Content Provider实现跨程序数据共享

自定义Content Provider

• 本次项目代码在实践–升级数据库最佳写法这篇博客的基础上增加的。
• 需要自定义Content Provider的代码如下：

public class MyDatabaseProvider extends ContentProvider {    public static final int BOOK_DIR=0;    public static final int BOOK_ITEM=1;    public static final int H_DIR=2;    public static final int H_ITEM=3;    public static final String PATH="com.lingzhuo.testdatabase.provider";    private MyDatabaseHelper myDatabaseHelper;    private static UriMatcher uriMatcher;    static {        uriMatcher=new UriMatcher(UriMatcher.NO_MATCH);        uriMatcher.addURI(PATH,"book",BOOK_DIR);        uriMatcher.addURI(PATH,"book/#",BOOK_ITEM);        uriMatcher.addURI(PATH,"helloword",H_DIR);        uriMatcher.addURI(PATH,"helloword/#",H_ITEM);    }    @Override    public boolean onCreate() {        myDatabaseHelper=new MyDatabaseHelper(getContext(),"school.db",null,2);        return true;    }    @Override    public Cursor query(Uri uri, String[] projection, String selection, String[] selectionArgs, String sortOrder) {        SQLiteDatabase db=myDatabaseHelper.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 H_DIR:                cursor=db.query("helloword",projection,selection,selectionArgs,null,null,sortOrder);                break;            case H_ITEM:                String helloid= uri.getPathSegments().get(1);                cursor=db.query("helloword",projection,"id=?",new String[]{helloid},null,null,sortOrder);                break;        }        return cursor;    }    @Override    public Uri insert(Uri uri, ContentValues values) {        SQLiteDatabase db=myDatabaseHelper.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://"+PATH+"/book/"+newBookId);                break;            case H_DIR:            case H_ITEM:                long newHId=db.insert("helloword",null,values);                uriReturn=Uri.parse("content://"+PATH+"/helloword/"+newHId);                break;        }        return uriReturn;    }    @Override    public int delete(Uri uri, String selection, String[] selectionArgs) {        SQLiteDatabase db=myDatabaseHelper.getWritableDatabase();        int deleteRows=0;        switch (uriMatcher.match(uri)){            case BOOK_DIR:                deleteRows=db.delete("book",selection,selectionArgs);                break;            case BOOK_ITEM:                String bookid=uri.getPathSegments().get(1);                deleteRows=db.delete("book","id=?",new String[]{bookid});                break;            case H_DIR:                deleteRows=db.delete("helloword",selection,selectionArgs);                break;            case H_ITEM:                String hid=uri.getPathSegments().get(1);                deleteRows=db.delete("helloword","id=?",new String[]{hid});                break;        }        return deleteRows;    }    @Override    public int update(Uri uri, ContentValues values, String selection, String[] selectionArgs) {        SQLiteDatabase db=myDatabaseHelper.getWritableDatabase();        int updateRows=0;        switch (uriMatcher.match(uri)){            case BOOK_DIR:                updateRows=db.update("book",values,selection,selectionArgs);                break;            case BOOK_ITEM:                String bookid=uri.getPathSegments().get(1);                updateRows=db.update("book",values,"id = ?",new String[]{bookid});                break;            case H_DIR:                updateRows=db.update("helloword",values,selection,selectionArgs);                break;            case H_ITEM:                String hid=uri.getPathSegments().get(1);                updateRows=db.update("helloword",values,"id=?",new String[]{hid});                break;        }        return updateRows;    }    @Override    public String getType(Uri uri) {        switch (uriMatcher.match(uri)){            case BOOK_DIR:                return "vnd.android.cursor.dir/vnd.com.lingzhuo.testdatabase.provider.book";            case BOOK_ITEM:                return "vnd.android.cursor.item/vnd.com.lingzhuo.testdatabase.provider.book";            case H_DIR:                return "vnd.android.cursor.dir/vnd.com.lingzhuo.testdatabase.provider.helloword";            case H_ITEM:                return "vnd.android.cursor.item/vnd.com.lingzhuo.testdatabase.provider.helloword";        }        return null;    }}

• Uri对象的getPathSegments()方法，它会将内容URI权限之后的部分以“/”符号进行分割，并把分割后的结果放入到一个字符串列表中，那这个列表的0个位置和1个位置存放的就分别是路径和id了。得到id之后，就可以进行约束查询了。

String hid=uri.getPathSegments().get(1);

1. onCreate()，初始化内容时调用，返回true表示初始化成功，false表示失败
2. query()，添加数据的方法，添加完成后，返回一个用于表示这条新记录的URI。
3. update()，更新数据的方法，返回值就是更新数据受影响的行数
4. delete()，删除数据的方法，返回值就是删除数据受影响的行数

5. getType(),根据传入的内容URI来返回相应的MIME类型。
   getType()的返回值要求：
   （1）必须以vnd开头
   （2）如果内容以URI路径结尾，则后接android.cursor.dir/，如果内容URI以id结尾，则后接android.cursor.item/
   （3）最后接上vnd.包名./provider.表名

