name = makeFragmentName(container.getId(), position);
        Fragment fragment = mFragmentManager.findFragmentByTag(name);
        if (fragment != null) {
            if (DEBUG) Log.v(TAG, "Attaching item #" + position + ": f=" + fragment);
            mCurTransaction.attach(fragment);
        } else {
            fragment = getItem(position);
            if (DEBUG) Log.v(TAG, "Adding item #" + position + ": f=" + fragment);
            mCurTransaction.add(container.getId(), fragment,
                    makeFragmentName(container.getId(), position));
        }

kingjxl2006的办法是清除FragmentManager里面全部缓存的fragment。这很暴力我不赞同,全部清除会造成fragment重新加载,造成不必要的性能损失。

    这个方案还是在instantiateItem方法里作文章,代码如下:

@Override

public Object instantiateItem(ViewGroup container,int position) {

//得到缓存的fragment

Fragment fragment = (Fragment)super.instantiateItem(container,

position);

//得到tag ❶

String fragmentTag = fragment.getTag();

if (fragmentsUpdateFlag[position %fragmentsUpdateFlag.length]) {

//如果这个fragment需要更新

FragmentTransaction ft =fm.beginTransaction();

//移除旧的fragment

ft.remove(fragment);

//换成新的fragment

fragment =fragments[position %fragments.length];

//添加新fragment时必须用前面获得的tag ❶

ft.add(container.getId(), fragment, fragmentTag);

ft.attach(fragment);

ft.commit();

//复位更新标志

fragmentsUpdateFlag[position %fragmentsUpdateFlag.length] =false;

}

return fragment;

}

代码注释得很清楚了,主要思路就是用新的fragment替换FragmentManager里缓存的旧的fragment,重点解释❶的地方,看kingjxl2006文章里的两条代码:

        String name = makeFragmentName(container.getId(), position);
        Fragment fragment = mFragmentManager.findFragmentByTag(name);
   说明fragmentpageadapter内部是用tag识别fragment的,并且有它自己的一套算法用于生成tag,所以我们这里必须用它生成的tag来添加新的fragment,否则fragmentpageadapter就无法识别这个新的fragment。
    fragmentsUpdateFlag如其名,是一个用来标识哪个fragment需要更新的boolean类型的数组。
    很多网友提问fm是什么东西?其实就是一个FragmentManager,在构造的时候传入即可:
    class MyFragmentPagerAdapter extends FragmentPagerAdapter {
        FragmentManager fm;
        MyFragmentPagerAdapter(FragmentManager fm) {
               super(fm);
               this.fm = fm;
        }
        ……
    下面贴完整一点的代码,以照顾新同学们:
package com.example.mainframework03;

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.app.FragmentTransaction;
import android.support.v4.view.ViewPager;
import android.support.v4.view.ViewPager.OnPageChangeListener;
import android.util.Log;
import android.view.ViewGroup;
import android.widget.ImageButton;
import android.widget.LinearLayout;

public class MainActivity extends FragmentActivity implements
FragmentEvent.OnEventListener {

ViewPager viewPager;
FragmentPagerAdapter adapter;

MainTab01 tab01 = new MainTab01();
MainTab02 tab02 = new MainTab02();
MainTab03 tab03 = new MainTab03();
MainTab04 tab04 = new MainTab04();
MainTab05 tab05 = new MainTab05();
Fragment[] fragments = { tab01, tab02, tab03, tab04 };
boolean[] fragmentsUpdateFlag = { false, false, false, false };

/**
* 底部四个按钮
*/
private LinearLayout tabBtnWeixin;
private LinearLayout tabBtnFrd;
private LinearLayout tabBtnAddress;
private LinearLayout tabBtnSettings;

Handler mainHandler = new Handler() {

/*
* (非 Javadoc)

* @see android.os.Handler#handleMessage(android.os.Message)
*/
@Override
public void handleMessage(Message msg) {
// TODO 自动生成的方法存根
super.handleMessage(msg);
switch (msg.what) {
case MSG.INTO_05:
fragments[3] = tab05;
fragmentsUpdateFlag[3] = true;
adapter.notifyDataSetChanged();
break;
default:
}
}
};

class MyFragmentPagerAdapter extends FragmentPagerAdapter {
FragmentManager fm;

