如何将Android MVVM模式与片段一起使用？
首先，我要求道歉我的英语不好 我已经开发了很多年的JavaSE软件，并且我曾经使用MVC设计模式。现在我开发了android应用程序，我不喜欢有人说android已经使用MVC模式，以xml文件作为视图 我在网上做了很多研究，但似乎在这个问题上没有达成一致意见。一些人使用MVC模式，另一些人使用MVP模式，但我认为，没有一致意见 最近我买了一本书（），在第二章中，您可以找到解释过的MVC、MVVM和依赖注入模式。在尝试了所有这些之后，我认为对于我的应用程序和我的工作模式来说，MVVM模式是最好的 我发现在使用活动编程时，这个模式非常容易使用，但我不知道在使用片段编程时如何使用它。我将重现应用于简单“todo应用程序”的MVVM模式示例，该示例从“Android最佳实践”一书的网站下载 视图（活动） 模型如何将Android MVVM模式与片段一起使用？,android,mvvm,android-fragments,Android,Mvvm,Android Fragments,首先，我要求道歉我的英语不好 我已经开发了很多年的JavaSE软件，并且我曾经使用MVC设计模式。现在我开发了android应用程序，我不喜欢有人说android已经使用MVC模式，以xml文件作为视图 我在网上做了很多研究，但似乎在这个问题上没有达成一致意见。一些人使用MVC模式，另一些人使用MVP模式，但我认为，没有一致意见 最近我买了一本书（），在第二章中，您可以找到解释过的MVC、MVVM和依赖注入模式。在尝试了所有这些之后，我认为对于我的应用程序和我的工作模式来说，MVVM模式是最好的
package com.example.mvvm;
import java.util.ArrayList;
import java.util.List;
import android.content.ContentValues;
import android.content.Context;
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteOpenHelper;
import android.util.Log;
final class TodoModel
{
//The Model should contain no logic specific to the view - only
//logic necessary to provide a minimal API to the ViewModel.
private static final String DB_NAME = "tasks";
private static final String TABLE_NAME = "tasks";
private static final int DB_VERSION = 1;
private static final String DB_CREATE_QUERY = "CREATE TABLE " + TodoModel.TABLE_NAME + " (id integer primary key autoincrement, title text not null);";
private final SQLiteDatabase storage;
private final SQLiteOpenHelper helper;
public TodoModel(final Context ctx)
{
this.helper = new SQLiteOpenHelper(ctx, TodoModel.DB_NAME, null, TodoModel.DB_VERSION)
{
@Override
public void onCreate(final SQLiteDatabase db)
{
db.execSQL(TodoModel.DB_CREATE_QUERY);
}
@Override
public void onUpgrade(final SQLiteDatabase db, final int oldVersion,
final int newVersion)
{
db.execSQL("DROP TABLE IF EXISTS " + TodoModel.TABLE_NAME);
this.onCreate(db);
}
};
this.storage = this.helper.getWritableDatabase();
}
/*Overrides are now done in the ViewModel. The Model only needs
*to add/delete, and the ViewModel can handle the specific needs of the View.
*/
public void addEntry(ContentValues data)
{
this.storage.insert(TodoModel.TABLE_NAME, null, data);
}
public void deleteEntry(final String field_params)
{
this.storage.delete(TodoModel.TABLE_NAME, field_params, null);
}
public Cursor findAll()
{
//Model only needs to return an accessor. The ViewModel will handle
//any logic accordingly.
return this.storage.query(TodoModel.TABLE_NAME, new String[]
{ "title" }, null, null, null, null, null);
}
}
package com.example.mvvm;
import android.content.ContentValues;
import android.content.Context;
import android.database.Cursor;
import android.view.View;
import android.widget.AdapterView;
import android.widget.ArrayAdapter;
import android.widget.EditText;
import android.widget.ListView;
import android.widget.TextView;
import java.util.ArrayList;
import java.util.List;
public class TodoViewModel implements TodoActivity.TaskListManager
{
/*The ViewModel acts as a delegate between the ToDoActivity (View)
*and the ToDoProvider (Model).
