I have created an app that is connected to a remote database. The items in the database are displayed through a spinner in my MainActivity class. I want to display the selected item in a separate class(Map.java) and XML page(map.xml), So I used this code in Map.java to try get the selected item and display it:
我创建了一个连接到远程数据库的应用程序。数据库中的项目通过MainActivity类中的微调器显示。我想在单独的类(Map.java)和XML页面(map.xml)中显示所选项目,所以我在Map.java中使用此代码来尝试获取所选项目并显示它:
Spinner mySpinner = (Spinner)findViewById(R.id.spinFood);
String text = mySpinner.getSelectedItem().toString();
EditText e = (EditText) findViewById (R.id.editText1);
e.setText(text);
To display this value I created an EditText in my map.xml file:
要显示此值,我在map.xml文件中创建了一个EditText:
<EditText
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:inputType="text"
android:text="@string/text"
android:id="@+id/editText1"
android:layout_alignBottom="@+id/textView"
android:layout_toRightOf="@+id/textView"
android:layout_alignRight="@+id/imageView"
android:layout_alignEnd="@+id/imageView" />
The android:input_type="text" is a string value I created:
android:input_type =“text”是我创建的字符串值:
<string name="text"> %s </string>
But whenever I open the map page my app crashes. Could someone please tell me where I am going wrong? Here all of my code for MainActivity and Map.java
但每当我打开地图页面时,我的应用程序崩溃了。有人可以告诉我哪里出错了吗?这里是MainActivity和Map.java的所有代码
MainActivity
package com.example.cillin.infoandroidhivespinnermysql;
import java.util.ArrayList;
..
public class MainActivity extends Activity implements OnItemSelectedListener {
private Button btnAddNewCategory;
private TextView txtCategory;
public Spinner spinnerFood;
// array list for spinner adapter
private ArrayList<Category> categoriesList;
ProgressDialog pDialog;
// API urls
// Url to create new category
private String URL_NEW_CATEGORY = "http://192.168.1.4/food_api/new_category.php";
// Url to get all categories
private String URL_CATEGORIES = "http://192.168.1.4/food_api/get_categories.php";
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
btnAddNewCategory = (Button) findViewById(R.id.btnAddNewCategory);
spinnerFood = (Spinner) findViewById(R.id.spinFood);
txtCategory = (TextView) findViewById(R.id.txtCategory);
categoriesList = new ArrayList<Category>();
// spinner item select listener
spinnerFood.setOnItemSelectedListener(this);
// Add new category click event
btnAddNewCategory.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
if (txtCategory.getText().toString().trim().length() > 0) {
// new category name
String newCategory = txtCategory.getText().toString();
// Call Async task to create new category
new AddNewCategory().execute(newCategory);
} else {
Toast.makeText(getApplicationContext(),
"Please enter category name", Toast.LENGTH_SHORT)
.show();
}
}
});
new GetCategories().execute();
}
/**
* Adding spinner data
* */
private void populateSpinner() {
List<String> lables = new ArrayList<String>();
txtCategory.setText("");
for (int i = 0; i < categoriesList.size(); i++) {
lables.add(categoriesList.get(i).getName());
}
// Creating adapter for spinner
ArrayAdapter<String> spinnerAdapter = new ArrayAdapter<String>(this,
android.R.layout.simple_spinner_item, lables);
// Drop down layout style - list view with radio button
spinnerAdapter
.setDropDownViewResource(android.R.layout.simple_spinner_dropdown_item);
// attaching data adapter to spinner
spinnerFood.setAdapter(spinnerAdapter);
//spinnerValue = spinnerFood.getSelectedItem().toString();
}
/**
* Async task to get all food categories
* */
private class GetCategories extends AsyncTask<Void, Void, Void> {
@Override
protected void onPreExecute() {
super.onPreExecute();
pDialog = new ProgressDialog(MainActivity.this);
pDialog.setMessage("Fetching food categories..");
pDialog.setCancelable(false);
pDialog.show();
}
@Override
