Fragment和ViewPager

本博文系本菜鳥第一次博文展示,有錯誤之處請雖然提出

FragmentPagerAdapter

谷歌官方提供了這麽一個adapter(FragmentPagerAdapter),

• 與正常的PagerAdapter相比:
  用FragmentPagerAdapter時:僅僅須要復寫getItem(int position),getCount()兩個方法

public MyPagerAdapter(FragmentManager fm) {
    super(fm)
}

@Override
public Fragment getItem
 
(int position) {
    return null;
}

@Override
public int getCount() {
    return 0;
}

• 用PagerAdapter時:通常要復寫大部分方法:

@Override
public int getCount() {
    return 0;
}

@Override
public boolean isViewFromObject(View view, Object object) {
    return false;
}

public MyPagerAdapter() {
    super();
}

@Override
 

public Object instantiateItem(ViewGroup container, int position) {
    return super.instantiateItem(container, position);
}

@Override
public void destroyItem(ViewGroup container, int position, Object object) {
    super.destroyItem(container, position, object);
}

以下附上FragmentPagerAdapter的代碼

/*
 * Copyright (C) 2011 The Android Open Source Project
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
 


package android.support.v4.app;

import android.os.Parcelable;
import android.support.v4.view.PagerAdapter;
import android.util.Log;
import android.view.View;
import android.view.ViewGroup;

/**
 * Implementation of [email protected] android.support.v4.view.PagerAdapter} that
 * represents each page as a [email protected] Fragment} that is persistently
 * kept in the fragment manager as long as the user can return to the page.
 *
 * <p>This version of the pager is best for use when there are a handful of
 * typically more static fragments to be paged through, such as a set of tabs.
 * The fragment of each page the user visits will be kept in memory, though its
 * view hierarchy may be destroyed when not visible.  This can result in using
 * a significant amount of memory since fragment instances can hold on to an
 * arbitrary amount of state.  For larger sets of pages, consider
 * [email protected] FragmentStatePagerAdapter}.
 *
 * <p>When using FragmentPagerAdapter the host ViewPager must have a
 * valid ID set.</p>
 *
 * <p>Subclasses only need to implement [email protected] #getItem(int)}
 * and [email protected] #getCount()} to have a working adapter.
 *
 * <p>Here is an example implementation of a pager containing fragments of
 * lists:
 *
 * [email protected] [email protected]v4/app/FragmentPagerSupport.java
 *      complete}
 *
 * <p>The <code>R.layout.fragment_pager</code> resource of the top-level fragment is:
 *
 * [email protected] development/samples/Support4Demos/res/layout/fragment_pager.xml
 *      complete}
 *
 * <p>The <code>R.layout.fragment_pager_list</code> resource containing each
 * individual fragment‘s layout is:
 *
 * [email protected] [email protected]xml
 *      complete}
 */
public abstract class FragmentPagerAdapter extends PagerAdapter {
    private static final String TAG = "FragmentPagerAdapter";
    private static final boolean DEBUG = false;

    private final FragmentManager mFragmentManager;
    private FragmentTransaction mCurTransaction = null;
    private Fragment mCurrentPrimaryItem = null;

    public FragmentPagerAdapter(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 (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;
    }

    @Override
    public void destroyItem(ViewGroup container, int position, Object object) {
        if (mCurTransaction == null) {
            mCurTransaction = mFragmentManager.beginTransaction();
        }
        if (DEBUG) Log.v(TAG, "Detaching item #" + getItemId(position) + ": f=" + object
                + " v=" + ((Fragment)object).getView());
        mCurTransaction.detach((Fragment)object);
    }

    @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() {
        return null;
    }

    @Override
    public void restoreState(Parcelable state, ClassLoader loader) {
    }

    /**
     * Return a unique identifier for the item at the given position.
     *
     * <p>The default implementation returns the given position.
     * Subclasses should override this method if the positions of items can change.</p>
     *
     * @param position Position within this adapter
     * @return Unique identifier for the item at position
     */
    public long getItemId(int position) {
        return position;
    }

    private static String makeFragmentName(int viewId, long id) {
        return "android:switcher:" + viewId + ":" + id;
    }
}

在代碼中能夠看出來,谷歌官方的api已經對Fragment的生命周期進行了一定的管理 大大的方便了有這樣的須要的程序員們

本菜鳥在開發過程中同一時候用了ViewPager和Fragment打造首頁展示頁面 可是之前封裝的Fragmrnt在使用過程中發生了一些錯誤
之前封裝過一個BaseFragment來幫助自己減輕代碼負擔, 封裝的時候並沒實用v4包的Fragment

註意事項:該api相應的Fragment必須是v4包的Fragment 假設不是的話會報錯,請註意.

                本人博文:轉載請註明  http://blog.csdn.net/qq_25436769/article/details/50765557

ViewPager+Fragmrnt最簡單結合方法