安卓学习笔记（七）内容提供器Content Provider

内容提供器（Content Provider）

使用内容提供器是Android实现跨程序共享数据的标准方式。

运行时权限

如果我们想要实现拨号功能，就必须获得权限，因为拨打电话涉及用户手机资费问题，在AndroidManifest中声明CALL_PHONE权限后，若为Android6.0以下则可以正常拨打电话，而在Android6.0以上则需要运行时权限才能拨打电话，运行时权限是用户是否有授权，授权的方式是会弹出一个权限申请对话框，若用户选择同意则才能正常运行。

MainActivity.java：

public class MainActivity extends AppCompatActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        Button makeCall = findViewById(R.id.make_call);
        makeCall.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                if(ContextCompat.checkSelfPermission(MainActivity.this, Manifest.permission.CALL_PHONE) != PackageManager.PERMISSION_GRANTED){//判断是否用户已授权
                    ActivityCompat.requestPermissions(MainActivity.this,new String[] {Manifest.permission.CALL_PHONE},1);//若没授权则弹出权限申请对话框
                }else{//若已授权则直接拨号
                    call();
                }
            }
        });
    }

    private void call(){
        try {
            Intent intent = new Intent(Intent.ACTION_CALL);
            intent.setData(Uri.parse("tel:10086"));
            startActivity(intent);
        }catch (SecurityException e){
            e.printStackTrace();
        }
    }
    
    //权限申请对话框选择后的回调方法
    @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){//用户同意授权
                    call();
                }else {
                    Toast.makeText(this,"You denied the permission",Toast.LENGTH_SHORT).show();
                }
                break;
                default:
        }
    }
}

访问其他程序中的数据

如果我们想获取手机系统联系人的数据的话，则需要使用ContentResolver。

新建ListView来显示联系人的数据，activity.main.xml：

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="vertical"
    android:layout_width="match_parent"
    android:layout_height="match_parent">

    <ListView
        android:id="@+id/contacts_view"
        android:layout_width="match_parent"
        android:layout_height="match_parent">
    ListView>
LinearLayout>

MainActivity.java：

public class MainActivity extends AppCompatActivity {

    ArrayAdapter<String > adapter;
    List<String> contactsList = new ArrayList<>();

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        ListView contactsView = findViewById(R.id.contacts_view);
        adapter = new ArrayAdapter<String>(this,android.R.layout.simple_list_item_1,contactsList);
        contactsView.setAdapter(adapter);
        if (ContextCompat.checkSelfPermission(this, Manifest.permission.READ_CONTACTS) != PackageManager.PERMISSION_GRANTED){
            ActivityCompat.requestPermissions(this,new String[] {Manifest.permission.READ_CONTACTS},1);
        }else{
            readContacts();
        }
    }

    private void readContacts(){
        Cursor cursor = null;
        try{
            //查询联系人数据
            cursor = getContentResolver().query(ContactsContract.CommonDataKinds.Phone.CONTENT_URI,null,null,null,null);
            if (cursor != null){
                while (cursor.moveToNext()){
                    //获取联系人姓名
                    String displayName = cursor.getString(cursor.getColumnIndex(ContactsContract.CommonDataKinds.Phone.DISPLAY_NAME));
                    //获取联系人手机号
                    String number = cursor.getString(cursor.getColumnIndex(ContactsContract.CommonDataKinds.Phone.NUMBER));
                    contactsList.add(displayName + "\n" + number);
                }
                adapter.notifyDataSetChanged();
            }
        }catch (Exception e){
            e.printStackTrace();
        }finally {
            if(cursor != null){
                cursor.close();
            }
        }
    }

    @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){
                    readContacts();
                }else {
                    Toast.makeText(this,"You denied the permission",Toast.LENGTH_SHORT).show();
                }
                break;
                default:
        }
    }
}

最后不要忘了在AndroidManifest中添加权限声明：

<uses-permission android:name="android.permission.READ_CONTACTS">uses-permission>

创建内容提供器

如果想实现程序的数据共享则需要使用ContentProvider和ContentResolver，例如我们想新建一个项目来对之前学习数据库存储时的BookStore.db数据库进行增删改查。

首先我们需要打开之前建立数据库的项目并且新建Content Provider并命名为DatabaseProvider：

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.youyu4.databasetest.provider";

    private static UriMatcher uriMatcher;

    private MyDatabaseHelper 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 MyDatabaseHelper(getContext(),"BookStore.db",null,2);
        return true;
    }

