Filter实现原理及内部流程

一、Filter简介 

APi中对Filter的描述极为精简，就是通过用户设置的过滤条件，通过Filter内部的一系列操作（对数据的过滤处理通常通过线程异步操作）实现过滤条件，最终获得过滤后的结果。一般通过实现Filterable接口调用（自定义的）Filter。

1、Filterable
Filterable定义一过滤行为，利用Filter对数据进行过滤处理。Filterable通常实现对Adapt的限制。

Public interface Filterable{
    //Returns a filter that can be used to constrain data with a filtering pattern.
    //This method is usually implemented by android.widget.Adapter classes.
    Filter getFilter();
}

2、Filter

Filter通过定义的filter pattern实现对数据的过滤行为，对数据的过滤操作是异步实现的，通过调用filter(CharSequence)或filter(CharSequence, android.widget.Filter.FilterListener)实现，如果这两个方法被调用，先前还未被执行的异步操作将被取消，而只是执行此次调用的异步操作。Filter通常由Filterable创建，即Filter getFilter()，此处得到的Filter必然是用户自定义的，通常需要实现

 FilterResults performFiltering(CharSequence constraint)

<pre name="code" class="java">publishResults(CharSequence,android.widget.Filter.FilterResults)

源码如下：

<pre name="code" class="java">public abstract class Filter {  
    
    //执行异步过滤操作，调用此方法将会终止所有先前还未被执行的异步操作
    public final void filter(CharSequence constraint) {
        filter(constraint, null);
    }
    
    //upon completion of the operation，the listener is notified
    public final void filter(CharSequence constraint, FilterListener listener)
    
    //在线程中调用该方法，根据提供的 constraint执行过滤操作，该操作返回FilterResults
    //在UI线程中，通过调用publishResults(CharSequence,android.widget.Filter.FilterResults)返回FilterResults
    protected abstract FilterResults performFiltering(CharSequence constraint);
    
    //在线程中调用此函数，将过滤后的结果FilterResults更新到UI界面，
    protected abstract void publishResults(CharSequence constraint,FilterResults results);
  
    //将过滤后的Item转换成字符串，根据实际需要重写
    public CharSequence convertResultToString(Object resultValue) {
        return resultValue == null ? "" : resultValue.toString();
    }
    
    //保存过滤操作后得到的结果，实际上就是一个数据封装
    protected static class FilterResults {
        public FilterResults() {           
        }
        // Contains all the values computed by the filtering operation.
        //一般是数组或Arraylist
        public Object values;
        //values个数
        public int count;
    }
    
    //Listener used to receive a notification upon completion of a filtering operation
    public static interface FilterListener {
    //Notifies the end of a filtering operation
    public void onFilterComplete(int count);
    }
}

二、AutoCompleteTextView利用ArrayAdapter实现提示原理

实现一个完整的Filter流程，一般是两个步骤：一是实现对数据的过滤操作，获得过滤结果后，通过观察者模式获知数据发生变化，并进行后续处理；二是在过滤操作完成后，调用监听器接口实现自定义操作：public static interface FilterListener 

1、ArrayAdapter 
ArrayAdapter实现继承自Filter的内部类ArrayFilter，主要是实现两个函数：performFiltering，主要是对ArrayAdapter中的数据项实现对某个前缀的匹配操作，并获得匹配的数据项；publishResults，获得符合过滤条件的结果后，通过观察者模式，实现刷新等操作。

public class ArrayAdapter<T> extends BaseAdapter implements Filterable {


    public Filter getFilter() {
        if (mFilter == null) {
            mFilter = new ArrayFilter();
        }
        return mFilter;
    }


    /**
     * An array filter constrains the content of the array adapter with  a prefix. 
     * Each item that does not start with the supplied prefix  is removed from the list.
     */
     
    private class ArrayFilter extends Filter {
        @Override
        protected FilterResults performFiltering(CharSequence prefix) {
        
            FilterResults results = new FilterResults();


            if (mOriginalValues == null) {
                synchronized (mLock) {
                    mOriginalValues = new ArrayList<T>(mObjects);
                }
            }


            if (prefix == null || prefix.length() == 0) {
                ArrayList<T> list;
                synchronized (mLock) {
                    list = new ArrayList<T>(mOriginalValues);
                }
                results.values = list;
                results.count = list.size();
            } else {
                String prefixString = prefix.toString().toLowerCase();


                ArrayList<T> values;
                synchronized (mLock) {
                    values = new ArrayList<T>(mOriginalValues);
                }


                final int count = values.size();
                final ArrayList<T> newValues = new ArrayList<T>();


                for (int i = 0; i < count; i++) {
                    final T value = values.get(i);
                    final String valueText = value.toString().toLowerCase();


                    // First match against the whole, non-splitted value
                    if (valueText.startsWith(prefixString)) {
                        newValues.add(value);
                    } else {
                        final String[] words = valueText.split(" ");
                        final int wordCount = words.length;


                        // Start at index 0, in case valueText starts with space(s)
                        for (int k = 0; k < wordCount; k++) {
                            if (words[k].startsWith(prefixString)) {
                                newValues.add(value);
                                break;
                            }
                        }
                    }
                }


                results.values = newValues;
                results.count = newValues.size();
            }


            return results;
        }


        @Override
        protected void publishResults(CharSequence constraint, FilterResults results) {
            //noinspection unchecked
            mObjects = (List<T>) results.values;
            if (results.count > 0) {
                notifyDataSetChanged();
            } else {
                notifyDataSetInvalidated();
            }
       }
}

