此文旨在能帮助有需要的Android新手实现一个小小的功能，代码质量不具有任何参考意义，文章最下面的格式也有点小问题，搞了一会没搞定，放弃了。
目前无论是PC上还是手机上，浏览器的地址栏都带有历史访问记录自动提示功能，例如之前访问过http://www.qq.com，那么当下次再次输入qq，或者www.q的时候（具体出发规则可定制），http://www.qq.com就会在地址栏下面以下拉窗口的形式自动给出提示，方便用户选择并完成地址的输入工作。
在Android中，通过sdk提供的AutoCompleteTextView我们可以完成类似的功能，当然这里布局限于浏览器的地址提示，任何历史记录都可以通过该控件来实现，下面将通过代码来说明具体的实现过程。
要实现历史记录的提示功能，首先要解决的问题就是历史记录的存储，Android中提供了几种存储方式，官方sdk文档中给出了详细的说明：http://developer.android.com/guide/topics/data/data-storage.html ，大概分析了一下，对于浏览器历史记录而言，SQLite应该是最合适的存储方式，Android原生浏览器也使用了SQLite的存储方式，因此本文也基于SQLite来保存历史记录。对于SQLite的介绍可以参考这篇文章：http://www.ibm.com/developerworks/cn/opensource/os-cn-sqlite/，下面就先来实现历史记录的存储部分。
Android 提供了 SQLiteOpenHelper 来创建数据库，我们只要继承 SQLiteOpenHelper 类，就可以轻松的创建数据库，并在onCreate()中创建需要用到的表，代码如下：
import android.content.Context;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteOpenHelper;
public class SuggestionDBHelper extends SQLiteOpenHelper{
private static final String DBNAME = "url.db";// 数据库名
public SuggestionDBHelper(Context context){
super(context, DBNAME, null, DATABASE_VERSION);
}
@Override
public void onCreate(SQLiteDatabase db) {
db.execSQL("CREATE TABLE IF NOT EXISTS history" +
"(_id INTEGER PRIMARY KEY AUTOINCREMENT, url TEXT, title TEXT)");//创建history表，包含id，url和title字段
}
@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {}
}为了解除上层逻辑和数据库操作之间的耦合，我们通过创建类SuggestionDBManage来封装url历史记录的添加和删除操作，这里主要实现了历史记录的insert和query函数，代码如下，代码不难理解：
import java.util.ArrayList;
import java.util.List;
import android.content.Context;
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;
import com.tencent.test.SuggestionItem;
public class SuggestionDBManage {
private SuggestionDBHelper mDateBaseHelper;
private SQLiteDatabase mDatabase;
public SuggestionDBManage(Context context) {
mDateBaseHelper = new SuggestionDBHelper(context);
mDatabase = mDateBaseHelper.getWritableDatabase();
}
public void insert(SuggestionItem urlitem) {
mDatabase.beginTransaction(); // 开始事务
try {
mDatabase.execSQL("INSERT INTO history VALUES(null, ?, ?)",
new Object[] { urlitem.getUrl(), urlitem.getTitle() });
mDatabase.setTransactionSuccessful(); // 设置事务成功完成
} finally {
mDatabase.endTransaction(); // 结束事务
}
}
public List<SuggestionItem> query(String prefix) {
String like = prefix + "%";
List<SuggestionItem> values = new ArrayList<SuggestionItem>();
final String selection = "(url LIKE ? OR url LIKE ? OR url LIKE ? OR url LIKE ?)";
String[] selectionArgs = new String[4];
selectionArgs[0] = "http://" + like;
selectionArgs[1] = "http://www." + like;
selectionArgs[2] = "https://" + like;
selectionArgs[3] = "https://www." + like;
Cursor cursor = mDatabase.query("history", new String[] { "url", "title" }, selection,
selectionArgs, null, null, null);
cursor.moveToFirst();
for (int i = 0; i < cursor.getCount(); i++) {
String url = cursor.getString(0);
String title = cursor.getString(1);
values.add(new SuggestionItem(url, title));
cursor.moveToNext();
}
return values;
}
public void close(){
mDatabase.close();
}
}
为了实现历史记录的自动提示功能，我们需要借助Android提供的AutoCompleteTextView控件，该控件使用了Adapter方式来绑定用来提示的数据，用过类似ListView控件的话应该对这种方式不会陌生，然而对于AutoCompleteTextView来说，绑定的Adapter必须是实现了Filterable接口的Adapter，关键字的过滤功能是通过Filter这个类来实现的，而AutoCompleteTextView会调用Filterable接口的getFilter()函数，得到具体的Filter实例后执行过滤，具体的过滤规则是通过继承Filter这个类，并且重载Filter类的performFiltering函数来定制的。
数据库的访问通过AsycTask来完成，这是考虑到数据库的query操作有可能是一个比较耗时的操作，因此不适合放到主线程中，通过AsycTask可以避免界面失去响应的问题，从数据库取得数据后通过notifyDataSetChanged()来更新界面，具体代码如下：
import java.util.ArrayList;
import java.util.List;
import android.content.Context;
import android.os.AsyncTask;
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.tencent.urldatabase.SuggestionDBManage;
public class SuggestionAdapter extends BaseAdapter implements Filterable {
private Context context;
private SuggestionDBManage mDbManage;
private ArrayFilter mFilter;
private List<SuggestionItem> mFilterItems = new ArrayList<SuggestionItem>();// 过滤后的item
public SuggestionAdapter(Context context, SuggestionDBManage dbManage) {
this.context = context;
mDbManage = dbManage;
}
@Override
public Filter getFilter() {
if (mFilter == null) {
mFilter = new ArrayFilter();
}
return mFilter;
}
private class SuggestionAsyncTask extends AsyncTask<String, Void, List<SuggestionItem>>{
@Override
protected List<SuggestionItem> doInBackground(String... params) {
List<SuggestionItem> suggestionItems = mDbManage.query(params[0]);
return suggestionItems;
}
