Question

感谢任何帮助。我还在学习Android并且已经查看了很多问题，但似乎无法找到解决方案。再次感谢您的帮助！

我收到一个错误，我无法在setupeverything方法的FragmentActivity中正确设置我的ArrayAdapter。我有提供年份和条款的微调器，但我不知道为什么list.setAdapter会抛出错误... 这是我到目前为止的代码......

public class MainActivity extends FragmentActivity {


private ViewPager _mViewPager;
private ViewPagerAdapter _adapter;
variables here...



@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.main);
    setUpView();
    setupeverything();    //LINE 49
}

private void setUpView(){
    _mViewPager= (ViewPager) findViewById(R.id.viewPager);
    _adapter = new ViewPagerAdapter(getApplicationContext(), getSupportFragmentManager());
    _mViewPager.setAdapter(_adapter);
    _mViewPager.setCurrentItem(0);
}

public static void refreshview()
{
    int year = spinner_year.getSelectedItemPosition();
    int term = spinner_term.getSelectedItemPosition();

    listofclasses.clear();
    for(int i=0;i<terms[year][term].getSize();i++)
    {
       listofclasses.add(terms[year][term].getCourse(i).getname() + "   " + terms[year][term].getCourse(i).getcredits()+ "   " + terms[year][term].getCourse(i).getgrade());

    }
    adapterthing.notifyDataSetChanged();
    setcreditandgpa();
}
public void buttonaddclass(View view)
{
    int year = spinner_year.getSelectedItemPosition();
    int term = spinner_term.getSelectedItemPosition();
    terms[year][term].addClass("test"+count, "B+", 4);

    refreshview();  
    //Intent openaddclass = new Intent("AddClassActivity");
    //startActivity(openaddclass);   //Removed because changed to fragments

}

public void setupeverything()
{
    ListView list = (ListView) findViewById(R.id.listview_classes);
adapterthing = new ArrayAdapter<String>(this,android.R.layout.simple_spinner_item, listofclasses);
    list.setAdapter(adapterthing);    //LINE 245
    list.setOnItemLongClickListener(new OnItemLongClickListener() {
        public boolean onItemLongClick(AdapterView<?> av, View v, int position, long id) {
            deleteclass(position);

          return true;

        }});


    array_year=new String[5];
    array_year[0]="1";
    array_year[1]="2";
    array_year[2]="3";
    array_year[3]="4";
    array_year[4]="5";
    spinner_year = (Spinner) findViewById(R.id.spinner_year);
    ArrayAdapter<String> adapter = new ArrayAdapter<String>(this,android.R.layout.simple_list_item_1, array_year);
    spinner_year.setAdapter(adapter);

    array_term=new String[4];
    array_term[0]="F";
    array_term[1]="W";
    array_term[2]="S";
    array_term[3]="S";

    spinner_term = (Spinner) findViewById(R.id.spinner_term);
    ArrayAdapter<String> adapter1 = new ArrayAdapter<String>(this,android.R.layout.simple_list_item_1, array_term);
    spinner_term.setAdapter(adapter1);

    for (int i = 0; i<5; i++)
    {
      for(int j = 0; j<4;j++)
      {
        terms[i][j] = new ClassList();
      }
    }

    spinner_year.setOnItemSelectedListener(new AdapterView.OnItemSelectedListener() {

        @Override
        public void onItemSelected(AdapterView<?> arg0, View arg1,
                int arg2, long arg3) {
            refreshview();

        }

        @Override
        public void onNothingSelected(AdapterView<?> arg0) {
            // TODO Auto-generated method stub

        }



    });
    spinner_term.setOnItemSelectedListener(new AdapterView.OnItemSelectedListener() {

        @Override
        public void onItemSelected(AdapterView<?> arg0, View arg1,
                int arg2, long arg3) {
            refreshview();

        }

        @Override
        public void onNothingSelected(AdapterView<?> arg0) {
            // TODO Auto-generated method stub

        }

    });

    edittotalcredit = (EditText) findViewById(R.id.edittext_credits);
    edittermcredit = (EditText) findViewById(R.id.edittext_credits_term);
    edittotalgpa = (EditText) findViewById(R.id.edittext_gpa);
    edittermgpa = (EditText) findViewById(R.id.edittext_gpa_term);


}

logcat的：

05-29 00:40:31.415    2713-2713/?                              E/AndroidRuntime: FATAL EXCEPTION: main
    java.lang.RuntimeException: Unable to start activity ComponentInfo{com.drexel.drexelgpacalc/com.drexel.drexelgpacalc.MainActivity}: java.lang.NullPointerException
    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2180)
    at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2230)
    at android.app.ActivityThread.access$600(ActivityThread.java:141)
    at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1234)
    at android.os.Handler.dispatchMessage(Handler.java:99)
    at android.os.Looper.loop(Looper.java:137)
    at android.app.ActivityThread.main(ActivityThread.java:5039)
    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:793)
    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:560)
    at dalvik.system.NativeStart.main(Native Method)
    Caused by: java.lang.NullPointerException
    at com.drexel.drexelgpacalc.MainActivity.setupeverything(MainActivity.java:245)
    at com.drexel.drexelgpacalc.MainActivity.onCreate(MainActivity.java:49)
    at android.app.Activity.performCreate(Activity.java:5104)
    at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1080)
    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2144)
    ... 11 more

XML布局：

activity_main.xml是第一个显示来自addclasslayout.xml所选课程列表数据的片段

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:id="@+id/LinearLayout1"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical"
tools:context=".MainActivity"
 >

<LinearLayout
    android:layout_width="fill_parent"
    android:layout_height="wrap_content"
    android:orientation="horizontal"
     >

