您好我已经创建了一个Android应用程序，它以列表的形式显示来自mysql数据库的数据。
这是代码。
public class MainActivity extends Activity {
ListView mListView;
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
// URL to the JSON data
String strUrl = "http://192.168.2.3/Flutura/PHP/Core/Data/android.data.php";
// Creating a new non-ui thread task to download json data
DownloadTask downloadTask = new DownloadTask();
// Starting the download process
downloadTask.execute(strUrl);
// Getting a reference to ListView of activity_main
mListView = (ListView) findViewById(R.id.lv_countries);
}
/** A method to download json data from url */
private String downloadUrl(String strUrl) throws IOException{
String data = "";
InputStream iStream = null;
try{
URL url = new URL(strUrl);
// Creating an http connection to communicate with url
HttpURLConnection urlConnection = (HttpURLConnection) url.openConnection();
// Connecting to url
urlConnection.connect();
// Reading data from url
iStream = urlConnection.getInputStream();
BufferedReader br = new BufferedReader(new InputStreamReader(iStream));
StringBuffer sb = new StringBuffer();
String line = "";
while( ( line = br.readLine()) != null){
sb.append(line);
}
data = sb.toString();
br.close();
}catch(Exception e){
Log.d("Exception while downloading url", e.toString());
}finally{
iStream.close();
}
return data;
}
/** AsyncTask to download json data */
private class DownloadTask extends AsyncTask<String, Integer, String>{
String data = null;
@Override
protected String doInBackground(String... url) {
try{
data = downloadUrl(url[0]);
}catch(Exception e){
Log.d("Background Task",e.toString());
}
return data;
}
@Override
protected void onPostExecute(String result) {
// The parsing of the xml data is done in a non-ui thread
ListViewLoaderTask listViewLoaderTask = new ListViewLoaderTask();
// Start parsing xml data
listViewLoaderTask.execute(result);
}
}
/** AsyncTask to parse json data and load ListView */
private class ListViewLoaderTask extends AsyncTask<String, Void, SimpleAdapter>{
JSONObject jObject;
// Doing the parsing of xml data in a non-ui thread
@Override
protected SimpleAdapter doInBackground(String... strJson) {
try{
jObject = new JSONObject(strJson[0]);
CountryJSONParser countryJsonParser = new CountryJSONParser();
countryJsonParser.parse(jObject);
}catch(Exception e){
Log.d("JSON Exception1",e.toString());
}
// Instantiating json parser class
CountryJSONParser countryJsonParser = new CountryJSONParser();
// A list object to store the parsed countries list
List<HashMap<String, Object>> countries = null;
try{
// Getting the parsed data as a List construct
countries = countryJsonParser.parse(jObject);
}catch(Exception e){
Log.d("Exception",e.toString());
}
// Keys used in Hashmap
String[] from = { "outlet_id","outlet_name","lat","lng","outlet_location"};
// Ids of views in listview_layout
int[] to = { R.id.tv_country,R.id.iv_flag,R.id.tv_country_details};
// Instantiating an adapter to store each items
// R.layout.listview_layout defines the layout of each item
SimpleAdapter adapter = new SimpleAdapter(getBaseContext(), countries, R.layout.lv_layout, from, to);
return adapter;
}
/* /** Invoked by the Android on "doInBackground" is executed
@Override
protected void onPostExecute(SimpleAdapter adapter) {
// Setting adapter for the listview
mListView.setAdapter(adapter);
/* for(int i=0;i<adapter.getCount();i++){
HashMap<String, Object> hm = (HashMap<String, Object>) adapter.getItem(i);
String imgUrl = (String) hm.get("flag_path");
//ImageLoaderTask imageLoaderTask = new ImageLoaderTask();
HashMap<String, Object> hmDownload = new HashMap<String, Object>();
hm.put("flag_path",imgUrl);
hm.put("position", i);
// Starting ImageLoaderTask to download and populate image in the listview
//imageLoaderTask.execute(hm);
}
}
}*/
/*
/** AsyncTask to download and load an image in ListView
private class ImageLoaderTask extends AsyncTask<HashMap<String, Object>, Void, HashMap<String, Object>>{
@Override
protected HashMap<String, Object> doInBackground(HashMap<String, Object>... hm) {
InputStream iStream=null;
String imgUrl = (String) hm[0].get("flag_path");
int position = (Integer) hm[0].get("position");
URL url;
try {
url = new URL(imgUrl);
// Creating an http connection to communicate with url
HttpURLConnection urlConnection = (HttpURLConnection) url.openConnection();
// Connecting to url
urlConnection.connect();
// Reading data from url
iStream = urlConnection.getInputStream();
// Getting Caching directory
File cacheDirectory = getBaseContext().getCacheDir();
// Temporary file to store the downloaded image
File tmpFile = new File(cacheDirectory.getPath() + "/wpta_"+position+".png");
// The FileOutputStream to the temporary file
FileOutputStream fOutStream = new FileOutputStream(tmpFile);
