在数据库项目中，我有一个包含三个变量的表，即'_id'，'item'表示食品名称，'type'表示食品类型。我有三种类型的食物：'Vege Soup'，'Non Vege Soup'和'Chai'。
在我的MainActivity Class中，我有一个组中的三个单选按钮，用于选择项目的“类型”，然后是“查看”按钮，以获取通过单选按钮选择的类型中所有项目的ListView。 / p>
我使用SimpleCursorAdapter，它用于将游标中的列映射到XML文件中定义的TextViews或ImageViews。
预期的结果是ListView包含行信息。当前结果是一个空白的ListView。我无法理解为什么。
MainActivity类：
public class MainActivity extends Activity implements OnClickListener,
OnCheckedChangeListener {
Button dinnerAdd, dinnerView;
RadioGroup dishType;
RadioButton vegeSoupView, nonVegeSoupView, chaiView;
Intent i, v;
String type;
DBAdapter myDb;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
initialize();
}
private void initialize() {
dinnerView = (Button) findViewById(R.id.bView);
dishType = (RadioGroup) findViewById(R.id.rgDishType);
vegeSoupView = (RadioButton) findViewById(R.id.rDtVegeSoup);
nonVegeSoupView = (RadioButton) findViewById(R.id.rDtNonVegeSoup);
chaiView = (RadioButton) findViewById(R.id.rDtChai);
dinnerAdd.setOnClickListener(this);
dinnerView.setOnClickListener(this);
dishType.setOnCheckedChangeListener(this);
}
@Override
public void onClick(View view) {
// TODO Auto-generated method stub
switch (view.getId()) {
case R.id.bAddDish:
i = new Intent("com.example.databaselist.ADDITEM");
startActivity(i);
break;
case R.id.bView:
didItWork = true;
if (vegeSoupView.isChecked()) {
type = "Vege Soup";
} else {
if (nonVegeSoupView.isChecked()) {
type = "Non Vege Soup";
} else {
if (chaiView.isChecked()) {
type = "Chai";
}
}
}
makeIntent();
startActivity(v);
break;
}
}
public void makeIntent(){
Bundle basket = new Bundle();
basket.putString("type", type);
v = new Intent(MainActivity.this, ItemListView.class);
v.putExtras(basket);
}
}
activity_main.xml中：
<RelativeLayout xmlns:tools="http://schemas.android.com/tools"
xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:paddingBottom="@dimen/activity_vertical_margin"
android:paddingLeft="@dimen/activity_horizontal_margin"
android:paddingRight="@dimen/activity_horizontal_margin"
android:paddingTop="@dimen/activity_vertical_margin"
tools:context=".MainActivity" >
<RadioGroup
android:id="@+id/rgDishType"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_centerHorizontal="true"
android:layout_marginTop="40dp"
android:layout_below="@id/bRandomise">
<RadioButton
android:id="@+id/rDtVegeSoup"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:checked="true"
android:text="Vege Soup" />
<RadioButton
android:id="@+id/rDtNonVegeSoup"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="Non Vege Soup"
android:textSize="15dp"/>
<RadioButton
android:id="@+id/rDtChai"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="Chai" />
</RadioGroup>
<Button
android:id="@+id/bView"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_below="@id/rgDishType"
android:layout_centerHorizontal="true"
android:text="View" />
<Button
android:id="@+id/bAddDish"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_below="@id/bView"
android:layout_centerHorizontal="true"
android:layout_marginTop="40dp"
android:text="Add Dish" />
</RelativeLayout>
按下“查看”按钮会创建打开列表视图活动的意图。
ItemListView类：
public class ItemListView extends Activity {
DBAdapter myDb;
MainActivity mA;
Intent a;
@Override
protected void onCreate(Bundle savedInstanceState) {
// TODO Auto-generated method stub
super.onCreate(savedInstanceState);
setContentView(R.layout.item_list_view);
Bundle gotBasket = getIntent().getExtras();
String from = gotBasket.getString("type");
openDB();
ListViewTypeFromDB_MainActivity(from);
}
private void openDB() {
myDb = new DBAdapter(this);
myDb.open();
}
private void closeDB() {
myDb.close();
}
@Override
protected void onDestroy() {
super.onDestroy();
closeDB();
}
private void ListViewTypeFromDB_MainActivity(String fromguy) {
Cursor cursor = myDb.getRows(fromguy);
startManagingCursor(cursor);
String[] fromFieldNames = new String[] { DBAdapter.KEY_ITEM };
int[] toViewIDs = new int[] { R.id.item_name };
SimpleCursorAdapter myCursorAdapter = new SimpleCursorAdapter(this,
R.layout.item_layout,
cursor,
fromFieldNames,
toViewIDs
);
ListView myList = (ListView) findViewById(R.id.listViewFromDB);
myList.setAdapter(myCursorAdapter);
}
}
item_list_view.xml：
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical" >
<ListView
android:id="@+id/listViewFromDB"
android:layout_width="match_parent"
android:layout_height="wrap_content" >
</ListView>
</LinearLayout>
这是listview每行的布局。
item_layout.xml：
<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent" >
<TextView
android:id="@+id/item_name"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_alignParentLeft="true"
android:layout_alignParentTop="true"
android:text="NAME!"
