Spinner 在调用条目值时抛出 NullPointerException

Question

我的 ActionBar 中有一个 Spinner，当我选择一个并将其转换为 String 时，我想获取 Spinner 中条目的值.每次我启动 Activity 时，它都是 thorwing NullPointerException。我该如何解决？

我已经阅读了许多指南和 Whosebug 问题，但我找不到任何更简单且接近我的情况的内容。这是代码。

spinner.xml

<Spinner
    android:id="@+id/SpinnerTerms"
    xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_height="wrap_content"
    android:layout_width="wrap_content"
    android:entries="@array/pmf"/>

menu_classviewstudents.xml

<menu xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools" tools:context=".ClassViewStudents">

    <item android:id="@+id/ViewStudentsClassesMenu"
        android:showAsAction="ifRoom|withText"
        android:icon="@drawable/addstudents"
        android:menuCategory="container"
        android:title="Add"/>

   <item android:id="@+id/AddGrades"
       android:showAsAction="ifRoom"
       android:actionLayout="@layout/spinner"
       android:title="Grades"/>

</menu>

array.xml

<?xml version="1.0" encoding="utf-8"?>
<resources>
    <string-array name="pmf">
        <item>Prelim</item>
        <item>Midterm</item>
        <item>Finals</item>
    </string-array>

</resources>

这是我的 onCreate，我在这里调用 Spinner 并将条目值放入字符串中：

protected void onCreate(Bundle savedInstanceState)
    {
        super.onCreate(savedInstanceState);
        getWindow().setFlags(WindowManager.LayoutParams.FLAG_FULLSCREEN, WindowManager.LayoutParams.FLAG_FULLSCREEN);
        setContentView(R.layout.classes_view);

        SpinnerPMF = (Spinner) findViewById(R.id.SpinnerTerms);

        spinnervalue = SpinnerPMF.getItemAtPosition(SpinnerPMF.getSelectedItemPosition()).toString();

        db = openOrCreateDatabase("ClassManager", MODE_WORLD_WRITEABLE, null);

        reciever = getIntent().getStringExtra("sender");

        Cursor c = db.rawQuery("SELECT * FROM '" + reciever + "'", null);

        int count= c.getCount();
        c.moveToFirst();
        TableLayout tableLayout = new TableLayout(getApplicationContext());
        tableLayout.setVerticalScrollBarEnabled(true);
        tableLayout.setHorizontalScrollBarEnabled(true);

        RelativeLayout rl=(RelativeLayout)findViewById(R.id.layout3);
        ScrollView sv = new ScrollView(this);
        sv.setHorizontalScrollBarEnabled(true);
        sv.addView(tableLayout);
        rl.addView(sv, new WindowManager.LayoutParams(WindowManager.LayoutParams.FILL_PARENT, WindowManager.LayoutParams.FILL_PARENT));


        for (Integer j = 0; j < count; j++)
        {
            tableRow = new TableRow(getApplicationContext());
            textView1 = new TextView(getApplicationContext());
            textView1.setText(c.getString(c.getColumnIndex("StudentID")));
            textView1.setPadding(20, 20, 20, 20);
            textView1.setTextColor(getResources().getColor(R.color.redactionbar));
            textView1.setTextSize(TypedValue.COMPLEX_UNIT_DIP,25);
            textView1.setTypeface(null, Typeface.BOLD);
            tableRow.addView(textView1);

            final TableRow finalTableRow = tableRow;

            textView = new TextView(getApplicationContext());
            textView.setText(c.getString(c.getColumnIndex("LastName")));
            textView.setPadding(20, 20, 20, 20);
            textView.setTextColor(getResources().getColor(R.color.redactionbar));
            textView.setTextSize(TypedValue.COMPLEX_UNIT_DIP,25);
            textView.setTypeface(null, Typeface.BOLD);
            tableRow.addView(textView);
            tableLayout.addView(tableRow);

            tableRow.setOnClickListener(new View.OnClickListener()
            {
                @Override
                public void onClick(View view)
                {

                    Toast toast = Toast.makeText(getApplicationContext(), spinnervalue, Toast.LENGTH_SHORT);
                    toast.show();

