ContentProvider使用

作为四大组件之一，ContentProvider 算是我直接使用次数最少的一个了。主要提供应用程序之间共享数据的接口

一、创建ContentProvider 实例

ContentProvider是一个抽象类。创建MyProvider类继承ContentProvider，实现6个抽象方法：onCreate、getType、query、insert、delete、update。

onCreate()方法会在创建的时候调用一次。其它方法通过ContentResolver的增删改查方法触发。

所以我们只需要在对应的方法下对数据库进行增删改查就行了。

public class MyProvider extends ContentProvider {private static final String TAG = "MyProvider";@Overridepublic boolean onCreate() {Log.d(TAG, "onCreate, Thread:" + Thread.currentThread().getName());return false;}@Nullable@Overridepublic String getType(@NonNull Uri uri) {Log.d(TAG, "getType, Thread:" + Thread.currentThread().getName());return null;}@Nullable@Overridepublic Cursor query(@NonNull Uri uri, @Nullable String[] projection, @Nullable String selection, @Nullable String[] selectionArgs, @Nullable String sortOrder) {Log.d(TAG, "query, Thread:" + Thread.currentThread().getName());return SqlHelper.getInstance().query(TeacherTable.TABLE_NAME, projection, selection, selectionArgs);}@Nullable@Overridepublic Uri insert(@NonNull Uri uri, @Nullable ContentValues values) {Log.d(TAG, "insert, Thread:" + Thread.currentThread().getName());SqlHelper.getInstance().insert(TeacherTable.TABLE_NAME, values);return null;}@Overridepublic int delete(@NonNull Uri uri, @Nullable String selection, @Nullable String[] selectionArgs) {Log.d(TAG, "delete, Thread:" + Thread.currentThread().getName());SqlHelper.getInstance().delete(TeacherTable.TABLE_NAME, selection, selectionArgs);return 0;}@Overridepublic int update(@NonNull Uri uri, @Nullable ContentValues values, @Nullable String selection, @Nullable String[] selectionArgs) {Log.d(TAG, "update, Thread:" + Thread.currentThread().getName());SqlHelper.getInstance().update(TeacherTable.TABLE_NAME, values, selection, selectionArgs);return 0;}
}

二、注册ContentProvider

        <providerandroid:authorities="test.com.provider.MyProvider"android:name=".provider.MyProvider"
//            android:process=":provider"
//            android:permission="com.zy.android.PROVIDER"/>

authorities : 是ContentProvider 的唯一标识，所以最好加上包名前缀
name ：需要注册的ContentProvider 名

三、使用

1、插入：

 Uri uri = Uri.parse("content://test.com.provider.MyProvider");ContentValues values = new ContentValues();values.put(TeacherTable.COLUMN_NAME, "张三");values.put(TeacherTable.COLUMN_GRADE,"1");values.put(TeacherTable.COLUMN_CLS,"3");values.put(TeacherTable.COLUMN_ID, id);getContentResolver().insert(uri,values);

在Uri 中指明ContentProvider 的标识，也就是注册的authorities属性值。
固定写法：Uri.parse("content://authorities")

通过getContentResolver()获得ContentResolver对象。

2、删除

getContentResolver().delete(uri, "name = ?", new String[]{"张三"});

3、修改

ContentValues values2 = new ContentValues();
values2.put(TeacherTable.COLUMN_NAME, "王二麻子");
values2.put(TeacherTable.COLUMN_GRADE,"1");
values2.put(TeacherTable.COLUMN_CLS,"3");
//values.put(TeacherTable.COLUMN_ID, id);
getContentResolver().update(uri, values2, "name = ? ", new String[]{"张三"});

将张三修改成王二麻子

4、查询

Cursor cursor = getContentResolver().query(uri, null, "name = ? ", new String[]{"张三"}, "1");

