如何自动刷新（添加/更新）listview项而不复制数据？

Question

我做了一个简单的代码从mysql数据库中检索一些数据并将它们放入android listview一切正常，但旧项目保留在列表视图中并添加新项目（数据重复），下面是php代码：

$sql = "SELECT * FROM persons";

$res = mysqli_query($con,$sql);

$result = array();

while($row = mysqli_fetch_array($res)){
array_push($result,
array('id'=>$row[0],
'name'=>$row[1],
'address'=>$row[2]
 ));
}

echo json_encode(array("result"=>$result));

mysqli_close($con);

这里的android代码：

    public class FetchData extends Activity{
    String myJSON;

    private static final String TAG_RESULTS="result";
    private static final String TAG_ID = "id";
    private static final String TAG_NAME = "name";
    private static final String TAG_ADD ="address";

    JSONArray peoples = null;

    ArrayList<HashMap<String, String>> personList;

    ListView list;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.test);
        list = (ListView) findViewById(R.id.listView);
        personList = new ArrayList<HashMap<String,String>>();
        getData();
        final Handler handler = new Handler();
        handler.postDelayed( new Runnable() {

            @Override
            public void run() {


                refreshData();
                handler.postDelayed( this, 2 * 100 );
            }
        }, 2 * 100 );

    }
    public void refreshData(){

    }
    public void getData(){
        class GetDataJSON extends AsyncTask<String, Void, String>{

            @Override
            protected String doInBackground(String... params) {
                DefaultHttpClient httpclient = new DefaultHttpClient(new BasicHttpParams());
                HttpPost httppost = new HttpPost("http://192.168.1.4/get-data.php");

                // Depends on your web service
                httppost.setHeader("Content-type", "application/json");

                InputStream inputStream = null;
                String result = null;
                try {
                    HttpResponse response = httpclient.execute(httppost);
                    HttpEntity entity = response.getEntity();

                    inputStream = entity.getContent();
                    // json is UTF-8 by default
                    BufferedReader reader = new BufferedReader(new InputStreamReader(inputStream, "UTF-8"), 8);
                    StringBuilder sb = new StringBuilder();

                    String line = null;
                    while ((line = reader.readLine()) != null)
                    {
                        sb.append(line + "\n");
                    }
                    result = sb.toString();
                } catch (Exception e) {
                    // Oops
                }
                finally {
                    try{if(inputStream != null)inputStream.close();}catch(Exception squish){}
                }
                return result;
            }

            @Override
            protected void onPostExecute(String result){
                myJSON=result;

                showdata();
            }
        }
        GetDataJSON g = new GetDataJSON();
        g.execute();
    }
    protected void showdata(){
        try {
            JSONObject jsonObj = new JSONObject(myJSON);
            peoples = jsonObj.getJSONArray(TAG_RESULTS);

            for(int i=0;i<peoples.length();i++){
                JSONObject c = peoples.getJSONObject(i);
                String id = c.getString(TAG_ID);
                String name = c.getString(TAG_NAME);
                String address = c.getString(TAG_ADD);

                HashMap<String,String> persons = new HashMap<String,String>();

                persons.put(TAG_ID,id);
                persons.put(TAG_NAME,name);
                persons.put(TAG_ADD,address);

                personList.add(persons);
            }

            ListAdapter adapter = new SimpleAdapter(
                    FetchData.this, personList, R.layout.list_item,
                    new String[]{TAG_ID,TAG_NAME,TAG_ADD},
                    new int[]{R.id.id, R.id.name, R.id.address}
            );

            list.setAdapter(adapter);

        } catch (JSONException e) {
            e.printStackTrace();
        }

    }


    }

如果针对该特定项目更改了mysql数据库数据并添加了新项目而没有重复，我想自动更新特定的listview项目

Answer 1

尝试像这样修改showdata()：

    protected void showdata(){
        try {
            JSONObject jsonObj = new JSONObject(myJSON);
            peoples = jsonObj.getJSONArray(TAG_RESULTS);

            personList.clear();
            for(int i=0;i<peoples.length();i++){
                JSONObject c = peoples.getJSONObject(i);
                String id = c.getString(TAG_ID);
                String name = c.getString(TAG_NAME);
                String address = c.getString(TAG_ADD);