* The ViewModel receives references from the View and uses them
* to update the UI.
*/
private TodoModel db_model;
private List<String> tasks;
private Context main_activity;
private ListView taskView;
private EditText newTask;
public TodoViewModel(Context app_context)
{
tasks = new ArrayList<String>();
main_activity = app_context;
db_model = new TodoModel(app_context);
}
//Overrides to handle View specifics and keep Model straightforward.
private void deleteTask(View view)
{
db_model.deleteEntry("title='" + ((TextView)view).getText().toString() + "'");
}
private void addTask(View view)
{
final ContentValues data = new ContentValues();
data.put("title", ((TextView)view).getText().toString());
db_model.addEntry(data);
}
private void deleteAll()
{
db_model.deleteEntry(null);
}
private List<String> getTasks()
{
final Cursor c = db_model.findAll();
tasks.clear();
if (c != null)
{
c.moveToFirst();
while (c.isAfterLast() == false)
{
tasks.add(c.getString(0));
c.moveToNext();
}
c.close();
}
return tasks;
}
private void renderTodos()
{
//The ViewModel handles rendering and changes to the view's
//data. The View simply provides a reference to its
//elements.
taskView.setAdapter(new ArrayAdapter<String>(main_activity,
android.R.layout.simple_list_item_1,
getTasks().toArray(new String[]
{})));
}
public void registerTaskList(ListView list)
{
this.taskView = list; //Keep reference for rendering later
if (list.getAdapter() == null) //Show items at startup
{
renderTodos();
}
list.setOnItemClickListener(new AdapterView.OnItemClickListener()
{
@Override
public void onItemClick(final AdapterView<?> parent, final View view, final int position, final long id)
{ //Tapping on any item in the list will delete that item from the database and re-render the list
deleteTask(view);
renderTodos();
}
});
}
public void registerTaskAdder(View button, EditText input)
{
this.newTask = input;
button.setOnClickListener(new View.OnClickListener()
{
@Override
public void onClick(final View view)
{ //Add task to database, re-render list, and clear the input
addTask(newTask);
renderTodos();
newTask.setText("");
}
});
}
}
package com.example.mvvm;
import java.util.ArrayList;
import java.util.List;
import android.content.ContentValues;
import android.content.Context;
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteOpenHelper;
import android.util.Log;
final class TodoModel
{
//The Model should contain no logic specific to the view - only
//logic necessary to provide a minimal API to the ViewModel.
private static final String DB_NAME = "tasks";
private static final String TABLE_NAME = "tasks";
private static final int DB_VERSION = 1;
private static final String DB_CREATE_QUERY = "CREATE TABLE " + TodoModel.TABLE_NAME + " (id integer primary key autoincrement, title text not null);";
private final SQLiteDatabase storage;
private final SQLiteOpenHelper helper;
public TodoModel(final Context ctx)
{
this.helper = new SQLiteOpenHelper(ctx, TodoModel.DB_NAME, null, TodoModel.DB_VERSION)
{
@Override
public void onCreate(final SQLiteDatabase db)
{
db.execSQL(TodoModel.DB_CREATE_QUERY);
}
@Override
public void onUpgrade(final SQLiteDatabase db, final int oldVersion,
final int newVersion)
{
db.execSQL("DROP TABLE IF EXISTS " + TodoModel.TABLE_NAME);
this.onCreate(db);
}
};
this.storage = this.helper.getWritableDatabase();
}
/*Overrides are now done in the ViewModel. The Model only needs
*to add/delete, and the ViewModel can handle the specific needs of the View.
