我想通过从数据库中获取数据来显示网格视图中的数据（图像和文本）。我想首先在数据库表中插入数据并尝试从数据库中获取数据并在gridview中显示它。
这是我的主要活动
public class MainActivity extends Activity {
private RelativeLayout rl;
private Tab TabOrder;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
rl = (RelativeLayout) findViewById(R.id.mainLayout);
ActionBar actionbar = getActionBar();
actionbar.setTitle("Select To Order");
actionbar.setNavigationMode(ActionBar.NAVIGATION_MODE_TABS);
TabOrder = actionbar.newTab().setText("ORDER");
Fragment FragmentOrder = new FragmentOrder();
TabOrder.setTabListener(new MyTablistenerClass(FragmentOrder));
actionbar.addTab(TabOrder);
}
@SuppressLint("ValidFragment")
public class FragmentOrder extends Fragment{
private Context context;
private int layoutResourceId;
private ArrayList<Category> data;
ArrayList<Category> imageArry = new ArrayList<Category>();
OrderAdapter adapter;
private ArrayList<Category> categories;
@SuppressLint("NewApi")
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
View view = inflater.inflate(R.layout.griddeal, null);
DatabaseManager db = new DatabaseManager(MainActivity.this);
// get image from drawable
// Bitmap image = BitmapFactory.decodeResource(getResources(),
// R.drawable.car);
//
// // convert bitmap to byte
// ByteArrayOutputStream stream = new ByteArrayOutputStream();
// image.compress(Bitmap.CompressFormat.JPEG, 100, stream);
// byte imageInByte[] = stream.toByteArray();
/**
* CRUD Operations
* */
// Inserting Contacts
Log.d("Insert: ", "Inserting ..");
Category c1 = new Category();
c1.setCategorydescription("vegetables");
Bitmap image = BitmapFactory.decodeResource(getResources(),
R.drawable.car);
// convert bitmap to byte
ByteArrayOutputStream stream = new ByteArrayOutputStream();
image.compress(Bitmap.CompressFormat.JPEG, 100, stream);
byte imageInByte[] = stream.toByteArray();
db.insertCategoriesDetail(c1);
//db.insertCategoriesDetail(new Category("Vegetables", imageInByte));
// display main List view bcard and contact name
// Reading all contacts from database
List<Category> categories = db.getCategoriesDetail();
for (Category cn : categories) {
String log = "ID:" + cn.getId() + " Name: " + cn.getCategorydescription()
+ " ,Image: " + cn.getCategoryimage();
// Writing Contacts to log
Log.d("Result: ", log);
//add contacts data in arrayList
imageArry.add(cn);
}
adapter = new OrderAdapter(MainActivity.this, R.layout.griddealitems,
imageArry);
GridView dataList = (GridView) findViewById(R.id.GridDeal);
dataList.setAdapter(adapter);
dataList.setOnItemClickListener(new OnItemClickListener() {
@Override
public void onItemClick(AdapterView<?> arg0, View arg1,
int arg2, long arg3) {
// TODO Auto-generated method stub
}
});
return view;
}
}
public class OrderAdapter extends ArrayAdapter<Category>{
Context context;
int layoutResourceId;
// BcardImage data[] = null;
ArrayList<Category> data=new ArrayList<Category>();
public OrderAdapter(Context context, int layoutResourceId, ArrayList<Category> data) {
// TODO Auto-generated constructor stub
super(context, layoutResourceId, data);
this.layoutResourceId = layoutResourceId;
this.context = context;
this.data = data;
}
@Override
public View getView(int position, View convertView, ViewGroup parent) {
View row = convertView;
ImageHolder holder = null;
if(row == null)
{
LayoutInflater inflater = ((Activity)context).getLayoutInflater();
row = inflater.inflate(layoutResourceId, parent, false);
holder = new ImageHolder();
holder.grid_deal_text = (TextView)row.findViewById(R.id.grid_deal_text);
holder.imgIcon = (ImageView)row.findViewById(R.id.grid_deal_image);
row.setTag(holder);
}
else
{
holder = (ImageHolder)row.getTag();
}
Category picture = data.get(position);
holder.grid_deal_text.setText(picture.categorydescription);
//convert byte to bitmap take from contact class
byte[] outImage=picture.categoryimage;
ByteArrayInputStream imageStream = new ByteArrayInputStream(outImage);
Bitmap theImage = BitmapFactory.decodeStream(imageStream);
