学习Android Studio开发工具之Activity2（&Fragment）

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本篇是介绍Google推荐使用的fragment以及其与activity的通信。
新建一个BlankFragment，

其中自动生成的代码如下：

package com.hitsz.xiaokai.fragmentcom;import android.content.Context;import android.net.Uri;import android.os.Bundle;import android.support.v4.app.Fragment;import android.view.LayoutInflater;import android.view.View;import android.view.ViewGroup;/** * A simple {@link Fragment} subclass. * Activities that contain this fragment must implement the * {@link BlankFragment.OnFragmentInteractionListener} interface * to handle interaction events. * Use the {@link BlankFragment#newInstance} factory method to * create an instance of this fragment. * 这里是说实现子Fragment需要继承Fragment，这里是Google推荐的模板，在fragment里定义一个接口，然后它所依附的activity必须实现这个接口来完成相应的交互事件。 * 对于Fragment本身是使用工厂方法来创建实例的。 */public class BlankFragment extends Fragment {    // TODO: Rename parameter arguments, choose names that match    // the fragment initialization parameters, e.g. ARG_ITEM_NUMBER    //此处声明Fragment对应变量，一般是布局控件    private static final String ARG_PARAM1 = "param1";    private static final String ARG_PARAM2 = "param2";    // TODO: Rename and change types of parameters    private String mParam1;    private String mParam2;    //接口引用    private OnFragmentInteractionListener mListener;    public BlankFragment() {        // Required empty public constructor    }    /**     * Use this factory method to create a new instance of     * this fragment using the provided parameters.     *     * @param param1 Parameter 1.     * @param param2 Parameter 2.     * @return A new instance of fragment BlankFragment.     * 使用相应的参数返回工厂方法创建的Fragment     */    // TODO: Rename and change types and number of parameters    public static BlankFragment newInstance(String param1, String param2) {        BlankFragment fragment = new BlankFragment();        //使用Bundle传递数据        Bundle args = new Bundle();        args.putString(ARG_PARAM1, param1);        args.putString(ARG_PARAM2, param2);        fragment.setArguments(args);        return fragment;    }    @Override    public void onCreate(Bundle savedInstanceState) {        super.onCreate(savedInstanceState);        if (getArguments() != null) {            mParam1 = getArguments().getString(ARG_PARAM1);            mParam2 = getArguments().getString(ARG_PARAM2);        }    }    @Override    public View onCreateView(LayoutInflater inflater, ViewGroup container,                             Bundle savedInstanceState) {        // Inflate the layout for this fragment        //加载特定布局文件到布局容器中        return inflater.inflate(R.layout.fragment_blank, container, false);    }    // TODO: Rename method, update argument and hook method into UI event    //更新参数到ui    public void onButtonPressed(Uri uri) {        if (mListener != null) {            mListener.onFragmentInteraction(uri);        }    }    @Override    public void onAttach(Context context) {        super.onAttach(context);        //判断activity是否实现了内部接口，如果没有实现抛出异常        if (context instanceof OnFragmentInteractionListener) {            mListener = (OnFragmentInteractionListener) context;        } else {            throw new RuntimeException(context.toString()                    + " must implement OnFragmentInteractionListener");        }    }   //解除依附关系，同时将接口对象置空，方便垃圾回收    @Override    public void onDetach() {        super.onDetach();        mListener = null;    }    /**     * This interface must be implemented by activities that contain this     * fragment to allow an interaction in this fragment to be communicated     * to the activity and potentially other fragments contained in that     * activity.     * <p/>     * See the Android Training lesson <a href=     * "http://developer.android.com/training/basics/fragments/communicating.html"     * >Communicating with Other Fragments</a> for more information.     * 此接口必须被activity实现     */    public interface OnFragmentInteractionListener {        // TODO: Update argument type and name        void onFragmentInteraction(Uri uri);    }}

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这里拿官网给的demo作为演示：

布局文件layout/article_view.xml

<TextView xmlns:android="http://schemas.android.com/apk/res/android"    android:id="@+id/article"    android:layout_width="match_parent"    android:layout_height="match_parent"    android:padding="16dp"    android:textSize="18sp" />

layout/news_articles.xml

<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"    android:id="@+id/fragment_container"    android:layout_width="match_parent"    android:layout_height="match_parent" />

layout_large/news_articles.xml

<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"    android:id="@+id/fragment_container"    android:layout_width="match_parent"    android:layout_height="match_parent" />

