403 lines
10 KiB
Markdown
403 lines
10 KiB
Markdown
# ContentProvider详解
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## 目录
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- [ContentProvider作用](#contentprovider作用)
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- [URI机制](#uri机制)
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- [ContentResolver使用](#contentresolver使用)
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- [数据访问权限](#数据访问权限)
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- [ContentObserver](#contentobserver)
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- [ContentProvider实现](#contentprovider实现)
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- [ContentProvider最佳实践](#contentprovider最佳实践)
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- [面试常见问题](#面试常见问题)
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---
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## ContentProvider作用
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### 主要作用
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1. **数据共享**：应用间共享数据
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2. **数据封装**：封装数据访问逻辑
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3. **统一接口**：提供统一的数据访问接口
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4. **权限控制**：控制数据访问权限
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### 使用场景
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```java
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// 场景1：应用间共享数据
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// 应用A提供联系人数据
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// 应用B访问联系人数据
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// 场景2：封装数据访问
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// 统一管理数据库访问
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// 隐藏数据存储细节
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// 场景3：跨进程数据访问
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// 通过 Binder 机制跨进程访问
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```
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---
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## URI机制
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### URI 格式
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```java
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// URI 格式
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content://authority/path/id
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// 示例
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content://com.example.provider/user/1
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content://com.example.provider/user
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content://com.example.provider/user/1/name
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```
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### URI 组成
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```java
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// authority：ContentProvider 的标识
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// path：数据路径
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// id：数据ID（可选）
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// 解析 URI
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Uri uri = Uri.parse("content://com.example.provider/user/1");
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String authority = uri.getAuthority(); // com.example.provider
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List<String> pathSegments = uri.getPathSegments(); // [user, 1]
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String id = uri.getLastPathSegment(); // 1
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```
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### URI 匹配
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```java
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// 使用 UriMatcher 匹配 URI
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private static final UriMatcher uriMatcher = new UriMatcher(UriMatcher.NO_MATCH);
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static {
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uriMatcher.addURI("com.example.provider", "user", USER);
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uriMatcher.addURI("com.example.provider", "user/#", USER_ID);
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}
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@Override
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public Cursor query(Uri uri, String[] projection, String selection,
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String[] selectionArgs, String sortOrder) {
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switch (uriMatcher.match(uri)) {
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case USER:
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// 查询所有用户
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break;
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case USER_ID:
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// 查询指定用户
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String id = uri.getLastPathSegment();
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break;
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}
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}
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```
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---
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## ContentResolver使用
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### 查询数据
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```java
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// 查询数据
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Uri uri = Uri.parse("content://com.example.provider/user");
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Cursor cursor = getContentResolver().query(
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uri,
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new String[]{"id", "name", "email"}, // projection
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"age > ?", // selection
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new String[]{"18"}, // selectionArgs
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"name ASC" // sortOrder
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);
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if (cursor != null) {
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while (cursor.moveToNext()) {
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int id = cursor.getInt(cursor.getColumnIndex("id"));
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String name = cursor.getString(cursor.getColumnIndex("name"));
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String email = cursor.getString(cursor.getColumnIndex("email"));
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}
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cursor.close();
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}
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```
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### 插入数据
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```java
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// 插入数据
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Uri uri = Uri.parse("content://com.example.provider/user");
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ContentValues values = new ContentValues();
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values.put("name", "John");
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values.put("email", "john@example.com");
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Uri newUri = getContentResolver().insert(uri, values);
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```
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### 更新数据
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```java
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// 更新数据
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Uri uri = Uri.parse("content://com.example.provider/user/1");
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ContentValues values = new ContentValues();
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values.put("name", "Jane");
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int count = getContentResolver().update(uri, values, null, null);
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```
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### 删除数据
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```java
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// 删除数据
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Uri uri = Uri.parse("content://com.example.provider/user/1");
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int count = getContentResolver().delete(uri, null, null);
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```
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---
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## 数据访问权限
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### 权限声明
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```xml
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<!-- AndroidManifest.xml -->
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<provider
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android:name=".MyProvider"
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android:authorities="com.example.provider"
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android:exported="true"
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android:readPermission="com.example.READ_PERMISSION"
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android:writePermission="com.example.WRITE_PERMISSION" />
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```
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### 权限检查
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```java
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public class MyProvider extends ContentProvider {
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@Override
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public Cursor query(Uri uri, String[] projection, String selection,
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String[] selectionArgs, String sortOrder) {
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// 检查读取权限
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if (getContext().checkCallingOrSelfPermission(
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"com.example.READ_PERMISSION") != PackageManager.PERMISSION_GRANTED) {
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throw new SecurityException("Permission denied");
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}
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// 查询数据
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return null;
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}
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}
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```
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---
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## ContentObserver
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### ContentObserver 使用
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```java
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// 监听数据变化
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public class MyObserver extends ContentObserver {
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public MyObserver(Handler handler) {
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super(handler);
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}
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@Override
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public void onChange(boolean selfChange) {
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super.onChange(selfChange);
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// 数据变化时调用
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}
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@Override
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public void onChange(boolean selfChange, Uri uri) {
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super.onChange(selfChange, uri);
