从零开始搞懂Android网络请求——异步加载ListView
实现思路:
- 自定义AsyncTask类，重写onPreExecute()、doInBackground()、 onPostExecute()三个方法。
- 网络请求数据
- 自定义接受数据的类
- 绑定listview与数据
请求的数据:
{
status: 1,
data: [
{
id: 1,
name: "如何学好Android——第1章"
},
{
id: 2,
name: "如何学好Android——第2章"
},
{
id: 3,
name: "如何学好Android——第3章"
},
{
id: 4,
name: "如何学好Android——第4章"
},
{
id: 5,
name: "如何学好Android——第5章"
},
{
id: 6,
name: "如何学好Android——第6章"
},
{
id: 7,
name: "如何学好Android——第7章"
},
{
id: 8,
name: "如何学好Android——第8章"
},
{
id: 9,
name: "如何学好Android——第9章"
},
{
id: 10,
name: "如何学好Android——第10章"
}
],
msg: "成功"
}界面效果:
添加网络权限:
<uses-permission android:name="android.permission.INTERNET"/>布局代码:
只需要一个listview就OK。
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
tools:context="com.zergen.csdnlistview.MainActivity">
<ListView
android:id="@+id/listview"
android:layout_width="match_parent"
android:layout_height="match_parent">
ListView>
LinearLayout>
单个item布局代码:
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent">
<TextView
android:layout_width="match_parent"
android:layout_height="60dp"
android:text="测试测试测试"
android:textSize="20sp"
android:gravity="center_vertical"
android:paddingLeft="5dp"
android:id="@+id/classname" />
LinearLayout>实现过程:
代码里面有非常详细的注释
MainActivity:
public class MainActivity extends AppCompatActivity {
private ListView listView;
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
listView = (ListView) findViewById(R.id.listview);
new ListViewAsyncTask().execute();
}
//自定义AsyncTask类，三个参数，第一个不定量入参，第二个：进度 第三个：结果
public class ListViewAsyncTask extends AsyncTask<Void,Void,String>{
//异步加载执行前所作的，可以用来Loading
protected void onPreExecute() {
super.onPreExecute();
//Loading
}
//开启另一个线程，用于后台异步加载的工作
protected String doInBackground(Void... voids) {
String result = request("http://139.199.171.179/csdn/api/listviewdata.php");
//返回Json数据
return result;
}
private String request(String url_data) {
try {
//网络请求数据
String responsedata = null;
URL url = new URL(url_data);
HttpURLConnection conn = (HttpURLConnection) url.openConnection();
conn.setRequestMethod("GET");
conn.setReadTimeout(6000);
if (conn.getResponseCode() == HttpURLConnection.HTTP_OK) {
InputStream in = conn.getInputStream();
byte[] b = new byte[1024 * 512];
int len;
ByteArrayOutputStream baos = new ByteArrayOutputStream();
while((len = in.read(b))>-1){
baos.write(b,0,len);
}
responsedata = baos.toString();
Log.e("TAG", responsedata);
}else {
Toast.makeText(getApplicationContext(), "连接网络错误", Toast.LENGTH_SHORT).show();
}
return responsedata;
} catch (java.io.IOException e) {
e.printStackTrace();
}
return null;
}
protected void onPostExecute(String responsedata) {
super.onPostExecute(responsedata);
//Loading结束，处理数据
//RequstData是用于存储对象信息的自定义类
RequstData requstdata = new RequstData();
//由于数据中有Json数据 所以需要一个ArrayList来存储
List lessondatas = new ArrayList<>();
try {
JSONObject obj = new JSONObject(responsedata);
requstdata.setStatus(obj.getInt("status"));
requstdata.setMsg("msg");
JSONArray jsonarray = obj.getJSONArray("data");
for(int i = 0;inew LesssonData();
JSONObject TempObj = jsonarray.getJSONObject(i);
String class_name = TempObj.getString("name");
lessondata.setClassName(class_name);
lessondatas.add(lessondata);
}
//绑定数据
listView.setAdapter(new MyListAdapter(MainActivity.this,lessondatas));
} catch (JSONException e) {
e.printStackTrace();
}
}
}
} RequstData:
public class RequstData {
public int status;
public String msg;
List lesssonDataList =new ArrayList<>();
public int getStatus() {
return status;
}
public void setStatus(int status) {
this.status = status;
}
public String getMsg() {
return msg;
}
public void setMsg(String msg) {
this.msg = msg;
}
public List getLesssonDataList() {
return lesssonDataList;
}
public void setLesssonDataList(List lesssonDataList) {
this.lesssonDataList = lesssonDataList;
}
}
LessonData:
public class LesssonData {
public String ClassName;
public String getClassName() {
return ClassName;
}
public void setClassName(String className) {
ClassName = className;
}
}
MyListAdapter :
public class MyListAdapter extends BaseAdapter {
List mlesssonDataList;
Context mContext;
public MyListAdapter(Context context,List lesssonDataList) {
this.mlesssonDataList = lesssonDataList;
this.mContext = context;
}
@Override
public int getCount() {
return mlesssonDataList.size();
}
@Override
public Object getItem(int i) {
return mlesssonDataList.get(i);
}
@Override
public long getItemId(int i) {
return i;
}
@Override
public View getView(int i, View view, ViewGroup viewGroup) {
ViewHolder viewHolder = new ViewHolder();
if (view==null){
LayoutInflater layoutInflater = (LayoutInflater) mContext.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
view =layoutInflater.inflate(R.layout.item_layout,null);
viewHolder.ClassName = (TextView) view.findViewById(R.id.classname);
view.setTag(viewHolder);
}else {
viewHolder = (ViewHolder) view.getTag();
}
viewHolder.ClassName.setText(mlesssonDataList.get(i).getClassName());
return view;
}
public class ViewHolder{
public TextView ClassName;
}
}
总结:
首先网络请求是一个耗时的操作，所以需要异步加载数据，并且需要对Adpter解析View时使用ViewHolder来优化ListView，防止数据量过大时，会出现卡顿的情况。