android - 从内容提供者检索数据并将其显示在其他 Activity 上

Question

我正在研究 Content Provider。我编写了用于插入数据及其工作的代码 我想从内容提供者检索数据并将其显示在其他 Activity 上 我不知道如何进行 任何人都可以帮助我解决示例代码吗？

MainActivity.Java

package com.example.cpdemo;
import android.net.Uri;
import android.os.Bundle;
import android.app.Activity;
import android.content.ContentUris;
import android.content.ContentValues;
import android.database.Cursor;
import android.database.SQLException;
import android.util.Log;
import android.view.Menu;
import android.view.View;
import android.widget.Button;
import android.widget.Toast;
import android.widget.EditText;

 public class MainActivity extends Activity {

@Override
  public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    Button btnAdd = (Button) findViewById(R.id.btnAdd);
    btnAdd.setOnClickListener(new View.OnClickListener() {
    public void onClick(View v) {

    //---add a book---
   ContentValues values = new ContentValues();                              values.put(BookProvider.TITLE((EditText)findViewById(R.id.txtTitle)).getText().toString());
  values.put(BookProvider.ISBN, ((EditText)findViewById(R.id.txtISBN)).getText().toString());
  Uri uri = getContentResolver().insert(BookProvider.CONTENT_URI, values);
   String str=    getContentResolver().getType(Uri.parse("content://com.contentprovider.demo/books"));
    Toast.makeText(getBaseContext(),str,Toast.LENGTH_LONG).show();
     }
    });
            Button btnRetrieve = (Button) findViewById(R.id.btnRetrieve);
            btnRetrieve.setOnClickListener(new View.OnClickListener() {
            public void onClick(View v) {

            //---retrieve the titles---
            Uri allTitles = Uri.parse(
            "content://com.contentprovider.demo/books/2");



            Cursor c = getContentResolver().query(allTitles, null, null, null, null);
            int i = getContentResolver().delete(allTitles, null, null);
            // instead of that use Loader FreamWork from Android 3.0
}
}

BookProvider.java

package com.example.cpdemo;
import android.content.ContentProvider;  
import android.content.ContentUris;
import android.content.ContentValues;
import android.content.Context;
import android.content.UriMatcher;
import android.database.Cursor;
import android.database.SQLException;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteOpenHelper;
import android.database.sqlite.SQLiteQueryBuilder;
import android.net.Uri;
import android.text.TextUtils;
import android.util.Log;

public class BookProvider extends ContentProvider {
public static final String PROVIDER_NAME = "com.contentprovider.demo";
        public static final Uri CONTENT_URI =
        Uri.parse("content://"+ PROVIDER_NAME + "/books");
        public static final String _ID = "_id";
        public static final String TITLE = "title";
        public static final String ISBN = "isbn";
        private static final int BOOKS = 100;
        private static final int BOOK_ID = 200;
        private static final UriMatcher uriMatcher;
        static{
        uriMatcher = new UriMatcher(UriMatcher.NO_MATCH);
        uriMatcher.addURI(PROVIDER_NAME, "books", BOOKS);
        uriMatcher.addURI(PROVIDER_NAME, "books/#", BOOK_ID);
        }
        //---for database use---
        private SQLiteDatabase booksDB;
        private static final String DATABASE_NAME = "Books";
        private static final String DATABASE_TABLE = "titles";
        private static final int DATABASE_VERSION = 1;
        private static final String DATABASE_CREATE =
        "create table " + DATABASE_TABLE +
        " (_id integer primary key autoincrement, "
        + "title text not null, isbn text not null);";
        private static class DatabaseHelper extends SQLiteOpenHelper
        {
        DatabaseHelper(Context context) {
        super(context, DATABASE_NAME, null, DATABASE_VERSION);
        }
        @Override
        public void onCreate(SQLiteDatabase db)
        {
        db.execSQL(DATABASE_CREATE);
        }
        @Override
        public void onUpgrade(SQLiteDatabase db, int oldVersion,
        int newVersion) {
        Log.w("Content provider database",
        "Upgrading database from version " +
        oldVersion + "to "+ newVersion +
        ", which will destroy all old data");
        db.execSQL("DROP TABLE IF EXISTS titles");
        onCreate(db);
        }
        }

