有人可以帮我解决这个问题吗？我试图在Listview中显示来自firebase的数据，但它崩溃了！我在堆栈和其他站点尝试了不同主题的不同代码，但在
处收到错误while(counter) {
$("#passwordStrength").removeClass("list" + counter--);
}
或
adapter=new ArrayAdapter<String>
(this,android.R.layout.simple_list_item_1,retrieve());
有nullexception，所以这里是代码和错误
JavaCode
尝试过Listview
现在我尝试了listview，它崩溃了。这是代码和错误
lv.setAdapter(adapter);
的JobDetail
public class WorkActivity extends AppCompatActivity {
// Spinner jobSpin;
ListView lv;
Button ShowButton;
// Define a String ArrayList for the job
private ArrayList<String> jobdes=new ArrayList<>();
// Define an ArrayAdapter for the list
private ArrayAdapter<String> arrayAdapter;
// Declaring String variable ( In which we are storing firebase server URL
).
public static final String Firebase_Server_URL =
"https://jobaps70.firebaseio.com/";
public static final String Firebase_Server_URL1 =
"https://jobaps70.firebaseio.com/jobs";
// Declaring String variables to store name & phone number get from
EditText.
String PriceHolder, JobDescriptionHolder;
FirebaseHelper helper;
// Declaring Firebase object.
Firebase firebase,firebase1;
// Creating FirebaseAuth.
FirebaseAuth firebaseAuth ;
// Creating FirebaseAuth.
FirebaseUser firebaseUser;
// Creating Boolean variable that holds EditText is empty or not status.
Boolean EditTextStatus ;
TextView ShowDataTextView ;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_edits_jobs);
// Actionbar
getSupportActionBar().setDisplayShowHomeEnabled(true);
getSupportActionBar().setIcon(R.drawable.logo);
getSupportActionBar().setBackgroundDrawable(new
ColorDrawable(getResources().getColor(R.color.Snow)));
ShowButton = (Button)findViewById(R.id.show);
// Adding MainActivity context into Firebase context.
Firebase.setAndroidContext(WorkActivity.this);
// Passing firebase Server URL into firebase object.
firebase = new Firebase(Firebase_Server_URL);
firebase1=new Firebase(Firebase_Server_URL1);
firebaseAuth = FirebaseAuth.getInstance();
// On activity start check whether there is user previously logged in or
not.
if(firebaseAuth.getCurrentUser() == null){
// Finishing current Profile activity.
finish();
// If user already not log in then Redirect to LoginActivity .
Intent intent = new Intent(WorkActivity.this, LoginActivity.class);
startActivity(intent);
// Showing toast message.
Toast.makeText(WorkActivity.this, "Please Log in to continue",
Toast.LENGTH_LONG).show();
}
// Adding firebaseAuth current user info into firebaseUser object.
firebaseUser = firebaseAuth.getCurrentUser();
// Getting logged in user email from firebaseUser.getEmail() method and
set into TextView.
setTitle( firebaseUser.getEmail());
setTitleColor(R.color.DarkGray);
firebase.child("jobs");
// Associate the jobs' list with the corresponding ListView
lv = (ListView) findViewById(R.id.lvshow);
// Set the ArrayAdapter to the ListView
arrayAdapter = new ArrayAdapter<String>(this,
android.R.layout.simple_list_item_1, jobdes);
lv.setAdapter(arrayAdapter);
// Attach a ChildEventListener to the teacher database, so we can
retrieve the job entries
firebase.addChildEventListener(new ChildEventListener() {
@Override
public void onChildAdded(DataSnapshot dataSnapshot, String s) {
// Get the value from the DataSnapshot and add it to the jobs'
list
JobDetails jo = (JobDetails)
dataSnapshot.getValue(JobDetails.class);
String joString = String.valueOf(jo);
arrayAdapter.add(joString);
//
// Notify the ArrayAdapter that there was a change
arrayAdapter.notifyDataSetChanged();
}
@Override
public void onChildChanged(DataSnapshot dataSnapshot, String s) {
}
@Override
public void onChildRemoved(DataSnapshot dataSnapshot) {
}
@Override
public void onChildMoved(DataSnapshot dataSnapshot, String s) {
}
@Override
public void onCancelled(FirebaseError databaseError) {
}
});
}
}
XML
public class JobDetails {
private String price;
private String jobDescription;
private String jobSpinner;
public String email;
public JobDetails() {
// This is default constructor.
}
public String getPrice() {
return price;
}
public void setPrice(String pri) {
this.price = pri;
}
public String getjobDescription() {
return jobDescription;
}
public void setjobDescription(String jobd) {
this.jobDescription = jobd;
}
public void setjob(String jry) {
this.jobSpinner = jry ;
}
public String getjob() {
return jobSpinner;
}
public void setemail(String jel) {
this.email = jel ;
}
public String getemail() {
return email;
}
@Override
public String toString() {
return this.jobSpinner + ": " + this.jobDescription+ ": " +price;
}
}
错误
<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
tools:context="com.gumption.zeeshanahmed.jobaps.WorkActivity">
<TextView
android:id="@+id/textdispjobs"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:text="@string/text_display_jobs"
android:textSize="40sp"
android:textAlignment="center"/>
<ListView
android:id="@+id/lvshow"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:layout_alignParentStart="true"
android:layout_below="@+id/show" />
</RelativeLayout>
java错误行
此处显示错误
E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.gumption.zeeshanahmed.jobaps, PID: 4774
java.lang.RuntimeException: Unable to start activity
ComponentInfo{com.gumption.zeeshanahmed.jobaps/
com.gumption.zeeshanahmed.jobaps.WorkActivity}:
java.lang.NullPointerException: Attempt to invoke virtual
method 'void
android.widget.ListView.setAdapter(android.widget.ListAdapter)'
on a null object reference at
android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2416)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2476)
at android.app.ActivityThread.-wrap11(ActivityThread.java)
at
android.app.ActivityThread$H.handleMessage(ActivityThread.java:1344)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:148)at
android.app.ActivityThread.main(ActivityThread.java:5417)
at java.lang.reflect.Method.invoke(Native Method) at
com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run
(ZygoteInit.java:726) at com.android.internal.os.ZygoteInit.main
(ZygoteInit.java:616)
Caused by: java.lang.NullPointerException: Attempt to invoke virtual method
'void android.widget.ListView.setAdapter(android.widget.ListAdapter)' on a
null object reference at
com.gumption.zeeshanahmed.jobaps.WorkActivity.onCreate
(WorkActivity.java:109)
at android.app.Activity.performCreate(Activity.java:6237) at
android.app.Instrumentation.callActivityOnCreate
(Instrumentation.java:1107) at
android.app.ActivityThread.performLaunchActivity
(ActivityThread.java:2369)atandroid.app.ActivityThread.handleLaunchActivity
(ActivityThread.java:2476) at android.app.ActivityThread.-
wrap11(ActivityThread.java) at android.app.ActivityThread$H.handleMessage
(ActivityThread.java:1344) at android.os.Handler.dispatchMessage
(Handler.java:102) at android.os.Looper.loop(Looper.java:148) at
android.app.ActivityThread.main(ActivityThread.java:5417) at
java.lang.reflect.Method.invoke(Native Method) at
com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run
(ZygoteInit.java:726) at com.android.internal.os.ZygoteInit.main
(ZygoteInit.java:616)
如果有人可以帮助我，那将非常有帮助。谢谢！