                HashMap<String,String> persons = new HashMap<String,String>();

                persons.put(TAG_ID,id);
                persons.put(TAG_NAME,name);
                persons.put(TAG_ADD,address);

                personList.add(persons);
            }

            ListAdapter adapter = new SimpleAdapter(
                    FetchData.this, personList, R.layout.list_item,
                    new String[]{TAG_ID,TAG_NAME,TAG_ADD},
                    new int[]{R.id.id, R.id.name, R.id.address}
            );

            list.setAdapter(adapter);

        } catch (JSONException e) {
            e.printStackTrace();
        }

    }

personList.clear(); - 用于清除旧结果。

Answer 2

解决问题的最佳方法是发送从php文件中恢复的最后一个id 所以你不会看到任何重复数据，默认情况下会加载更多项目发送id为零，每次你发出请求时发送最后一个id存储

$id = abs(intval($_GET['id']));
$sql = "SELECT * FROM persons where id > ".$id;
$res = mysqli_query($con,$sql);
$result = array();

while($row = mysqli_fetch_array($res)){
array_push($result,
array('id'=>$row[0],
'name'=>$row[1],
'address'=>$row[2]
 ));
}

echo json_encode(array("result"=>$result));

mysqli_close($con);

java class

public class FetchData extends Activity{
String myJSON;

private static final String TAG_RESULTS="result";
private static final String TAG_ID = "id";
private static final String TAG_NAME = "name";
private static final String TAG_ADD ="address";

JSONArray peoples = null;

ArrayList<HashMap<String, String>> personList;

ListView list;
private static int lastid = 0;
@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.test);
    list = (ListView) findViewById(R.id.listView);
    personList = new ArrayList<HashMap<String,String>>();
    getData();
    final Handler handler = new Handler();
    handler.postDelayed( new Runnable() {

        @Override
        public void run() {


            refreshData();
            handler.postDelayed( this, 2 * 100 );
        }
    }, 2 * 100 );

}
public void refreshData(){

}
public void getData(){
    class GetDataJSON extends AsyncTask<String, Void, String>{

        @Override
        protected String doInBackground(String... params) {
            DefaultHttpClient httpclient = new DefaultHttpClient(new BasicHttpParams());
            HttpPost httppost = new HttpPost("http://192.168.1.4/get-data.php?id="+lastid);

            // Depends on your web service
            httppost.setHeader("Content-type", "application/json");

            InputStream inputStream = null;
            String result = null;
            try {
                HttpResponse response = httpclient.execute(httppost);
                HttpEntity entity = response.getEntity();

                inputStream = entity.getContent();
                // json is UTF-8 by default
                BufferedReader reader = new BufferedReader(new InputStreamReader(inputStream, "UTF-8"), 8);
                StringBuilder sb = new StringBuilder();

                String line = null;
                while ((line = reader.readLine()) != null)
                {
                    sb.append(line + "\n");
                }
                result = sb.toString();
            } catch (Exception e) {
                // Oops
            }
            finally {
                try{if(inputStream != null)inputStream.close();}catch(Exception squish){}
            }
            return result;
        }

        @Override
        protected void onPostExecute(String result){
            myJSON=result;

            showdata();
        }
    }
    GetDataJSON g = new GetDataJSON();
    g.execute();
}
protected void showdata(){
    try {
        JSONObject jsonObj = new JSONObject(myJSON);
        peoples = jsonObj.getJSONArray(TAG_RESULTS);

        for(int i=0;i<peoples.length();i++){
            JSONObject c = peoples.getJSONObject(i);
            String id = c.getString(TAG_ID);
            String name = c.getString(TAG_NAME);
            String address = c.getString(TAG_ADD);

            HashMap<String,String> persons = new HashMap<String,String>();

            persons.put(TAG_ID,id);
            persons.put(TAG_NAME,name);
            persons.put(TAG_ADD,address);

            personList.add(persons);
            lastid = Integer.parseInt(id);
        }

        ListAdapter adapter = new SimpleAdapter(
                FetchData.this, personList, R.layout.list_item,
                new String[]{TAG_ID,TAG_NAME,TAG_ADD},
                new int[]{R.id.id, R.id.name, R.id.address}
        );

        list.setAdapter(adapter);

    } catch (JSONException e) {
        e.printStackTrace();
    }

}


}