java - android应用程序与网站数据库的连接

Question

我是 android 的新手，我正在开发一个通过 PHP 将数据从 android 传递到 MySQL 的应用程序。我现在正在注册用户部分。我从搜索中得到了一些代码，但在我实现它时，我遇到了运行时错误。这是我的代码。 logcat 也在底部。

public class RegisterActivity extends Activity {

    // Progress Dialog
    private ProgressDialog pDialog;

    JSONParser jsonParser = new JSONParser();
    EditText registerName;
    EditText registerRollno;
    EditText inputDesc;

    // url to create new product
    private static String url_create_voter = "http://10.0.2.2/evoting/create_voter.php";

    // JSON Node names
    private static final String TAG_SUCCESS = "success";

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.register1);

        // Edit Text
        EditText registerName = (EditText) findViewById(R.id.registerName);
        EditText registerRollno = (EditText) findViewById(R.id.registerRollno);
       // inputDesc = (EditText) findViewById(R.id.inputDesc);

        // Create button
        Button btnSubmit = (Button) findViewById(R.id.btnSubmit);

        // button click event
        btnSubmit.setOnClickListener(new View.OnClickListener() {


            public void onClick(View view) {
                // creating new product in background thread
                new CreateNewVoter().execute();
            }
        });
    }

    /**
     * Background Async Task to Create new product
     * */
    class CreateNewVoter extends AsyncTask<String, String, String> {

        /**
         * Before starting background thread Show Progress Dialog
         * */
        @Override
        protected void onPreExecute() {
            super.onPreExecute();
            pDialog = new ProgressDialog(RegisterActivity.this);
            pDialog.setMessage("Creating Voter..");
            pDialog.setIndeterminate(false);
            pDialog.setCancelable(true);
            pDialog.show();
        }

        /**
         * Creating product
         * */
        protected String doInBackground(String... args) {
            String name = registerName.getText().toString();
            String rollno = registerRollno.getText().toString();
            //String description = inputDesc.getText().toString();

            // Building Parameters
            List<NameValuePair> params = new ArrayList<NameValuePair>();
            params.add(new BasicNameValuePair("name", name));
            params.add(new BasicNameValuePair("rollno", rollno));
           // params.add(new BasicNameValuePair("description", description));

            // getting JSON Object
            // Note that create product url accepts POST method
            JSONObject json = jsonParser.makeHttpRequest(url_create_voter,
                    "POST", params);

            // check log cat fro response
            Log.d("Create Response", json.toString());

            // check for success tag




            try {
                int success = json.getInt(TAG_SUCCESS);

                if (success == 1) {
                    // successfully created product
                    Intent i = new Intent(getApplicationContext(), CreateVoterSuccess.class);
                    startActivity(i);

                    // closing this screen
                    finish();
                } else {
                    Intent i = new Intent(getApplicationContext(), CreateVoterFail.class);
                    startActivity(i);
                    // failed to create product
                }
            } catch (JSONException e) {
                e.printStackTrace();
            }





            return null;
        }

        /**
         * After completing background task Dismiss the progress dialog
         * **/
        protected void onPostExecute(String file_url) {
            // dismiss the dialog once done
            pDialog.dismiss();
        }

    }
}

这是logcat:

