1. 程式人生 > >Android TabLayout+ViewPager+Fragment實現tab欄的時候,無法實時更新ViewPager內的Fragment問題終極解決方法

Android TabLayout+ViewPager+Fragment實現tab欄的時候,無法實時更新ViewPager內的Fragment問題終極解決方法

TabLayout+ViewPager+Fragment模式在應用中必不可少,有時候我們可能會遇到tab欄會動態改變的問題,如新增,或刪減,這時候就需要把viewpager內相應的fragment新增或刪減;

如想做以下等操作?

1、更新單個item

mDataList.remove(0);
mPagerAdapter.notifyDataSetChanged();

1、刪掉viewpager內的所有view   

viewpage.removeAllViews();

2、在adapter中重現以下方法

@Override

public int getItemPosition(Object object) {

// 最簡單解決 notifyDataSetChanged() 頁面不重新整理問題的方法

return POSITION_NONE;

}

@Override

public void destroyItem(ViewGroup container, int position, Object object) {

// 把 Object 強轉為 View,然後將 view 從 ViewGroup 中清除

container.removeView((View) object);

}

...................

你會發現都會無效,

具體原因如下:

罪魁禍首是

FragmentPagerAdapter,相關文章介紹,這個adapter會預設把我們的所有載入的view放到快取中,每次會先從快取中載入,提升效率,這就難怪了,怎麼刪都刪不掉。

最終發現了 我們還有另外一個PagerAdapter可以使用,那就是FragmentStatePagerAdapter也是最終的解決方法,該 PagerAdapter 的實現將只保留當前頁面,當頁面離開視線後,就會被消除,釋放其資源。

一下是兩種場景的使用方法

1、繼承v4包的fragment使用

直接繼承FragmentStatePagerAdapter即可跟FragmentPagerAdapter

一樣使用,但還是需要重寫一下方法

@Override

public int getItemPosition(Object object) {

// 最簡單解決 notifyDataSetChanged() 頁面不重新整理問題的方法

return POSITION_NONE;

}

@Override

public void destroyItem(ViewGroup container, int position, Object object) {

// 把 Object 強轉為 View,然後將 view 從 ViewGroup 中清除

container.removeView((View) object);

}

2、繼承app包的fragment的使用,

由於相關的adapter預設的都是繼承v4包的,但當我們的fragment是繼承app包的時候就會出現問題,解決方法就是把繼承v4包的FragmentStatePagerAdapter原始碼拷貝出來把裡面的繼承v4包的類全部改為繼承app包,當然最終的父類PagerAdapter是不能修改的還是繼承的v4包,這個可以不用管。同時在你的子類中同樣需要重寫以下方法

@Override

public int getItemPosition(Object object) {

// 最簡單解決 notifyDataSetChanged() 頁面不重新整理問題的方法

return POSITION_NONE;

}

@Override

public void destroyItem(ViewGroup container, int position, Object object) {

// 把 Object 強轉為 View,然後將 view 從 ViewGroup 中清除

container.removeView((View) object);

}

 

以下是繼承app包的FragmentStatePagerAdapter類,可直接使用:

package cn.longmaster.hospital.doctor.ui.college.adapter;

import android.app.Fragment;
import android.app.FragmentManager;
import android.app.FragmentTransaction;
import android.os.Bundle;
import android.os.Parcelable;
import android.support.v4.view.PagerAdapter;
import android.util.Log;
import android.view.View;
import android.view.ViewGroup;

import java.util.ArrayList;

/**
 * Created by W·H·K on 2018/9/17.
 */

public abstract class MyFragmentStatePagerAdapter extends PagerAdapter {
    private static final String TAG = "FragmentStatePagerAdapter";
    private static final boolean DEBUG = false;

    private final FragmentManager mFragmentManager;
    private FragmentTransaction mCurTransaction = null;

    private ArrayList<Fragment.SavedState> mSavedState = new ArrayList<Fragment.SavedState>();
    private ArrayList<Fragment> mFragments = new ArrayList<Fragment>();
    private Fragment mCurrentPrimaryItem = null;

    public MyFragmentStatePagerAdapter(FragmentManager fm) {
        mFragmentManager = fm;
    }

