从零开始搞懂Android网络请求——异步加载ListView

实现思路:

1. 自定义AsyncTask类，重写onPreExecute()、doInBackground()、 onPostExecute()三个方法。
2. 网络请求数据
3. 自定义接受数据的类
4. 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<LesssonData> 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;i<jsonarray.length();i++){                    LesssonData lessondata = new 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<LesssonData> 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<LesssonData> getLesssonDataList() {        return lesssonDataList;    }    public void setLesssonDataList(List<LesssonData> 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<LesssonData> mlesssonDataList;    Context mContext;    public MyListAdapter(Context context,List<LesssonData> 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。