09-22 05:47:52.343: W/KeyCharacterMap(279): No keyboard for id 0
09-22 05:47:52.343: W/KeyCharacterMap(279): Using default keymap: /system/usr/keychars/qwerty.kcm.bin
09-22 05:47:54.403: W/dalvikvm(279): threadid=7: thread exiting with uncaught exception (group=0x4001d800)
09-22 05:47:54.414: E/AndroidRuntime(279): FATAL EXCEPTION: AsyncTask #1
09-22 05:47:54.414: E/AndroidRuntime(279): java.lang.RuntimeException: An error occured while executing doInBackground()
09-22 05:47:54.414: E/AndroidRuntime(279):  at android.os.AsyncTask$3.done(AsyncTask.java:200)
09-22 05:47:54.414: E/AndroidRuntime(279):  at java.util.concurrent.FutureTask$Sync.innerSetException(FutureTask.java:273)
09-22 05:47:54.414: E/AndroidRuntime(279):  at java.util.concurrent.FutureTask.setException(FutureTask.java:124)
09-22 05:47:54.414: E/AndroidRuntime(279):  at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:307)
09-22 05:47:54.414: E/AndroidRuntime(279):  at java.util.concurrent.FutureTask.run(FutureTask.java:137)
09-22 05:47:54.414: E/AndroidRuntime(279):  at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1068)
09-22 05:47:54.414: E/AndroidRuntime(279):  at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:561)
09-22 05:47:54.414: E/AndroidRuntime(279):  at java.lang.Thread.run(Thread.java:1096)
09-22 05:47:54.414: E/AndroidRuntime(279): Caused by: java.lang.NullPointerException
09-22 05:47:54.414: E/AndroidRuntime(279):  at com.example.evoting.RegisterActivity$CreateNewVoter.doInBackground(RegisterActivity.java:83)
09-22 05:47:54.414: E/AndroidRuntime(279):  at com.example.evoting.RegisterActivity$CreateNewVoter.doInBackground(RegisterActivity.java:1)
09-22 05:47:54.414: E/AndroidRuntime(279):  at android.os.AsyncTask$2.call(AsyncTask.java:185)
09-22 05:47:54.414: E/AndroidRuntime(279):  at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:305)
09-22 05:47:54.414: E/AndroidRuntime(279):  ... 4 more
09-22 05:47:55.313: E/WindowManager(279): Activity com.example.evoting.RegisterActivity has leaked window com.android.internal.policy.impl.PhoneWindow$DecorView@44f28db0 that was originally added here
09-22 05:47:55.313: E/WindowManager(279): android.view.WindowLeaked: Activity com.example.evoting.RegisterActivity has leaked window com.android.internal.policy.impl.PhoneWindow$DecorView@44f28db0 that was originally added here
09-22 05:47:55.313: E/WindowManager(279):   at android.view.ViewRoot.<init>(ViewRoot.java:247)
09-22 05:47:55.313: E/WindowManager(279):   at android.view.WindowManagerImpl.addView(WindowManagerImpl.java:148)
09-22 05:47:55.313: E/WindowManager(279):   at android.view.WindowManagerImpl.addView(WindowManagerImpl.java:91)
09-22 05:47:55.313: E/WindowManager(279):   at android.view.Window$LocalWindowManager.addView(Window.java:424)
09-22 05:47:55.313: E/WindowManager(279):   at android.app.Dialog.show(Dialog.java:241)
09-22 05:47:55.313: E/WindowManager(279):   at com.example.evoting.RegisterActivity$CreateNewVoter.onPreExecute(RegisterActivity.java:76)
09-22 05:47:55.313: E/WindowManager(279):   at android.os.AsyncTask.execute(AsyncTask.java:391)
09-22 05:47:55.313: E/WindowManager(279):   at com.example.evoting.RegisterActivity$1.onClick(RegisterActivity.java:56)
09-22 05:47:55.313: E/WindowManager(279):   at android.view.View.performClick(View.java:2408)
09-22 05:47:55.313: E/WindowManager(279):   at android.view.View$PerformClick.run(View.java:8816)
09-22 05:47:55.313: E/WindowManager(279):   at android.os.Handler.handleCallback(Handler.java:587)
09-22 05:47:55.313: E/WindowManager(279):   at android.os.Handler.dispatchMessage(Handler.java:92)
09-22 05:47:55.313: E/WindowManager(279):   at android.os.Looper.loop(Looper.java:123)
09-22 05:47:55.313: E/WindowManager(279):   at android.app.ActivityThread.main(ActivityThread.java:4627)
09-22 05:47:55.313: E/WindowManager(279):   at java.lang.reflect.Method.invokeNative(Native Method)
09-22 05:47:55.313: E/WindowManager(279):   at java.lang.reflect.Method.invoke(Method.java:521)
09-22 05:47:55.313: E/WindowManager(279):   at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:868)
09-22 05:47:55.313: E/WindowManager(279):   at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:626)
09-22 05:47:55.313: E/WindowManager(279):   at dalvik.system.NativeStart.main(Native Method)
09-22 05:47:57.133: I/Process(279): Sending signal. PID: 279 SIG: 9
09-22 05:56:34.157: W/KeyCharacterMap(291): No keyboard for id 0
09-22 05:56:34.157: W/KeyCharacterMap(291): Using default keymap: /system/usr/keychars/qwerty.kcm.bin
