深入分析 Android ContentProvider (六)

作者：我家自动化 | 2024-07-27 23:44:34

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文章目录

深入分析 Android ContentProvider (六)

ContentProvider 的性能优化和实践案例（续）

在上一节中，我们介绍了 ContentProvider 的性能优化技巧和两个实际案例。本节将继续深入探讨更多的优化技巧，并提供更详细的实际案例分析。

1. 性能优化技巧（续）

1.6. 使用批量插入优化性能

在需要插入大量数据时，逐行插入会非常低效。可以使用 ContentProvider 的 bulkInsert 方法进行批量插入，从而显著提升性能。

示例：批量插入实现

@Override
public int bulkInsert(@NonNull Uri uri, @NonNull ContentValues[] values) {
    final SQLiteDatabase db = dbHelper.getWritableDatabase();
    switch (uriMatcher.match(uri)) {
        case MEDIA:
            db.beginTransaction();
            try {
                for (ContentValues value : values) {
                    db.insertOrThrow(DatabaseHelper.TABLE_MEDIA, null, value);
                }
                db.setTransactionSuccessful();
            } finally {
                db.endTransaction();
            }
            getContext().getContentResolver().notifyChange(uri, null);
            return values.length;
        default:
            return super.bulkInsert(uri, values);
    }
}
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1.7. 使用 Projections 优化查询

当查询数据库时，如果只需要部分字段，可以使用 Projections 来指定需要的列，以减少数据传输和内存消耗。

示例：使用 Projections

String[] projection = {
    DatabaseHelper.COLUMN_ID,
    DatabaseHelper.COLUMN_NAME
};

Cursor cursor = getContentResolver().query(
    CONTENT_URI,    // Uri
    projection,     // Projection
    null,           // Selection
    null,           // Selection arguments
    null            // Sort order
);
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1.8. 减少频繁通知

在数据变化时，ContentProvider 会通知所有监听该 URI 的内容观察者。频繁的通知可能会导致性能问题。可以通过合并通知或使用 ContentResolver#notifyChange(Uri, ContentObserver, boolean) 的第三个参数控制通知范围。

示例：减少频繁通知

public int bulkUpdate(@NonNull Uri uri, @NonNull ContentValues[] values) {
    final SQLiteDatabase db = dbHelper.getWritableDatabase();
    db.beginTransaction();
    try {
        for (ContentValues value : values) {
            db.update(DatabaseHelper.TABLE_MEDIA, value, selection, selectionArgs);
        }
        db.setTransactionSuccessful();
    } finally {
        db.endTransaction();
    }
    getContext().getContentResolver().notifyChange(uri, null, false);
    return values.length;
}
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1.9. 优化查询语句

复杂查询可能会降低性能，可以通过优化 SQL 语句，避免不必要的嵌套查询和表连接来提升性能。

示例：优化查询语句

Cursor cursor = db.query(
    DatabaseHelper.TABLE_MEDIA,
    projection,
    DatabaseHelper.COLUMN_NAME + " LIKE ?",
    new String[]{"%keyword%"},
    null,
    null,
    DatabaseHelper.COLUMN_NAME + " ASC"
);
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2. 实践案例（续）

2.3 案例三：联系人应用的数据管理

在联系人应用中，管理联系人数据需要高效的数据存储和检索。ContentProvider 可以提供统一的接口来管理联系人数据，并通过批量操作和异步任务优化性能。

联系人 ContentProvider 实现

public class ContactsProvider extends ContentProvider {
    private static final String AUTHORITY = "com.example.contactsprovider";
    private static final String BASE_PATH = "contacts";
    public static final Uri CONTENT_URI = Uri.parse("content://" + AUTHORITY + "/" + BASE_PATH);

    private static final int CONTACTS = 1;
    private static final int CONTACT_ID = 2;
    private static final UriMatcher uriMatcher = new UriMatcher(UriMatcher.NO_MATCH);

    static {
        uriMatcher.addURI(AUTHORITY, BASE_PATH, CONTACTS);
        uriMatcher.addURI(AUTHORITY, BASE_PATH + "/#", CONTACT_ID);
    }

    private SQLiteDatabase database;