查询操作会返回一个Cursor对象，通过对Cursor 操作，获得值。

        if (cursor == null){return;}cursor.moveToFirst();StringBuffer sb = new StringBuffer();while (!cursor.isAfterLast()){sb.append("ID:" + cursor.getInt(cursor.getColumnIndex(TeacherTable.COLUMN_ID))+ " name:" + cursor.getString(cursor.getColumnIndex(TeacherTable.COLUMN_NAME))+ " grade:"+ cursor.getString(cursor.getColumnIndex(TeacherTable.COLUMN_GRADE))+ " cls: " + cursor.getString(cursor.getColumnIndex(TeacherTable.COLUMN_CLS))+ "\n");cursor.moveToNext();}cursor.close();

ContentProvider的query方法需要返回Cursor 才行，否则获得的是一个空对象。

TeacherTable表结构

public class TeacherTable {//表名public static final String TABLE_NAME = "teacher";//列public static final String COLUMN_ID    = "id";public static final String COLUMN_NAME  = "name";public static final String COLUMN_GRADE = "grade";public static final String COLUMN_CLS   = "cls";//创建teacher表public static final String CREATE_TABLE = "CREATE TABLE "  //"CREATE TABLE IF NOT EXISTS "+ TABLE_NAME + "("+ COLUMN_ID + " INTEGER PRIMARY KEY AUTOINCREMENT,"+ COLUMN_NAME + " TEXT,"+ COLUMN_GRADE + " TEXT,"+ COLUMN_CLS + " TEXT"+ ")";private int id;private String name;private String grade;private String cls;
}

SqlHelper

/*** Created by zy* date 2019/12/24 0024.* desc:*/
public class SqlHelper extends SQLiteOpenHelper {//数据库名private static final String DB_NAME = "test_db";//数据库版本private static final int DB_VERSION = 1;public static SqlHelper instance;public static SqlHelper getInstance(){if (instance == null){instance = new SqlHelper(MyApp.context);}return instance;}/*** @param context 上下文*                数据库名称*                数据库游标工厂类(可选)*                数据库版本*/public SqlHelper(@Nullable Context context) {super(context, DB_NAME, null, DB_VERSION);}@Overridepublic void onCreate(SQLiteDatabase db) {//创建教师表db.execSQL(TeacherTable.CREATE_TABLE);}@Overridepublic void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {String drop = "DROP TABLE IF EXISTS ";//drop older table existeddb.execSQL(drop + TeacherTable.TABLE_NAME);onCreate(db);}/*** 插入** @param tableName 表名* @param values* @return 插入是否成功*/public boolean insert(String tableName, ContentValues values) {SQLiteDatabase db = this.getWritableDatabase();long res = db.insert(tableName, null, values);return res != -1;}/*** 根据条件删除* @param tableName* @param where* @param args* @return*/public boolean delete(String tableName, String where, String[] args) {try {SQLiteDatabase db = this.getWritableDatabase();db.delete(tableName, where, args);return true;} catch (Exception e) {e.printStackTrace();}return false;}/*** 修改* @param tableName* @param id* @param values* @return*/public boolean update(String tableName, String id, ContentValues values) {try {SQLiteDatabase db = this.getWritableDatabase();db.update(tableName, values, TeacherTable.COLUMN_ID + " = ? ", new String[]{id});return true;} catch (Exception e) {e.printStackTrace();Log.e("tag","update Exception: " + e.toString());}return false;}/*** 更新* @param tableName* @param values* @param selection* @param selectionArgs*/public void update(String tableName, ContentValues values, String selection, String[] selectionArgs){SQLiteDatabase db = this.getWritableDatabase();db.update(tableName, values, selection, selectionArgs);}/*** 查询* @param tableName* @param columns* @param selection* @param selectionArgs* @return*/public Cursor query(String tableName, String[] columns, String selection, String[] selectionArgs) {try {SQLiteDatabase db = this.getReadableDatabase();Cursor cursor = db.query(tableName, columns, selection, selectionArgs, null, null, null);return cursor;} catch (Exception e) {e.printStackTrace();}return null;}
}

总结

关于SQLite使用，可以看我的另一篇文字：Android SQLite简单使用

因为四大组件中ContentProvider主动使用频率比较低，所以没有去过多深入了解，只是记录使用方式。

其它三大组件工作流程：

Activity的启动流程

BroadcastReceiver 工作过程

Service启动流程