Fragment和ViewPager

本博文系本菜鸟第一次博文展示,有错误之处请虽然提出

FragmentPagerAdapter

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

  • 与正常的PagerAdapter相比:

    用FragmentPagerAdapter时:仅仅须要复写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);
}

以下附上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;
}
}

在代码中能够看出来,谷歌官方的api已经对Fragment的生命周期进行了一定的管理 大大的方便了有这样的须要的程序员们

本菜鸟在开发过程中同一时候用了ViewPager和Fragment打造首页展示页面 可是之前封装的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, 封装的时候并没实用v4包的Fragment

注意事项:该api相应的Fragment必须是v4包的Fragment 假设不是的话会报错,请注意.

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

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