@Override
public int delete(Uri arg0, String arg1, String[] arg2) {
    int count=0;
    switch (uriMatcher.match(arg0)){
    case BOOKS:
    count = booksDB.delete(DATABASE_TABLE,arg1, arg2);
    break;
    case BOOK_ID:
    String id = arg0.getPathSegments().get(1);
    count = booksDB.delete(DATABASE_TABLE,
    _ID + " = " + id +
    (!TextUtils.isEmpty(arg1) ? " AND (" +arg1 + ')' : ""),arg2);
    break;
    default: throw new IllegalArgumentException("Unknown URI " + arg0);
    }
    getContext().getContentResolver().notifyChange(arg0, null);
    return count;
}
 //Returns the MIME type of the data at the given URI
@Override
public String getType(Uri arg0) {
    Log.d("hello","with in the getType method");
    switch (uriMatcher.match(arg0)){

    //---get all books---
    case BOOKS:

    return "vnd.android.cursor.dir/vnd.contentprovider.books ";
    //---get a particular book---
    case BOOK_ID:
        Log.d("hello","with in the getType method_1");
    return "vnd.android.cursor.item/vnd.contentprovider.books ";
    default:
    throw new IllegalArgumentException("Unsupported URI: " + arg0);
    }
}

@Override
public Uri insert(Uri uri, ContentValues values) {
    Log.d("hello","we are in insert block");
//---add a new book---
long rowID = booksDB.insert(DATABASE_TABLE,"",values);
//---if added successfully---
if (rowID>0)
{
Uri _uri = ContentUris.withAppendedId(CONTENT_URI, rowID);
//---notify register to change the  content URI ---
getContext().getContentResolver().notifyChange(_uri, null);
return _uri;
}
throw new SQLException("Failed to insert row into " + uri);

}


@Override
public boolean onCreate() {
    Context context = getContext();
    DatabaseHelper dbHelper = new DatabaseHelper(context);
    booksDB = dbHelper.getWritableDatabase();
    return (booksDB == null)? false:true;
}

@Override
public Cursor query(Uri uri, String[] projection, String selection,String[] selectionArgs, String sortOrder) {
SQLiteQueryBuilder sqlBuilder = new SQLiteQueryBuilder();
//tablename1 ;;;; id , name
//tablename2 ::: ide ,name
//map.put(tablename1.name,name AS NewName);
//map.put(tablename2.name,name AS exname);

//sqlBuilder.setProjectionMap(map)
//c.getValues(tablename1.name);
//String str = tablename1 left Outer join tablename2 on tablename1.id == tablename2.id;     
sqlBuilder.setTables(DATABASE_TABLE);

if (uriMatcher.match(uri) == BOOK_ID)
//---if getting a particular book---
    Log.d("hi","we are in query block1");
sqlBuilder.appendWhere(_ID + "= " + uri.getPathSegments().get(1));
Log.d("hi","we are in query block2");
//if (sortOrder==null || sortOrder=="")
//sortOrder = TITLE;
Log.d("hi","we are in query block3");
Cursor c = sqlBuilder.query(booksDB,projection,selection,selectionArgs,
null,
null,
null);
Log.d("hi","we are in query block4");
//---register to watch a content URI for changes---
c.setNotificationUri(getContext().getContentResolver(), uri);
return c;
}

@Override
public int update(Uri uri, ContentValues values, String selection,String[] selectionArgs) {
int count = 0;
switch (uriMatcher.match(uri)){
case BOOKS:
count = booksDB.update(DATABASE_TABLE,values,selection,selectionArgs);
break;
case BOOK_ID:
count = booksDB.update(DATABASE_TABLE,values,_ID + " = " + uri.getPathSegments().get(1) +
(!TextUtils.isEmpty(selection) ? " AND (" +selection + ')' : ""),selectionArgs);
break;
default: throw new IllegalArgumentException("Unknown URI " + uri);
}
getContext().getContentResolver().notifyChange(uri, null);
return count;
}
 }

Answer 1

我创建了一个简单的自定义 ContentProvider 演示，其中包含从 ContentProvider 插入、更新、删除和获取数据。 Here是相同的完整示例。我还使用了 AssetFileDescriptor，它允许您从另一个应用程序播放此应用程序的 assets 文件夹中的声音。还从另一个应用程序访问 ContentProvider。您只需取消注释所需的方法并使其正常工作。