Android studio viewholder中viewgroup是什么

ViewGroup是一种特殊的视图，它包含其他视图（也可以是其他ViewGroup）作为其子视图。在Android Studio中的ViewHolder中，ViewGroup是一种用于管理子视图的容器。通常在RecyclerView中使用ViewHolder来管理列表项的布局。ViewHolder可以使用ViewGroup作为其根视图，以便能够添加和管理列表项中的其他视图。

相关问题

android studio中recyclerview

RecyclerView是Android中的一个高级视图组件，用于展示大量数据的列表和网格视图。它拥有比ListView更多的灵活性和性能。
在Android Studio中使用RecyclerView需要以下步骤：

在build.gradle文件中添加RecyclerView依赖：

implementation 'androidx.recyclerview:recyclerview:1.1.0'

在布局文件中添加RecyclerView：

<androidx.recyclerview.widget.RecyclerView
android:id="@+id/recyclerView"
android:layout_width="match_parent"
android:layout_height="match_parent" />

创建RecyclerView的Adapter类来管理数据和视图：

public class MyAdapter extends RecyclerView.Adapter<MyAdapter.MyViewHolder> {

private List<MyData> mData;

public MyAdapter(List<MyData> data) {
mData = data;
}

@NonNull
@Override
public MyViewHolder onCreateViewHolder(@NonNull ViewGroup parent, int viewType) {
View view = LayoutInflater.from(parent.getContext()).inflate(R.layout.my_item_layout, parent, false);
return new MyViewHolder(view);
}

@Override
public void onBindViewHolder(@NonNull MyViewHolder holder, int position) {
MyData data = mData.get(position);
holder.mTextView.setText(data.getText());
holder.mImageView.setImageResource(data.getImageResource());
}

@Override
public int getItemCount() {
return mData.size();
}

public static class MyViewHolder extends RecyclerView.ViewHolder {

public TextView mTextView;
public ImageView mImageView;

public MyViewHolder(@NonNull View itemView) {
super(itemView);
mTextView = itemView.findViewById(R.id.text);
mImageView = itemView.findViewById(R.id.image);
}
}
}

在Activity或Fragment中设置RecyclerView的LayoutManager和Adapter：

RecyclerView recyclerView = findViewById(R.id.recyclerView);
recyclerView.setLayoutManager(new LinearLayoutManager(this));
List<MyData> data = getData();
MyAdapter adapter = new MyAdapter(data);
recyclerView.setAdapter(adapter);

以上是使用RecyclerView的基本步骤，具体可以根据需要进行更多的自定义和扩展。

Android Studio中实现通讯录代码

以下是一个简单的示例，演示如何在Android Studio中实现通讯录代码。该示例使用SQLite数据库来存储联系人信息。

创建一个新的Android Studio项目，包含一个Activity和一个布局文件。

在布局文件中添加一个RecyclerView，用于显示联系人列表。

创建一个数据模型类，用于表示联系人信息。例如：

public class Contact {
private int id;
private String name;
private String phoneNumber;

public Contact(int id, String name, String phoneNumber) {
this.id = id;
this.name = name;
this.phoneNumber = phoneNumber;
}

public int getId() {
return id;
}

public String getName() {
return name;
}

public String getPhoneNumber() {
return phoneNumber;
}
}

创建一个SQLite数据库帮助类，用于管理联系人信息的存储和检索。例如：

public class DatabaseHelper extends SQLiteOpenHelper {
private static final String DATABASE_NAME = "contacts.db";
private static final int DATABASE_VERSION = 1;
private static final String TABLE_NAME = "contacts";
private static final String COLUMN_ID = "id";
private static final String COLUMN_NAME = "name";
private static final String COLUMN_PHONE_NUMBER = "phone_number";

public DatabaseHelper(Context context) {
super(context, DATABASE_NAME, null, DATABASE_VERSION);
}

@Override
public void onCreate(SQLiteDatabase db) {
String query = "CREATE TABLE " + TABLE_NAME + " (" +
COLUMN_ID + " INTEGER PRIMARY KEY AUTOINCREMENT, " +
COLUMN_NAME + " TEXT, " +
COLUMN_PHONE_NUMBER + " TEXT)";
db.execSQL(query);
}

@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
db.execSQL("DROP TABLE IF EXISTS " + TABLE_NAME);
onCreate(db);
}

public void addContact(Contact contact) {
SQLiteDatabase db = this.getWritableDatabase();
ContentValues values = new ContentValues();
values.put(COLUMN_NAME, contact.getName());
values.put(COLUMN_PHONE_NUMBER, contact.getPhoneNumber());
db.insert(TABLE_NAME, null, values);
db.close();
}

public Contact getContact(int id) {
SQLiteDatabase db = this.getReadableDatabase();
Cursor cursor = db.query(TABLE_NAME, new String[] { COLUMN_ID, COLUMN_NAME, COLUMN_PHONE_NUMBER },
COLUMN_ID + "=?", new String[] { String.valueOf(id) }, null, null, null, null);
if (cursor != null)
cursor.moveToFirst();
Contact contact = new Contact(Integer.parseInt(cursor.getString(0)),
cursor.getString(1), cursor.getString(2));
cursor.close();
db.close();
return contact;
}

