學習Android Studio開發工具之Activity2（&Fragment）

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本篇是介紹Google推薦使用的fragment以及其與activity的通信。
新建一個BlankFragment，

其中自動生成的代碼如下：<喎?/kf/ware/vc/" target="_blank" class="keylink">vcD4NCjxwcmUgY2xhc3M9"brush:java;"> 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. * 這裡是說實現子Fragment需要繼承Fragment，這裡是Google推薦的模板，在fragment裡定義一個接口，然後它所依附的activity必須實現這個接口來完成相應的交互事件。 * 對於Fragment本身是使用工廠方法來創建實例的。 */ public class BlankFragment extends Fragment { // TODO: Rename parameter arguments, choose names that match // the fragment initialization parameters, e.g. ARG_ITEM_NUMBER //此處聲明Fragment對應變量，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. * 使用相應的參數返回工廠方法創建的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傳遞數據 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 //加載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 //更新參數到ui public void onButtonPressed(Uri uri) { if (mListener != null) { mListener.onFragmentInteraction(uri); } } @Override public void onAttach(Context context) { super.onAttach(context); //判斷activity是否實現了內部接口，如果沒有實現拋出異常 if (context instanceof OnFragmentInteractionListener) { mListener = (OnFragmentInteractionListener) context; } else { throw new RuntimeException(context.toString() + " must implement OnFragmentInteractionListener"); } } //解除依附關系，同時將接口對象置空，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. *

* See the Android Training lesson Communicating with Other Fragments for more information. * 此接口必須被activity實現 */ public interface OnFragmentInteractionListener { // TODO: Update argument type and name void onFragmentInteraction(Uri uri); } }

這裡拿官網給的demo作為演示：

布局文件layout/article_view.xml

layout/news_articles.xml

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

layout_large/news_articles.xml

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

顯示數據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."
    };
}

導航Fragment，繼承自ListFragment，自帶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 {
    //定義內部接口引用
    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，當點擊list item時回調，攜帶點擊位置信息 
        */
        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 創建一個適配器ArrayAdapter顯示listview內容
        setListAdapter(new ArrayAdapter(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.)
        //根據id獲取Fragment，需要在布局文件中使用Fragment標簽加載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.確保依附的activity實現接口
        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選中的item
        mCallback.onArticleSelected(position);

        // Set the item as checked to be highlighted when in two-pane layout,設為高亮
        getListView().setItemChecked(position, true);
    }
}

顯示詳細內容的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通信參數
    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.考慮的activity非正常退出，還原狀態
        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;
//實現需要通信Fragment的內部接口
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加載需要使用Fragment事務加載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();
            //通過bundle攜帶數據，傳遞數據給articleFragment，Fragment之間的通信方式
            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 添加返回棧
            transaction.replace(R.id.fragment_container, newFragment);
            transaction.addToBackStack(null);

            // Commit the transaction提交事務
            transaction.commit();
        }
    }
}

運行效果：