android:textAppearance="?android:attr/textAppearanceLarge" />
</RelativeLayout>
因此，正如您在ItemListView类中看到的那样，我使用了SimpleCursorAdapter。虽然它设法进入item_list_view活动，但它完全是空白的。这是我的DatabaseAdapter。
DBAdapter类：
private static final String TAG = "DBAdapter";
public static final String KEY_ROWID = "_id";
public static final int COL_ROWID = 0;
// TODO: Setup your fields here:
public static final String KEY_ITEM = "item";
public static final String KEY_TYPE = "type";
// TODO: Setup your field numbers here (0 = KEY_ROWID, 1=...)
public static final int COL_ITEM = 1;
public static final int COL_TYPE= 2;
public static final String[] ALL_KEYS = new String[] {KEY_ROWID, KEY_ITEM,
KEY_TYPE};
public static final String[] KEY_ITEM_ONLY = new String[] {KEY_ITEM};
public static final String DATABASE_NAME = "MyDb";
public static final String DATABASE_TABLE = "mainTable";
public static final int DATABASE_VERSION = 3;
private static final String DATABASE_CREATE_SQL =
"create table " + DATABASE_TABLE
+ " (" + KEY_ROWID + " integer primary key autoincrement, "
+ KEY_ITEM + " string not null unique, "
+ KEY_TYPE + " string not null"
+ ");";
private final Context context;
private DatabaseHelper myDBHelper;
private SQLiteDatabase db;
/////////////////////////////////////////////////////////////////////
// Public methods:
/////////////////////////////////////////////////////////////////////
public DBAdapter(Context ctx) {
this.context = ctx;
myDBHelper = new DatabaseHelper(context);
}
public DBAdapter open() {
db = myDBHelper.getWritableDatabase();
return this;
}
public void close() {
myDBHelper.close();
}
public long insertRow(String item, String type) {
ContentValues initialValues = new ContentValues();
initialValues.put(KEY_ITEM, item);
initialValues.put(KEY_TYPE, type);
// Insert it into the database.
return db.insert(DATABASE_TABLE, null, initialValues);
}
public Cursor getRows(String type){
String where = KEY_TYPE + "='" + type + "'";
Cursor c = db.query(true, DATABASE_TABLE, ALL_KEYS,
where, null, null, null, null, null);
if (c != null) {
c.moveToFirst();
}
return c;
}
/////////////////////////////////////////////////////////////////////
// Private Helper Classes:
/////////////////////////////////////////////////////////////////////
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_SQL);
}
@Override
public void onUpgrade(SQLiteDatabase _db, int oldVersion, int newVersion) {
Log.w(TAG, "Upgrading application's database from version " +
oldVersion + " to " + newVersion + ", which will destroy all old
data!");
// Destroy old database:
_db.execSQL("DROP TABLE IF EXISTS " + DATABASE_TABLE);
// Recreate new database:
onCreate(_db);
}
}
}
那么，SimpleCursorAdapter是否有问题，或者它是DBAdapter类中的问题？