public List<Contact> getAllContacts() {
List<Contact> contactList = new ArrayList<>();
String query = "SELECT * FROM " + TABLE_NAME;
SQLiteDatabase db = this.getWritableDatabase();
Cursor cursor = db.rawQuery(query, null);
if (cursor.moveToFirst()) {
do {
Contact contact = new Contact(Integer.parseInt(cursor.getString(0)),
cursor.getString(1), cursor.getString(2));
contactList.add(contact);
} while (cursor.moveToNext());
}
cursor.close();
db.close();
return contactList;
}

public void updateContact(Contact contact) {
SQLiteDatabase db = this.getWritableDatabase();
ContentValues values = new ContentValues();
values.put(COLUMN_NAME, contact.getName());
values.put(COLUMN_PHONE_NUMBER, contact.getPhoneNumber());
db.update(TABLE_NAME, values, COLUMN_ID + "=?", new String[] { String.valueOf(contact.getId()) });
db.close();
}

public void deleteContact(Contact contact) {
SQLiteDatabase db = this.getWritableDatabase();
db.delete(TABLE_NAME, COLUMN_ID + "=?", new String[] { String.valueOf(contact.getId()) });
db.close();
}
}

在Activity中初始化RecyclerView和数据库帮助类，并为其提供数据源。例如：

public class MainActivity extends AppCompatActivity {
private RecyclerView recyclerView;
private RecyclerView.Adapter adapter;
private List<Contact> contactList = new ArrayList<>();
private DatabaseHelper databaseHelper;

@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);

recyclerView = findViewById(R.id.recycler_view);
recyclerView.setHasFixedSize(true);
recyclerView.setLayoutManager(new LinearLayoutManager(this));

databaseHelper = new DatabaseHelper(this);
contactList = databaseHelper.getAllContacts();

adapter = new ContactAdapter(contactList);
recyclerView.setAdapter(adapter);
}
}

创建一个RecyclerView的适配器，用于将联系人信息显示在列表中。例如：

public class ContactAdapter extends RecyclerView.Adapter<ContactAdapter.ViewHolder> {
private List<Contact> contactList;

public static class ViewHolder extends RecyclerView.ViewHolder {
public TextView nameTextView;
public TextView phoneNumberTextView;

public ViewHolder(View view) {
super(view);
nameTextView = view.findViewById(R.id.name_text_view);
phoneNumberTextView = view.findViewById(R.id.phone_number_text_view);
}
}

public ContactAdapter(List<Contact> contactList) {
this.contactList = contactList;
}

@Override
public ViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
View view = LayoutInflater.from(parent.getContext())
.inflate(R.layout.contact_item, parent, false);
return new ViewHolder(view);
}

@Override
public void onBindViewHolder(ViewHolder holder, int position) {
Contact contact = contactList.get(position);
holder.nameTextView.setText(contact.getName());
holder.phoneNumberTextView.setText(contact.getPhoneNumber());
}

@Override
public int getItemCount() {
return contactList.size();
}
}

最后，我们可以在Activity中添加一些逻辑来处理用户添加、编辑和删除联系人的操作。例如：

public class MainActivity extends AppCompatActivity {
private RecyclerView recyclerView;
private RecyclerView.Adapter adapter;
private List<Contact> contactList = new ArrayList<>();
private DatabaseHelper databaseHelper;

@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);

recyclerView = findViewById(R.id.recycler_view);
recyclerView.setHasFixedSize(true);
recyclerView.setLayoutManager(new LinearLayoutManager(this));

databaseHelper = new DatabaseHelper(this);
contactList = databaseHelper.getAllContacts();

adapter = new ContactAdapter(contactList);
recyclerView.setAdapter(adapter);

FloatingActionButton fab = findViewById(R.id.fab);
fab.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
showAddContactDialog();
}
});
}

private void showAddContactDialog() {
AlertDialog.Builder builder = new AlertDialog.Builder(this);
builder.setTitle("Add contact");

LayoutInflater inflater = getLayoutInflater();
View dialogView = inflater.inflate(R.layout.dialog_add_contact, null);
final EditText nameEditText = dialogView.findViewById(R.id.name_edit_text);
final EditText phoneNumberEditText = dialogView.findViewById(R.id.phone_number_edit_text);
builder.setView(dialogView);

builder.setPositiveButton("OK", new DialogInterface.OnClickListener() {
@Override
public void onClick(DialogInterface dialogInterface, int i) {
String name = nameEditText.getText().toString();
String phoneNumber = phoneNumberEditText.getText().toString();
Contact contact = new Contact(-1, name, phoneNumber);
databaseHelper.addContact(contact);
contactList.add(contact);
adapter.notifyDataSetChanged();
}
});

builder.setNegativeButton("Cancel", null);

AlertDialog dialog = builder.create();
dialog.show();
}
}

这样，我们就完成了一个简单的通讯录应用程序。用户可以使用该应用程序添加、编辑和删除联系人，并在RecyclerView中查看所有联系人信息。