所以我一直在尝试使用预先存在的数据在Android Studio中创建一个sqlite数据库。我也试图向用户显示这些数据，虽然每次启动应用程序时它都会在我搜索数据库中的项目时崩溃，所以我不确定我是否正确创建了数据库。任何事都有帮助，非常感谢。
这是我的数据库助手
public class MyDBHandler {
myDbHelper myhelper;
public MyDBHandler(Context context)
{
myhelper = new myDbHelper(context);
}
public void addBear(Bears bear)
{
SQLiteDatabase dbb = myhelper.getWritableDatabase();
ContentValues values = new ContentValues();
values.put(myhelper.COLUMN_ID, bear.getID());
values.put(myhelper.COLUMN_BEARNAME, bear.getbearname());
values.put(myhelper.COLUMN_STUFFING, bear.getstuffing());
values.put(myhelper.COLUMN_BEARHEALTH, bear.getbearhealth());
values.put(myhelper.COLUMN_HEALTHCOST, bear.gethpcost());
values.put(myhelper.COLUMN_HEALTHCOUNT, bear.gethpcount());
values.put(myhelper.COLUMN_BEARATTACK, bear.getbearattack());
dbb.insert(myDbHelper.TABLE_BEARS, null , values);
}
public Bears findBear(int bearID)
{
SQLiteDatabase db = myhelper.getWritableDatabase();
Bears bear = new Bears();
String[] columns =
{myDbHelper.COLUMN_ID,myDbHelper.COLUMN_BEARNAME,myDbHelper.COLUMN_STUFFING,
myDbHelper.COLUMN_BEARHEALTH,myDbHelper.COLUMN_HEALTHCOST,
myDbHelper.COLUMN_HEALTHCOUNT, myDbHelper.COLUMN_BEARATTACK,};
String query = myDbHelper.COLUMN_ID + " = ?";
String[] selections = {String.valueOf(bearID)};
Cursor cursor =
db.query(myDbHelper.TABLE_BEARS,columns,query,
selections,null,null,null,null);
if(null != cursor) {
bear.setID(Integer.parseInt(cursor.getString(0)));
bear.setbearname(cursor.getString(1));
bear.setstuffing(Integer.parseInt(cursor.getString(2)));
bear.setbearhealth(Integer.parseInt(cursor.getString(3)));
bear.sethpcost(Integer.parseInt(cursor.getString(4)));
bear.sethpcount(Integer.parseInt(cursor.getString(5)));
bear.setbearattack(Integer.parseInt(cursor.getString(6)));
}
db.close();
return bear;
}
static class myDbHelper extends SQLiteOpenHelper
{
private static final String DATABASE_NAME = "bearDB.db"; // Database
private static final String TABLE_BEARS = "bears"; // Table Name
private static final int DATABASE_Version = 1; // Database Version
private static final String COLUMN_ID="_id"; // Column I (Primary Key)
public static final String COLUMN_BEARNAME = "bearname";
public static final String COLUMN_STUFFING = "stuffing";
public static final String COLUMN_BEARHEALTH = "bearhealth";
public static final String COLUMN_HEALTHCOST = "healthcost";
public static final String COLUMN_HEALTHCOUNT = "healthcount";
public static final String COLUMN_BEARATTACK = "bearattack"; // Column III
String CREATE_BEARS_TABLE = "CREATE TABLE " +
TABLE_BEARS + "("
+ COLUMN_ID + " INTEGER PRIMARY KEY," +
COLUMN_BEARNAME + " TEXT," +
COLUMN_STUFFING + " INTEGER," +
COLUMN_BEARHEALTH + " INTEGER," +
COLUMN_HEALTHCOST + " INTEGER, " +
COLUMN_HEALTHCOUNT + " INTEGER, "+
COLUMN_BEARATTACK + " INTEGER" +
")";
private static final String DROP_TABLE ="DROP TABLE IF EXISTS "+TABLE_BEARS;
private Context context;
public myDbHelper(Context context) {
super(context, DATABASE_NAME, null, DATABASE_Version);
this.context=context;
}
public void onCreate(SQLiteDatabase db) {
try {
db.execSQL(CREATE_BEARS_TABLE);
ContentValues beary = new ContentValues();
beary.put(COLUMN_ID, 1 );
