使用视图模型和实时数据的联系提供者

Question

我的Android应用程序正在contacts providers用来向用户显示所有联系人。我正在Loaders按照https://developer.android.com/training/contacts-provider/retrieve-names上的教程/文档加载联系人

但是从链接https://developer.android.com/guide/components/loaders，提到从Android P开始不推荐使用加载器。

从Android P（API 28）开始，不推荐使用加载程序。建议在处理活动和片段生命周期时处理加载数据的选项是结合使用ViewModels和LiveData。ViewModels能够像Loader这样的配置更改得以保留，但样板更少。LiveData提供了一种生命周期感知的方式加载数据，您可以在多个ViewModel中重用。您还可以使用MediatorLiveData组合LiveData，并且可以使用任何可观察到的查询（例如来自Room数据库的查询）来观察数据的变化。在无法访问LoaderManager的情况下（例如在Service中），ViewModels和LiveData也可用。串联使用两者提供了一种简单的方法，无需处理UI生命周期即可访问应用程序所需的数据。

所以我的问题是：

1.我们如何使用android view model和联系人提供者的实时数据来获取联系人？
2.我们可以使用会议室数据库作为联系提供者吗？

在下面，您可以找到指向源代码的链接，在该链接中，我尝试使用Android View Model和Live数据从ContactProviders中获取联系人。

https://github.com/deepak786/phonebook-contacts
3.可以在上述源代码中进行哪些改进，以便更快地进行获取？

谢谢与问候
Deepak

Answer 1

您可以在下面找到一个非常简单的加载联系人的解决方案MVVM：

https://github.com/NaarGes/Android-Contact-List

这里有一些代码，以防链接不再有效。

首先，让我们创建一个简单的POJO联系人UserObject.java

public class UserObject {

    private String email, name, phone;

    public UserObject() {
        // EMPTY CONSTRUCTOR FOR FIREBASE REALTIME DATABASE
    }

    public UserObject(String email, String name, String phone) {
        this.email = email;
        this.name = name;
        this.phone = phone;
    }

    public String getEmail() {
        return email;
    }

    public void setEmail(String email) {
        this.email = email;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public String getPhone() {
        return phone;
    }

    public void setPhone(String phone) {
        this.phone = phone;
    }
}

现在，让我们创建我们的存储库ContactRepository.java

public class ContactRepository {

    private Context context;

    private static final String TAG = "debinf ContRepo";

    public ContactRepository(Context context) {
        this.context = context;
    }

    public List<UserObject> fetchContacts() {
        List<UserObject> contacts = new ArrayList<>();

        Cursor cursor = context.getContentResolver().query(ContactsContract.CommonDataKinds.Phone.CONTENT_URI, null, null, null, null);
        Log.i(TAG, "fetchContacts: cursor.getCount() is "+cursor.getCount());
        if ((cursor != null ? cursor.getCount() : 0) > 0) {
            while (cursor.moveToNext()) {

                String name = cursor.getString(cursor.getColumnIndex(ContactsContract.CommonDataKinds.Phone.DISPLAY_NAME));
                String phone = cursor.getString(cursor.getColumnIndex(ContactsContract.CommonDataKinds.Phone.NUMBER));

                UserObject contact = new UserObject("",name, phone);

                Log.i(TAG, "fetchContacts: phone is "+phone);

                contacts.add(contact);
            }
        }
        if (cursor != null) {
            cursor.close();
        }
        return contacts;
    }
}

接下来，我们创建ContactViewModel.java

public class ContactViewModel extends ViewModel {

    private ContactRepository repository;
    private MutableLiveData<List<UserObject>> contacts;

    public ContactViewModel(Context context) {
        repository = new ContactRepository(context);
        contacts = new MutableLiveData<>();
    }

    public MutableLiveData<List<UserObject>> getContacts() {
        contacts.setValue(repository.fetchContacts());
        return contacts;
    }
}

factory接下来，我们为我们的ContactViewModelFactory.java创建一个ViewModel

public class ContactViewModelFactory implements ViewModelProvider.Factory {

    private Context context;

    public ContactViewModelFactory(Context context) {
        this.context = context;
    }

