Android中用ContentProvider实现跨程序访问

使用Android手机中的应用时,经常会出现访问其他应用中数据的场景.比如读取用户联系人,获取其它应用的登录状态等.不同应用间的数据访问,涉及到数据访问安全的问题.作为应用的开发者,一方面我们希望自己应用中关系到用户隐私的信息,如账户和密码等,要绝对安全,不能被其他应用获取.另一方面,一些并非私密的数据可以公开,供其他应用读取使用,从而减少用户重复设置的麻烦,提高用户使用该应用活跃度.基于上述目的,Anroid在6.0时推出了ContentProvider.

使用ContentProvider,需要先了解Android的权限.权限是基于对用户隐私的保护,比如安装摩拜,ofo等应用时,都会遇到获取用户位置权限的请求.如果有一天,自己不想行踪被应用获取,我们可以在设置/应用管理中,关闭位置请求权限.同理,其它的拨打电话,获取信息,使用通知等都涉及到权限,也都可以由用户进行打开或者关闭的选择.

Android中所有的私人权限如下图.

Android私有权限

下面是一个简单的调用打电话的示例.

public class MainActivity extends AppCompatActivity {

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

        Button btn_makeCall = (Button)findViewById(R.id.make_call);
        btn_makeCall.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                if (ContextCompat.checkSelfPermission(MainActivity.this, Manifest.permission.CALL_PHONE) !=
                        PackageManager.PERMISSION_GRANTED){
                    ActivityCompat.requestPermissions(MainActivity.this, new String[] { Manifest.permission.CALL_PHONE}, 1);

                }else {
                    call();
                }
            }
        });
    }

    private void call() {
        Intent intent = new Intent(Intent.ACTION_CALL);
        intent.setData(Uri.parse("tel:10086"));
        try {
            startActivity(intent);
        }catch (SecurityException e){
            e.printStackTrace();
        }
    }

    @Override
    public void onRequestPermissionsResult(int requestCode, @NonNull String[] permissions, @NonNull int[] grantResults) {
        switch (requestCode) {
            case 1:
                if (grantResults.length > 0 && grantResults[0] == PackageManager.PERMISSION_GRANTED){
                    call();
                }else {
                    Toast.makeText(this, "HAVE NOT PERMISSION", Toast.LENGTH_SHORT).show();
                }
                break;
                default:
        }
    }
}

btn_makeCall是在布局中添加的Button组件.
注最后需要在AndroidManifest.xml文件中进行注册.

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.example.zhudong.makecalltest">
    <uses-permission android:name="android.permission.CALL_PHONE" />
    <application
        android:allowBackup="true"
        android:icon="@mipmap/ic_launcher"
        android:label="@string/app_name"
        android:roundIcon="@mipmap/ic_launcher_round"
        android:supportsRtl="true"
        android:theme="@style/AppTheme">
        <activity android:name=".MainActivity">
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />

                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>
    </application>
</manifest>

类似请求系统权限,不同的应用程序之间的数据访问,可以通过ContentProvider实现.下面实现一个ProviderTest应用访问DatabaseTest应用.

DatabaseTest应用中用MyOpenHelper类新建数据库,并提供给ProviderTest应用.其中MyOpenHelper类的实现参考Andoid数据持久化的方式.

新建DatabaseProvider,继承至ContentProvider,实现抽象方法query, insert, update, delete方法,就可以方便的供其它应用来查询,插入,更新和删除数据了.

public class DatabaseProvider extends ContentProvider {
    public static final int BOOK_DIR = 0;

    public static final int BOOK_ITEM = 1;

    public static final int CATEGORY_DIR = 2;

    public static final int CATEGORY_ITEM = 3;

    public static final String AUTHORITY = "com.example.databasetest.provider";

    private static UriMatcher uriMatcher;

    private MyOpenHelper dbHelper;

    static {
        uriMatcher = new UriMatcher(UriMatcher.NO_MATCH);
        uriMatcher.addURI(AUTHORITY, "book", BOOK_DIR);
        uriMatcher.addURI(AUTHORITY, "book/#", BOOK_ITEM);
        uriMatcher.addURI(AUTHORITY, "category", CATEGORY_DIR);
        uriMatcher.addURI(AUTHORITY, "category/#", CATEGORY_ITEM);
    }

