Hey guys i am getting an error (NullPointerException) and need your help.I cant find my mistake no matter how hard i look.
My general discussion activity wont even open.Thanks in advance.Part of my codes are the following:
GENERALDISCUSSION
public class GeneralDiscussion extends ListActivity {
SQLiteDatabase sqLiteDatabase;
SQLiteHandler sqLiteHandler;
Cursor cursor;
ListView l;
private static final String TAG = GeneralDiscussion.class.getSimpleName();
private Button btnposting;
private Button btnLinkToLogin;
private EditText inputPost;
private EditText inputEmail;
private EditText inputPassword;
private ProgressDialog pDialog;
private SessionManager session;
private SQLiteHandler db;
private TextView txtName;
private TextView txtPost;
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_general_discussion);
ArrayList<HashMap<String, String>> emaillist = db.getMessage();
if (emaillist.size() != 0) {
Toast.makeText(getApplicationContext(), "this" + emaillist.get(1), Toast.LENGTH_SHORT).show();
ListAdapter adapter = new SimpleAdapter(GeneralDiscussion.this, emaillist,
R.layout.raw_layout,
new String[]{"user_posted", "post", "posted_at", "post_id"}, new int[]{
R.id.text_user_name, R.id.text_user_post, R.id.text_user_date, R.id.text_user_number});
setListAdapter(adapter);
}
txtName = (TextView) findViewById(R.id.name);
inputPost = (EditText) findViewById(R.id.post);
btnposting = (Button) findViewById(R.id.btnposting);
// Progress dialog
pDialog = new ProgressDialog(this);
pDialog.setCancelable(false);
// Session manager
session = new SessionManager(getApplicationContext());
// SQLite database handler
db = new SQLiteHandler(getApplicationContext())
HashMap<String, String> user = db.getUserDetails();
String name = user.get("name");
txtName.setText(name);
// Posting Button Click event
btnposting.setOnClickListener(new View.OnClickListener() {
public void onClick(View view) {
String post = inputPost.getText().toString().trim();
String user_posted = txtName.getText().toString().trim();
if (!post.isEmpty()) {
postThreads(post, user_posted)
} else {
Toast.makeText(getApplicationContext(),
"Please enter your details!", Toast.LENGTH_LONG)
.show();
}
}
});
}
private void postThreads(final String post,final String user_posted) {
// Tag used to cancel the request
String tag_string_req = "req_posting";
pDialog.setMessage("Posting ...");
showDialog();
StringRequest strReq = new StringRequest(Method.POST,
AppConfig.URL_POSTING, new Response.Listener<String>() {
@Override
public void onResponse(String response) {
Log.d(TAG, "Posting Response: " + response.toString());
hideDialog();
try {
JSONObject jObj = new JSONObject(response);
boolean error = jObj.getBoolean("error");
if (!error) {
// User successfully stored in MySQL
// Now store the user in sqlite
JSONObject posting = jObj.getJSONObject("posting");
String post = posting.getString("post");
String user_posted = posting.getString("user_posted");
String posted_at = posting
.getString("posted_at");
// Inserting row in users table
db.addPosting(user_posted,post,posted_at);
Toast.makeText(getApplicationContext(), "User successfully posted!", Toast.LENGTH_LONG).show();
} else {
// Error occurred in registration. Get the error
// message
String errorMsg = jObj.getString("error_msg");
Toast.makeText(getApplicationContext(),
errorMsg, Toast.LENGTH_LONG).show();
}
} catch (JSONException e) {
e.printStackTrace();
}
}
}, new Response.ErrorListener() {
@Override
public void onErrorResponse(VolleyError error) {
Log.e(TAG, "Posting Error: " + error.getMessage());
Toast.makeText(getApplicationContext(),
error.getMessage(), Toast.LENGTH_LONG).show();
hideDialog();
}
}) {
@Override
protected Map<String, String> getParams() {
// Posting params to register url
Map<String, String> params = new HashMap<String, String>();
params.put("post", post);
params.put("user_posted", user_posted);
return params;
}
};
// Adding request to request queue
AppController.getInstance().addToRequestQueue(strReq, tag_string_req);
}
private void showDialog() {
if (!pDialog.isShowing())
pDialog.show();
}
private void hideDialog() {
if (pDialog.isShowing())
pDialog.dismiss();
}
}
ACTIVITY_GENERAL_DISCUSSION
<?xml version="1.0" encoding="utf-8"?> <LinearLayout android:id="@+id/main"
xmlns:android="http://schemas.android.com/apk/res/android"
android:orientation="vertical"
android:layout_height="fill_parent"
android:layout_width="fill_parent">
<LinearLayout android:id="@+id/layout"
android:layout_width="wrap_content"
android:layout_height="286dp">
<ListView
android:id="@android:id/list"
android:layout_height="251dp"
android:layout_width="fill_parent">
</ListView>
</LinearLayout>
<Button
android:id="@+id/btnposting"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_marginTop="20dip"
android:background="#0000"
android:text="Write..."
