Android Studio通过微调器选择从SQLite数据库中选择项目

Question

I am working on a project where I open up a random link in the browser after an imagebutton is pressed. I have created and populated a database table with different links and assigned them to categories. I would like to be able to filter which links are selected based upon a users' selection from a spinner dropdown. Right now, I am only able to select a random recipe from the database.

This is the main activity with all the relevant methods (I have left out the import statements and any other unnecessary code :

package com.example.randomrecipeapp;


public class MainActivity extends AppCompatActivity {

//fields
ImageButton randomizer;
Spinner spinner_filter;
DatabaseHelper db;


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

    db = new DatabaseHelper(getApplicationContext());
    //connect fields
    randomizer = (ImageButton) findViewById(R.id.logo);
    //spinner things
    spinner_filter = (Spinner) findViewById(R.id.spinner_filter);
    // Create an ArrayAdapter using the string array and a default spinner layout
    ArrayAdapter<CharSequence> adapter = ArrayAdapter.createFromResource(this,
            R.array.category_array, android.R.layout.simple_spinner_item);
    // Specify the layout to use when the list of choices appears
    adapter.setDropDownViewResource(android.R.layout.simple_spinner_dropdown_item);
    // Apply the adapter to the spinner
    spinner_filter.setAdapter(adapter);

    //initialize methods
    openRandomRecipe();

}

///////////////////////////////////////////////////////////////////
//spinner response
public void onItemSelected(AdapterView<?> parent, View view,
                           int pos, long id) {
    // An item was selected. You can retrieve the selected item using
    Object item = parent.getItemAtPosition(pos);
}

public void onNothingSelected(AdapterView<?> parent) {
    // Another interface callback
}

public void openRandomRecipe() {

    randomizer.setOnClickListener(
            new View.OnClickListener() {
                @Override
                public void onClick(View v) {
                    Cursor res = db.getRandomData();

                    //if no data exists
                    if (res.getCount() == 0) {
                        // show message
                        showMessage("Error", "Nothing found");
                        return;
                    }

                    //add recipe link (columnIndex 1) to buffer sequence
                    StringBuffer buffer = new StringBuffer();
                    while (res.moveToNext()) {
                        buffer.append(res.getString(1));
                    }
                    //convert buffer to st
                    String sr = buffer.toString();
                    //open link in browser
                    startActivity(new Intent(Intent.ACTION_VIEW,Uri.parse(sr)));

                }
            }
    );
}
}

The openRandomRecipe() method calls this other method in my DatabaseHelper class:

 //get one random recipe
public Cursor getRandomData() {
    SQLiteDatabase db = this.getWritableDatabase();
    Cursor res = db.rawQuery("SELECT * FROM "+TABLE_RECIPES+" ORDER BY RANDOM() LIMIT 1",null);
    return res;

}

Where TABLE_RECIPES is the name of the table. What I'm thinking I need to do is create a new method such as this:

public Cursor getRandomDataByCategory(String category) {
SQLiteDatabase db = this.getWritableDatabase();
    Cursor res = db.rawQuery("SELECT "+category+ " FROM "+TABLE_RECIPES+" ORDER BY RANDOM() LIMIT 1",null);
    return res;

And then in the onClickListener in the MainActivity file do

Cursor res = db.getRandomData(category);

I'm just not sure how to figure out how to pull in the user selected item from the spinner into the getRandomData method. Is this even a correct way of solving this problem? Thanks for the help.

Answer 1

I believe he query would be along the lines of :-

SELECT * FROM your_table WHERE your_category_column LIKE '%your_value%' ORDER BY random() LIMIT 1

• where your_table represents the table name
• your_value represents the value select from the spinner
• The above assumes LIKE so if you had categories of Dinner and AfterDinner then selecting Dinner from the spinner would select from both (easy to change to = for a specific match).

Saying that I'd suggest that you could have a single getRandaomData method would suit both eg :-

public Cursor getRandomData(String category) {
    SQLiteDatabase db = this.getWritableDatabase();
    String whereclause = null;
    String[] whereargs = null;
    if (category.length() > 0 ) {
        whereclause = COLUMN_RECIPES_CATEGORY + " LIKE ?";
        whereargs = new String[]{"%" + category + "%"};
    }
    return db.query(TABLE_RECIPES,null,whereclause,whereargs,null,null,"random()","1");
    //Cursor res = db.rawQuery("SELECT * FROM "+TABLE_RECIPES+" ORDER BY RANDOM() LIMIT 1",null);
}

• This assumes that the category is never null (see working example), and also LIKE.

WORKING EXAMPLE

The following is a working example based upon the code you have supplied (omitting (commenting out) code not necessary to demonstrate eg calling the next activity).

