如何从搜索中获取布尔结果 - SQLite 数据库 [重复]

Question

美好的一天，我总是使用getString() 和getInt() 来获得结果。我正在做一个简单的搜索，如果找到它，我想得到一个布尔结果。

这是我的示例代码：ForgotPassword.java

 @Override
public void onClick(View v) {

    String strUserForget = edtForgotPassword.getText().toString().trim();

    switch (v.getId()){
        case R.id.buttonSubmit:

            if (strUserForget.matches("")){
                Toast.makeText(ForgotPasswordActivity.this, "Please Provide Complete Info", Toast.LENGTH_LONG).show();
            }else {
                //String forgetPassProject = "";
                Cursor cursor = (registerDatabase.getSingleRecordForgetPass(strUserForget));
                boolean value = (cursor.getInt(registerDatabase.ID) == 1);

                Toast.makeText(ForgotPasswordActivity.this, "Your password is: " , Toast.LENGTH_LONG).show();
            }
            break;

        case R.id.buttonGoBackWelcome:
            startActivity( new Intent(getApplicationContext(),WelcomeActivity.class));
            finish();
            break;
    }

}

对于 registerSQLDatabase.java

public Cursor getSingleRecordForgetPass(String username){

    String querySingleRecord = "SELECT * FROM " + DB_TABLE + "WHERE = " +FULL_NAME+ "LIKE" +username ;
    return  sqLiteDatabase.rawQuery(querySingleRecord,null);
}

布尔值 = (cursor.getInt(registerDatabase.ID) > 0);不兼容。

Answer 1

boolean value = (cursor.getInt(registerDatabase.ID) == 1); 抛出 NPE 因为它没有结果，为避免此异常，请使用 Objects.equals 并检查 Cursor 的结果数：

if (!Objects.equals(cursor, null) && cursor.getCount() > 0) {
    // has results
} else {
    // has NO results
}

Java 1.7 之前的版本：

if (cursor != null && cursor.getCount() > 0) {
    // has results
} else {
    // has NO results
}

---

作为一个附带问题，正如Rohit5k2 指出的那样，您的查询中有一个不必要的=：

String querySingleRecord = 
    "SELECT * FROM " + DB_TABLE + " WHERE " + FULL_NAME + " LIKE " + username ;

---

如果您不需要Cursor 信息，只需创建一个返回布尔值的方法：

public boolean existsUser(String username)
{
    String querySingleRecord = "SELECT * FROM " + DB_TABLE + "WHERE " +FULL_NAME+ "LIKE" +username ;
    Cursor cursor = sqLiteDatabase.rawQuery(querySingleRecord,null);

    // now you have the results, DON'T return them, just check if contains
    // > Java 7: if (!Objects.equals(cursor, null) && cursor.getCount() > 0) {
    if (cursor != null && cursor.getCount() > 0) {
        return true;
    }

    return false;
}

并以这种方式使用它：

if (strUserForget.matches("")){
    Toast.makeText(ForgotPasswordActivity.this, "Username cannot be empty.", Toast.LENGTH_LONG).show();
} else if (registerDatabase.existsUser(strUserForget)) {
    Toast.makeText(ForgotPasswordActivity.this, "Your password is: " , Toast.LENGTH_LONG).show();
} else {
    Toast.makeText(ForgotPasswordActivity.this, "User does not exists" , Toast.LENGTH_LONG).show();
}