Question

我想从数据库中检索数据，以便只有那些数据应该是listview才能在真实条件下工作。我在XML文件中添加了两个微调器。一个微调器包含存储在java文件中的默认值，用于获取血型选项，第二个包含城市名称。我希望如果用户选择BloodGroup作为O + ve从微调器和City作为Gurgaon并单击搜索按钮，那么该人员的详细信息将显示在两个微调器查询之后的列表视图中。

Answer 1

以下是如何应用来自两个微调器的 SelectedItem 的工作示例，然后通过单击“搜索”按钮显示，仅列出包含这两个项目的行（如果有）。

示例基于您提供的方案。也就是说，有一个特定的城市和血型组列表可以通过Spinners选择。记录表包括两列以及两列 _id 和名称的列。测试数据库中填充了100个随机名称，城市和血型。

布局 activity_main.xml

<?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:orientation="vertical"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".MainActivity">

    <TextView
        android:id="@+id/title"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Blood Bank" />

    <Spinner
        android:id="@+id/select_bloodgroup"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content">
    </Spinner>
    <Spinner
        android:id="@+id/select_city"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content">
    </Spinner>
    <Button
        android:id="@+id/search"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Search"/>
    <ListView
        android:id="@+id/records_list"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content">
    </ListView>
</LinearLayout>

DatabaseHelper DBHelper.java

public class DBHelper extends SQLiteOpenHelper {

    public static final String DBNAME = "bloodbank";
    public static final int DBVERSION = 1;
    public static final String TB_RECORDS = "records";
    public static final String COl_RECORDS_ID = BaseColumns._ID;
    public static final String COL_RECORDS_NAME = "_name";
    public static final String COL_RECORDS_BLOODGROUP = "_blood_group";
    public static final String COL_RECORDS_CITY = "_city";

    SQLiteDatabase mDB;

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

    }

    @Override
    public void onCreate(SQLiteDatabase db) {
        String crtrecords = "CREATE TABLE IF NOT EXISTS " +
                TB_RECORDS + "(" +
                COl_RECORDS_ID + " INTEGER PRIMARY KEY," +
                COL_RECORDS_NAME + " TEXT," +
                COL_RECORDS_CITY + " TEXT, " +
                COL_RECORDS_BLOODGROUP + " TEXT" +
                ")";
        db.execSQL(crtrecords);
    }

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

    }

    public long addRecord(String name, String city, String bloodgroup) {
        ContentValues cv = new ContentValues();
        cv.put(COL_RECORDS_NAME,name);
        cv.put(COL_RECORDS_CITY,city);
        cv.put(COL_RECORDS_BLOODGROUP,bloodgroup);
        return mDB.insert(TB_RECORDS,null,cv);
    }

    public Cursor getrecords(String city, String bloodgroup) {
        ArrayList<String> baseargs = new ArrayList<>();
        String whereclause = null;
        if (city != null && city.length() > 0) {
            whereclause = COL_RECORDS_CITY + "=?";
            baseargs.add(city);
        }
        if (bloodgroup != null && bloodgroup.length() > 0) {
            if (whereclause != null && whereclause.length() > 0) {
                whereclause = whereclause + " AND ";
            } else whereclause = "";
            whereclause = whereclause + COL_RECORDS_BLOODGROUP + "=?";
            baseargs.add(bloodgroup);
        }
        String[] whereargs = null;
        if (baseargs.size() > 0) {
            whereargs = new String[baseargs.size()];
            for (int i =0; i < baseargs.size();i++) {
                whereargs[i] = baseargs.get(i);
            }
        }
        return mDB.query(TB_RECORDS,null,whereclause,whereargs,null,null,COL_RECORDS_NAME);
    }
}

调用活动 MainActivity.java ： -

public class MainActivity extends AppCompatActivity {

    //Specific Blood groups
    public static final String[] BLOODGROUPS = new String[]{
            "A+","A-","B+","B-","0+","0-","AB+","AB-"
    };