@Override
protected void onPostExecute(List<SuggestionItem> result) {
mFilterItems = result;
notifyDataSetChanged();
super.onPostExecute(result);
}
}
private class ArrayFilter extends Filter {
@Override
protected FilterResults performFiltering(CharSequence prefix) {
String prefixString = prefix.toString().toLowerCase();
startSuggestionsAsync(prefixString);
return null;
}
private void startSuggestionsAsync(String prefixString) {
new SuggestionAsyncTask().execute(prefixString.toString());
}
@Override
protected void publishResults(CharSequence constraint,
FilterResults results) {}
}
@Override
public int getCount() {
return mFilterItems.size();
}
@Override
public Object getItem(int position) {
return mFilterItems.get(position);
}
@Override
public long getItemId(int position) {
return position;
}
@Override
public View getView(final int position, View convertView, ViewGroup parent) {
ViewHolder holder = null;
if (convertView == null) {
holder = new ViewHolder();
LayoutInflater inflater = (LayoutInflater) context
.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
convertView = inflater.inflate(
R.layout.simple_list_item_for_autocomplete, null);
holder.url = (TextView) convertView.findViewById(R.id.url);
holder.title = (TextView) convertView.findViewById(R.id.title);
convertView.setTag(holder);
} else {
holder = (ViewHolder) convertView.getTag();
}
holder.url.setText(mFilterItems.get(position).getUrl());
holder.title.setText(mFilterItems.get(position).getTitle());
return convertView;
}
class ViewHolder {
TextView url;
TextView title;
}
}SuggestionItem
public class SuggestionItem {
private String mUrl;
private String mTitle;
public SuggestionItem(String url, String title) {
mUrl = url;
mTitle = title;
}
public String getUrl() {
return mUrl;
}
public String getTitle() {
return mTitle;
}
}MainActivity.java
import android.app.Activity;
import android.os.Bundle;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.AdapterView;
import android.widget.AdapterView.OnItemClickListener;
import android.widget.AutoCompleteTextView;
import android.widget.Button;
import android.widget.TextView;
import com.tencent.urldatabase.SuggestionDBManage;
public class MainActivity extends Activity implements OnItemClickListener{
private AutoCompleteTextView mAutoCompleteTextView;
private Button mSaveButton;
private SuggestionDBManage mUrlDBManage;
/** Called when the activity is first created. */
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
mUrlDBManage = new SuggestionDBManage(getApplicationContext());
mAutoCompleteTextView = (AutoCompleteTextView)findViewById(R.id.autotextview);
mAutoCompleteTextView.setText("");
mAutoCompleteTextView.setOnItemClickListener(this);
SuggestionAdapter adapter = new SuggestionAdapter(this, mUrlDBManage);
mAutoCompleteTextView.setAdapter(adapter);
mSaveButton = (Button)findViewById(R.id.savaurl);
mSaveButton.setOnClickListener(new OnClickListener() {
//这部分代码只是为了添加初始数据，只考虑http://开头的地址
@Override
public void onClick(View v) {
String prefix = "http://";
String urlString = mAutoCompleteTextView.getText().toString();
if (!urlString.startsWith(prefix)) {
mUrlDBManage.insert(new SuggestionItem(prefix + urlString, "unknow"));
}
else {
mUrlDBManage.insert(new SuggestionItem(urlString, "unknow"));
}
}
});
}
@Override
protected void onDestroy() {
mUrlDBManage.close();
super.onDestroy();
}
@Override
public void onItemClick(AdapterView<?> parent, View view, int position,
long id) {
TextView urlteTextView = (TextView)view.findViewById(R.id.title);
mAutoCompleteTextView.setText(urlteTextView.getText());
}
}main.xml
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:orientation="horizontal" >
<AutoCompleteTextView
android:id="@+id/autotextview"
android:layout_width="0dp"
android:layout_weight="1"
android:layout_height="wrap_content"
android:singleLine="true" />
<Button
android:id="@+id/savaurl"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="save"/>
</LinearLayout>simple_list_item_for_autocomplete.xml
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="horizontal" >
<TextView
android:id="@+id/url"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_weight="1"
android:textSize="16sp"/>
<TextView
android:id="@+id/title"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_weight="1"
android:gravity="right"
android:textSize="16sp"/>
</LinearLayout>
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