CriminalIntent项目开发笔记(三)----ListFragment的使用

本节主要学习ListFragment的用法。

1.更新模型层，创建一个 CrimeLab 类用于存储多个Crime对象

　　CrimeLab采用单例模式，以便数据的集中存储

package com.criminalintent;

import android.content.Context;

import java.util.ArrayList;
import java.util.List;
import java.util.UUID;

public class CrimeLab {
    private List<Crime> crimeList;
    private Context context;

    private CrimeLab(Context context){
        this.context=context;
        crimeList=new ArrayList<Crime>();
        for(int i=0;i<100;i++){
            Crime crime=new Crime();
            crime.setTitle("item"+i);
            crime.setSolved(i%2==0);
            crimeList.add(crime);
        }
    }
    private static CrimeLab instance;
    public static CrimeLab getInstance(Context context){
        if(instance==null)
            instance=new CrimeLab(context.getApplicationContext());
        return instance;
    }
    public List<Crime> getCrimeList(){
        return crimeList;
    }
    public Crime getCrime(UUID uuid){
        for(Crime c:crimeList){
            if(c.getUuid()==uuid)
                return c;
        }
        return null;
    }
}

2.创建 CrimeListFragment类以及CrimeAdapter内部类

　　该类继承于ListFragment类，也就是本节主要的学习内容，ListFragment中默认有一个ListView对象，所以我们不用再新创建一个ListView控件的视图，只需要实现Adapter控制器对象，然后调用setListAdapter（adapter）方法即可。

在此之前，我们先准备好Adapter需要的子布局视图 list_item_crime.xml

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="wrap_content">
    <CheckBox android:id="@+id/crime_list_item_solvedCheckBox"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:gravity="center"
        android:layout_alignParentRight="true"
        android:enabled="false"
        android:focusable="false"
        android:padding="4dp" />
    <TextView android:id="@+id/crime_list_item_titleTextView"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_toLeftOf="@id/crime_list_item_solvedCheckBox"
        android:textStyle="bold"
        android:paddingLeft="4dp"
        android:paddingRight="4dp"
        android:text="Crime title" />
    <TextView android:id="@+id/crime_list_item_dateTextView"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_below="@id/crime_list_item_titleTextView"
        android:layout_toLeftOf="@id/crime_list_item_solvedCheckBox"
        android:paddingLeft="4dp"
        android:paddingRight="4dp"
        android:paddingTop="4dp"
        android:text="Crime date" />
</RelativeLayout>

接下来创建CrimeListFragment

public class CrimeListFragment extends ListFragment {
    private List<Crime> crimeList;
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        crimeList=CrimeLab.getInstance(getActivity()).getCrimeList();
        getActivity().setTitle(R.string.crimes_title);
//       构造adpter
        CrimeAdapter adapter=new CrimeAdapter(getActivity(),R.layout.list_item_crime,crimeList);
        setListAdapter(adapter);
    }

    @Override
    public void onListItemClick(ListView l, View v, int position, long id) {
        Crime crime= (Crime) getListAdapter().getItem(position);
        Log.d("item",crime.getTitle() + " was clicked");
    }
//    CrimeAdapter控制ListView控件中的每个子布局如何显示，所以构造 CrimeAdapter需要一个子项布局视图，和数据链表
 //   在此为 R.layout.list_item_crime和crimeList
    class CrimeAdapter extends ArrayAdapter<Crime>{

        public CrimeAdapter(Context context, int resource, List<Crime> objects) {
            super(context, resource, objects);
        }

        @Override
        public View getView(int position, View convertView, ViewGroup parent) {

            Crime crime=getItem(position);
            if(convertView==null){
                convertView=LayoutInflater.from(getContext()).inflate(R.layout.list_item_crime,null);
            }
            TextView titleTextView= (TextView) convertView.findViewById(R.id.crime_list_item_titleTextView);
            titleTextView.setText(crime.getTitle());
            TextView dateTextView= (TextView) convertView.findViewById(R.id.crime_list_item_dateTextView);
            dateTextView.setText(crime.getDate().toString());
            CheckBox checkBox= (CheckBox) convertView.findViewById(R.id.crime_list_item_solvedCheckBox);
            checkBox.setChecked(crime.isSolved());
            return convertView;
        }
    }
}

3.抽象Activity类

　　在Activity的代码中，除了创建fragment的代码不同，其他都一样，所以可以将相同的代码抽出来，形成一个抽象父类。创建fragment的代码，写成一个抽象方法createFragment（），以后每创建一个Activity都只需重写creatFragment()方法即可。下面就是抽象出来的类

public abstract class SingleFragmentActivity extends FragmentActivity {
    protected abstract Fragment createFragment();
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        FragmentManager fm=getSupportFragmentManager();
        Fragment fragment=fm.findFragmentById(R.id.fragmentContainer);
        if(fragment==null){
            fragment=createFragment();
            fm.beginTransaction()
                    .add(R.id.fragmentContainer,fragment)
                    .commit();
        }
    }
}

4.修改MainActivity类，让其继承SingleFragmentActivtity,并重写createFragment方法　　

public class MainActivity extends SingleFragmentActivity {

    @Override
    protected Fragment createFragment() {
        return new CrimeListFragment();
    }

}

最后运行效果如下：