显示数据Ipsum.java

package com.hitsz.xiaokai.fragmentcom;public class Ipsum {    static String[] Headlines = {        "Article One",        "Article Two"    };    static String[] Articles = {        "Article One\n\nExcepteur pour-over occaecat squid biodiesel umami gastropub, nulla laborum salvia dreamcatcher fanny pack. Ullamco culpa retro ea, trust fund excepteur eiusmod direct trade banksy nisi lo-fi cray messenger bag. Nesciunt esse carles selvage put a bird on it gluten-free, wes anderson ut trust fund twee occupy viral. Laboris small batch scenester pork belly, leggings ut farm-to-table aliquip yr nostrud iphone viral next level. Craft beer dreamcatcher pinterest truffaut ethnic, authentic brunch. Esse single-origin coffee banksy do next level tempor. Velit synth dreamcatcher, magna shoreditch in american apparel messenger bag narwhal PBR ennui farm-to-table.",        "Article Two\n\nVinyl williamsburg non velit, master cleanse four loko banh mi. Enim kogi keytar trust fund pop-up portland gentrify. Non ea typewriter dolore deserunt Austin. Ad magna ethical kogi mixtape next level. Aliqua pork belly thundercats, ut pop-up tattooed dreamcatcher kogi accusamus photo booth irony portland. Semiotics brunch ut locavore irure, enim etsy laborum stumptown carles gentrify post-ironic cray. Butcher 3 wolf moon blog synth, vegan carles odd future."    };}

导航Fragment，继承自ListFragment，自带listview。
HeadlinesFragment.java

package com.hitsz.xiaokai.fragmentcom;import android.app.Activity;import android.os.Build;import android.os.Bundle;import android.support.v4.app.ListFragment;import android.view.View;import android.widget.ArrayAdapter;import android.widget.ListView;public class HeadlinesFragment extends ListFragment {    //定义内部接口引用    OnHeadlineSelectedListener mCallback;    // The container Activity must implement this interface so the frag can deliver messages    public interface OnHeadlineSelectedListener {        /** Called by HeadlinesFragment when a list item is selected，当点击list item时回调，携带点击位置信息         */        public void onArticleSelected(int position);    }    @Override    public void onCreate(Bundle savedInstanceState) {        super.onCreate(savedInstanceState);        // We need to use a different list item layout for devices older than Honeycomb        int layout = Build.VERSION.SDK_INT >= Build.VERSION_CODES.HONEYCOMB ?                android.R.layout.simple_list_item_activated_1 : android.R.layout.simple_list_item_1;        // Create an array adapter for the list view, using the Ipsum headlines array 创建一个适配器ArrayAdapter<String>显示listview内容        setListAdapter(new ArrayAdapter<String>(getActivity(), layout, Ipsum.Headlines));    }    @Override    public void onStart() {        super.onStart();        // When in two-pane layout, set the listview to highlight the selected list item        // (We do this during onStart because at the point the listview is available.)        //根据id获取Fragment，需要在布局文件中使用Fragment标签加载Fragment        if (getFragmentManager().findFragmentById(R.id.article_fragment) != null) {            getListView().setChoiceMode(ListView.CHOICE_MODE_SINGLE);        }    }    @Override    public void onAttach(Activity activity) {        super.onAttach(activity);        // This makes sure that the container activity has implemented        // the callback interface. If not, it throws an exception.确保依附的activity实现接口        try {            mCallback = (OnHeadlineSelectedListener) activity;        } catch (ClassCastException e) {            throw new ClassCastException(activity.toString()                    + " must implement OnHeadlineSelectedListener");        }    }    @Override    public void onListItemClick(ListView l, View v, int position, long id) {        // Notify the parent activity of selected item        //通知activity选中的item        mCallback.onArticleSelected(position);        // Set the item as checked to be highlighted when in two-pane layout,设为高亮        getListView().setItemChecked(position, true);    }}