                    /*
                    if(SpinnerValue == "Prelim")
                    {
                        Toast toast = Toast.makeText(getApplicationContext(), "Prelim Selected", Toast.LENGTH_SHORT);
                        toast.show();
                    }

                    else if (SpinnerValue == "Midterm")
                    {
                        Toast toast = Toast.makeText(getApplicationContext(), "Midterm Selected", Toast.LENGTH_SHORT);
                        toast.show();
                    }

                    else if (SpinnerValue == "Finals")
                    {
                        Toast toast = Toast.makeText(getApplicationContext(), "Finals Selected", Toast.LENGTH_SHORT);
                        toast.show();
                    }
                    */
                }
            });

            c.moveToNext() ;
        }
        rl.requestLayout();
        db.close();

    }

这是 logcat 错误：

02-16 14:10:29.784: E/AndroidRuntime(29837): FATAL EXCEPTION: main
02-16 14:10:29.784: E/AndroidRuntime(29837): Process: test.com.classmanagertest, PID: 29837
02-16 14:10:29.784: E/AndroidRuntime(29837): java.lang.RuntimeException: Unable to start activity ComponentInfo{test.com.classmanagertest/test.com.classmanagertest.ClassViewStudents}: java.lang.NullPointerException
02-16 14:10:29.784: E/AndroidRuntime(29837):    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2318)
02-16 14:10:29.784: E/AndroidRuntime(29837):    at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2396)
02-16 14:10:29.784: E/AndroidRuntime(29837):    at android.app.ActivityThread.access0(ActivityThread.java:139)
02-16 14:10:29.784: E/AndroidRuntime(29837):    at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1293)
02-16 14:10:29.784: E/AndroidRuntime(29837):    at android.os.Handler.dispatchMessage(Handler.java:102)
02-16 14:10:29.784: E/AndroidRuntime(29837):    at android.os.Looper.loop(Looper.java:149)
02-16 14:10:29.784: E/AndroidRuntime(29837):    at android.app.ActivityThread.main(ActivityThread.java:5257)
02-16 14:10:29.784: E/AndroidRuntime(29837):    at java.lang.reflect.Method.invokeNative(Native Method)
02-16 14:10:29.784: E/AndroidRuntime(29837):    at java.lang.reflect.Method.invoke(Method.java:515)
02-16 14:10:29.784: E/AndroidRuntime(29837):    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:793)
02-16 14:10:29.784: E/AndroidRuntime(29837):    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:609)
02-16 14:10:29.784: E/AndroidRuntime(29837):    at dalvik.system.NativeStart.main(Native Method)
02-16 14:10:29.784: E/AndroidRuntime(29837): Caused by: java.lang.NullPointerException
02-16 14:10:29.784: E/AndroidRuntime(29837):    at test.com.classmanagertest.ClassViewStudents.onCreate(ClassViewStudents.java:43)
02-16 14:10:29.784: E/AndroidRuntime(29837):    at android.app.Activity.performCreate(Activity.java:5411)
02-16 14:10:29.784: E/AndroidRuntime(29837):    at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1087)
02-16 14:10:29.784: E/AndroidRuntime(29837):    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2270)
02-16 14:10:29.784: E/AndroidRuntime(29837):    ... 11 more

Answer 1

首先检查你的微调器它包含value.If它没有值，你必须排列到你的微调器中。

使用这一行

String[] mTestArray =   getResources().getStringArray(R.array.pmf);
SpinnerPMF.setAdapter(new ArrayAdapter<String>(context,android.R.layout.sipmle_spinner_item,mTestArray))

之后

SpinnerPMF = (Spinner) findViewById(R.id.SpinnerTerms);

这一行

希望对您有所帮助

Answer 2

I have a Spinner in my ActionBar, I want to get the value of the entries in the Spinner when I pick one and convert it to String

如果微调器在 ActionBar 内，则使用 onCreateOptionsMenu 设置选定值：

private String SpinnerSelectedValue="";
@Override
public boolean onCreateOptionsMenu(Menu menu) {
   MenuInflater inflater = getMenuInflater();
   inflater.inflate(R.menu.menu_classviewstudents, menu);
   MenuItem item = menu.findItem(R.id.AddGrades);
   SpinnerPMF = (Spinner)item.getActionView();
   SpinnerPMF.setOnItemSelectedListener(new OnItemSelectedListener() {

     @Override
     public void onItemSelected(AdapterView<?> parentView, View selectedItemView, 
                                                         int position, long id) {
       SpinnerSelectedValue=parentView.getItemAtPosition(position).toString();
    }

  });
 return true;
}

现在使用 SpinnerSelectedValue 在 table 行的 onClick 中获取选定值。

Spinner 在调用条目值时抛出 NullPointerException

Spinner throws NullPointerException when calling an entries value

java

android

spinner

spinner.xml

menu_classviewstudents.xml

array.xml