// Creating a bitmap from the downloaded inputstream
Bitmap b = BitmapFactory.decodeStream(iStream);
// Writing the bitmap to the temporary file as png file
b.compress(Bitmap.CompressFormat.PNG,100, fOutStream);
// Flush the FileOutputStream
fOutStream.flush();
//Close the FileOutputStream
fOutStream.close();
// Create a hashmap object to store image path and its position in the listview
HashMap<String, Object> hmBitmap = new HashMap<String, Object>();
// Storing the path to the temporary image file
hmBitmap.put("flag",tmpFile.getPath());
// Storing the position of the image in the listview
hmBitmap.put("position",position);
// Returning the HashMap object containing the image path and position
return hmBitmap;
}catch (Exception e) {
e.printStackTrace();
}
return null;
}
*/
protected void onPostExecute(HashMap<String, Object> result) {
// Getting the path to the downloaded image
//String path = (String) result.get("flag");
// Getting the position of the downloaded image
//int position = (Integer) result.get("position");
// Getting adapter of the listview
SimpleAdapter adapter = (SimpleAdapter ) mListView.getAdapter();
// Getting the hashmap object at the specified position of the listview
//HashMap<String, Object> hm = (HashMap<String, Object>) adapter.getItem(position);
// Overwriting the existing path in the adapter
//hm.put("flag",path);
// Noticing listview about the dataset changes
adapter.notifyDataSetChanged();
}
public boolean onCreateOptionsMenu(Menu menu) {
getMenuInflater().inflate(R.menu.activity_main, menu);
return true;
}
}
}
这是我使用JSONParser解析数据的类。
/** A class to parse json data */
public class CountryJSONParser {
// Receives a JSONObject and returns a list
public List<HashMap<String,Object>> parse(JSONObject jObject){
JSONArray jCountries = null;
try {
// Retrieves all the elements in the 'countries' array
jCountries = jObject.getJSONArray("countries");
} catch (JSONException e) {
e.printStackTrace();
}
// Invoking getCountries with the array of json object
// where each json object represent a country
return getCountries(jCountries);
}
private List<HashMap<String, Object>> getCountries(JSONArray jCountries){
int countryCount = jCountries.length();
List<HashMap<String, Object>> countryList = new ArrayList<HashMap<String,Object>>();
HashMap<String, Object> country = null;
// Taking each country, parses and adds to list object
for(int i=0; i<countryCount;i++){
try {
// Call getCountry with country JSON object to parse the country
country = getCountry((JSONObject)jCountries.get(i));
countryList.add(country);
} catch (JSONException e) {
e.printStackTrace();
}
}
return countryList;
}
// Parsing the Country JSON object
private HashMap<String, Object> getCountry(JSONObject jCountry){
HashMap<String, Object> country = new HashMap<String, Object>();
String countryName = "";
String flag="";
String language = "";
String capital = "";
String location = "";
//String currencyCode = "";
//String currencyName = "";
try {
countryName = jCountry.getString("outlet_id");
flag = jCountry.getString("outlet_name");
language = jCountry.getString("lat");
capital = jCountry.getString("lng");
location = jCountry.getString("outlet_location");
//currencyCode = jCountry.getJSONObject("outlet_image").getString("outlet_image");
//currencyName = jCountry.getJSONObject("outlet_location").getString("outlet_location");
String details = "Language : " + language + "\n" +
"Capital : " + capital + "\n" ;
// "Currency : " + currencyName + "(" + currencyCode + ")";
country.put("country", countryName);
//country.put("flag", R.drawable.blank);
country.put("flag_path", flag);
country.put("details", details);
} catch (JSONException e) {
e.printStackTrace();
}
return country;
}
}
我的问题是列表视图没有显示。请帮助。
答案 0 :(得分：0)
所以这里的代码非常混乱，最重要的是你永远不会在setAdapter上调用ListView。做它，它应该工作。
我的建议是，您首先创建并初始化ListView个实例，并为Adapter设置ListView空List。创建BaseAdapter的子类以更好地控制Adapter并通过构造函数传递List：
public MyAdapter extends BaseAdapter {
public MyAdapter(Context c, int layout, List<HashMap<String, Object>> countries) {
}
// implement methods as getItem, getItemId, ...
public View getView(int position, View convertView, ViewGroup parent) {
if (convertView == null) {
// inflate row, use RowHolder design pattern to hold data of each row in
// wrapping object like RowHolder and set it as tag to convertView
}
else {
//get existing tag from convertView
}
if (!countries.isEmpty()) {
// set data to elements in row
}
}
}
当您从服务器下载某个项目时，在AsyncWorker中，将其添加到List并在yourAdapter.notifyDataSetChanged()上致电Adapter。
以下是示例：Android ListView。
答案 1 :(得分：0)
OnPostExecute添加ListViewLoaderTask
mListView.setAdapter(adapter);
另一方面，你没有对结果做任何事情。你只需致电
SimpleAdapter adapter = mListView.getAdapter();
然后将其设置回列表视图。这基本上没什么。您必须使用检索到的数据填充适配器。