2、AutoCompleteTextView

实现Filter中的接口Filter.FilterListener

public class AutoCompleteTextView extends EditText implements Filter.FilterListener {


    public void onFilterComplete(int count) {
        updateDropDownForFilter(count);
    }


    private void updateDropDownForFilter(int count) {
        // Not attached to window, don't update drop-down
        if (getWindowVisibility() == View.GONE) return;


        /*
         * This checks enoughToFilter() again because filtering requests
         * are asynchronous, so the result may come back after enough text
         * has since been deleted to make it no longer appropriate
         * to filter.
         */


        final boolean dropDownAlwaysVisible = mPopup.isDropDownAlwaysVisible();
        final boolean enoughToFilter = enoughToFilter();
        if ((count > 0 || dropDownAlwaysVisible) && enoughToFilter) {
            if (hasFocus() && hasWindowFocus() && mPopupCanBeUpdated) {
                showDropDown();
            }
        } else if (!dropDownAlwaysVisible && isPopupShowing()) {
            dismissDropDown();
            // When the filter text is changed, the first update from the adapter may show an empty
            // count (when the query is being performed on the network). Future updates when some
            // content has been retrieved should still be able to update the list.
            mPopupCanBeUpdated = true;
        }
    }

三、自定义Filter

ArrayAdapter只能实现一个TextView，通过自定义一个ContactAdapter，实现两个TextView，配合AutoCompleteTextview使用

自定义ContactAdapter：

package com.study.contactadapter;

import java.util.ArrayList;

import android.content.Context;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.BaseAdapter;
import android.widget.Filter;
import android.widget.Filterable;
import android.widget.TextView;

import com.example.autotipphonenumber.R;
import com.study.remind.Contact;

public class ContactAdapter extends BaseAdapter implements Filterable{
	
	private Context context;
	private ArrayList<Contact> Datas;
	private LayoutInflater inflater;
	
	public ContactAdapter(Context context,ArrayList<Contact> Datas){
		this.context=context;
		this.Datas=Datas;	
		//设置inflater的两种方式
		//inflater=(LayoutInflater) context.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
		inflater=LayoutInflater.from(context);
	}

	@Override
	public int getCount() {
		// TODO Auto-generated method stub
		return Datas.size();
	}

	@Override
	public Object getItem(int position) {
		// TODO Auto-generated method stub
		return Datas.get(position);
	}

	@Override
	public long getItemId(int position) {
		// TODO Auto-generated method stub
		return position;
	}

	@Override
	public View getView(int position, View convertView, ViewGroup parent) {
		View root = inflater.inflate(R.layout.contcat,null);
		
		TextView name=(TextView) root.findViewById(R.id.name);
		TextView phoneNum=(TextView) root.findViewById(R.id.phoneNum);
		
		name.setText(Datas.get(position).getName());
		phoneNum.setText(Datas.get(position).getPhoneNum());
		return root;
	}

	//实现Filterabale接口
	@Override
	public Filter getFilter() {
		return new ContactFilter();
	}
	
	private class ContactFilter extends Filter{

		@Override
		//两个textview中的任意一个<span style="font-family: KaiTi_GB2312;">首字母符合过滤条件，则将其加入到过滤结果中</span>

protected FilterResults performFiltering(CharSequence constraint) {
			
			FilterResults results = new FilterResults();
			ArrayList<Contact> filterResult=new ArrayList<Contact>();
					
			
			for(int i=0;i<Datas.size();i++){
				if(Datas.get(i).getName().startsWith((String) constraint) || Datas.get(i).getPhoneNum().startsWith((String) constraint) ){
					filterResult.add(Datas.get(i));
				}
			}
			
            results.values = filterResult;
            results.count = filterResult.size();
			return results;
		}

		@Override
		protected void publishResults(CharSequence constraint,
				FilterResults results) {

            if (results.count > 0) {
                notifyDataSetChanged();
            } else {
                notifyDataSetInvalidated();
            }
			
		}
		
	}

}

MainActivity源码：

package com.example.autotipphonenumber;

import java.util.ArrayList;

import android.app.Activity;
import android.os.Bundle;
import android.util.Log;
import android.view.View;
import android.widget.AdapterView;
import android.widget.AdapterView.OnItemClickListener;
import android.widget.AdapterView.OnItemSelectedListener;
import android.widget.AutoCompleteTextView;

import com.study.contactadapter.ContactAdapter;
import com.study.remind.Contact;

public class MainActivity extends Activity {

	@Override
	protected void onCreate(Bundle savedInstanceState) {
		super.onCreate(savedInstanceState);
		setContentView(R.layout.activity_main);
	
		final AutoCompleteTextView autoTip=(AutoCompleteTextView) this.findViewById(R.id.autoTip);
		autoTip.setThreshold(1);
		
		//初始化数据
		ArrayList<Contact> Contacts=Contact.generateContact();	
		
		//自定义adapter
		ContactAdapter adapter=new ContactAdapter(this,Contacts);
		autoTip.setAdapter(adapter);		
		
		//设置点击事件获取文本		
		autoTip.setOnItemClickListener(new OnItemClickListener() {

			@Override
			public void onItemClick(AdapterView<?> parent, View view,
					int position, long id) {
				Contact contact=(Contact) parent.getItemAtPosition(position);
				autoTip.setText(contact.getPhoneNum());
	
			}
		});

	}
}

结果：