Android 使用数据库发布列表视图

我试图使列表视图显示保存在数据库中的数据

@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
                         Bundle savedInstanceState) {
    // Inflate the layout for this fragment
    View view = inflater.inflate(R.layout.fragment_main, container, false);
    ImageView contactImage;
    final EditText nametxt, emailTxt, phoneTxt, addressTxt;
    nametxt = (EditText) view.findViewById(R.id.txtName);
    emailTxt = (EditText) view.findViewById(R.id.txtEmail);
    phoneTxt = (EditText) view.findViewById(R.id.txtPhone);
    addressTxt = (EditText) view.findViewById(R.id.txtAddress);
    dbHandler = new DatabaseHandler(getActivity().getApplicationContext());
    contactListView=(ListView)view.findViewById(R.id.listView);
    contactListView.setAdapter(contactAdapter);

    final Button addBtn = (Button) view.findViewById(R.id.btnadd);
    addBtn.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View view) {
            Uri imageUri = Uri.parse("android.resource://org.intracode.contactmanager/drawable/no_user_logo.png");
            import_fragment.Contact contact = new import_fragment.Contact(dbHandler.getContactsCount(), String.valueOf(nametxt.getText()), String.valueOf(phoneTxt.getText()), String.valueOf(emailTxt.getText()), String.valueOf(addressTxt.getText()), imageUri);
            if (!contactExists(contact)) {
                dbHandler.createContact(contact);
                Contacts.add(contact);
                if (contactAdapter != null) contactAdapter.notifyDataSetChanged();
                Toast.makeText(getActivity().getApplicationContext(), String.valueOf(nametxt.getText()) + " has been added to your Contacts!", Toast.LENGTH_SHORT).show();
                resetAddContactPanel();
                return;
            }
            Toast.makeText(getActivity().getApplicationContext(), String.valueOf(nametxt.getText()) + " already exists. Please use a different name.", Toast.LENGTH_SHORT).show();
        }
    });



    final Button addContact = (Button) view.findViewById(R.id.btnadd);

    nametxt.addTextChangedListener(new TextWatcher() {
        @Override
        public void beforeTextChanged(CharSequence s, int start, int count, int after) {

        }

        @Override
        public void onTextChanged(CharSequence s, int start, int before, int count) {

            addContact.setEnabled(!nametxt.getText().toString().trim().equals(""));


        }

        @Override
        public void afterTextChanged(Editable s) {

        }
    });


    return view;


}

ArrayAdapter<import_fragment.Contact> contactAdapter;
ListView contactListView;
DatabaseHandler dbHandler;
int longClickedItemIndex;



public void onActivityResult(int reqCode, int resCode, Intent data) {
    Uri imageUri = Uri.parse("android.resource://org.intracode.contactmanager/drawable/no_user_logo.png");
    ImageView contactImageImgView;
    contactImageImgView = (ImageView) getActivity().findViewById(R.id.ivContactImage);

    if (resCode == Activity.RESULT_OK) {
        if (reqCode == 1) {
            imageUri = data.getData();
            contactImageImgView.setImageURI(data.getData());
        }
    }
}


private void resetAddContactPanel() {
    final EditText nametxt, emailTxt, phoneTxt, addressTxt;
    nametxt = (EditText) getActivity().findViewById(R.id.txtName);
    emailTxt = (EditText) getActivity().findViewById(R.id.txtEmail);
    phoneTxt = (EditText) getActivity().findViewById(R.id.txtPhone);
    addressTxt = (EditText) getActivity().findViewById(R.id.txtAddress);
    nametxt.setText("");
    phoneTxt.setText("");
    emailTxt.setText("");
    addressTxt.setText("");
}

public void onCreateContextMenu(ContextMenu menu, View view, ContextMenu.ContextMenuInfo menuInfo) {
    super.onCreateContextMenu(menu, view, menuInfo);

    {
        ImageView contactImageImgView;

        contactImageImgView = (ImageView) view.findViewById(R.id.ivContactImage);

        contactImageImgView.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                Intent intent = new Intent();
                intent.setType("image/*");
                intent.setAction(Intent.ACTION_GET_CONTENT);
                startActivityForResult(Intent.createChooser(intent, "Select Contact Image"), 1);
            }

        });


        if (dbHandler.getContactsCount() != 0)
            Contacts.addAll(dbHandler.getAllContacts());

        populateList();
    }


    menu.setHeaderIcon(R.drawable.pencil_icon);
    menu.setHeaderTitle("Contact Options");
    menu.add(Menu.NONE, EDIT, menu.NONE, "Edit Contact");
    menu.add(Menu.NONE, DELETE, menu.NONE, "Delete Contact");
}


public boolean onContextItemSelected(MenuItem item) {
    switch (item.getItemId()) {
        case EDIT:
            // TODO: Implement editing a contact
            break;
        case DELETE:
            dbHandler.deleteContact(Contacts.get(longClickedItemIndex));
            Contacts.remove(longClickedItemIndex);
            contactAdapter.notifyDataSetChanged();
            break;
    }

    return super.onContextItemSelected(item);
}



private boolean contactExists(import_fragment.Contact contact) {

    String name = contact.getName();
    int contactCount = Contacts.size();

    for (int i = 0; i < contactCount; i++) {
        if (name.compareToIgnoreCase(Contacts.get(i).getName()) == 0)
            return true;
    }
    return false;
}


private void populateList() {
    contactAdapter = new ContactListAdapter(getActivity());
    contactListView.setAdapter(contactAdapter);
}


final List<import_fragment.Contact> Contacts = new ArrayList<import_fragment.Contact>();

private class ContactListAdapter extends ArrayAdapter<import_fragment.Contact> {
    public ContactListAdapter(Context cntx) {
        super(cntx, R.layout.fragment_import, Contacts);
    }