显示详细内容的ArticleFragment.java

package com.hitsz.xiaokai.fragmentcom;import android.support.v4.app.Fragment;import android.os.Bundle;import android.view.LayoutInflater;import android.view.View;import android.view.ViewGroup;import android.widget.TextView;public class ArticleFragment extends Fragment {    //Fragment通信参数    final static String ARG_POSITION = "position";    int mCurrentPosition = -1;    @Override    public View onCreateView(LayoutInflater inflater, ViewGroup container,         Bundle savedInstanceState) {        // If activity recreated (such as from screen rotate), restore        // the previous article selection set by onSaveInstanceState().        // This is primarily necessary when in the two-pane layout.考虑的activity非正常退出，还原状态        if (savedInstanceState != null) {            mCurrentPosition = savedInstanceState.getInt(ARG_POSITION);        }        // Inflate the layout for this fragment        return inflater.inflate(R.layout.article_view, container, false);    }    @Override    public void onStart() {        super.onStart();        // During startup, check if there are arguments passed to the fragment.        // onStart is a good place to do this because the layout has already been        // applied to the fragment at this point so we can safely call the method        // below that sets the article text.        Bundle args = getArguments();        if (args != null) {            // Set article based on argument passed in            updateArticleView(args.getInt(ARG_POSITION));        } else if (mCurrentPosition != -1) {            // Set article based on saved instance state defined during onCreateView            updateArticleView(mCurrentPosition);        }    }    public void updateArticleView(int position) {        TextView article = (TextView) getActivity().findViewById(R.id.article);        article.setText(Ipsum.Articles[position]);        mCurrentPosition = position;    }    @Override    public void onSaveInstanceState(Bundle outState) {        super.onSaveInstanceState(outState);        // Save the current article selection in case we need to recreate the fragment        outState.putInt(ARG_POSITION, mCurrentPosition);    }}

主activity，MainActivity.java

package com.hitsz.xiaokai.fragmentcom;import android.os.Bundle;import android.support.v4.app.FragmentActivity;import android.support.v4.app.FragmentTransaction;import com.hitsz.xiaokai.fragmentcom.ArticleFragment;import com.hitsz.xiaokai.fragmentcom.R;//实现需要通信Fragment的内部接口public class MainActivity extends FragmentActivity        implements HeadlinesFragment.OnHeadlineSelectedListener {    /** Called when the activity is first created. */    @Override    public void onCreate(Bundle savedInstanceState) {        super.onCreate(savedInstanceState);        setContentView(R.layout.news_articles);        // Check whether the activity is using the layout version with        // the fragment_container FrameLayout. If so, we must add the first fragment如果不是xml加载需要使用Fragment事务加载Fragment        if (findViewById(R.id.fragment_container) != null) {            // However, if we're being restored from a previous state,            // then we don't need to do anything and should return or else            // we could end up with overlapping fragments.            if (savedInstanceState != null) {                return;            }            // Create an instance of ExampleFragment            HeadlinesFragment firstFragment = new HeadlinesFragment();            // In case this activity was started with special instructions from an Intent,            // pass the Intent's extras to the fragment as arguments            firstFragment.setArguments(getIntent().getExtras());            // Add the fragment to the 'fragment_container' FrameLayout添加Fragment到activity的主要方法            getSupportFragmentManager().beginTransaction()                    .add(R.id.fragment_container, firstFragment).commit();        }    }    public void onArticleSelected(int position) {        // The user selected the headline of an article from the HeadlinesFragment        // Capture the article fragment from the activity layout          ArticleFragment articleFrag = (ArticleFragment)                getSupportFragmentManager().findFragmentById(R.id.article_fragment);        if (articleFrag != null) {            // If article frag is available, we're in two-pane layout...            // Call a method in the ArticleFragment to update its content            articleFrag.updateArticleView(position);        } else {            // If the frag is not available, we're in the one-pane layout and must swap frags...            // Create fragment and give it an argument for the selected article            ArticleFragment newFragment = new ArticleFragment();            //通过bundle携带数据，传递数据给articleFragment，Fragment之间的通信方式            Bundle args = new Bundle();            args.putInt(ArticleFragment.ARG_POSITION, position);            newFragment.setArguments(args);            FragmentTransaction transaction = getSupportFragmentManager().beginTransaction();            // Replace whatever is in the fragment_container view with this fragment,            // and add the transaction to the back stack so the user can navigate back 添加返回栈            transaction.replace(R.id.fragment_container, newFragment);            transaction.addToBackStack(null);            // Commit the transaction提交事务            transaction.commit();        }    }}

运行效果：