*/
public void addEntry(ContentValues data)
{
this.storage.insert(TodoModel.TABLE_NAME, null, data);
}
public void deleteEntry(final String field_params)
{
this.storage.delete(TodoModel.TABLE_NAME, field_params, null);
}
public Cursor findAll()
{
//Model only needs to return an accessor. The ViewModel will handle
//any logic accordingly.
return this.storage.query(TodoModel.TABLE_NAME, new String[]
{ "title" }, null, null, null, null, null);
}
}
package com.example.mvvm;
import android.content.ContentValues;
import android.content.Context;
import android.database.Cursor;
import android.view.View;
import android.widget.AdapterView;
import android.widget.ArrayAdapter;
import android.widget.EditText;
import android.widget.ListView;
import android.widget.TextView;
import java.util.ArrayList;
import java.util.List;
public class TodoViewModel implements TodoActivity.TaskListManager
{
/*The ViewModel acts as a delegate between the ToDoActivity (View)
*and the ToDoProvider (Model).
* The ViewModel receives references from the View and uses them
* to update the UI.
*/
private TodoModel db_model;
private List<String> tasks;
private Context main_activity;
private ListView taskView;
private EditText newTask;
public TodoViewModel(Context app_context)
{
tasks = new ArrayList<String>();
main_activity = app_context;
db_model = new TodoModel(app_context);
}
//Overrides to handle View specifics and keep Model straightforward.
private void deleteTask(View view)
{
db_model.deleteEntry("title='" + ((TextView)view).getText().toString() + "'");
}
private void addTask(View view)
{
final ContentValues data = new ContentValues();
data.put("title", ((TextView)view).getText().toString());
db_model.addEntry(data);
}
private void deleteAll()
{
db_model.deleteEntry(null);
}
private List<String> getTasks()
{
final Cursor c = db_model.findAll();
tasks.clear();
if (c != null)
{
c.moveToFirst();
while (c.isAfterLast() == false)
{
tasks.add(c.getString(0));
c.moveToNext();
}
c.close();
}
return tasks;
}
private void renderTodos()
{
//The ViewModel handles rendering and changes to the view's
//data. The View simply provides a reference to its
//elements.
taskView.setAdapter(new ArrayAdapter<String>(main_activity,
android.R.layout.simple_list_item_1,
getTasks().toArray(new String[]
{})));
}
public void registerTaskList(ListView list)
{
this.taskView = list; //Keep reference for rendering later
if (list.getAdapter() == null) //Show items at startup
{
renderTodos();
}
list.setOnItemClickListener(new AdapterView.OnItemClickListener()
{
@Override
public void onItemClick(final AdapterView<?> parent, final View view, final int position, final long id)
{ //Tapping on any item in the list will delete that item from the database and re-render the list
deleteTask(view);
renderTodos();
}
});
}
public void registerTaskAdder(View button, EditText input)
{
this.newTask = input;
button.setOnClickListener(new View.OnClickListener()
{
@Override
public void onClick(final View view)
{ //Add task to database, re-render list, and clear the input
addTask(newTask);
renderTodos();
newTask.setText("");
}
});
}
}
package com.example.mvvm；
导入android.content.ContentValues；
导入android.content.Context；
导入android.database.Cursor；
导入android.view.view；
导入android.widget.AdapterView；
导入android.widget.ArrayAdapter；
导入android.widget.EditText；
导入android.widget.ListView；
导入android.widget.TextView；
导入java.util.ArrayList；
导入java.util.List；
公共类TodoViewModel实现TodoActivity.TaskListManager
{
/*ViewModel充当ToDoActivity（视图）之间的委托
*以及ToDoProvider（模型）。
*ViewModel从视图接收引用并使用它们
*更新用户界面。
*/
私有到模型db_模型；
私有列表任务；
私人背景主要活动；
私有ListView任务视图；
私人编辑任务；
public-to-oviewmodel（上下文应用程序\u上下文）
{
tasks=newarraylist（）；
主要活动=应用程序上下文；
db_模型=新的TodoModel（应用程序_上下文）；
}
//覆盖以处理视图细节并保持模型直观。
私有void deleteTask（视图）
{
db_model.deleteEntry（“title=”+（（TextView）视图）.getText（）.toString（）+”）；
}
