本篇文章翻译自Ravi Tamada的Android Swipe Down to Refresh ListView Tutorial
首先来看一下效果图
你应该发现很多的android app比如Twitter，Google+都提供了一个下拉刷新数据的功能。仅仅要用户从上往下滑动，新的内容就会载入出来，这篇文章我们将学习怎样开发出相同的功能。
1.Android SwipeRefreshLayout
实现SwipeRefreshLayout很easy。我们将SwipeRefreshLayout作为根布局，将一个子布局包裹在内。本例中我们使用ListView，而且在Activity中中实现SwipeRefreshLayout.OnRefreshListener接口，当用户下拉时，会触发onRefresh()方法。在onRefresh()中我们发起网络请求而且获取最新的数据。
<android.support.v4.widget.SwipeRefreshLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:id="@+id/swipe_refresh_layout"
android:layout_width="match_parent"
android:layout_height="wrap_content">
<!-- place your view here -->
</android.support.v4.widget.SwipeRefreshLayout>2.JSON URL
URL:http://api.androidhive.info/json/imdb_top_250.php?
offset=0
3.新建一个project
1.打开Android Studio，选择File->New Project project起名为MySwipeRefreshLayout
2.右键MySwipeRefreshLayout，选择New->Module 加入我们的Volley库，起名为Volley
将Volley.jar拷贝到Volley的libs目录下
打开Volley下的build.gradle。加入例如以下代码
dependencies {
compile fileTree(dir: 'libs', include: ['*.jar'])
compile 'com.android.support:appcompat-v7:22.2.0'
compile files('libs/volley.jar')
}3.打开src/res/values/colors.xml。加入例如以下代码
<?xml version="1.0" encoding="utf-8"?>
<resources>
<string-array name="movie_serial_bg">
<item>#24c6d5</item>
<item>#57dd86</item>
<item>#ad7dcf</item>
<item>#ff484d</item>
<item>#fcba59</item>
<item>#24c6d5</item>
</string-array>
</resources>4.新建一个Application来初始化我们的Volley
public class MyApplication extends Application {
public static final String TAG = MyApplication.class
.getSimpleName();
private RequestQueue mRequestQueue;
private static MyApplication mInstance;
@Override
public void onCreate() {
super.onCreate();
mInstance = this;
}
public static synchronized MyApplication getInstance() {
return mInstance;
}
public RequestQueue getRequestQueue() {
if (mRequestQueue == null) {
mRequestQueue = Volley.newRequestQueue(getApplicationContext());
}
return mRequestQueue;
}
public <T> void addToRequestQueue(Request<T> req, String tag) {
req.setTag(TextUtils.isEmpty(tag) ? TAG : tag);
getRequestQueue().add(req);
}
public <T> void addToRequestQueue(Request<T> req) {
req.setTag(TAG);
getRequestQueue().add(req);
}
public void cancelPendingRequests(Object tag) {
if (mRequestQueue != null) {
mRequestQueue.cancelAll(tag);
}
}
}
5.打开AndroidManifest.xml加入网络权限
<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
package="info.androidhive.swiperefresh">
<uses-permission android:name="android.permission.INTERNET"/>
<application
android:name="com.example.zhangqi.myswiperefreshlayout.MyApplication"
android:allowBackup="true"
android:icon="@mipmap/ic_launcher"
android:label="@string/app_name"
android:theme="@style/AppTheme">
<activity
android:name="com.example.zhangqi.myswiperefreshlayout.MainActivity"
android:label="@string/app_name">
<intent-filter>
<action android:name="android.intent.action.MAIN" />
<category android:name="android.intent.category.LAUNCHER" />
</intent-filter>
</activity>
</application>
</manifest>6.创建list_row.xml 作为ListView每一个item的布局
<?xml version="1.0" encoding="utf-8"?