    //Specific Cities
    public static final String[] CITIES = new String[]{
            "London","Paris","New York","Montreal","Gurgaon"
    };

    // Some names for auto generation of test data
    static final String[] peoples_names = new String[]{
            "Fred","Mary","Bert","Anne","James","Susan","Tom","Theresa",
            "Cherles","Corrine","David","Diana","Edward","Esmerelda",
            "George","Gorgina","Harrold","Heather"

    };

    TextView mTitle;
    Spinner mBloodGroups, mCities;
    Button mSearch;
    DBHelper mDBHlpr;
    ArrayAdapter<String> mCitiesAdapter, mBloodGroupsAdapater;
    ListView mRecordsList;
    SimpleCursorAdapter mSCA;
    String mCurrentCities = "", mCurrentBloodGroups = "";
    Cursor mCsr;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        mTitle = this.findViewById(R.id.title);
        mBloodGroups = this.findViewById(R.id.select_bloodgroup);
        mCities = this.findViewById(R.id.select_city);
        mSearch = this.findViewById(R.id.search);
        mRecordsList = this.findViewById(R.id.records_list);
        mCurrentCities = "";
        mCurrentBloodGroups = "";

        // Add some test data
        mDBHlpr = new DBHelper(this);
        if (DatabaseUtils.queryNumEntries(mDBHlpr.getWritableDatabase(),DBHelper.TB_RECORDS) < 1) {
            Random rnd = new Random();
            rnd.setSeed(System.currentTimeMillis());
            for (int i = 0; i < 100; i++) {
                mDBHlpr.addRecord(
                        peoples_names[rnd.nextInt(peoples_names.length)],
                        CITIES[rnd.nextInt(CITIES.length)],
                        BLOODGROUPS[rnd.nextInt(BLOODGROUPS.length)]
                );
            }
        }

        //Setup City Spinner
        mCitiesAdapter = new ArrayAdapter<>(this,android.R.layout.simple_dropdown_item_1line,CITIES);
        mCities.setAdapter(mCitiesAdapter);
        //Setup Bloodgroups Spinner
        mBloodGroupsAdapater = new ArrayAdapter<>(this,android.R.layout.simple_dropdown_item_1line,BLOODGROUPS);
        mBloodGroups.setAdapter(mBloodGroupsAdapater);
        // Add Search Buitton Click Listener
        mSearch.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                mCurrentCities = mCities.getSelectedItem().toString();
                mCurrentBloodGroups = mBloodGroups.getSelectedItem().toString();
                refreshList();
            }
        });
        // Initial List (All)
        refreshList();

    }

    //Setup or refresh the ListView
    private void refreshList() {
        // Grab the data
        mCsr = mDBHlpr.getrecords(mCurrentCities,mCurrentBloodGroups);
        // If first time then setup the Cursor Adapter
        if (mSCA == null) {
            mSCA = new SimpleCursorAdapter(this,
                    android.R.layout.simple_list_item_2,
                    mCsr,
                    new String[]{DBHelper.COL_RECORDS_NAME,DBHelper.COL_RECORDS_CITY},
                    new int[]{android.R.id.text1, android.R.id.text2},
                    0
            );
            mRecordsList.setAdapter(mSCA);
        }
        // If not first time then swap the cursor
        else {
            mSCA.swapCursor(mCsr);
        }
    }
}

结果

最初会显示以下内容（因为数据是随机生成的，但可能会有所不同，尽管会列出100个项目）： -

选择City Gurgaon之后： - （注意结果可能会因随机数据而有所不同）： -

选择血型A-： - 后（结果可能会有所不同）： -

请注意，此示例有效，目的是您从提供的代码中学习并进行研究，如果您有后续问题，那么您应该将它们作为Stack Overflow上的单独且不同的问题提出。

从微调器中获取条件，并根据条件从数据库中检索列表视图中的数据并

1 个答案:

结果