ViewPager+Fragmrnt最简单结合方法

Fragment和ViewPager

本博文系本菜鸟第一次博文展示,有错误之处请尽管提出

FragmentPagerAdapter

谷歌官方提供了这么一个adapter(FragmentPagerAdapter),

• 与正常的PagerAdapter相比:
  用FragmentPagerAdapter时:只需要复写getItem(int position),getCount()两个方法

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

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

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

• 用PagerAdapter时:通常要复写大部分方法:

@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);
}

下面附上FragmentPagerAdapter的代码

/* * 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 {@link android.support.v4.view.PagerAdapter} that * represents each page as a {@link 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 * {@link FragmentStatePagerAdapter}. * * <p>When using FragmentPagerAdapter the host ViewPager must have a * valid ID set.</p> * * <p>Subclasses only need to implement {@link #getItem(int)} * and {@link #getCount()} to have a working adapter. * * <p>Here is an example implementation of a pager containing fragments of * lists: * * {@sample development/samples/Support4Demos/src/com/example/android/supportv4/app/FragmentPagerSupport.java * complete} * * <p>The <code>R.layout.fragment_pager</code> resource of the top-level fragment is: * * {@sample 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: * * {@sample development/samples/Support4Demos/res/layout/fragment_pager_list.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;
    }
}

在代码中可以看出来,谷歌官方的api已经对Fragment的生命周期进行了一定的管理 大大的方便了有这种需要的程序猿们

本菜鸟在开发过程中同时用了ViewPager和Fragment打造首页展示页面 但是之前封装的Fragmrnt在使用过程中发生了一些错误
之前封装过一个BaseFragment来帮助自己减轻代码负担, 封装的时候并没有用v4包的Fragment

注意事项:该api对应的Fragment必须是v4包的Fragment 如果不是的话会报错,请注意.

                本人博文:转载请注明  http://blog.csdn.net/qq_25436769/article/details/50765557