    @Override
    public boolean onCreate() {
        DatabaseHelper dbHelper = new DatabaseHelper(getContext());
        database = dbHelper.getWritableDatabase();
        return true;
    }

    @Nullable
    @Override
    public Cursor query(@NonNull Uri uri, @Nullable String[] projection, @Nullable String selection,
                        @Nullable String[] selectionArgs, @Nullable String sortOrder) {
        switch (uriMatcher.match(uri)) {
            case CONTACTS:
                return database.query(DatabaseHelper.TABLE_CONTACTS, projection, selection, selectionArgs, null, null, sortOrder);
            case CONTACT_ID:
                selection = DatabaseHelper.COLUMN_ID + "=?";
                selectionArgs = new String[]{String.valueOf(ContentUris.parseId(uri))};
                return database.query(DatabaseHelper.TABLE_CONTACTS, projection, selection, selectionArgs, null, null, sortOrder);
            default:
                throw new IllegalArgumentException("Unknown URI: " + uri);
        }
    }

    @Nullable
    @Override
    public Uri insert(@NonNull Uri uri, @Nullable ContentValues values) {
        long id = database.insert(DatabaseHelper.TABLE_CONTACTS, null, values);
        getContext().getContentResolver().notifyChange(uri, null);
        return ContentUris.withAppendedId(CONTENT_URI, id);
    }

    @Override
    public int delete(@NonNull Uri uri, @Nullable String selection, @Nullable String[] selectionArgs) {
        int rowsDeleted;
        switch (uriMatcher.match(uri)) {
            case CONTACTS:
                rowsDeleted = database.delete(DatabaseHelper.TABLE_CONTACTS, selection, selectionArgs);
                break;
            case CONTACT_ID:
                selection = DatabaseHelper.COLUMN_ID + "=?";
                selectionArgs = new String[]{String.valueOf(ContentUris.parseId(uri))};
                rowsDeleted = database.delete(DatabaseHelper.TABLE_CONTACTS, selection, selectionArgs);
                break;
            default:
                throw new IllegalArgumentException("Unknown URI: " + uri);
        }
        getContext().getContentResolver().notifyChange(uri, null);
        return rowsDeleted;
    }

    @Override
    public int update(@NonNull Uri uri, @Nullable ContentValues values, @Nullable String selection, @Nullable String[] selectionArgs) {
        int rowsUpdated;
        switch (uriMatcher.match(uri)) {
            case CONTACTS:
                rowsUpdated = database.update(DatabaseHelper.TABLE_CONTACTS, values, selection, selectionArgs);
                break;
            case CONTACT_ID:
                selection = DatabaseHelper.COLUMN_ID + "=?";
                selectionArgs = new String[]{String.valueOf(ContentUris.parseId(uri))};
                rowsUpdated = database.update(DatabaseHelper.TABLE_CONTACTS, values, selection, selectionArgs);
                break;
            default:
                throw new IllegalArgumentException("Unknown URI: " + uri);
        }
        getContext().getContentResolver().notifyChange(uri, null);
        return rowsUpdated;
    }

    @Nullable
    @Override
    public String getType(@NonNull Uri uri) {
        switch (uriMatcher.match(uri)) {
            case CONTACTS:
                return "vnd.android.cursor.dir/vnd.com.example.contactsprovider.contacts";
            case CONTACT_ID:
                return "vnd.android.cursor.item/vnd.com.example.contactsprovider.contact";
            default:
                throw new IllegalArgumentException("Unknown URI: " + uri);
        }
    }
}
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2.4 案例四：日历应用的数据管理

在日历应用中，管理事件和提醒需要高效的数据存储和检索。通过 ContentProvider，可以方便地管理日历数据，并通过缓存机制和异步操作优化性能。

日历 ContentProvider 实现

public class CalendarProvider extends ContentProvider {
    private static final String AUTHORITY = "com.example.calendarprovider";
    private static final String BASE_PATH = "events";
    public static final Uri CONTENT_URI = Uri.parse("content://" + AUTHORITY + "/" + BASE_PATH);

    private static final int EVENTS = 1;
    private static final int EVENT_ID = 2;
    private static final UriMatcher uriMatcher = new UriMatcher(UriMatcher.NO_MATCH);

    static {
        uriMatcher.addURI(AUTHORITY, BASE_PATH, EVENTS);
        uriMatcher.addURI(AUTHORITY, BASE_PATH + "/#", EVENT_ID);
    }

    private SQLiteDatabase database;