    @NonNull
    @Override
    public <T extends ViewModel> T create(@NonNull Class<T> modelClass) {
        if (modelClass.isAssignableFrom(ContactViewModel.class)) {
            return (T) new ContactViewModel(context);
        }
        throw new IllegalArgumentException("Unknown ViewModel class");
    }
}

我们不要忘记在我们的AndroidManifest

<uses-permission android:name="android.permission.READ_CONTACTS" />

最后，我们在MainActivity.java中请求许可

if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.M) {
        requestPermissions(new String[]{Manifest.permission.WRITE_CONTACTS,Manifest.permission.READ_CONTACTS,
                Manifest.permission.WRITE_EXTERNAL_STORAGE,Manifest.permission.READ_EXTERNAL_STORAGE}, PERMISSION_REQUEST);
}

并让我们的联系人浮出水面

ContactViewModelFactory factory = new ContactViewModelFactory(this);
viewModel = ViewModelProviders.of(this, factory).get(ContactViewModel.class);

viewModel.getContacts().observe(this, new Observer<List<UserObject>>() {
    @Override
    public void onChanged(@Nullable List<UserObject> userObjects) {
        Log.i(TAG, "ViewModel: userObjects size is "+userObjects.size());
        Log.i(TAG, "ViewModel: userObjects size is "+userObjects.get(1).getPhone());
    }
});

Answer 2

class ContactsViewModel(private val contentResolver: ContentResolver) : ViewModel() 
{

    lateinit var contactsList: LiveData<PagedList<Contact>>

    fun loadContacts() {
        val config = PagedList.Config.Builder()
                .setPageSize(20)
                .setEnablePlaceholders(false)
                .build()
        contactsList = LivePagedListBuilder<Int, Contact>(
                ContactsDataSourceFactory(contentResolver), config).build()
    }
}

class ContactsDataSourceFactory(private val contentResolver: ContentResolver) :
        DataSource.Factory<Int, Contact>() {

    override fun create(): DataSource<Int, Contact> {
        return ContactsDataSource(contentResolver)
    }
}

class ContactsDataSource(private val contentResolver: ContentResolver) :
        PositionalDataSource<Contact>() {

    companion object {
        private val PROJECTION = arrayOf(
                ContactsContract.Contacts._ID,
                ContactsContract.Contacts.LOOKUP_KEY,
                ContactsContract.Contacts.DISPLAY_NAME_PRIMARY
        )
    }

    override fun loadInitial(params: LoadInitialParams, callback: LoadInitialCallback<Contact>) {
        callback.onResult(getContacts(params.requestedLoadSize, params.requestedStartPosition), 0)
    }

    override fun loadRange(params: LoadRangeParams, callback: LoadRangeCallback<Contact>) {
        callback.onResult(getContacts(params.loadSize, params.startPosition))
    }

    private fun getContacts(limit: Int, offset: Int): MutableList<Contact> {
        val cursor = contentResolver.query(ContactsContract.Contacts.CONTENT_URI,
                PROJECTION,
                null,
                null,
                ContactsContract.Contacts.DISPLAY_NAME_PRIMARY +
                        " ASC LIMIT " + limit + " OFFSET " + offset)

        cursor.moveToFirst()
        val contacts: MutableList<Contact> = mutableListOf()
        while (!cursor.isAfterLast) {
            val id = cursor.getLong(cursor.getColumnIndex(PROJECTION[0]))
            val lookupKey = cursor.getString(cursor.getColumnIndex(PROJECTION[0]))
            val name = cursor.getString(cursor.getColumnIndex(PROJECTION[2]))
            contacts.add(Contact(id, lookupKey, name))
            cursor.moveToNext()
        }
        cursor.close()

        return contacts
    }
}

请在此处找到完整的源代码。