MyFragmentPagerAdapter(FragmentManager fm) {
super(fm);
this.fm = fm;
}

@Override
public int getCount() {
return fragments.length;
}

@Override
public Fragment getItem(int position) {
Fragment fragment = fragments[position % fragments.length];
Log.i(Common.TAG, "getItem:position=" + position + ",fragment:"
+ fragment.getClass().getName() + ",fragment.tag="
+ fragment.getTag());
return fragments[position % fragments.length];
}

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

@Override
public Object instantiateItem(ViewGroup container, int position) {
//得到缓存的fragment
Fragment fragment = (Fragment) super.instantiateItem(container,
position);
//得到tag,这点很重要
String fragmentTag = fragment.getTag();

if (fragmentsUpdateFlag[position % fragmentsUpdateFlag.length]) {
//如果这个fragment需要更新

FragmentTransaction ft = fm.beginTransaction();
//移除旧的fragment
ft.remove(fragment);
//换成新的fragment
fragment = fragments[position % fragments.length];
//添加新fragment时必须用前面获得的tag,这点很重要
ft.add(container.getId(), fragment, fragmentTag);
ft.attach(fragment);
ft.commit();

//复位更新标志
fragmentsUpdateFlag[position % fragmentsUpdateFlag.length] = false;
}

return fragment;
}
}

@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
viewPager = (ViewPager) findViewById(R.id.id_viewpager);

tabBtnWeixin = (LinearLayout) findViewById(R.id.id_tab_bottom_weixin);
tabBtnFrd = (LinearLayout) findViewById(R.id.id_tab_bottom_friend);
tabBtnAddress = (LinearLayout) findViewById(R.id.id_tab_bottom_contact);
tabBtnSettings = (LinearLayout) findViewById(R.id.id_tab_bottom_setting);

adapter = new MyFragmentPagerAdapter(getSupportFragmentManager());

viewPager.setAdapter(adapter);

viewPager.setOnPageChangeListener(new OnPageChangeListener() {

private int currentIndex;

@Override
public void onPageSelected(int position) {
resetTabBtn();
switch (position) {
case 0:
((ImageButton) tabBtnWeixin
.findViewById(R.id.btn_tab_bottom_weixin))
.setImageResource(R.drawable.tab_weixin_pressed);
break;
case 1:
((ImageButton) tabBtnFrd
.findViewById(R.id.btn_tab_bottom_friend))
.setImageResource(R.drawable.tab_find_frd_pressed);
break;
case 2:
((ImageButton) tabBtnAddress
.findViewById(R.id.btn_tab_bottom_contact))
.setImageResource(R.drawable.tab_address_pressed);
break;
case 3:
((ImageButton) tabBtnSettings
.findViewById(R.id.btn_tab_bottom_setting))
.setImageResource(R.drawable.tab_settings_pressed);
break;
}

currentIndex = position;
}

@Override
public void onPageScrolled(int arg0, float arg1, int arg2) {

}

@Override
public void onPageScrollStateChanged(int arg0) {
}
});

}

protected void resetTabBtn() {
((ImageButton) tabBtnWeixin.findViewById(R.id.btn_tab_bottom_weixin))
.setImageResource(R.drawable.tab_weixin_normal);
((ImageButton) tabBtnFrd.findViewById(R.id.btn_tab_bottom_friend))
.setImageResource(R.drawable.tab_find_frd_normal);
((ImageButton) tabBtnAddress.findViewById(R.id.btn_tab_bottom_contact))
.setImageResource(R.drawable.tab_address_normal);
((ImageButton) tabBtnSettings.findViewById(R.id.btn_tab_bottom_setting))
.setImageResource(R.drawable.tab_settings_normal);
}

@Override
public void onEvent(int what, Bundle data, Object object) {
// TODO 自动生成的方法存根
mainHandler.sendEmptyMessage(what);
}
}

    我的这个例程是在鸿洋_大大(http://blog.csdn.net/lmj623565791/article/details/24740977)的基础上改来的,再此感谢鸿洋_大大。