useListView.md

使用ListView

---

• ListView是ViewGroup的子类,每个列表项都是作为ListView的一个View子对象显示的;

• 每个Record列表只需要显示对应的日期,View对象是一个简单的TextView;

• 当ListView需要显示某个列表项时,它才会去申请一个可用的视图对象;

• adapter是一个控制器对象,从模型层获取数据,并将其提供给ListView显示,它有三个作用

  • 创建必要的视图对象;
  • 用模型层数据填充视图对象;
  • 将准备好的视图对象返回给ListView;

• 当ListView需要显示视图对象时,会与其adapter展开会话沟通

  • 首先调用adapter.getCount()询问数组列表对象个数;
  • 然后调用adapter.getView(int,View,ViewGroup);

• RecordListFragment.java(simple_list_item_1是Android SDK提供的预定义布局资源)

   public class RecordListFragment extends ListFragment {
   	private ArrayList<Record> mRecords;
  
   	@Override
   	public void onCreate(Bundle savedInstanceState) {
   		super.onCreate(savedInstanceState);
   		mRecords = RecordLab.get(getActivity()).getRecords();
  
   		ArrayAdapter<Record> adapter =
   				new ArrayAdapter<Record>(getActivity(),
   						android.R.layout.simple_list_item_1,
   						mRecords);
   		setListAdapter(adapter);
   	}
   }

• 默认的ArrayAdapter<T>.getView(...)实现依赖于toString()方法,所以需要覆盖Record.toString()方法

   @Override
   public String toString() {
   	return DateFormat.format("MMMM dd",mDate).toString();
   }

• 当数据更新时,需要手动进行ListView的刷新,否则自行刷新会很慢

   adapter.notifyDataSetChanged();

• 响应列表项点击事件(自行处理),RecordListFragment.java

   @Override
   public void onListItemClick(ListView l, View v, int position, long id) {
   	//Record r = (Record)(getListAdapter()).getItem(position);
   	//wait to update
   }

• 预定义的列表项显示的可能不是我们想要的信息,所以需要定制列表项

  • 首先创建列表项视图的XML布局文件;

    • RelativeLayout子视图相对于根布局及子视图相对于子视图的布置排列,需要使用一些布局参数加以控制;

    • 我想要消费金额对齐RelativeLayout布局的右手边,日期相对于消费金额左对齐;

    • list_item_record.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="match_parent">
      
       	<TextView
       		android:id="@+id/record_list_item_dateTextView"
       		android:layout_width="match_parent"
       		android:layout_height="wrap_content"
       		android:gravity="start"
       		android:textStyle="bold"
       		android:paddingLeft="4dp"
       		android:paddingRight="4dp"
       		android:text="@string/record_list_item_dateText"
       		/>
       	<TextView
       		android:id="@+id/record_list_item_totalTodayTextView"
       		android:layout_width="match_parent"
       		android:layout_height="wrap_content"
       		android:layout_below="@id/record_list_item_dateTextView"
       		android:gravity="end"
       		android:layout_alignParentRight="true"
       		android:layout_alignParentEnd="true"
       		android:paddingLeft="4dp"
       		android:paddingRight="4dp"
       		android:text="@string/record_list_item_totalTodayText"
       		/>
      
       </RelativeLayout>

  • 构建自己的ListView适配器RecordAdapter并使用

     public class RecordListFragment extends ListFragment {
     	private ArrayList<Record> mRecords;
    
     	private class RecordAdapter extends ArrayAdapter<Record>{
     		public RecordAdapter(ArrayList<Record> records){
     			super(getActivity(),0,records);
     		}
    
     		@NonNull
     		@Override
     		public View getView(int position, View convertView, ViewGroup parent) {
     			// if we weren't given a view, inflate one
     			if(null == convertView){
     				convertView = getActivity().getLayoutInflater()
     						.inflate(R.layout.list_item_record, null);
     			}
    
     			// configure the view for this record
     			Record record = getItem(position);
    
     			TextView dateTextView =
     					(TextView)convertView.findViewById(R.id.record_list_item_dateTextView);
     			dateTextView.setText(DateFormat.format("MMMM dd",record.getmDate()));
    
     			TextView totalTodayTextView =
     					(TextView)convertView.findViewById(R.id.record_list_item_totalTodayTextView);
     			totalTodayTextView.setText(String.valueOf(record.getmTotal_today()));
    
     			return convertView;
     		}
     	}
    
     	@Override
     	public void onCreate(Bundle savedInstanceState) {
     		super.onCreate(savedInstanceState);
     		mRecords = RecordLab.get(getActivity()).getRecords();
    
     		RecordAdapter adapter = new RecordAdapter(mRecords);
     		setListAdapter(adapter);
     	}
    
     	@Override
     	public void onListItemClick(ListView l, View v, int position, long id) {
     		//Record r = ((RecordAdapter)getListAdapter()).getItem(position);
     		//wait to update
     	}
     }

• 最后,空的list视图一点也不好看,所以为空list视图设置空视图

   private TextView noItems(String text) {
   	TextView emptyView = new TextView(getActivity());
   	//Make sure you import android.widget.LinearLayout.LayoutParams;
   	emptyView.setLayoutParams(new LinearLayout.LayoutParams(LinearLayout.LayoutParams.MATCH_PARENT,
   			LinearLayout.LayoutParams.MATCH_PARENT));
   	emptyView.setText(text);
   	emptyView.setTextSize(12);
   	emptyView.setVisibility(View.GONE);
   	emptyView.setGravity(Gravity.CENTER_VERTICAL
   			| Gravity.CENTER_HORIZONTAL);
  
   	//Add the view to the list view. This might be what you are missing
   	((ViewGroup) getListView().getParent()).addView(emptyView);
  
   	return emptyView;
   }
  
   @Override
   public void onStart() {
   	super.onStart();
   	getListView().setEmptyView(
   			noItems(getResources().getString(R.string.empty_text)));
   }