    /**
     * Return the Fragment associated with a specified position.
     */
    public abstract Fragment getItem(int position);

    @Override
    public void startUpdate(ViewGroup container) {
    }

    @Override
    public Object instantiateItem(ViewGroup container, int position) {
        // If we already have this item instantiated, there is nothing
        // to do.  This can happen when we are restoring the entire pager
        // from its saved state, where the fragment manager has already
        // taken care of restoring the fragments we previously had instantiated.
        if (mFragments.size() > position) {
            Fragment f = mFragments.get(position);
            if (f != null) {
                return f;
            }
        }

        if (mCurTransaction == null) {
            mCurTransaction = mFragmentManager.beginTransaction();
        }

        Fragment fragment = getItem(position);
        if (mSavedState.size() > position) {
            Fragment.SavedState fss = mSavedState.get(position);
            if (fss != null) {
                fragment.setInitialSavedState(fss);
            }
        }
        while (mFragments.size() <= position) {
            mFragments.add(null);
        }
        fragment.setMenuVisibility(false);
        fragment.setUserVisibleHint(false);
        mFragments.set(position, fragment);
        mCurTransaction.add(container.getId(), fragment);

        return fragment;
    }

    @Override
    public void destroyItem(ViewGroup container, int position, Object object) {
        Fragment fragment = (Fragment) object;

        if (mCurTransaction == null) {
            mCurTransaction = mFragmentManager.beginTransaction();
        }
        while (mSavedState.size() <= position) {
            mSavedState.add(null);
        }
        mSavedState.set(position, mFragmentManager.saveFragmentInstanceState(fragment));
        mFragments.set(position, null);

        mCurTransaction.remove(fragment);
    }

    @Override
    public void setPrimaryItem(ViewGroup container, int position, Object object) {
        Fragment fragment = (Fragment) object;
        if (fragment != mCurrentPrimaryItem) {
            if (mCurrentPrimaryItem != null) {
                mCurrentPrimaryItem.setMenuVisibility(false);
                mCurrentPrimaryItem.setUserVisibleHint(false);
            }
            if (fragment != null) {
                fragment.setMenuVisibility(true);
                fragment.setUserVisibleHint(true);
            }
            mCurrentPrimaryItem = fragment;
        }
    }

    @Override
    public void finishUpdate(ViewGroup container) {
        if (mCurTransaction != null) {
            mCurTransaction.commitAllowingStateLoss();
            mCurTransaction = null;
            mFragmentManager.executePendingTransactions();
        }
    }

    @Override
    public boolean isViewFromObject(View view, Object object) {
        return ((Fragment) object).getView() == view;
    }

    @Override
    public Parcelable saveState() {
        Bundle state = null;
        if (mSavedState.size() > 0) {
            state = new Bundle();
            Fragment.SavedState[] fss = new Fragment.SavedState[mSavedState.size()];
            mSavedState.toArray(fss);
            state.putParcelableArray("states", fss);
        }
        for (int i = 0; i < mFragments.size(); i++) {
            Fragment f = mFragments.get(i);
            if (f != null && f.isAdded()) {
                if (state == null) {
                    state = new Bundle();
                }
                String key = "f" + i;
                mFragmentManager.putFragment(state, key, f);
            }
        }
        return state;
    }

    @Override
    public void restoreState(Parcelable state, ClassLoader loader) {
        if (state != null) {
            Bundle bundle = (Bundle) state;
            bundle.setClassLoader(loader);
            Parcelable[] fss = bundle.getParcelableArray("states");
            mSavedState.clear();
            mFragments.clear();
            if (fss != null) {
                for (int i = 0; i < fss.length; i++) {
                    mSavedState.add((Fragment.SavedState) fss[i]);
                }
            }
            Iterable<String> keys = bundle.keySet();
            for (String key : keys) {
                if (key.startsWith("f")) {
                    int index = Integer.parseInt(key.substring(1));
                    Fragment f = mFragmentManager.getFragment(bundle, key);
                    if (f != null) {
                        while (mFragments.size() <= index) {
                            mFragments.add(null);
                        }
                        f.setMenuVisibility(false);
                        mFragments.set(index, f);
                    } else {
                        Log.w(TAG, "Bad fragment at key " + key);
                    }
                }
            }
        }
    }
}