protected Void doInBackground(Void... arg0) {
ServiceHandler jsonParser = new ServiceHandler();
String json = jsonParser.makeServiceCall(URL_CATEGORIES, ServiceHandler.GET);
Log.e("Response: ", "> " + json);
if (json != null) {
try {
JSONObject jsonObj = new JSONObject(json);
if (jsonObj != null) {
JSONArray categories = jsonObj
.getJSONArray("categories");
for (int i = 0; i < categories.length(); i++) {
JSONObject catObj = (JSONObject) categories.get(i);
Category cat = new Category(catObj.getInt("id"),
catObj.getString("name"));
categoriesList.add(cat);
}
}
} catch (JSONException e) {
e.printStackTrace();
}
} else {
Log.e("JSON Data", "Didn't receive any data from server!");
}
return null;
}
@Override
protected void onPostExecute(Void result) {
super.onPostExecute(result);
if (pDialog.isShowing())
pDialog.dismiss();
populateSpinner();
}
}
/**
* Async task to create a new food category
* */
private class AddNewCategory extends AsyncTask<String, Void, Void> {
boolean isNewCategoryCreated = false;
@Override
protected void onPreExecute() {
super.onPreExecute();
pDialog = new ProgressDialog(MainActivity.this);
pDialog.setMessage("Creating new category..");
pDialog.setCancelable(false);
pDialog.show();
}
@Override
protected Void doInBackground(String... arg) {
String newCategory = arg[0];
// Preparing post params
List<NameValuePair> params = new ArrayList<NameValuePair>();
params.add(new BasicNameValuePair("name", newCategory));
ServiceHandler serviceClient = new ServiceHandler();
String json = serviceClient.makeServiceCall(URL_NEW_CATEGORY,
ServiceHandler.POST, params);
Log.d("Create Response: ", "> " + json);
if (json != null) {
try {
JSONObject jsonObj = new JSONObject(json);
boolean error = jsonObj.getBoolean("error");
// checking for error node in json
if (!error) {
// new category created successfully
isNewCategoryCreated = true;
} else {
Log.e("Create Category Error: ", "> " + jsonObj.getString("message"));
}
} catch (JSONException e) {
e.printStackTrace();
}
} else {
Log.e("JSON Data", "Didn't receive any data from server!");
}
return null;
}
@Override
protected void onPostExecute(Void result) {
super.onPostExecute(result);
if (pDialog.isShowing())
pDialog.dismiss();
if (isNewCategoryCreated) {
runOnUiThread(new Runnable() {
@Override
public void run() {
// fetching all categories
new GetCategories().execute();
}
});
}
}
}
@Override
public void onItemSelected(AdapterView<?> parent, View view, int position,
long id) {
Toast.makeText(
getApplicationContext(),
parent.getItemAtPosition(position).toString() + " Selected" ,
Toast.LENGTH_LONG).show();
}
@Override
public void onNothingSelected(AdapterView<?> arg0) {
}
}
Map.java
package com.example.cillin.infoandroidhivespinnermysql;
import android.app.Activity;
import android.content.Intent;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.ImageView;
import android.widget.Spinner;
import android.widget.TextView;
public class Map extends Activity {
公共类Map扩展Activity {
public void onCreate(Bundle savedInstanceState)
{
super.onCreate(savedInstanceState);
//This page layout is located in the menu XML file
//SetContentView links a Java file, to its XML file for the layout
setContentView(R.layout.map);
/*TextView.setText(spinnerValue);
TextView spinv = (TextView)findViewById(R.id.textView2);
spinv.setText(getspin());
spinv = getspin();*/
Spinner mySpinner = (Spinner)findViewById(R.id.spinFood);
String text = mySpinner.getSelectedItem().toString();
EditText e = (EditText) findViewById (R.id.editText1);
e.setText(text);
Button mainm = (Button)findViewById(R.id.mainmenu);
mainm.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
//This button is linked to the map page
Intent i = new Intent(Map.this, MainMenu.class);
//Activating the intent
startActivity(i);
}
});
}
}
Any help would be much appreciated!!
任何帮助将非常感激!!