android:textColorHighlight="#000000" />
<EditText
android:id="@+id/name"
android:layout_width="203dp"
android:layout_height="wrap_content"
android:layout_marginTop="20dip"
android:background="#ffffff"
android:textColor="#000000" />
<EditText
android:id="@+id/post"
android:layout_width="234dp"
android:layout_height="87dp"
android:layout_marginBottom="10dp"
android:padding="10dp"
android:singleLine="true" />
</LinearLayout>
SQLITEHANDLER
public ArrayList<HashMap<String, String>> getMessage(){
ArrayList<HashMap<String, String>> message = new ArrayList<HashMap<String, String>>();
String selectQuery = "SELECT * FROM " + TABLE_USER;
SQLiteDatabase db = this.getReadableDatabase();
Cursor cursor = db.rawQuery(selectQuery, null);
// Move to first row
if ( cursor.moveToFirst()) {
do {
HashMap<String, String> map = new HashMap<String, String>();
map.put("post_id", cursor.getString(0));
map.put("user_posted", cursor.getString(1));
map.put("post", cursor.getString(2));
map.put("posted_at", cursor.getString(3));
message.add(map);
} while (cursor.moveToNext());
}
// return contact list
return message;
}
RAW_LAYOUT
<TextView
android:layout_width="100dp"
android:layout_height="wrap_content"
android:id="@+id/text_user_post"
android:text="Post"
android:gravity="center"
/>
<TextView
android:layout_width="100dp"
android:layout_height="wrap_content"
android:id="@+id/text_user_name"
android:text="Name"
android:gravity="center"
/>
<TextView
android:layout_width="100dp"
android:layout_height="wrap_content"
android:id="@+id/text_user_number"
android:text="Number"
android:gravity="center"
/>
<TextView
android:layout_width="100dp"
android:layout_height="wrap_content"
android:id="@+id/text_user_date"
android:text="Date"
android:gravity="center"
ERROR LOG
java.lang.RuntimeException: Unable to start activity ComponentInfo{com.tonia/com.tonia.activity.GeneralDiscussion}: java.lang.NullPointerException
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1956)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1981)
at android.app.ActivityThread.access$600(ActivityThread.java:123)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1147)
at android.os.Handler.dispatchMessage(Handler.java:99)
at android.os.Looper.loop(Looper.java:137)
at android.app.ActivityThread.main(ActivityThread.java:4424)
at java.lang.reflect.Method.invokeNative(Native Method)
at java.lang.reflect.Method.invoke(Method.java:511)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:784)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:551)
at dalvik.system.NativeStart.main(Native Method)
Caused by: java.lang.NullPointerException
at com.tonia.activity.GeneralDiscussion.onCreate(GeneralDiscussion.java:86)
at android.app.Activity.performCreate(Activity.java:4466)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1049)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1920)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1981)
at android.app.ActivityThread.access$600(ActivityThread.java:123)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1147)
at android.os.Handler.dispatchMessage(Handler.java:99)
at android.os.Looper.loop(Looper.java:137)
at android.app.ActivityThread.main(ActivityThread.java:4424)
at java.lang.reflect.Method.invokeNative(Native Method)
at java.lang.reflect.Method.invoke(Method.java:511)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:784)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:551)
at dalvik.system.NativeStart.main(Native Method)
答案 0 :(得分：0)
你在onCreate()方法 -
ArrayList<HashMap<String, String>> emaillist = db.getMessage();//db is not instantiated yet.
您正在访问尚未实例化的db上的方法getMessage（）。 在调用方法之前，需要实例化它。