    @Override
    public View getView(int position, View view, ViewGroup parent) {
        if (view == null)
            view = getActivity().getLayoutInflater().inflate(R.layout.fragment_import, parent, false);

        import_fragment.Contact currentContact = Contacts.get(position);

        TextView name = (TextView) view.findViewById(R.id.contactName);
        name.setText(currentContact.getName());
        TextView phone = (TextView) view.findViewById(R.id.phoneNumber);
        phone.setText(currentContact.getPhone());
        TextView email = (TextView) view.findViewById(R.id.emailAddress);
        email.setText(currentContact.getEmail());
        TextView address = (TextView) view.findViewById(R.id.cAddress);
        address.setText(currentContact.getAddress());


        return view;
    }
}

这是logcat

01-27 07:45:45.795 3034-3034/com.al3almya.users.al3almya E/AndroidRuntime: FATAL EXCEPTION: main
                                                                       Process: com.al3almya.users.al3almya, PID: 3034
                                                                       java.lang.RuntimeException: Unable to start activity ComponentInfo{com.al3almya.users.al3almya/com.al3almya.users.al3almya.MainActivity}: 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.al3almya.users.al3almya.main_fragment.onCreateView(main_fragment.java:65)
                                                                           at android.support.v4.app.Fragment.performCreateView(Fragment.java:1962)
                                                                           at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1067)
                                                                           at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1248)
                                                                           at android.support.v4.app.BackStackRecord.run(BackStackRecord.java:738)
                                                                           at android.support.v4.app.FragmentManagerImpl.execPendingActions(FragmentManager.java:1613)
                                                                           at android.support.v4.app.FragmentController.execPendingActions(FragmentController.java:330)
                                                                           at android.support.v4.app.FragmentActivity.onStart(FragmentActivity.java:547)
                                                                           at android.app.Instrumentation.callActivityOnStart(Instrumentation.java:1237)
                                                                           at android.app.Activity.performStart(Activity.java:6253)
                                                                           at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2379)
                                                                           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) 

这里是import_fragment.xml[此处列表视图]不在main_fragment.xml中

<ImageView
    android:layout_width="75dp"
    android:layout_height="75dp"
    android:id="@+id/ivContactImage" />

<LinearLayout
    android:orientation="vertical"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent">


    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Contact Name"
        android:id="@+id/contactName"
        android:textSize="10dp" />

    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Phone"
        android:id="@+id/phoneNumber"
        android:layout_gravity="left|center_vertical"
        android:layout_marginTop="5dp"/>

    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Email"
        android:id="@+id/emailAddress"
        android:layout_gravity="left|center_vertical"/>

    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Address"
        android:id="@+id/cAddress"
        android:layout_gravity="left|center_vertical"/>

    <ListView
        android:layout_width="fill_parent"
        android:layout_height="fill_parent"
        android:id="@+id/listView"
        android:layout_gravity="center"/>

</LinearLayout>

我添加了所有内容，但我现在想知道如何在列表视图中显示我的数据请给我代码不要告诉我setAdapter，因为当我设置它时，我会出错，

---

提前感谢您

您正在

main\u fragment

中搜索

listview

，而在

main\u fragment

列表视图中不可用，这就是它给出空指针异常的原因

在com.al3almya.users.al3almya.main\u fragment.onCreateView（main\u fragment.java:65）的主\u片段行65上有任何引用为null的对象

您已经编写了

contactListView.setAdapter（contactAdapter）2次，那么您在哪种情况下得到了nullpointer？@IntelliJAmiya更新了我的主题我想，您没有在onCreateView中实例化contactAdapter，因此它得到了null@RRR如果我将其替换为populateList（），我会得到同样的错误too@USKMobility然后如何实例化它？好的，我现在可以做什么来修复这个问题并让列表视图出现？首先调试您的代码，我认为您的列表视图是空的，而不是contactAdapter。请在oncreateview中调试、检查并移动您的populateList，而不是在onCreateContextMenuas中，因为您会遇到评论中提到的相同错误。我认为您应该检查列表视图。我认为您的列表视图为空。请调试并检查我将其移动到onCreateView，但我在其中得到空错误，我认为列表视图是空的，而不是contactAdapter，有什么帮助吗？
<ImageView
    android:layout_width="75dp"
    android:layout_height="75dp"
    android:id="@+id/ivContactImage" />

<LinearLayout
    android:orientation="vertical"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent">


    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Contact Name"
        android:id="@+id/contactName"
        android:textSize="10dp" />

    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Phone"
        android:id="@+id/phoneNumber"
        android:layout_gravity="left|center_vertical"
        android:layout_marginTop="5dp"/>

    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Email"
        android:id="@+id/emailAddress"
        android:layout_gravity="left|center_vertical"/>

    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Address"
        android:id="@+id/cAddress"
        android:layout_gravity="left|center_vertical"/>

    <ListView
        android:layout_width="fill_parent"
        android:layout_height="fill_parent"
        android:id="@+id/listView"
        android:layout_gravity="center"/>

</LinearLayout>