Here are the errors in my logcat when is crashes:
以下是崩溃时我的logcat中的错误:
E/DatabaseUtils﹕ Writing exception to parcel
java.lang.SecurityException: Permission Denial: get/set setting for user asks to run as user -2 but is calling from user 0; this requires android.permission.INTERACT_ACROSS_USERS_FULL
at com.android.server.am.ActivityManagerService.handleIncomingUser(ActivityManagerService.java:14643)
at android.app.ActivityManager.handleIncomingUser(ActivityManager.java:2469)
at com.android.providers.settings.SettingsProvider.call(SettingsProvider.java:688)
at android.content.ContentProvider$Transport.call(ContentProvider.java:325)
at android.content.ContentProviderNative.onTransact(ContentProviderNative.java:275)
at android.os.Binder.execTransact(Binder.java:404)
E/AndroidRuntime﹕ FATAL EXCEPTION: main
Process: com.example.cillin.infoandroidhivespinnermysql, PID: 14691
java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.cillin.infoandroidhivespinnermysql/com.example.cillin.infoandroidhivespinnermysql.Map}: java.lang.NullPointerException
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2305)
at
android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2363)
at android.app.ActivityThread.access$900(ActivityThread.java:161)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1265)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:157)
at android.app.ActivityThread.main(ActivityThread.java:5356)
at java.lang.reflect.Method.invokeNative(Native Method)
at java.lang.reflect.Method.invoke(Method.java:515)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1265)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1081)
at dalvik.system.NativeStart.main(Native Method)
Caused by: java.lang.NullPointerException
at com.example.cillin.infoandroidhivespinnermysql.Map.onCreate(Map.java:34)
at android.app.Activity.performCreate(Activity.java:5426)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1105)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2269)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2363)
at android.app.ActivityThread.access$900(ActivityThread.java:161)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1265)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:157)
at android.app.ActivityThread.main(ActivityThread.java:5356)
at java.lang.reflect.Method.invokeNative(Native Method)
at java.lang.reflect.Method.invoke(Method.java:515)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1265)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1081)
at dalvik.system.NativeStart.main(Native Method)
1 个解决方案
#1
0
I'm guessing that you're getting a NullPointerException in your Map.class
我猜你在Map.class中得到了NullPointerException
Spinner mySpinner = (Spinner)findViewById(R.id.spinFood);
String text = mySpinner.getSelectedItem().toString();
EditText e = (EditText) findViewById (R.id.editText1);
e.setText(text);
You get a reference to Spinner, then you try to get the selected item and then convert that item to a string. As far as I can tell you haven't actually added any items to the spinner. My guess is that you are trying to access an object in the spinner and since it doesn't exist it returns null. Then you try to call a method on the null object and get an NPE.
您获得了对Spinner的引用,然后您尝试获取所选项目,然后将该项目转换为字符串。据我所知,你实际上并没有向微调器添加任何物品。我的猜测是你试图访问微调器中的一个对象,因为它不存在,它返回null。然后你尝试在null对象上调用一个方法并获得一个NPE。
This is just a guess. A stacktrace is very helpful in trying to diagnose this.
这只是猜测。堆栈跟踪在尝试诊断时非常有用。
Where I think you're going wrong is that you populate the spinner in MainActivity and then expect to be able to select an item from that spinner from a different activity. This isn't how it works. Map.class won't be able to reference anything in MainActivity.class. You could try passing the object from MainActivity.class to Map.class or use a different method of passing data, but trying to reference data in MainAcitivity.class from Map.class won't work.
我认为你出错的地方是你在MainActivity中填充微调器,然后期望能够从不同的活动中选择来自该微调器的项目。这不是它的工作原理。 Map.class将无法在MainActivity.class中引用任何内容。您可以尝试将对象从MainActivity.class传递给Map.class或使用另一种传递数据的方法,但尝试从Map.class引用MainAcitivity.class中的数据将不起作用。
Edit: If you just want to pass a String from MainActivity.class to Map.class you can add the string as an 'extra' to the intent that you use to start Map.class.
编辑:如果您只想将MainActivity.class中的String传递给Map.class,则可以将该字符串作为'extra'添加到用于启动Map.class的intent中。
In your MainActivity.class code. When the item from the spinner is selected, create an intent and set the string as an extra using the putExtra() method. You will need to supply a key that basically tags the extra so you can identify it in the receiving activity and the string you want to send.
在您的MainActivity.class代码中。选择微调器中的项目时,使用putExtra()方法创建一个intent并将该字符串设置为extra。您需要提供一个基本上标记额外的密钥,以便您可以在接收活动和要发送的字符串中识别它。
Intent intent = new Intent(this, Map.class);
intent.putExtra("KEY_SPINNER_STRING", variableRepresentingString);
startActivity(intent);
In the Map.class activity, in the onCreate() method you will need to receive the intent, check for the extra, then unpack the extra. Then you will have the String.
