Null Pointer exception on JSON.getString JSONObject

问题

I am trying to get the username from a database using PHP on android. I have it set up on my localhost. the output on localhost is: [{"id":"1","username":"Josh","password":"pass"}]

The PHP is:

<?php
$con = $con = mysql_connect("localhost", "root", "root");
if (!$con) {
    die('Could not connect: ' . mysql_error());
}
mysql_select_db("natter", $con);

$result = mysql_query("SELECT * FROM users");

while($row = mysql_fetch_assoc($result)) {
    $output[] = $row;
}

print(json_encode($output));

mysql_close($con);

The java is:

public void setTextToTextView(JSONArray jsonArray) {
    String s = "";
    for (int i = 0; i < jsonArray.length(); i++) {
        JSONObject json = null;

        try {
            json = jsonArray.getJSONObject(i);
            s = s + "Username : " + json.getString("username");
        } catch (JSONException e) {
            e.printStackTrace();
        }
    } 
    status.setText(s);
}

and the LOGCAT:

05-17 05:09:49.616: E/AndroidRuntime(1846): FATAL EXCEPTION: main
05-17 05:09:49.616: E/AndroidRuntime(1846): Process: me.docci.natter, PID: 1846
05-17 05:09:49.616: E/AndroidRuntime(1846): java.lang.NullPointerException
05-17 05:09:49.616: E/AndroidRuntime(1846):     at me.docci.natter.Login.setTextToTextView(Login.java:75)
05-17 05:09:49.616: E/AndroidRuntime(1846):     at me.docci.natter.Login$CheckUser.onPostExecute(Login.java:97)
05-17 05:09:49.616: E/AndroidRuntime(1846):     at me.docci.natter.Login$CheckUser.onPostExecute(Login.java:1)
05-17 05:09:49.616: E/AndroidRuntime(1846):     at android.os.AsyncTask.finish(AsyncTask.java:632)
05-17 05:09:49.616: E/AndroidRuntime(1846):     at android.os.AsyncTask.access$600(AsyncTask.java:177)
05-17 05:09:49.616: E/AndroidRuntime(1846):     at android.os.AsyncTask$InternalHandler.handleMessage(AsyncTask.java:645)
05-17 05:09:49.616: E/AndroidRuntime(1846):     at android.os.Handler.dispatchMessage(Handler.java:102)
05-17 05:09:49.616: E/AndroidRuntime(1846):     at android.os.Looper.loop(Looper.java:136)
05-17 05:09:49.616: E/AndroidRuntime(1846):     at android.app.ActivityThread.main(ActivityThread.java:5017)
05-17 05:09:49.616: E/AndroidRuntime(1846):     at java.lang.reflect.Method.invokeNative(Native Method)
05-17 05:09:49.616: E/AndroidRuntime(1846):     at java.lang.reflect.Method.invoke(Method.java:515)
05-17 05:09:49.616: E/AndroidRuntime(1846):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:779)
05-17 05:09:49.616: E/AndroidRuntime(1846):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:595)
05-17 05:09:49.616: E/AndroidRuntime(1846):     at dalvik.system.NativeStart.main(Native Method)

I have not dealt with JSON before, I used this tutorial to get this code:

youtube tutorial

Any ideas?

** UPDATE ** Apparently it is giving null in the jsonArray:

here is the code

public JSONArray getUserInfo() {
    String URL = "http://localhost/natter/index.php";

    HttpEntity httpEntity = null;
    try {
        DefaultHttpClient httpClient = new DefaultHttpClient();
        HttpGet httpGet = new HttpGet(URL);

        HttpResponse httpResponse = httpClient.execute(httpGet);

        httpEntity = httpResponse.getEntity();
    } catch (IOException e) {
        e.printStackTrace();
    }

    JSONArray jsonArray = null;

    if(httpEntity != null) {
        try {
            String entityResponse = EntityUtils.toString(httpEntity);

            Log.e("Entity Response : ", entityResponse);

            jsonArray = new JSONArray(entityResponse);
        } catch (JSONException e) {
            e.printStackTrace();
        } catch(IOException e) {
            e.printStackTrace();
        }
    }

    return jsonArray;
}

回答1:

Thanks to Squonk, I did not know that localhost was pointing to localhost on the emulator / device. So I changed the URL link to String URL = "http://10.0.2.2/natter/index.php"; and it worked.

回答2:

I am not sure but i idea that your code should be like this.

public void setTextToTextView(JSONArray jsonArray) {
    String s = "";
    for (int i = 0; i < jsonArray.length(); i++) {
        JSONObject json = new JSONObject();

        try {
            json = jsonArray.getJSONObject(i);
            s = s + "Username : " + json.getString("username");
        } catch (JSONException e) {
            e.printStackTrace();
        }
    } 
    status.setText(s);
}

Please try this.

来源：https://stackoverflow.com/questions/23709592/null-pointer-exception-on-json-getstring-jsonobject

标签

android

json

jsonobject