   • 对于content://com.lingzhuo.testdatabase/provider/book内容URI
   • vnd.android.cursor.dir/vnd.com.lingzhuo.testdatabase/provider.book
   • 对于content://com.lingzhuo.testdatabase/provider/book/1内容URI
   • vnd.android.cursor.item/vnd.com.lingzhuo.testdatabase/provider.book

    private static UriMatcher uriMatcher;    static {        uriMatcher=new UriMatcher(UriMatcher.NO_MATCH);        uriMatcher.addURI(PATH,"book",BOOK_DIR);        uriMatcher.addURI(PATH,"book/#",BOOK_ITEM);        uriMatcher.addURI(PATH,"helloword",H_DIR);        uriMatcher.addURI(PATH,"helloword/#",H_ITEM);    }

• 我们借助UriMatcher这个类可以轻松的实现匹配内容URI的功能。
• UriMatcher提供一个addURI()，这个方法接受三个参数
• 第一个参数权限
• 第二个参数路径
• 第三个参数自定义的代码
• 将这些代码静态代码块，就可以先执行了

 @Override    public Cursor query(Uri uri, String[] projection, String selection, String[] selectionArgs, String sortOrder) {        switch (uriMatcher.match(uri)){            case case BOOK_DIR:                //查询book表中的所有数据                break;            case BOOK_ITEM:                //查询book表中的单条数据                break;            case H_DIR:                //查询helloword表中的所有数据                break;            case H_ITEM:                //查询helloword表中的单条数据                break;        }        return null;    }

• 通过这样的判断语句就可以判断出要访问哪一张表，从而进行操作
• 以此类推，其余的方法，执行操作的时候，都可以这样判断一下

另建项目测试

• 简单布局，增删改查

<?xml version="1.0" encoding="utf-8"?><LinearLayout    xmlns:android="http://schemas.android.com/apk/res/android"    xmlns:tools="http://schemas.android.com/tools"    android:layout_width="match_parent"    android:layout_height="match_parent"    android:orientation="vertical"    tools:context="com.lingzhuo.testprovider2.MainActivity">    <Button        android:layout_width="match_parent"        android:layout_height="wrap_content"        android:text="增"        android:id="@+id/button_add" />    <Button        android:layout_width="match_parent"        android:layout_height="wrap_content"        android:text="删"        android:id="@+id/button_delete" />    <Button        android:layout_width="match_parent"        android:layout_height="wrap_content"        android:text="改"        android:id="@+id/button_change" />    <Button        android:layout_width="match_parent"        android:layout_height="wrap_content"        android:text="查"        android:id="@+id/button_search" /></LinearLayout>

• 逻辑代码

public class MainActivity extends AppCompatActivity implements View.OnClickListener{    private Button button_add,button_delete,button_change,button_search;    private String newId;    private Uri uri;    protected void onCreate(Bundle savedInstanceState) {        super.onCreate(savedInstanceState);        setContentView(R.layout.activity_main);        init();    }    private void init() {        button_add= (Button) findViewById(R.id.button_add);        button_change= (Button) findViewById(R.id.button_change);        button_delete= (Button) findViewById(R.id.button_delete);        button_search= (Button) findViewById(R.id.button_search);        button_add.setOnClickListener(this);        button_search.setOnClickListener(this);        button_delete.setOnClickListener(this);        button_change.setOnClickListener(this);        uri=Uri.parse("content://com.lingzhuo.testdatabase.provider/book");    }    @Override    public void onClick(View v) {        switch (v.getId()){            case R.id.button_add:                ContentValues values=new ContentValues();                values.put("name","Jack");                values.put("age","10086");                values.put("clazz","968574");                Uri newUri=getContentResolver().insert(uri,values);                newId=newUri.getPathSegments().get(1);                Log.d("**************id",newId);                break;            case R.id.button_delete:                Uri uri_delete=Uri.parse("content://com.lingzhuo.testdatabase.provider/book/"+newId);                getContentResolver().delete(uri_delete,null,null);                break;            case R.id.button_change:                Uri uri_change=Uri.parse("content://com.lingzhuo.testdatabase.provider/book/"+newId);                ContentValues values2=new ContentValues();                values2.put("name","aaaaaaaaaaaa");                values2.put("age","86001");                values2.put("clazz","135426");                getContentResolver().update(uri_change,values2,null,null);                break;            case R.id.button_search:                Cursor cursor=getContentResolver().query(uri,null,null,null,null);                if (cursor!=null){                    while(cursor.moveToNext()){                        String name=cursor.getString(cursor.getColumnIndex("name"));                        int age=cursor.getInt(cursor.getColumnIndex("age"));                        String clazz=cursor.getString(cursor.getColumnIndex("clazz"));                        Toast.makeText(MainActivity.this, name + age + clazz, Toast.LENGTH_SHORT).show();                        Log.d("**************",name+age+clazz);                    }                }                break;        }    }}

• 效果图如下：