    @Override
    public Cursor query(Uri uri, String[] projection, String selection,
                        String[] selectionArgs, String sortOrder) {
        //查询数据
        SQLiteDatabase db = dbHelper.getWritableDatabase();
        Cursor cursor = null;
        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) {
        //添加数据
        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) {
        //更新数据
        SQLiteDatabase db = dbHelper.getWritableDatabase();
        int updatedRows = 0;
        switch (uriMatcher.match(uri)){
            case BOOK_DIR:
                updatedRows = db.update("Book",values,selection,selectionArgs);
                break;
            case BOOK_ITEM:
                String bookId = uri.getPathSegments().get(1);
                updatedRows = db.update("Book",values,"id = ?",new String[] {bookId});
                break;
            case CATEGORY_DIR:
                updatedRows = db.update("Category",values,selection,selectionArgs);
                break;
            case CATEGORY_ITEM:
                String categoryId = uri.getPathSegments().get(1);
                updatedRows = db.update("Category",values,"id = ?",new String[] {categoryId});
                break;
            default:
                break;
        }
        return updatedRows;
    }

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

    @Override
    public String getType(Uri uri) {
        switch (uriMatcher.match(uri)){
            case BOOK_DIR:
                return "vnd.android.cursor.dir/vnd.com.example.youyu4.databasetest.provider.book";
            case BOOK_ITEM:
                return "vnd.android.cursor.item/vnd.com.example.youyu4.databasetest.provider.book";
            case CATEGORY_DIR:
                return "vnd.android.cursor.dir/vnd.com.example.youyu4.databasetest.provider.category";
            case CATEGORY_ITEM:
                return "vnd.android.cursor.item/vnd.com.example.youyu4.databasetest.provider.category";
        }
        return null;
    }
}

新建完contentprovider后我们新建一个新的项目并布局4个按钮用于对上面数据库项目中的数据库数据进行增删改查，主要原理是使用Uri.parse()方法将内容URI解析成Uri对象，然后调用ContentResolver中的增删改查方法执行数据库操作。

MainActivity.java：

public class MainActivity extends AppCompatActivity {

    private String newId;
    private static final String TAG = "MainActivity";

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

        Button addData = findViewById(R.id.add_data);
        Button queryData = findViewById(R.id.query_data);
        Button updateData = findViewById(R.id.update_data);
        Button deleteData = findViewById(R.id.delete_data);

        addData.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                //添加数据
                Uri uri = Uri.parse("content://com.example.youyu4.databasetest.provider/book");
                ContentValues values = new ContentValues();
                values.put("name","abc");
                values.put("author","sjlqmt");
                values.put("pages",1234);
                values.put("price",55.55);
                Uri newUri = getContentResolver().insert(uri,values);
                newId = newUri.getPathSegments().get(1);
            }
        });

        queryData.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                //查询数据
                Uri uri = Uri.parse("content://com.example.youyu4.databasetest.provider/book");
                Cursor cursor = getContentResolver().query(uri,null,null,null,null);
                if(cursor != null){
                    while(cursor.moveToNext()){
                        String name = cursor.getString(cursor.getColumnIndex("name"));
                        String author = cursor.getString(cursor.getColumnIndex("author"));
                        int pages = cursor.getInt(cursor.getColumnIndex("pages"));
                        double price = cursor.getDouble(cursor.getColumnIndex("price"));
                        Log.d(TAG, "book name is " + name);
                        Log.d(TAG, "book author is " + author);
                        Log.d(TAG, "book pages is " + pages);
                        Log.d(TAG, "book price is " + price);
                    }
                    cursor.close();
                }
            }
        });

        updateData.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                //更新数据
                Uri uri = Uri.parse("content://com.example.youyu4.databasetest.provider/book/" + newId);
                ContentValues values = new ContentValues();
                values.put("name","qqq");
                values.put("pages",5678);
                values.put("price",999.99);
                getContentResolver().update(uri,values,null,null);
            }
        });

        deleteData.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                //删除数据
                Uri uri = Uri.parse("content://com.example.youyu4.databasetest.provider/book/" + newId);
                getContentResolver().delete(uri,null,null);
            }
        });

    }
}