    @Override
    public boolean onCreate() {
        DatabaseHelper dbHelper = new DatabaseHelper(getContext());
        database = dbHelper.getWritableDatabase();
        return true;
    }

    @Nullable
    @Override
    public Cursor query(@NonNull Uri uri, @Nullable String[] projection, @Nullable String selection,
                        @Nullable String[] selectionArgs, @Nullable String sortOrder) {
        switch (uriMatcher.match(uri)) {
            case EVENTS:
                return database.query(DatabaseHelper.TABLE_EVENTS, projection, selection, selectionArgs, null, null, sortOrder);
            case EVENT_ID:
                selection = DatabaseHelper.COLUMN_ID + "=?";
                selectionArgs = new String[]{String.valueOf(ContentUris.parseId(uri))};
                return database.query(DatabaseHelper.TABLE_EVENTS, projection, selection, selectionArgs, null, null, sortOrder);
            default:
                throw new IllegalArgumentException("Unknown URI: " + uri);
        }
    }

    @Nullable
    @Override
    public Uri insert(@NonNull Uri uri, @Nullable ContentValues values) {
        long id = database.insert(DatabaseHelper.TABLE_EVENTS, null, values);
        getContext().getContentResolver().notifyChange(uri, null);
        return ContentUris.withAppendedId(CONTENT_URI, id);
    }

    @Override
    public int delete(@NonNull Uri uri, @Nullable String selection, @Nullable String[] selectionArgs) {
        int

 rowsDeleted;
        switch (uriMatcher.match(uri)) {
            case EVENTS:
                rowsDeleted = database.delete(DatabaseHelper.TABLE_EVENTS, selection, selectionArgs);
                break;
            case EVENT_ID:
                selection = DatabaseHelper.COLUMN_ID + "=?";
                selectionArgs = new String[]{String.valueOf(ContentUris.parseId(uri))};
                rowsDeleted = database.delete(DatabaseHelper.TABLE_EVENTS, selection, selectionArgs);
                break;
            default:
                throw new IllegalArgumentException("Unknown URI: " + uri);
        }
        getContext().getContentResolver().notifyChange(uri, null);
        return rowsDeleted;
    }

    @Override
    public int update(@NonNull Uri uri, @Nullable ContentValues values, @Nullable String selection, @Nullable String[] selectionArgs) {
        int rowsUpdated;
        switch (uriMatcher.match(uri)) {
            case EVENTS:
                rowsUpdated = database.update(DatabaseHelper.TABLE_EVENTS, values, selection, selectionArgs);
                break;
            case EVENT_ID:
                selection = DatabaseHelper.COLUMN_ID + "=?";
                selectionArgs = new String[]{String.valueOf(ContentUris.parseId(uri))};
                rowsUpdated = database.update(DatabaseHelper.TABLE_EVENTS, values, selection, selectionArgs);
                break;
            default:
                throw new IllegalArgumentException("Unknown URI: " + uri);
        }
        getContext().getContentResolver().notifyChange(uri, null);
        return rowsUpdated;
    }

    @Nullable
    @Override
    public String getType(@NonNull Uri uri) {
        switch (uriMatcher.match(uri)) {
            case EVENTS:
                return "vnd.android.cursor.dir/vnd.com.example.calendarprovider.events";
            case EVENT_ID:
                return "vnd.android.cursor.item/vnd.com.example.calendarprovider.event";
            default:
                throw new IllegalArgumentException("Unknown URI: " + uri);
        }
    }
}
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3. 总结

ContentProvider 是 Android 中用于数据共享和管理的核心机制，特别适用于跨进程数据访问。在开发中，通过合理设计和优化，可以充分利用 ContentProvider 的优势，实现高效的数据操作。实践中，通过批量操作、异步任务、缓存机制等手段，可以显著提升 ContentProvider 的性能，确保应用的稳定性和用户体验。结合实际场景，选择合适的优化技巧和设计模式，是开发高性能 Android 应用的关键。

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