导读

1.Loader简介
2.用Loader读取联系人(含筛选)
3.自定义Loader

Loader简介

用Loader读取联系人

AndroidManifest.xml

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.hala.loader">

    <uses-permission android:name="android.permission.READ_CONTACTS"/>
    <uses-permission android:name="android.permission.WRITE_CONTACTS"/>

    <application
        android:allowBackup="true"
        android:icon="@mipmap/ic_launcher"
        android:label="@string/app_name"
        android:roundIcon="@mipmap/ic_launcher_round"
        android:supportsRtl="true"
        android:theme="@style/AppTheme">
        <activity android:name=".MainActivity">
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />

                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>
    </application>

</manifest>

activity_main.xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical"
    tools:context="com.hala.loader.MainActivity">

   <EditText
       android:id="@+id/et"
       android:hint="input your name:"
       android:layout_width="match_parent"
       android:layout_height="wrap_content" />

   <ListView
       android:id="@+id/listview"
       android:layout_width="match_parent"
       android:layout_height="match_parent"></ListView>

</LinearLayout>

MainActivity.java

package com.hala.loader;

import android.database.Cursor;
import android.net.Uri;
import android.provider.ContactsContract;
import android.support.v4.app.LoaderManager;
import android.support.v4.content.CursorLoader;
import android.support.v4.content.Loader;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.text.Editable;
import android.text.TextUtils;
import android.text.TextWatcher;
import android.view.View;
import android.widget.CursorAdapter;
import android.widget.EditText;
import android.widget.ListView;
import android.widget.SimpleCursorAdapter;

public class MainActivity extends AppCompatActivity implements LoaderManager.LoaderCallbacks<Cursor> {

    private LoaderManager loaderManager;
    private ListView mContactsListView;
    private SimpleCursorAdapter mCursorAdapter;
    private EditText mNameEt;
    private String filterName;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        mContactsListView = (ListView) findViewById(R.id.listview);
        //设置游标适配器
        mCursorAdapter = new SimpleCursorAdapter(this,
                android.R.layout.simple_expandable_list_item_1,
                null,
                new String[]{ContactsContract.Contacts.DISPLAY_NAME},
                new int[]{android.R.id.text1},
                CursorAdapter.FLAG_REGISTER_CONTENT_OBSERVER);

        mContactsListView.setAdapter(mCursorAdapter);

        mNameEt = (EditText) findViewById(R.id.et);
        //联系人文本框改变后，重新加载Loader的数据
        mNameEt.addTextChangedListener(new TextWatcher() {
            @Override
            public void beforeTextChanged(CharSequence s, int start, int count, int after) {

            }

            @Override
            public void onTextChanged(CharSequence s, int start, int before, int count) {
                filterName=s.toString();
                //重新创建Loader
                loaderManager.restartLoader(0,null,MainActivity.this);
            }

            @Override
            public void afterTextChanged(Editable s) {

            }
        });

        loaderManager = getSupportLoaderManager();
        //初始化Loader 参数1：Loader的ID 参数2：给Loader传递的参数 参数3：LoaderCallbacks接口
        loaderManager.initLoader(0,null,this);
    }

    /**
     * 创建Loader对象
     * @param id 对应于loaderManager.initLoader参数1
     * @param args 对应于loaderManager.initLoader参数2
     * @return 这里要遵循范型，上边实现什么接口，这里就返回什么类型
     */
    @Override
    public Loader<Cursor> onCreateLoader(int id, Bundle args) {

        Uri uri=ContactsContract.Contacts.CONTENT_URI;
        if(!TextUtils.isEmpty(filterName)){
            uri=Uri.withAppendedPath(
                    ContactsContract.Contacts.CONTENT_FILTER_URI,
                    Uri.encode(filterName));
        }
        CursorLoader cursorLoader = new CursorLoader(this,
                uri,
                null,
                null,
                null,
                null);
        return cursorLoader;
    }

    /**
     * 加载数据完成
     * @param loader
     * @param data
     */
    @Override
    public void onLoadFinished(Loader<Cursor> loader, Cursor data) {
        //在主线程中完成，更新UI
        //这里转换到新游标的同时，会返回原来的游标，我们要把原来的游标释放掉
        Cursor oldCursor = mCursorAdapter.swapCursor(data);
        if(oldCursor!=null){
            oldCursor.close();
        }
    }

    /**
     * 重置Loader
     * @param loader
     */
    @Override
    public void onLoaderReset(Loader<Cursor> loader) {
        //释放当前游标
        Cursor oldCursor = mCursorAdapter.swapCursor(null);
        if(oldCursor!=null){
            oldCursor.close();
        }
    }
}

自定义Loader

AndroidManifest.xml

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.hala.loader">

    <uses-permission android:name="android.permission.READ_CONTACTS"/>
    <uses-permission android:name="android.permission.WRITE_CONTACTS"/>

    <application
        android:allowBackup="true"
        android:icon="@mipmap/ic_launcher"
        android:label="@string/app_name"
        android:roundIcon="@mipmap/ic_launcher_round"
        android:supportsRtl="true"
        android:theme="@style/AppTheme">
        <activity android:name=".MainActivity">
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />

                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>
    </application>

</manifest>

activity_main.xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical"
    tools:context="com.hala.loader.MainActivity">

   <EditText
       android:id="@+id/et"
       android:hint="input your name:"
       android:layout_width="match_parent"
       android:layout_height="wrap_content" />

   <ListView
       android:id="@+id/listview"
       android:layout_width="match_parent"
       android:layout_height="match_parent"></ListView>

</LinearLayout>

user_item.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/username_tv"
        android:layout_width="0dp"
        android:layout_height="wrap_content"
        android:layout_weight="1"
        android:text="username:"
        android:textSize="25sp"/>

    <TextView
        android:id="@+id/password_tv"
        android:layout_width="0dp"
        android:layout_height="wrap_content"
        android:layout_weight="2"
        android:hint="password"
        android:textSize="25sp"/>



</LinearLayout>

UserBean.java

package com.hala.loader;

/**
 * 自定义数据类型
 * Created by air on 2018/5/8.
 */

public class UserBean {

    private String username;
    private String password;

    public UserBean(String username, String password) {
        this.username = username;
        this.password = password;
    }

    public String getUsername() {
        return username;
    }

    public void setUsername(String username) {
        this.username = username;
    }

    public String getPassword() {
        return password;
    }

    public void setPassword(String password) {
        this.password = password;
    }
}

UserLoader.java

package com.hala.loader;


import android.content.Context;
import android.support.v4.content.AsyncTaskLoader;

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

/**
 * 自定义loader
 * Created by air on 2018/5/8.
 */

//这里注意AsyncTaskLoader要导入v4包的那一个
public class UserLoader extends AsyncTaskLoader<List<UserBean>> {

    public UserLoader(Context context) {
        super(context);
    }

    @Override
    protected void onStartLoading() {
        super.onStartLoading();
        //如果Loader启动了，强制执行loadInBackground()方法
        if(isStarted()){
            forceLoad();
        }
    }

    /**
     * 在子线程加载数据
     * @return
     */
    @Override
    public List<UserBean> loadInBackground() {
        //模拟从网络返回数据
        List<UserBean> list=new ArrayList<>();
        list.add(new UserBean("Emilia","123"));
        list.add(new UserBean("Clark","123"));
        list.add(new UserBean("Neymar","123"));
        list.add(new UserBean("Henry","123"));
        return list;
    }
}

MainActivity.java

package com.hala.loader;



import android.support.v4.app.LoaderManager;
import android.support.v4.content.Loader;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.BaseAdapter;
import android.widget.ListView;
import android.widget.TextView;

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

//这里LoaderManager.LoaderCallbacks<List<UserBean>> 也要导入v4包的那个，与UserLoader保持一致
public class MainActivity extends AppCompatActivity implements LoaderManager.LoaderCallbacks<List<UserBean>> {

    private List<UserBean> users=new ArrayList<>();
    private LoaderManager loaderManager;
    private ListView mContactsListView;
    private UserAdapter adapter;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        mContactsListView = (ListView) findViewById(R.id.listview);

        adapter=new UserAdapter();
        mContactsListView.setAdapter(adapter);

        loaderManager = getSupportLoaderManager();
        //初始化Loader 参数1：Loader的ID 参数2：给Loader传递的参数 参数3：LoaderCallbacks接口
        loaderManager.initLoader(0,null,this);
    }

    /**
     * 创建Loader对象
     * @param id 对应于loaderManager.initLoader参数1
     * @param args 对应于loaderManager.initLoader参数2
     * @return 这里要遵循范型，上边实现什么接口，这里就返回什么类型
     */
    @Override
    public Loader<List<UserBean>> onCreateLoader(int id, Bundle args) {
        if(id==0){
            return new UserLoader(this);
        }else {
            return null;
        }

    }

    /**
     * 加载数据完成
     * @param loader
     * @param data
     */
    @Override
    public void onLoadFinished(Loader<List<UserBean>> loader, List<UserBean> data) {
      users.addAll(data);
      adapter.notifyDataSetChanged();
    }

    /**
     * 重置Loader
     * @param loader
     */
    @Override
    public void onLoaderReset(Loader<List<UserBean>> loader) {

    }

    class UserAdapter extends BaseAdapter{

        @Override
        public int getCount() {
            return users.size();
        }

        @Override
        public Object getItem(int position) {
            return users.get(position);
        }

        @Override
        public long getItemId(int position) {
            return position;
        }

        @Override
        public View getView(int position, View convertView, ViewGroup parent) {
            View view=convertView;
            ViewHolder holder=null;
            if(view==null){
                view= LayoutInflater.from(MainActivity.this).inflate(R.layout.user_item,null);
                holder=new ViewHolder();
                holder.usernameTv=(TextView)findViewById(R.id.username_tv);
                holder.passwordTv=(TextView)findViewById(R.id.password_tv);
                view.setTag(holder);
            }else{
                holder=(ViewHolder) view.getTag();
            }

            UserBean userBean=users.get(position);
            holder.usernameTv.setText(userBean.getUsername());
            holder.passwordTv.setText(userBean.getPassword());
            return view;
        }

        class ViewHolder{
            TextView usernameTv;
            TextView passwordTv;
        }
    }
}