beary.put(COLUMN_BEARNAME, "Beary");
beary.put(COLUMN_STUFFING, 5);
beary.put(COLUMN_BEARHEALTH, 10);
beary.put(COLUMN_HEALTHCOST, 1);
beary.put(COLUMN_HEALTHCOUNT, 0);
beary.put(COLUMN_BEARATTACK,4);
db.insert(TABLE_BEARS, null, beary);
ContentValues honey = new ContentValues();
honey.put(COLUMN_ID, 2 );
honey.put(COLUMN_BEARNAME, "Honey");
honey.put(COLUMN_STUFFING, 5);
honey.put(COLUMN_BEARHEALTH, 8);
honey.put(COLUMN_HEALTHCOST, 1);
honey.put(COLUMN_HEALTHCOUNT, 0);
honey.put(COLUMN_BEARATTACK, 3);
db.insert(TABLE_BEARS, null, honey);
ContentValues baobao = new ContentValues();
baobao.put(COLUMN_ID, 3 );
baobao.put(COLUMN_BEARNAME, "BaoBao");
baobao.put(COLUMN_STUFFING, 5);
baobao.put(COLUMN_BEARHEALTH,11);
baobao.put(COLUMN_HEALTHCOST, 1);
baobao.put(COLUMN_HEALTHCOUNT, 0);
baobao.put(COLUMN_BEARATTACK, 3);
db.insert(TABLE_BEARS, null, baobao);
} catch (Exception e) {
// do nothing
}
}
@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
try {
db.execSQL(DROP_TABLE);
onCreate(db);
}catch (Exception e) {
// do nothing
}
}
}
这是我的活动页面，
public class BearSelectActivity extends AppCompatActivity {
TextView idBear, healthBear, hpcost, attackBear, abilityBear, stuffingBear;
public int hpcount;
EditText nameBear;
public int beartype = 1;
public String Fighter = "Fighter";
public String Healer = "Healer";
public String Tank = "Tank";
MyDBHandler helper;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_bear_select);
helper = new MyDBHandler(this);
Button changeBear = (Button)findViewById(R.id.bearChange);
idBear = (TextView) findViewById(R.id.bearID);
nameBear = (EditText) findViewById(R.id.bearName);
stuffingBear = (TextView) findViewById(R.id.bearStuffing);
healthBear = (TextView) findViewById(R.id.bearHealth);
hpcost = (TextView)findViewById(R.id.HPCOST);
Button plushp = (Button)findViewById(R.id.plusbearhp);
Button minushp = (Button)findViewById(R.id.minusbearhp);
attackBear = (TextView) findViewById(R.id.bearAttack);
abilityBear = (TextView) findViewById(R.id.bearAbility);
abilityBear.setText(Fighter);
Bears bear = helper.findBear(beartype);
idBear.setText(String.valueOf(bear.getID()));
nameBear.setText(String.valueOf(bear.getbearname()));
healthBear.setText(String.valueOf(bear.getbearhealth()));
attackBear.setText(String.valueOf(bear.getbearattack()));
stuffingBear.setText(String.valueOf(bear.getstuffing()));
}
public void changeBearClick (View view){
//MyDBHandler dbHandler = new MyDBHandler(this, null, null, 1);
ImageView image = (ImageView) findViewById(R.id.bearimage);
//Bears bear;
beartype++;
beartype = bearmod(beartype, 3);
if(beartype == 2) {
image.setImageResource(R.drawable.bear2);
abilityBear.setText(Healer);
}
else if(beartype == 3){
image.setImageResource(R.drawable.bear3);
abilityBear.setText(Tank);
}
else if(beartype == 1){
image.setImageResource(R.drawable.bear1);
abilityBear.setText(Fighter);
}
lookupBear(view);
}
public int bearmod(int a, int b){
if (a < b && a > 0){
return a;
}
else if(a == b){
return a;
}
else if(a == 0 || a > b){
a = 1;
}
return a;
}
public void lookupBear (View view) {
Bears bear = helper.findBear(beartype);
if(bear == null) {
if (beartype == 1) {
bear = new Bears(1, "Beary", 5, 10, 1, 0, 4);
