【Android】ContentProvider_android contentprovider

ContentProvider做为跨进程通信的手段之一，一般用于暴露本应用数据给到外部应用，提供一套标准的数据访问模型，常常与本地数据库联合使用

1. xml中声明provider

<provider
            android:name="包名.ProductProvider"
            android:authorities="包名.ProductProvider"
            android:enabled="true"
            android:exported="true"
            android:multiprocess="true" />
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2. 继承ContentProvider实现增删改查的接口，定义UriMatcher，matcher名为包名+类名，访问端通过match设置好的uri进行访问

public class ProductProvider extends ContentProvider {

    private static final String MAUTHORITIESNAME="包名.ProductProvider";
    private static UriMatcher matcher=new UriMatcher(UriMatcher.NO_MATCH);
    private static final int PRODUCT=1;
    //构建URI
    static {
        matcher.addURI(MAUTHORITIESNAME,"product",PRODUCT);
    }
    @Override
    public boolean onCreate() {
       // Log.i("testProductProvider","onCreate");
        ProductDatabase.getInstance(getContext());

        return true;
    }

    @Nullable
    @Override
    public Cursor query(@NonNull Uri uri, @Nullable String[] projection, @Nullable String selection, @Nullable String[] selectionArgs, @Nullable String sortOrder) {
        Log.i("testProductProvider","query");
        int match=matcher.match(uri);
        Log.i("testProductProvider","query match:"+match);
        switch (match){
            case PRODUCT:
                return ProductDatabase.getInstance(getContext()).getProductDao().getProduct();
        }
        return  null;
    }

    @Nullable
    @Override
    public String getType(@NonNull Uri uri) {
        int match=matcher.match(uri);
        switch (match){
            case PRODUCT:
                return "vnd.android.cursor.dir/product";
        }
       return null;
    }

    @Nullable
    @Override
    public Uri insert(@NonNull Uri uri, @Nullable ContentValues values) {
        return null;
    }

    @Override
    public int delete(@NonNull Uri uri, @Nullable String selection, @Nullable String[] selectionArgs) {
        return 0;
    }

    @Override
    public int update(@NonNull Uri uri, @Nullable ContentValues values, @Nullable String selection, @Nullable String[] selectionArgs) {
        return 0;
    }
}

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3. 访问数据端先设置包名可见性

<queries>
        			<package android:name="要访问的包名"/>
    		</queries>
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4.使用URI查询

Uri uri=Uri.parse("content://包名.类名/路径")；
 		Cursor cursor=getContentResolver().query(uri,null,null,null,null);
		//打印结果	     
		while (cursor.moveToNext()){
                            	Log.i("testCourse","id:"+cursor.getLong(0)
			+" content:"+cursor.getString(1)
                                    	+" cover:"+cursor.getString(2)
			+" type:"+cursor.getInt(3));
                       	 }
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