私有void addTask（视图）
{
最终ContentValues数据=新ContentValues（）；
data.put（“title”，（（TextView）view.getText（）.toString（））；
db_模型。加法（数据）；
}
私有void deleteAll（）
{
db_model.deleteEntry（null）；
}
私有列表getTasks（）
{
最终游标c=db_model.findAll（）；
任务。清除（）；
如果（c！=null）
{
c、 moveToFirst（）；
while（c.isAfterLast（）==false）
{
tasks.add（c.getString（0））；
c、 moveToNext（）；
}
c、 close（）；
}
返回任务；
}
私有void rendertos（）
{
//ViewModel处理视图的渲染和更改
//视图只是提供对其
//元素。
taskView.setAdapter（新阵列适配器）（主活动，
android.R.layout.simple\u list\u item\u 1，
getTasks（）.toArray（新字符串[]）
{})));
}
公共无效注册表tasklist（列表视图列表）
{
this.taskView=list；//保留引用以供以后渲染
if（list.getAdapter（）==null）//在启动时显示项目
{
rendertos（）；
}
list.setOnItemClickListener（新的AdapterView.OnItemClickListener（）
{
@凌驾
public void onItemClick（最终适配器视图父视图、最终视图视图、最终整型位置、最终长id）
{//点击列表中的任何项目都将从数据库中删除该项目并重新呈现列表
删除任务（视图）；
rendertos（）；
}
});
}
公共无效注册表taskadder（查看按钮，编辑文本输入）
{
this.newTask=输入；
setOnClickListener（新视图.OnClickListener（）
{
@凌驾
公共void onClick（最终视图）
{//将任务添加到数据库，重新呈现列表，然后清除输入
addTask（newTask）；
rendertos（）；
newTask.setText（“”）；
}
});
}
}
提前感谢。注意：以下内容已经过时，我不再推荐它。主要是因为在此设置中很难测试Viewsmodel。请查看Google架构蓝图 旧答案： 就个人而言，我更喜欢另一种设置：
@Override
public void onAttach(final Activity activity) {
super.onAttach(activity);
try {
delegate = (ITaskListManager) activity;
} catch (ClassCastException ignore) {
throw new IllegalStateException("Activity " + activity + " must implement ITaskListManager");
}
}
@Override
public void onDetach() {
delegate = sDummyDelegate;
super.onDetach();
}
public class ViewFragment extends Fragment {
private ListView taskView;
private Button btNewTask;
private EditText etNewTask;
private ITaskListManager delegate;
/**
* Dummy delegate to avoid nullpointers when
* the fragment is not attached to an activity
*/
private final ITaskListManager sDummyDelegate = new ITaskListManager() {
@Override
public void registerTaskList(final ListView list) {
}
@Override
public void registerTaskAdder(final View button, final EditText input) {
}
};
/*
* The View handles UI setup only. All event logic and delegation
* is handled by the ViewModel.
*/
public static interface ITaskListManager {
// Through this interface the event logic is
// passed off to the ViewModel.
void registerTaskList(ListView list);
void registerTaskAdder(View button, EditText input);
}
@Override
public void onAttach(final Activity activity) {
super.onAttach(activity);
try {
delegate = (ITaskListManager) activity;
} catch (ClassCastException ignore) {
throw new IllegalStateException("Activity " + activity + " must implement ITaskListManager");
}
}
@Override
public void onDetach() {
delegate = sDummyDelegate;
super.onDetach();
}
@Override
public View onCreateView(final LayoutInflater inflater, final ViewGroup container, final Bundle savedInstanceState) {
View view = inflater.inflate(R.layout.activity_view_model, container, false);
taskView = (ListView) view.findViewById(R.id.tasklist);
btNewTask = (Button) view.findViewById(R.id.btNewTask);
etNewTask = (EditText) view.findViewById(R.id.etNewTask);
delegate.registerTaskList(taskView);
delegate.registerTaskAdder(btNewTask, etNewTask);
return view;
}
}
public class ViewModelActivity extends ActionBarActivity implements ITaskListManager {
@Override
protected void onCreate(final Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_view_model);
if (savedInstanceState == null) {
getSupportFragmentManager().beginTransaction().add(R.id.container, new ViewFragment()).commit();
}
initViewModel();
}
@Override
public boolean onCreateOptionsMenu(final Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.view_model, menu);
return true;
}
@Override
public boolean onOptionsItemSelected(final MenuItem item) {
// Handle action bar item clicks here. The action bar will
// automatically handle clicks on the Home/Up button, so long
// as you specify a parent activity in AndroidManifest.xml.