helper.addBear(bear);
} else if (beartype == 2) {
bear = new Bears(2, "Honey", 5, 8, 1, 0, 3);
helper.addBear(bear);
} else if (beartype == 3) {
bear = new Bears(3, "Baobao", 5, 11, 1, 0, 2);
helper.addBear(bear);
}
}
if(bear != null) {
idBear.setText(String.valueOf(bear.getID()));
nameBear.setText(String.valueOf(bear.getbearname()));
stuffingBear.setText(String.valueOf(bear.getstuffing()));
healthBear.setText(String.valueOf(bear.getbearhealth()));
hpcost.setText(String.valueOf(bear.gethpcost()));
hpcount = bear.gethpcount();
attackBear.setText(String.valueOf(bear.getbearattack()));
}
}
}
答案 0 :(得分：0)
我发现了很多问题。
定义列的以下行有一个额外的尾随逗号，所以： -
function req1() {
fetch('https://jsonplaceholder.typicode.com/posts/1')
.then(function (res) {return res.json()})
.then(function (json) {
var title = json.title;
var body = json.body;
var body = Math.ceil(str.length / 2);
var s1 = str.slice(0, body);
var s2 = str.slice(body);
document.getElementById("newsTitle").innerHTML = title;
document.getElementById("newsContent").innerHTML = s1;
document.getElementById("newsContent2").innerHTML = s2;
});
}
req1();
应该是： -
String[] columns =
{myDbHelper.COLUMN_ID,myDbHelper.COLUMN_BEARNAME,myDbHelper.COLUMN_STUFFING,
myDbHelper.COLUMN_BEARHEALTH,myDbHelper.COLUMN_HEALTHCOST,
myDbHelper.COLUMN_HEALTHCOUNT, myDbHelper.COLUMN_BEARATTACK,};
返回Cursor时，它位于第一行（-1）之前。要从光标访问数据，您需要移动到光标内的一行。你不是这样做的。
此外，返回的Cursor不会为null。因此，检查null Cursor是没用的。
此外，使用硬编码偏移可能存在问题且不灵活。 Cursor有一个String[] columns =
{myDbHelper.COLUMN_ID,myDbHelper.COLUMN_BEARNAME,myDbHelper.COLUMN_STUFFING,
myDbHelper.COLUMN_BEARHEALTH,myDbHelper.COLUMN_HEALTHCOST,
myDbHelper.COLUMN_HEALTHCOUNT, myDbHelper.COLUMN_BEARATTACK};
方法，它将根据列名返回偏移量。
光标还有getColumnIndex以外的方法，可以直接提取其他类型的数据，例如getInt，getLong，getBlob ...... Cursor
我建议改变： -
getString： -
if(null != cursor) {
bear.setID(Integer.parseInt(cursor.getString(0)));
bear.setbearname(cursor.getString(1));
bear.setstuffing(Integer.parseInt(cursor.getString(2)));
bear.setbearhealth(Integer.parseInt(cursor.getString(3)));
bear.sethpcost(Integer.parseInt(cursor.getString(4)));
bear.sethpcount(Integer.parseInt(cursor.getString(5)));
bear.setbearattack(Integer.parseInt(cursor.getString(6)));
}
db.close();
return bear;
所以我不确定我是否正确创建数据库。
您可以添加的类here at :- Are there any methods that assist with resolving common SQLite issues? 包含一些可以帮助您了解数据库包含内容的方法。
您所要做的就是通过复制和粘贴代码（从第二个答案）添加该类，然后在 if(cursor.moveToFirst) {
bear.setID(cursor.getInt(cursor.getColumnIndex(myDbHelper.COLUMN_ID)));
bear.setbearname(cursor.getString(cursor.getColumnIndex(myDbHelper.COLUMN_BEARNAME)));
bear.setstuffing(cursor.getInt(cursor.getColumnIndex(myDbHelper.COLUMN_STUFFING)));
bear.setbearhealth(cursor.getInt(cursor.getColumnIndex(myhelper.COLUMN_BEARHEALTH)));
bear.sethpcost(cursor.getInt(cursor.getColumnIndex(myDbHelper.COLUMN_HEALTHCOST)));
bear.sethpcount(cursor.getInt(cursor.getColumnIndex(myhelper.COLUMN_HEALTHCOUNT))));
bear.setbearattack(cursor.getInt(cursor.getColumnIndex(myDbHelper.COLUMN_BEARATTACK))));
}
cursor.close(); //<<< ADDED SHOULD ALWAYS CLOSE CURSORS WHEN DONE WITH THEM
db.close();
return bear;
行之后添加以下内容： -
helper = new MyDBHandler(this);运行应用程序时，请检查日志，它将在日志中显示DatabaseInformation。