holder.imgIcon.setImageBitmap(theImage);
return row;
}
public class ImageHolder
{
ImageView imgIcon;
TextView grid_deal_text;
}
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.main, menu);
return true;
}
public class MyTablistenerClass implements android.app.ActionBar.TabListener {
Fragment fragment1;
@SuppressLint("NewApi")
public MyTablistenerClass(Fragment fragment){
this.fragment1 = fragment;
}
@Override
public void onTabReselected(Tab tab, FragmentTransaction ft) {
// TODO Auto-generated method stub
}
@SuppressLint("NewApi")
@Override
public void onTabSelected(Tab tab, FragmentTransaction ft) {
// TODO Auto-generated method stub
FragmentTransaction fragMentTra;
ActionBar actionBar = getActionBar();
actionBar.show();
actionBar.setTitle("Select Category");
//actionBar.setIcon(R.id.search);
FragmentOrder Fram2 = new FragmentOrder();
//fragMentTra.addToBackStack(null);
fragMentTra = getFragmentManager().beginTransaction();
fragMentTra.add(rl.getId(), Fram2);
fragMentTra.commit();
}
@Override
public void onTabUnselected(Tab tab, FragmentTransaction ft) {
}
}
}
这是我的databaseManager类：
public class DatabaseManager {
private Context context = null;
private SQLiteDatabase database=null;
private DatabaseHelper dbHelper=null;
public DatabaseManager(Context context) {
this.context = context;
dbHelper = new DatabaseHelper(context);
}
public void open() throws SQLException {
if (dbHelper==null) {
dbHelper = new DatabaseHelper(context);
}
if (database==null) {
database = dbHelper.getWritableDatabase();
}
}
public void close() {
dbHelper.close();
database = null;
dbHelper = null;
}
public long insertCategoriesDetail(Category categorydetail){
long result = 0;
try{
if (database==null) {
open();
}
ContentValues values = new ContentValues();
values.put(DatabaseContract.RetailDatabaseEntry.COLUMN_CATEGORYDESCRIPTION, categorydetail.getCategorydescription());
values.put(DatabaseContract.RetailDatabaseEntry.COLUMN_CATEGORYIMAGE, categorydetail.getCategoryimage());
result = database.insert(DatabaseContract.RetailDatabaseEntry.TABLE_NAME_CATEGORY, null, values);
Toast.makeText(context, "Res : " + result, Toast.LENGTH_SHORT).show();
close();
}catch(Exception ex){
Toast.makeText(context, "crashed" + ex.toString(), Toast.LENGTH_SHORT).show();
}
return result;
}
public List<Category> getCategoriesDetail() {
if (database==null) {
open();
}
List<Category> categoriesdetailsList = new ArrayList<Category>();
// Select All Query
String selectQuery = "SELECT * FROM " + DatabaseContract.RetailDatabaseEntry.TABLE_NAME_CATEGORY;
Cursor cursor = database.rawQuery(selectQuery, null);
// looping through all rows and adding to list
if (cursor.moveToFirst()) {
do {
Category detailList = new Category();
detailList.setId(Integer.parseInt(cursor.getString(0)));
detailList.setCategorydescription(cursor.getString(1));
detailList.setCategoryimage(cursor.getBlob(2));
categoriesdetailsList.add(detailList);
} while (cursor.moveToNext());
}
close();
return categoriesdetailsList;
}
}
logcat的：
11-15 16:57:39.127: E/AndroidRuntime(703): FATAL EXCEPTION: main
11-15 16:57:39.127: E/AndroidRuntime(703): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.orderdatabase/com.example.orderdatabase.MainActivity}: java.lang.NullPointerException
11-15 16:57:39.127: E/AndroidRuntime(703): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1955)
无论我做什么都行不通。我得到了nullpointerexception。 请有人告诉我哪里错了。
感谢。
答案 0 :(得分：0)
您可以使用下面给出的示例来解决您的问题。
public List<UserInfo> getUerInfoDetails() {
SQLiteDatabase db;
db=getReadableDatabase();
List<UserInfo> userInfoList=new ArrayList<UserInfo>();
// Select All Query
String selectQuery = "SELECT * FROM mainToDo";
Cursor cursor =db.rawQuery(selectQuery, null);
// looping through all rows and adding to list
while(cursor.moveToNext())
{
UserInfo obj=new UserInfo();
obj.setId(cursor.getInt(0));
obj.setName(cursor.getString(1));
userInfoList.add(obj);
}
close();
return userInfoList;
}