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// 指定 URI 的数据变化
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}
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}
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// 注册观察者
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Uri uri = Uri.parse("content://com.example.provider/user");
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ContentObserver observer = new MyObserver(new Handler());
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getContentResolver().registerContentObserver(uri, true, observer);
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// 注销观察者
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getContentResolver().unregisterContentObserver(observer);
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```
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---
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## ContentProvider实现
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### 完整实现
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```java
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public class UserProvider extends ContentProvider {
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private static final String AUTHORITY = "com.example.provider";
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private static final String TABLE_USER = "user";
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private static final UriMatcher uriMatcher = new UriMatcher(UriMatcher.NO_MATCH);
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private static final int USER = 1;
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private static final int USER_ID = 2;
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static {
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uriMatcher.addURI(AUTHORITY, TABLE_USER, USER);
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uriMatcher.addURI(AUTHORITY, TABLE_USER + "/#", USER_ID);
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}
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private SQLiteDatabase database;
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@Override
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public boolean onCreate() {
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DatabaseHelper helper = new DatabaseHelper(getContext());
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database = helper.getWritableDatabase();
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return database != null;
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}
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@Override
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public Cursor query(Uri uri, String[] projection, String selection,
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String[] selectionArgs, String sortOrder) {
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SQLiteQueryBuilder queryBuilder = new SQLiteQueryBuilder();
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queryBuilder.setTables(TABLE_USER);
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switch (uriMatcher.match(uri)) {
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case USER:
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break;
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case USER_ID:
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queryBuilder.appendWhere("id = " + uri.getLastPathSegment());
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break;
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default:
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throw new IllegalArgumentException("Unknown URI: " + uri);
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}
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Cursor cursor = queryBuilder.query(database, projection, selection,
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selectionArgs, null, null, sortOrder);
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cursor.setNotificationUri(getContext().getContentResolver(), uri);
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return cursor;
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}
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@Override
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public Uri insert(Uri uri, ContentValues values) {
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long id = database.insert(TABLE_USER, null, values);
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if (id > 0) {
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Uri newUri = ContentUris.withAppendedId(uri, id);
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getContext().getContentResolver().notifyChange(newUri, null);
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return newUri;
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}
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return null;
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}
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@Override
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public int update(Uri uri, ContentValues values, String selection,
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String[] selectionArgs) {
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int count;
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switch (uriMatcher.match(uri)) {
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case USER:
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count = database.update(TABLE_USER, values, selection, selectionArgs);
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break;
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case USER_ID:
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String id = uri.getLastPathSegment();
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count = database.update(TABLE_USER, values, "id = ?", new String[]{id});
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break;
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default:
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throw new IllegalArgumentException("Unknown URI: " + uri);
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}
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getContext().getContentResolver().notifyChange(uri, null);
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return count;
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}
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@Override
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public int delete(Uri uri, String selection, String[] selectionArgs) {
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int count;
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switch (uriMatcher.match(uri)) {
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case USER:
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count = database.delete(TABLE_USER, selection, selectionArgs);
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break;
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case USER_ID:
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String id = uri.getLastPathSegment();
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count = database.delete(TABLE_USER, "id = ?", new String[]{id});
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break;
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default:
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throw new IllegalArgumentException("Unknown URI: " + uri);
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}
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getContext().getContentResolver().notifyChange(uri, null);
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return count;
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}
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@Override
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public String getType(Uri uri) {
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switch (uriMatcher.match(uri)) {
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case USER:
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return "vnd.android.cursor.dir/user";
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case USER_ID:
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return "vnd.android.cursor.item/user";
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default:
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return null;
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}
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}
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}
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```
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---
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## ContentProvider最佳实践
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### 1. 通知数据变化
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```java
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// 数据变化时通知观察者
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getContext().getContentResolver().notifyChange(uri, null);
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```
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### 2. 使用事务
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```java
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database.beginTransaction();
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try {
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// 批量操作
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database.setTransactionSuccessful();
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} finally {
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database.endTransaction();
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}
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```
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### 3. 权限控制
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```java
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// 检查权限
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if (getContext().checkCallingOrSelfPermission(permission)
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!= PackageManager.PERMISSION_GRANTED) {
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throw new SecurityException("Permission denied");
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}
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```
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---
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## 面试常见问题
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### Q1: ContentProvider 的作用？
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**答案：**
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1. 数据共享：应用间共享数据
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2. 数据封装：封装数据访问逻辑
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3. 统一接口：提供统一的数据访问接口
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4. 权限控制：控制数据访问权限
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### Q2: URI 的格式？
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**答案：**
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`content://authority/path/id`
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- authority：ContentProvider 标识
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- path：数据路径
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- id：数据ID（可选）
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### Q3: ContentResolver 和 ContentProvider 的关系？
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**答案：**
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- **ContentResolver**：客户端，用于访问数据
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- **ContentProvider**：服务端，提供数据访问接口
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- 通过 URI 和 Binder 机制通信
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### Q4: ContentObserver 的作用？
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**答案：**
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- 监听 ContentProvider 数据变化
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- 数据变化时自动通知
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- 实现数据更新通知机制
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---
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*最后更新：2024年*
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