    @Override
    public boolean onCreate() {
        dbHelper = new MyOpenHelper(getContext(), "BookStore.db", null, 1);
        return true;
    }

    @Override
    public Cursor query(Uri uri, String[] projection, String selection,
                        String[] selectionArgs, String sortOrder) {
        Cursor cursor = null;
        SQLiteDatabase db = dbHelper.getReadableDatabase();
        switch (uriMatcher.match(uri)){
            case BOOK_DIR:
                cursor = db.query("Book", projection, selection, selectionArgs, null, null, sortOrder);
                break;
            case BOOK_ITEM:
                String bookId = uri.getPathSegments().get(1);
                cursor = db.query("Book", projection, "id = ?", new String[] {bookId}, null, null, sortOrder);
                break;
            case CATEGORY_DIR:
                cursor = db.query("Category", projection, selection, selectionArgs, null, null, sortOrder);
                break;
            case CATEGORY_ITEM:
                String categoryId = uri.getPathSegments().get(1);
                cursor = db.query("Category", projection, "id = ?", new String[] {categoryId}, null, null, sortOrder);
                break;
            default:
                break;
        }
        return cursor;
    }

    @Override
    public Uri insert(Uri uri, ContentValues values) {
        SQLiteDatabase db = dbHelper.getWritableDatabase();
        Uri uriReturn = null;
        switch (uriMatcher.match(uri)){
            case BOOK_DIR:
            case BOOK_ITEM:
                long newBookId = db.insert("Book", null, values);
                uriReturn = Uri.parse("content://" + AUTHORITY + "/book/" + newBookId);
                break;
            case CATEGORY_DIR:
            case CATEGORY_ITEM:
                long newCategoryId = db.insert("Category", null, values);
                uriReturn = Uri.parse("content://" + AUTHORITY + "/category/" + newCategoryId);
                break;
            default:
                break;
        }
        return uriReturn;
    }

    @Override
    public int update(Uri uri, ContentValues values, String selection,
                      String[] selectionArgs) {
        SQLiteDatabase db = dbHelper.getWritableDatabase();
        int rowReturn = 0;
        switch (uriMatcher.match(uri)){
            case BOOK_DIR:
                rowReturn = db.update("Book", values, selection, selectionArgs);
                break;
            case BOOK_ITEM:
                String bookId = uri.getPathSegments().get(1);
                rowReturn = db.update("Book", values, "id = ?", new String[]{bookId});
                break;
            case CATEGORY_DIR:
                rowReturn = db.update("Category", values, selection, selectionArgs);
                break;
            case CATEGORY_ITEM:
                String categoryId = uri.getPathSegments().get(1);
                rowReturn = db.update("Category", values, "id = ?", new String[]{categoryId});
                break;
            default:
                break;
        }
        return rowReturn;
    }

    @Override
    public int delete(Uri uri, String selection, String[] selectionArgs) {
        SQLiteDatabase db = dbHelper.getWritableDatabase();
        int deleteReturn = 0;
        switch (uriMatcher.match(uri)){
            case BOOK_DIR:
                deleteReturn = db.delete("Book", selection, selectionArgs);
                break;
            case BOOK_ITEM:
                String bookId = uri.getPathSegments().get(1);
                deleteReturn = db.delete("Book", "id = ?", new String[]{bookId});
                break;
            case CATEGORY_DIR:
                deleteReturn = db.delete("Category", selection, selectionArgs);
                break;
            case CATEGORY_ITEM:
                String categoryId = uri.getPathSegments().get(1);
                deleteReturn = db.delete("Category", "id = ?", new String[]{categoryId});
                break;
            default:
                break;
        }
        return deleteReturn;
    }

