应用于Android Studio中URL结尾的"null"EditText出错

Question

所以每次我运行应用程序时,输入一个ID并点击提交; 最终结果以null作为ID.

例如:我想输入12345它应该去http://www.hiddenlink.com/12345,但它转到http://www.hiddenlink.com/null

这是我的代码:

public class SearchActivity extends Activity {
Button btnSearchStudent;
String studentID;
private String url = "http://www.hiddenlink.com/" + studentID; // This is test SID just to confirm connection
private static final String TAG_ALLRECORDS = "Objects";
private static final String TAG_ENAME = "emer_name1";
private static final String TAG_EPHONE1 = "emer_Phone1";
private static final String TAG_EPHONE2 = "emer_Phone2";


@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_search);
    EditText txtStudentID = (EditText) findViewById(R.id.txtStudentID);
    studentID = txtStudentID.getText().toString();
    btnSearchStudent = (Button) findViewById(R.id.btnSearchSID);
    btnSearchStudent.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View view) {
            Intent intent = new Intent(SearchActivity.this, SearchResults.class);
            startActivity(intent);
            new JSONParse().execute();
        }

    });
}

private class JSONParse extends AsyncTask<Void, Void, Void> {
    private ProgressDialog pDialog;

    @Override
    protected void onPreExecute() {
        super.onPreExecute();

        pDialog = new ProgressDialog(SearchActivity.this);
        pDialog.setMessage("Connection Test: Logging into Student Database...");
        pDialog.setIndeterminate(false);
        pDialog.setCancelable(true);
        pDialog.show();
    }

    // Login to APIs
    @Override
    protected Void doInBackground(Void... args) {

        String _username = "hidden";
        String _password = "hidden123";
        String content = MyHttpURLConnection.getData(url, _username, _password);
        try {
// Getting JSON Object from URL Content
            JSONObject json = new JSONObject(content);
            JSONArray jsonArray = json.getJSONArray(TAG_ALLRECORDS);
            for (int i = 0; i < jsonArray.length(); i++) {
                JSONObject c = jsonArray.getJSONObject(i);
// Storing JSON item in a Variable
                String emer_name1 = c.getString(TAG_ENAME);
                String emer_Phone1 = c.getString(TAG_EPHONE1);
                String emer_Phone2 = c.getString(TAG_EPHONE2);
// Adding value HashMap key => value
                HashMap<String, String> add = new HashMap<String, String>();
                add.put(TAG_EPHONE1, emer_Phone1);
                add.put(TAG_ENAME, emer_name1);
                add.put(TAG_EPHONE2, emer_Phone2);
            }

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

Answer 1

String studentID;
private String url = "http://www.hiddenlink.com/" + studentID;

studentID尚未在此处初始化,因此其值为null.删除+ studentID零件并在studentID设置值时添加.