>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:orientation="horizontal"
android:layout_width="match_parent"
android:layout_height="wrap_content">
<TextView
android:id="@+id/serial"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:padding="25dp"
android:layout_margin="5dp"
android:layout_alignParentLeft="true"
android:textSize="20dp"
android:textStyle="bold" />
<TextView
android:id="@+id/title"
android:layout_toRightOf="@id/serial"
android:layout_centerVertical="true"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:textStyle="bold"
android:paddingLeft="20dp"
android:textSize="18dp" />
</RelativeLayout>7.创建实体类Movie.java
public class Movie {
public int id;
public String title;
public Movie() {
}
public Movie(int id, String title) {
this.title = title;
this.id = id;
}
}8.创建Adapter
public class SwipeListAdapter extends BaseAdapter {
private Activity activity;
private LayoutInflater inflater;
private List<Movie> movieList;
private String[] bgColors;
public SwipeListAdapter(Activity activity, List<Movie> movieList) {
this.activity = activity;
this.movieList = movieList;
bgColors = activity.getApplicationContext().getResources().getStringArray(R.array.movie_serial_bg);
}
@Override
public int getCount() {
return movieList.size();
}
@Override
public Object getItem(int location) {
return movieList.get(location);
}
@Override
public long getItemId(int position) {
return position;
}
@Override
public View getView(int position, View convertView, ViewGroup parent) {
if (inflater == null)
inflater = (LayoutInflater) activity
.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
if (convertView == null)
convertView = inflater.inflate(R.layout.list_row, null);
TextView serial = (TextView) convertView.findViewById(R.id.serial);
TextView title = (TextView) convertView.findViewById(R.id.title);
serial.setText(String.valueOf(movieList.get(position).id));
title.setText(movieList.get(position).title);
String color = bgColors[position % bgColors.length];
serial.setBackgroundColor(Color.parseColor(color));
return convertView;
}
}9.如今我们在activity_main.xml的SwipeRefreshLayout下加入一个ListView
<android.support.v4.widget.SwipeRefreshLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:id="@+id/swipe_refresh_layout"
android:layout_width="match_parent"
android:layout_height="wrap_content">
<ListView
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:id="@+id/listView">
</ListView>
</android.support.v4.widget.SwipeRefreshLayout>
10.最后。打开MainActivity.java来完毕最后工作
实现SwipeRefreshLayout.OnRefreshListener而且重写OnRefresh()方法
使用Volley的JsonArrayRequest来获取最新的数据而且更新listview，抽取为一个方法fetchMovies()
当用户下拉刷新时触发OnRefresh()，在这里调用fetchMovies()
public class MainActivity extends ActionBarActivity implements SwipeRefreshLayout.OnRefreshListener {
private String TAG = MainActivity.class.getSimpleName();
private String URL_TOP_250 = "http://api.androidhive.info/json/imdb_top_250.php?offset="
;
private SwipeRefreshLayout swipeRefreshLayout;
private ListView listView;
private SwipeListAdapter adapter;
private List<Movie> movieList;
// initially offset will be 0, later will be updated while parsing the json
private int offSet = 0;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
listView = (ListView) findViewById(R.id.listView);
swipeRefreshLayout = (SwipeRefreshLayout) findViewById(R.id.swipe_refresh_layout);
movieList = new ArrayList<>();
adapter = new SwipeListAdapter(this, movieList);
listView.setAdapter(adapter);
swipeRefreshLayout.setOnRefreshListener(this);
/**
* Showing Swipe Refresh animation on activity create
* As animation won't start on onCreate, post runnable is used
*/
swipeRefreshLayout.post(new Runnable() {
@Override
public void run() {
swipeRefreshLayout.setRefreshing(true);
fetchMovies();
}
}
);
}
/**
* This method is called when swipe refresh is pulled down
*/
@Override
public void onRefresh() {
fetchMovies();
}
/**
* Fetching movies json by making http call
*/
private void fetchMovies() {
// showing refresh animation before making http call
swipeRefreshLayout.setRefreshing(true);
// appending offset to url
String url = URL_TOP_250 + offSet;
// Volley's json array request object
JsonArrayRequest req = new JsonArrayRequest(url,
new Response.Listener<JSONArray>() {
@Override
public void onResponse(JSONArray response) {
Log.d(TAG, response.toString());
if (response.length() > 0) {
// looping through json and adding to movies list
for (int i = 0; i < response.length(); i++) {
try {
JSONObject movieObj = response.getJSONObject(i);
int rank = movieObj.getInt("rank");
String title = movieObj.getString("title");
Movie m = new Movie(rank, title);
movieList.add(0, m);
// updating offset value to highest value
if (rank >= offSet)
offSet = rank;
} catch (JSONException e) {
Log.e(TAG, "JSON Parsing error: " + e.getMessage());
}
}
adapter.notifyDataSetChanged();
}
// stopping swipe refresh
swipeRefreshLayout.setRefreshing(false);
}
}, new Response.ErrorListener() {
@Override
public void onErrorResponse(VolleyError error) {
Log.e(TAG, "Server Error: " + error.getMessage());
Toast.makeText(getApplicationContext(), error.getMessage(), Toast.LENGTH_LONG).show();
// stopping swipe refresh
swipeRefreshLayout.setRefreshing(false);
}
});
// Adding request to request queue
MyApplication.getInstance().addToRequestQueue(req);
}
}大功告成。