int id = item.getItemId();
if (id == R.id.action_settings) {
return true;
}
return super.onOptionsItemSelected(item);
}
private Model db_model;
private List<String> tasks;
private ListView taskView;
private EditText newTask;
/**
* Initialize the ViewModel
*/
private void initViewModel() {
tasks = new ArrayList<String>();
db_model = new Model(this);
}
private void deleteTask(final View view) {
db_model.deleteEntry("title='" + ((TextView) view).getText().toString() + "'");
}
private void addTask(final View view) {
final ContentValues data = new ContentValues();
data.put("title", ((TextView) view).getText().toString());
db_model.addEntry(data);
}
private void deleteAll() {
db_model.deleteEntry(null);
}
private List<String> getTasks() {
final Cursor c = db_model.findAll();
tasks.clear();
if (c != null) {
c.moveToFirst();
while (c.isAfterLast() == false) {
tasks.add(c.getString(0));
c.moveToNext();
}
c.close();
}
return tasks;
}
private void renderTodos() {
// The ViewModel handles rendering and changes to the view's
// data. The View simply provides a reference to its
// elements.
taskView.setAdapter(new ArrayAdapter<String>(this, android.R.layout.simple_list_item_1, getTasks().toArray(new String[] {})));
}
@Override
public void registerTaskList(final ListView list) {
taskView = list; // Keep reference for rendering later
if (list.getAdapter() == null) // Show items at startup
{
renderTodos();
}
list.setOnItemClickListener(new AdapterView.OnItemClickListener() {
@Override
public void onItemClick(final AdapterView<?> parent, final View view, final int position, final long id) { // Tapping on any
// item in the list
// will delete that
// item from the
// database and
// re-render the list
deleteTask(view);
renderTodos();
}
});
}
@Override
public void registerTaskAdder(final View button, final EditText input) {
newTask = input;
button.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(final View view) { // Add task to database, re-render list, and clear the input
addTask(newTask);
renderTodos();
newTask.setText("");
}
});
}
}
<layout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:bind="http://schemas.android.com/apk/res-auto">
<data class=".UserBinding">
<variable name="user" type="com.darxstudios.databind.example.User"/>
</data>
<RelativeLayout
xmlns:tools="http://schemas.android.com/tools" android:layout_width="match_parent"
android:layout_height="match_parent" android:paddingLeft="@dimen/activity_horizontal_margin"
android:paddingRight="@dimen/activity_horizontal_margin"
android:paddingTop="@dimen/activity_vertical_margin"
android:paddingBottom="@dimen/activity_vertical_margin" tools:context=".MainActivityFragment">
<TextView android:text='@{user.firstName+" "+user.lastName}' android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:id="@+id/textView" />
<Button
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="New Button"
android:id="@+id/button"
android:layout_below="@+id/textView"
android:layout_toEndOf="@+id/textView"
android:layout_marginStart="40dp"
android:layout_marginTop="160dp" />
</RelativeLayout>
</layout>
public class MainActivityFragment extends Fragment {
public MainActivityFragment() {
}
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
final User user = new User();
user.setFirstName("Michael");
user.setLastName("Cameron");
UserBinding binding = DataBindingUtil.inflate(inflater,R.layout.fragment_main, container, false);
binding.setUser(user);
View view = binding.getRoot();
final Button button = (Button) view.findViewById(R.id.button);
button.setOnClickListener(new View.OnClickListener() {
public void onClick(View v) {
user.setFirstName("@Darx");
user.setLastName("Val");
}
});
return view;
}
}