09-22 05:56:36.553: W/dalvikvm(291): threadid=7: thread exiting with uncaught exception (group=0x4001d800)
09-22 05:56:36.563: E/AndroidRuntime(291): FATAL EXCEPTION: AsyncTask #1
09-22 05:56:36.563: E/AndroidRuntime(291): java.lang.RuntimeException: An error occured while executing doInBackground()
09-22 05:56:36.563: E/AndroidRuntime(291):  at android.os.AsyncTask$3.done(AsyncTask.java:200)
09-22 05:56:36.563: E/AndroidRuntime(291):  at java.util.concurrent.FutureTask$Sync.innerSetException(FutureTask.java:273)
09-22 05:56:36.563: E/AndroidRuntime(291):  at java.util.concurrent.FutureTask.setException(FutureTask.java:124)
09-22 05:56:36.563: E/AndroidRuntime(291):  at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:307)
09-22 05:56:36.563: E/AndroidRuntime(291):  at java.util.concurrent.FutureTask.run(FutureTask.java:137)
09-22 05:56:36.563: E/AndroidRuntime(291):  at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1068)
09-22 05:56:36.563: E/AndroidRuntime(291):  at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:561)
09-22 05:56:36.563: E/AndroidRuntime(291):  at java.lang.Thread.run(Thread.java:1096)
09-22 05:56:36.563: E/AndroidRuntime(291): Caused by: java.lang.NullPointerException
09-22 05:56:36.563: E/AndroidRuntime(291):  at com.example.evoting.RegisterActivity$CreateNewVoter.doInBackground(RegisterActivity.java:83)
09-22 05:56:36.563: E/AndroidRuntime(291):  at com.example.evoting.RegisterActivity$CreateNewVoter.doInBackground(RegisterActivity.java:1)
09-22 05:56:36.563: E/AndroidRuntime(291):  at android.os.AsyncTask$2.call(AsyncTask.java:185)
09-22 05:56:36.563: E/AndroidRuntime(291):  at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:305)
09-22 05:56:36.563: E/AndroidRuntime(291):  ... 4 more
09-22 05:56:37.203: E/WindowManager(291): Activity com.example.evoting.RegisterActivity has leaked window com.android.internal.policy.impl.PhoneWindow$DecorView@44f21560 that was originally added here
09-22 05:56:37.203: E/WindowManager(291): android.view.WindowLeaked: Activity com.example.evoting.RegisterActivity has leaked window com.android.internal.policy.impl.PhoneWindow$DecorView@44f21560 that was originally added here
09-22 05:56:37.203: E/WindowManager(291):   at android.view.ViewRoot.<init>(ViewRoot.java:247)
09-22 05:56:37.203: E/WindowManager(291):   at android.view.WindowManagerImpl.addView(WindowManagerImpl.java:148)
09-22 05:56:37.203: E/WindowManager(291):   at android.view.WindowManagerImpl.addView(WindowManagerImpl.java:91)
09-22 05:56:37.203: E/WindowManager(291):   at android.view.Window$LocalWindowManager.addView(Window.java:424)
09-22 05:56:37.203: E/WindowManager(291):   at android.app.Dialog.show(Dialog.java:241)
09-22 05:56:37.203: E/WindowManager(291):   at com.example.evoting.RegisterActivity$CreateNewVoter.onPreExecute(RegisterActivity.java:76)
09-22 05:56:37.203: E/WindowManager(291):   at android.os.AsyncTask.execute(AsyncTask.java:391)
09-22 05:56:37.203: E/WindowManager(291):   at com.example.evoting.RegisterActivity$1.onClick(RegisterActivity.java:56)
09-22 05:56:37.203: E/WindowManager(291):   at android.view.View.performClick(View.java:2408)
09-22 05:56:37.203: E/WindowManager(291):   at android.view.View$PerformClick.run(View.java:8816)
09-22 05:56:37.203: E/WindowManager(291):   at android.os.Handler.handleCallback(Handler.java:587)
09-22 05:56:37.203: E/WindowManager(291):   at android.os.Handler.dispatchMessage(Handler.java:92)
09-22 05:56:37.203: E/WindowManager(291):   at android.os.Looper.loop(Looper.java:123)
09-22 05:56:37.203: E/WindowManager(291):   at android.app.ActivityThread.main(ActivityThread.java:4627)
09-22 05:56:37.203: E/WindowManager(291):   at java.lang.reflect.Method.invokeNative(Native Method)
09-22 05:56:37.203: E/WindowManager(291):   at java.lang.reflect.Method.invoke(Method.java:521)
09-22 05:56:37.203: E/WindowManager(291):   at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:868)
09-22 05:56:37.203: E/WindowManager(291):   at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:626)
09-22 05:56:37.203: E/WindowManager(291):   at dalvik.system.NativeStart.main(Native Method)
09-22 05:56:41.412: I/Process(291): Sending signal. PID: 291 SIG: 9

Answer 1

局部变量影子对象变量:

    EditText registerName;
    EditText registerRollno;

// [...]
 public void onCreate(Bundle savedInstanceState) {

 [...]
        EditText registerName = (EditText) findViewById(R.id.registerName);
        EditText registerRollno = (EditText) findViewById(R.id.registerRollno);

创建与对象变量同名的局部变量默认情况下不是错误，但在这里看起来像是错误。

这样对象变量仍然是null，因此是 NPE。