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我寫一個應用程序中，我試圖來從服務器PHPMYADMIN以前的訂單詳細信息，並希望顯示在ListView的這些訂單的詳細信息，但每當我跑我的應用越來越NullPointerException異常，請檢查我的代碼，並告訴我，我很想念我所在的地方做錯誤..空指針異常 - 試圖從PHPMYADMIN服務器檢索數據
日誌說：
05-22 12:33:35.652: E/AndroidRuntime(786): Caused by: java.lang.NullPointerException
05-22 12:33:35.652: E/AndroidRuntime(786): at OrdersActivity.showInfo(OrdersActivity.java:121)
05-22 12:33:35.652: E/AndroidRuntime(786): at OrdersActivity.onCreate(OrdersActivity.java:75)
05-22 12:33:35.652: E/AndroidRuntime(786): at android.app.Activity.performCreate(Activity.java:5104)
05-22 12:33:35.652: E/AndroidRuntime(786): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1080)
05-22 12:33:35.652: E/AndroidRuntime(786): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2144)
05-22 12:33:35.652: E/AndroidRuntime(786): ... 11 more
錯誤行數75：showinfo();
錯誤行號121：if(!strMemberID.equals(""))
OrdersActivity.java：
public class OrdersActivity extends Activity {
TextView total, items ;
String strMemberID,resultServer,MemberID;
ListView list;
OrdersAdapter adapter;
ArrayList<HashMap<String, String>> itemsList;
/** Called when the activity is first created. */
@SuppressWarnings("deprecation")
@Override
protected void onCreate(Bundle savedInstanceState) {
// TODO Auto-generated method stub
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_orders);
// Permission StrictMode
if (android.os.Build.VERSION.SDK_INT > 9) {
StrictMode.ThreadPolicy policy = new StrictMode.ThreadPolicy.Builder().permitAll().build();
StrictMode.setThreadPolicy(policy);
}
showInfo();
itemsList = new ArrayList<HashMap<String, String>>();
list = (ListView) findViewById(R.id.listView1);
adapter = new OrdersAdapter(this, itemsList);
list.setAdapter(adapter);
if (isNetworkAvailable()) {
new MyAsyncTask().execute();
} else {
AlertDialog alertDialog = new AlertDialog.Builder(OrdersActivity.this).create();
alertDialog.setMessage("The Internet connection appears to be offline.");
alertDialog.setButton("OK", new DialogInterface.OnClickListener() {
public void onClick(DialogInterface dialog, int which) {
}
});
alertDialog.show();
}
}
public void showInfo()
{
total = (TextView)findViewById(R.id.txtTotalAmount);
items = (TextView)findViewById(R.id.txtItemDetails);
String url = "http://172.16.0.4/res/order_fetch.php";
Intent intent= getIntent();
MemberID = intent.getStringExtra("MemberID");
List<NameValuePair> params = new ArrayList<NameValuePair>();
params.add(new BasicNameValuePair("sMemberID", MemberID));
resultServer = getHttpPost(url,params);
String strTotal = "";
String strItems = "";
JSONObject c;
try {
c = new JSONObject(resultServer);
strTotal = c.getString("TotalAmount");
strItems = c.getString("ItemDetails");
if(!strMemberID.equals(""))
{
total.setText(strTotal);
items.setText(strItems);
}
else
{
total.setText("-");
items.setText("-");
}
} catch (JSONException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
public String getHttpPost(String url,List<NameValuePair> params) {
StringBuilder str = new StringBuilder();
HttpClient client = new DefaultHttpClient();
HttpPost httpPost = new HttpPost(url);
try {
httpPost.setEntity(new UrlEncodedFormEntity(params));
HttpResponse response = client.execute(httpPost);
StatusLine statusLine = response.getStatusLine();
int statusCode = statusLine.getStatusCode();
if (statusCode == 200) { // Status OK
HttpEntity entity = response.getEntity();
InputStream content = entity.getContent();
BufferedReader reader = new BufferedReader(new InputStreamReader(content));
String line;
while ((line = reader.readLine()) != null) {
str.append(line);
}
} else {
Log.e("Log", "Failed to download result..");
}
} catch (ClientProtocolException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
}
return str.toString();
}
private boolean isNetworkAvailable() {
ConnectivityManager cm = (ConnectivityManager) getSystemService(CONNECTIVITY_SERVICE);
NetworkInfo info = cm.getActiveNetworkInfo();
return (info != null);
}
class MyAsyncTask extends
AsyncTask<String, Integer, ArrayList<HashMap<String, String>>> {
private ProgressDialog progressDialog = new ProgressDialog(
OrdersActivity.this);
@Override
protected void onPreExecute() {
progressDialog.setMessage("Loading, Please wait.....");
progressDialog.show();
}
@Override
protected ArrayList<HashMap<String, String>> doInBackground(
String... params) {
// TODO Auto-generated method stub
return null;
}
@Override
protected void onPostExecute(ArrayList<HashMap<String, String>> result) {
list = (ListView) findViewById(R.id.listView1);
adapter = new OrdersAdapter(OrdersActivity.this, itemsList);
list.setAdapter(adapter);
this.progressDialog.dismiss();
list.setOnItemClickListener(new OnItemClickListener() {
public void onItemClick(AdapterView<?> parent, View view,
int position, long id) {
}
});
}
}
}
OrdersAdapter.java：
public class OrdersAdapter extends BaseAdapter {
private Activity activity;
private ArrayList<HashMap<String, String>> data;
private static LayoutInflater inflater=null;
String strName,strMemberID ;
public OrdersAdapter(Activity a, ArrayList<HashMap<String, String>> d) {
activity = a;
data=d;
inflater = (LayoutInflater)activity.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
}
public int getCount() {
return data.size();
}
public Object getItem(int position) {
return position;
}
public long getItemId(int position) {
return position;
}
public View getView(int position, View convertView, ViewGroup parent) {
View vi=convertView;
if(convertView==null)
vi = inflater.inflate(R.layout.listrow_orders, null);
TextView title = (TextView)vi.findViewById(R.id.txtTotalAmount);
TextView description = (TextView)vi.findViewById(R.id.txtItemDetails);
HashMap<String, String> item = new HashMap<String, String>();
item = data.get(position);
title.setText(item.get(strName));
description.setText(strMemberID);
return vi;
}
}