在Map.class活动中,在onCreate()方法中,您需要接收intent,检查extra,然后解压缩额外的。然后你将拥有String。
onCreate(Bundle savedInstanceState) {
String spinnerString;
if (getIntent() != null && getIntent().getExtras() != null) {
Bundle bundle = getIntent().getExtras();
if (bundle.getString("KEY_SPINNER_STRING") != null) {
spinnerString = bundle.getString("KEY_SPINNER_STRING");
}
}
}
If everything is done correctly the String will be passed from MainActivity.class and received by Map.class
如果一切正确完成,String将从MainActivity.class传递并由Map.class接收
#1
0
I'm guessing that you're getting a NullPointerException in your Map.class
我猜你在Map.class中得到了NullPointerException
Spinner mySpinner = (Spinner)findViewById(R.id.spinFood);
String text = mySpinner.getSelectedItem().toString();
EditText e = (EditText) findViewById (R.id.editText1);
e.setText(text);
You get a reference to Spinner, then you try to get the selected item and then convert that item to a string. As far as I can tell you haven't actually added any items to the spinner. My guess is that you are trying to access an object in the spinner and since it doesn't exist it returns null. Then you try to call a method on the null object and get an NPE.
您获得了对Spinner的引用,然后您尝试获取所选项目,然后将该项目转换为字符串。据我所知,你实际上并没有向微调器添加任何物品。我的猜测是你试图访问微调器中的一个对象,因为它不存在,它返回null。然后你尝试在null对象上调用一个方法并获得一个NPE。
This is just a guess. A stacktrace is very helpful in trying to diagnose this.
这只是猜测。堆栈跟踪在尝试诊断时非常有用。
Where I think you're going wrong is that you populate the spinner in MainActivity and then expect to be able to select an item from that spinner from a different activity. This isn't how it works. Map.class won't be able to reference anything in MainActivity.class. You could try passing the object from MainActivity.class to Map.class or use a different method of passing data, but trying to reference data in MainAcitivity.class from Map.class won't work.
我认为你出错的地方是你在MainActivity中填充微调器,然后期望能够从不同的活动中选择来自该微调器的项目。这不是它的工作原理。 Map.class将无法在MainActivity.class中引用任何内容。您可以尝试将对象从MainActivity.class传递给Map.class或使用另一种传递数据的方法,但尝试从Map.class引用MainAcitivity.class中的数据将不起作用。
Edit: If you just want to pass a String from MainActivity.class to Map.class you can add the string as an 'extra' to the intent that you use to start Map.class.
编辑:如果您只想将MainActivity.class中的String传递给Map.class,则可以将该字符串作为'extra'添加到用于启动Map.class的intent中。
In your MainActivity.class code. When the item from the spinner is selected, create an intent and set the string as an extra using the putExtra() method. You will need to supply a key that basically tags the extra so you can identify it in the receiving activity and the string you want to send.
在您的MainActivity.class代码中。选择微调器中的项目时,使用putExtra()方法创建一个intent并将该字符串设置为extra。您需要提供一个基本上标记额外的密钥,以便您可以在接收活动和要发送的字符串中识别它。
Intent intent = new Intent(this, Map.class);
intent.putExtra("KEY_SPINNER_STRING", variableRepresentingString);
startActivity(intent);
In the Map.class activity, in the onCreate() method you will need to receive the intent, check for the extra, then unpack the extra. Then you will have the String.
在Map.class活动中,在onCreate()方法中,您需要接收intent,检查extra,然后解压缩额外的。然后你将拥有String。
onCreate(Bundle savedInstanceState) {
String spinnerString;
if (getIntent() != null && getIntent().getExtras() != null) {
Bundle bundle = getIntent().getExtras();
if (bundle.getString("KEY_SPINNER_STRING") != null) {
spinnerString = bundle.getString("KEY_SPINNER_STRING");
}
}
}
If everything is done correctly the String will be passed from MainActivity.class and received by Map.class
如果一切正确完成,String将从MainActivity.class传递并由Map.class接收