DatabaseHelper.java

public class DatabaseHelper extends SQLiteOpenHelper {

    SQLiteDatabase mDB;

    public static final String DBNAME = "recipee";
    public static final int DBVERSION = 1;
    public static final String TABLE_RECIPES = "recipes";
    public static final String COLUMN_RECIPES_ID = BaseColumns._ID;
    public static final String COLUMN_RECIPES_NAME = "name";
    public static final String COLUMN_RECIPES_CATEGORY = "category";

    public DatabaseHelper(Context context) {
        super(context, DBNAME, null, DBVERSION);
        mDB = this.getWritableDatabase();
    }

    @Override
    public void onCreate(SQLiteDatabase db) {
        mDB = db;
        String crt_recipes_sql = "CREATE TABLE IF NOT EXISTS " + TABLE_RECIPES + "(" +
                COLUMN_RECIPES_ID + "INTEGER PRIMARY KEY," +
                COLUMN_RECIPES_NAME + " TEXT," +
                COLUMN_RECIPES_CATEGORY + " TEXT" +
                ")";
        db.execSQL(crt_recipes_sql);
        addRecipee("Egg on Toast","Breakfast");
        addRecipee("Bangers and Mash", "Dinner");
        addRecipee("Cheese Sandwich","Snack");
        addRecipee("Mud Cake","Desert");
        addRecipee("Spaghetti Bolognaise","Dinner");
        addRecipee("Blueberry Cheesecake","Desert");
    }

    @Override
    public void onUpgrade(SQLiteDatabase db, int i, int i1) {

    }

    public long addRecipee(String name, String category) {
        if (mDB == null) {
            mDB = this.getWritableDatabase();
        }
        ContentValues cv = new ContentValues();
        cv.put(COLUMN_RECIPES_NAME,name);
        cv.put(COLUMN_RECIPES_CATEGORY,category);
        return mDB.insert(TABLE_RECIPES,null,cv);
    }

    public Cursor getRandomData(String category) {
        SQLiteDatabase db = this.getWritableDatabase();
        String whereclause = null;
        String[] whereargs = null;
        if (category.length() > 0 ) {
            whereclause = COLUMN_RECIPES_CATEGORY + " LIKE ?";
            whereargs = new String[]{"%" + category + "%"};
        }
        return db.query(TABLE_RECIPES,null,whereclause,whereargs,null,null,"random()","1");
        //Cursor res = db.rawQuery("SELECT * FROM "+TABLE_RECIPES+" ORDER BY RANDOM() LIMIT 1",null);
    }
}

• Note this adds a few recipes (with categories when the database is created)

Strings.xml

ie just the Spinner items :-

<array name="category_array">
    <item>A</item>
    <item>B</item>
    <item>C</item>
    <item>Dinner</item>
    <item>Breakfast</item>
    <item>Desert</item>
    <item>Snack</item>
</array>

MainActivity.java

public class MainActivity extends AppCompatActivity {

    //fields
    ImageButton randomizer;
    Spinner spinner_filter;
    TextView random_recipee;
    DatabaseHelper db;
    String current_category;


    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        random_recipee = this.findViewById(R.id.recipee);
        current_category = "";

        db = new DatabaseHelper(getApplicationContext());
        //connect fields
        randomizer = (ImageButton) findViewById(R.id.logo);
        //spinner things
        spinner_filter = (Spinner) findViewById(R.id.spinner_filter);
        // Create an ArrayAdapter using the string array and a default spinner layout
        ArrayAdapter<CharSequence> adapter = ArrayAdapter.createFromResource(this,
                R.array.category_array, android.R.layout.simple_spinner_item);
        // Specify the layout to use when the list of choices appears
        adapter.setDropDownViewResource(android.R.layout.simple_spinner_dropdown_item);
        // Apply the adapter to the spinner
        spinner_filter.setAdapter(adapter);
        spinner_filter.setOnItemSelectedListener(new AdapterView.OnItemSelectedListener() {
            @Override
            public void onItemSelected(AdapterView<?> parent, View view, int pos, long id) {
                Object item = parent.getItemAtPosition(pos);
                current_category = item.toString();
            }

            @Override
            public void onNothingSelected(AdapterView<?> adapterView) {

            }
        });

        //initialize methods
        openRandomRecipe();
    }

    public void openRandomRecipe() {
        randomizer.setOnClickListener(
                new View.OnClickListener() {
                    @Override
                    public void onClick(View v) {
                        Cursor res = db.getRandomData(current_category);
                        random_recipee.setText("Nothing Found");
                        if (res.moveToFirst()) {
                            random_recipee.setText(
                                    "Recipee is " +res.getString(
                                            res.getColumnIndex(DatabaseHelper.COLUMN_RECIPES_NAME)
                                    ) +
                                            ". Category is " +
                                            res.getString(
                                                    res.getColumnIndex(DatabaseHelper.COLUMN_RECIPES_CATEGORY)
                                            )
                            );
                        }
                        res.close(); //<<<<<<<<<< should always close cursor when done with it.
                        return;
                        //add recipe link (columnIndex 1) to buffer sequence
                        //StringBuffer buffer = new StringBuffer();
                        /*
                        while (res.moveToNext()) {
                            buffer.append(res.getString(1));
                        }
                        */
                        //convert buffer to st
                        //String sr = buffer.toString();
                        //open link in browser
                        //startActivity(new Intent(Intent.ACTION_VIEW,Uri.parse(sr)));

                    }
                }
        );
    }
}

• Note a TextView has been added that will show the selected recipe along with it's category.
• No image was used for the ImageButton

Result

• Note Spinner clicked to show items

After clicking on the button with Dinner as the selected item :-

• Note as only 2 recipes with Dinner as the category clicking the button will often show the same recipe.