    @Override
    public String getType(Uri uri) {
        String strReturn = null;
        switch (uriMatcher.match(uri)){
            case BOOK_DIR:
                strReturn = "vnd.android.cursor.dir/vnd.com.example.databasetest.provider.book";
                break;
            case BOOK_ITEM:
                strReturn = "vnd.android.cursor.item/vnd.com.example.databasetest.provider.book";
                break;
            case CATEGORY_DIR:
                strReturn = "vnd.android.cursor.dir/vnd.com.example.databasetest.provider.category";
                break;
            case CATEGORY_ITEM:
                strReturn = "vnd.android.cursor.item/vnd.com.example.databasetest.provider.category";
                break;
            default:
                break;
        }
        return strReturn;
    }
}

然后在AndroidManifest.xml文件中进行注册:

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.example.zhudong.databasetest2">

    <application
        android:allowBackup="true"
        android:icon="@mipmap/ic_launcher"
        android:label="@string/app_name"
        android:roundIcon="@mipmap/ic_launcher_round"
        android:supportsRtl="true"
        android:theme="@style/AppTheme">
        <activity android:name=".MainActivity">
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />

                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>

        <provider
            android:name=".DatabaseProvider"
            android:authorities="com.example.databasetest.provider"
            android:enabled="true"
            android:exported="true"></provider>
    </application>

</manifest>

运行工程,生成DatabaseTest应用.

接下来新建ProviderTest工程.在activity_main.xml布局文件中添加Button组件:

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout
    android:orientation="vertical"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    xmlns:android="http://schemas.android.com/apk/res/android">

    <Button
        android:id="@+id/button_add"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="add to book"/>
    <Button
        android:id="@+id/button_query"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="query from book"/>
    <Button
        android:id="@+id/button_upate"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="upate to book"/>
    <Button
        android:id="@+id/button_delete"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="delete from book"/>

</LinearLayout>

然后在MainActivity中使用添加的Button组件.

public class MainActivity extends AppCompatActivity {

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

        Button button_add = (Button)findViewById(R.id.button_add);
        button_add.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) { 
                Uri uri = Uri.parse("content://com.example.databasetest.provider/book");
                ContentValues values = new ContentValues();
                values.put("author", "StormZhang");
                values.put("price", "21.99");
                values.put("pages", "199.11");
                values.put("name", "First Git");
                Uri newUri = getContentResolver().insert(uri,values);
                newId = newUri.getPathSegments().get(1);
                Log.d("newId", "onClick:" + newId);
            }
        });

        Button button_query = (Button)findViewById(R.id.button_query);
        button_query.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                Uri uri = Uri.parse("content://com.example.databasetest.provider/book");
                Cursor cursor = getContentResolver().query(uri, null, null, null,null);
                if (cursor != null){
                    while (cursor.moveToNext()){
                        String author = cursor.getString(cursor.getColumnIndex("author"));
                        double price = cursor.getDouble(cursor.getColumnIndex("price"));
                        String name = cursor.getString(cursor.getColumnIndex("name"));
                        int pages = cursor.getInt(cursor.getColumnIndex("pages"));
                        Log.e("MainActivity", author + price + name + pages);
                    }
                }
                cursor.close();
            }
        });

        Button button_update = (Button)findViewById(R.id.button_upate);
        button_update.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                Uri uri = Uri.parse("content://com.example.databasetest.provider/book/" + newId);
                ContentValues values = new ContentValues();
                values.put("name", "a New Name");
                values.put("pages", "1999");
                values.put("price", "199.9");
                getContentResolver().update(uri, values, null, null);
            }
        });

        Button button_delete = (Button)findViewById(R.id.button_delete);
        button_delete.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                Uri uri = Uri.parse("content://com.example.databasetest.provider/book/" + newId);
                getContentResolver().delete(uri,null,null);
            }
        });
    }
}

运行应用,点击不同的Button后,我们能在Anroid Monitor的控制台中看到打印的信息:

E/MainActivity: StormZhang199.9a New Name1999
E/MainActivity: StormZhang21.99First Git199
E/MainActivity: StormZhang21.99First Git199

E/MainActivity: StormZhang199.9a New Name1999
E/MainActivity: StormZhang21.99First Git199
E/MainActivity: StormZhang199.9a New Name1999

总结
Android的权限控制,增加了不同应用数据的安全性,更好地保护了用户隐私.其提供的ContentProvider可以让开发者方便的暴露给其他应用数据,并保证其他数据的安全性.

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