    <Spinner
        android:id="@+id/spinner_year"
        android:layout_width="0dp"
        android:layout_height="wrap_content"
        android:layout_weight="1"
        />

    <Spinner
        android:id="@+id/spinner_term"
        android:layout_width="0dp"
        android:layout_height="wrap_content"
        android:layout_weight="1"
         />
</LinearLayout>

<ListView
    android:id="@+id/listview_classes"
    android:layout_width="fill_parent"
    android:layout_height="0dp"
    android:layout_marginTop="15dp"
    android:layout_weight="4" >
</ListView>

<Button
    android:id="@+id/button_submit"
    android:layout_width="fill_parent"
    android:layout_height="0dp"
    android:layout_weight="1"
    android:text="Add Class"
    android:onClick="buttonaddclass" />

<LinearLayout
    android:layout_width="fill_parent"
    android:layout_height="0dp"
    android:layout_weight="1"
    android:orientation="horizontal" >

    <TextView
        android:id="@+id/textview_credits_term"
        android:layout_width="0dp"
        android:layout_height="wrap_content"
        android:layout_weight="2"
        android:text="Credits This Term:"
        android:textSize="18sp" />

    <EditText
        android:id="@+id/edittext_credits_term"
        android:layout_width="0dp"
        android:layout_height="fill_parent"
        android:layout_weight="1"
        android:focusable="false"
        android:hint=" "
        android:longClickable="false" />

    <TextView
        android:id="@+id/textview_gpa_term"
        android:layout_width="0dp"
        android:layout_height="wrap_content"
        android:layout_weight="2"
        android:text="GPA This Term:"
        android:paddingLeft="20dp"
        android:textSize="18sp" />

    <EditText
        android:id="@+id/edittext_gpa_term"
        android:layout_width="0dp"
        android:layout_height="fill_parent"
        android:layout_weight="1"
        android:focusable="false"
        android:hint=" "
        android:longClickable="false" />
</LinearLayout>

<LinearLayout
    android:layout_width="fill_parent"
    android:layout_height="0dp"
    android:layout_weight="1"
    android:orientation="horizontal" >

    <TextView
        android:id="@+id/textview_credits"
        android:layout_width="0dp"
        android:layout_height="wrap_content"
        android:layout_weight="2"
        android:text="Credits Overall:"
        android:textSize="18sp" />

    <EditText
        android:id="@+id/edittext_credits"
        android:layout_width="0dp"
        android:layout_height="fill_parent"
        android:layout_weight="1"
        android:focusable="false"
        android:hint=" "
        android:longClickable="false" />

    <TextView
        android:id="@+id/textview_gpa"
        android:layout_width="0dp"
        android:layout_height="wrap_content"
        android:layout_weight="2"
        android:text="GPA Overall:"
        android:paddingLeft="20dp"
        android:textSize="18sp" />

    <EditText
        android:id="@+id/edittext_gpa"
        android:layout_width="0dp"
        android:layout_height="fill_parent"
        android:layout_weight="1"
        android:focusable="false"
        android:hint=" "
        android:longClickable="false" />
</LinearLayout>

</LinearLayout>

main.xml中

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
          android:orientation="vertical"
          android:layout_width="match_parent"
          android:layout_height="match_parent">


<android.support.v4.view.ViewPager
        android:layout_width="fill_parent" 
        android:layout_height="fill_parent"
        android:id="@+id/viewPager" />


</LinearLayout>

AddClassLayout.xml Second Fragment，它从列表中提取数据并应该发送到listofclasses。

<Button
    android:id="@+id/button1"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:onClick="buttonclick"
    android:text="Add Class" />

<LinearLayout
    android:orientation="horizontal"
    android:layout_width="fill_parent"
    android:layout_height="wrap_content">
<EditText
    android:id="@+id/editText1"
    android:layout_width="0dp"
    android:layout_weight="3.5"
    android:layout_height="wrap_content"
    android:hint="Start Entering Class Here"
    android:ems="10" 
    android:singleLine="true"/>

<Spinner
    android:id="@+id/expandableListView2"
    android:layout_width="0dp"
    android:layout_weight="1"
    android:layout_height="fill_parent"
    android:hint="Grade"
    android:entries="@array/gradeArray" />
</LinearLayout>


<ListView
    android:id="@+id/listView1"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
     >
</ListView>

Answer 1

我认为您在没有实例化的情况下使用listofclasses。因此得到NullPointerException。

BTW

您是否正在调用refreshview()方法来填充矢量？

Answer 2

这是因为传递给数组适配器的listOfClasses为null。在你把它传递到那里之前你必须填写这个清单...尝试这个解决方案......

只是你NullPointerException

Caused by: java.lang.NullPointerException
at com.drexel.drexelgpacalc.MainActivity.setupeverything(MainActivity.java:245)
at com.drexel.drexelgpacalc.MainActivity.onCreate(MainActivity.java:49)

只需点击两次

at com.drexel.drexelgpacalc.MainActivity.setupeverything(MainActivity.java:245)

和eclipse会告诉你麻烦在哪里。你必须认识到什么变量有空值.. 认为这是list_of_classes。

LogCat对开发人员来说是一个强大的收费;）

Answer 3

正如评论中指出的那样。

在onCreate setContentView(R.layout.main) main.xml但R.layout.activity_main没有在其中定义列表视图且ID为“listview_classes”。

您有一个视图寻呼机，但我没有看到您使用layoutinflater的任何地方。您需要使用R.layout.activity_main来设置setContentView(R.layout.activity_main)并在视图寻呼机上设置它，或者只是放弃查看寻呼机的整个想法。

看起来只是{{1}}会更简单，并删除有关视图寻呼机的代码，除非你有其他理由想要它。

FragmentActivity中的List.setAdapter（适配器）向spinners抛出错误

3 个答案: