Question

我是Android应用程序开发的新手。最近，我通过自己开发GPA计算器来磨练自己的技能。目前，我有以下代码可以帮助我获得一个人的累积GPA

public class MainActivity extends AppCompatActivity implements View.OnClickListener {

SQLiteDatabase sqLiteDatabase;
DataManager sqLiteHelper;
Cursor cursor;
Button Delete, Edit;
SQLiteDatabase sqLiteDatabaseObj;
String SQLiteDataBaseQueryHolder ;

TextView semester,gpa;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);

    gpa = (TextView) findViewById(R.id.textViewGPA);
    groupgpa = (TextView) findViewById(R.id.textViewgroupGPA);
    /*semester = (TextView) findViewById(R.id.textViewSEMESTER);*/

    SQLiteDataBaseBuild();
    sqLiteHelper = new DataManager(this);

    SQLiteTableBuild();
    double groupgpa2 =semestralgpa();

    groupgpa.setText(Double.toString(groupgpa2));

    double gpa2 = totalgpa();

    gpa.setText(Double.toString(gpa2));
}

@Override
public boolean onCreateOptionsMenu(Menu menu){
    super.onCreateOptionsMenu(menu);
    MenuInflater inflater = getMenuInflater();
    inflater.inflate(R.menu.menu_main, menu);
    return true;
}

@Override
public boolean onOptionsItemSelected(MenuItem item){
    switch (item.getItemId()){
        case R.id.about:
            // Do Something
            Toast.makeText(getApplicationContext(),"About...",
                    Toast.LENGTH_SHORT).show();
            return true;
        case R.id.addsem:
            // Do Something
            startActivity(new Intent(this, ADDSEMESTERACTIVITY.class));
            return true;

        case R.id.allgrade:
            // Do Something
            startActivity(new Intent(this, DISPLAYALLGRADEACTIVITY.class));
            return true;


    }
    return false;

}
@Override
public void onClick(View view) {
/*        switch (view.getId()){
        case R.id.photoalbum:
            Intent i = new Intent(this, PhotoAlbum.class);
            startActivity(i);
            break;
    }*/
}
@Override
protected void onResume() {

    totalgpa();

    super.onResume();
}





public void OpenSQLiteDataBase(){

    sqLiteDatabaseObj = openOrCreateDatabase(DataManager.DATABASE_NAME, Context.MODE_PRIVATE, null);

}
public void SQLiteDataBaseBuild(){

    sqLiteDatabaseObj = openOrCreateDatabase(DataManager.DATABASE_NAME, Context.MODE_PRIVATE, null);

}

public void SQLiteTableBuild(){

    sqLiteDatabaseObj.execSQL("CREATE TABLE IF NOT EXISTS "+DataManager.TABLE_NAME+"("+DataManager.Table_Column_ID+" INTEGER PRIMARY KEY AUTOINCREMENT NOT NULL, "+DataManager.Table_Column_1_SUBJECT+" VARCHAR, "+DataManager.Table_Column_2_GRADE+" VARCHAR, "+DataManager.Table_Column_3_CREDIT+" INTEGER, "+DataManager.Table_Column_4_GCPRODUCT+" DECIMAL, "+DataManager.Table_Column_5_SEMESTER+" VARCHAR);");

}

public double totalgpa(){

    double gpa = 0;

    sqLiteDatabase = sqLiteHelper.getWritableDatabase();

    cursor = sqLiteDatabase.rawQuery("SELECT sum(gcproduct)/sum(credit) FROM " + DataManager.TABLE_NAME +" group by Semester", null);
    if(cursor.moveToFirst()){
        gpa = cursor.getDouble(0);
    }
    return gpa;
}


}

计算GPA的方法。

public double totalgpa(){

    double gpa = 0;

    sqLiteDatabase = sqLiteHelper.getWritableDatabase();

    cursor = sqLiteDatabase.rawQuery("SELECT sum(gcproduct)/sum(credit) FROM " + DataManager.TABLE_NAME +"", null);
    if(cursor.moveToFirst()){
        gpa = cursor.getDouble(0);
    }
    return gpa;
}

能够显示可用的总和。但是，如果我要添加更多值，则不会更新。有人能告诉我我做错了什么吗？

另外，如果我按照学期的分组运行一种方法来获得学期的gpa，我只能打印出一个学期的gpa。

有问题的方法：

public double semestralgpa(){

    double gpa = 0;

    sqLiteDatabase = sqLiteHelper.getWritableDatabase();

    cursor = sqLiteDatabase.rawQuery("SELECT sum(gcproduct)/sum(credit) FROM " + DataManager.TABLE_NAME +" group by Semester", null);
    if(cursor.moveToFirst()){
        gpa = cursor.getDouble(0);
    }
    return gpa;
}

Answer 1

您遇到的问题是在检索onResume方法中的值后需要更新视图（TextView）。

目前你有： -

@Override
protected void onResume() {
    totalgpa();
    super.onResume();
}

这只检索新值。您还应该让超级电话进行业务并恢复活动。因此，而不是上述用途： -

@Override
protected void onResume() {
    super.onResume();
    gpa.setText(Double.toString(totalgpa));
}

这将检索该值，并将其应用于一行中的TextView。

关于： -

另外，如果我要运行一种方法来获得学期的gpa 按学期分组，我只能打印出1的gpa 学期。

听起来您想要显示分组的semestralgpa的列表，您可以使用： -

public String semestralgpa(){

    StringBuilder sb = new StringBuilder();   
    sqLiteDatabase = sqLiteHelper.getWritableDatabase();    
    cursor = sqLiteDatabase.rawQuery("SELECT sum(gcproduct)/sum(credit) FROM " + DataManager.TABLE_NAME +" group by Semester", null);
    if(cursor.moveToNext()){

        // Add separator between values.
        if (cursor.getPosition() > 0) {
            sb.append(", ");
        }
        sb.append(String.valueOf(cusror.getDouble(0)));
        // or sb.append(cursor.getString(0));
        // or sb.append(Double.toString(cursor.getDouble(0)));    
    }
    return sb.toString;
}

请注意！以上未经过测试，因此可能包含一些错误。

然后，您可能会看到该列表只是gpa，而且没有指示他们所用的学期。因此，您可能想要/更喜欢： -

public String semestralgpa(){

    StringBuilder sb = new StringBuilder();   
    sqLiteDatabase = sqLiteHelper.getWritableDatabase();    
    cursor = sqLiteDatabase.rawQuery("SELECT sum(gcproduct)/sum(credit) AS Semestergpa, Semester FROM " + DataManager.TABLE_NAME +" group by Semester", null);
    if(cursor.moveToNext()){

        // Add separator between values.
        if (cursor.getPosition() > 0) {
            sb.append(", ");
        }
        sb.append(String.valueOf(cusror.getDouble(cursor.getColumnIndex("Semestergpa")));
        sb.append(" for ");
        sb.append(cursor.getString(cursor.getColumnIndex("Semester")));
        sb.append(".");    
    }
    return sb.toString;
}

备注

AS Semestergpa将结果列从sum(gcproduct)/sum(credit)重命名为Semestergpa（显示示例）
使用硬编码偏移很容易导致错误，因此显示了getColumnIndex的原因。这将根据列名称获取偏移量。如果您要使用派生的偏移量，则可以使用： -

cursor = sqLiteDatabase.rawQuery("SELECT Semester, sum(gcproduct)/sum(credit) AS Semestergpa FROM " + DataManager.TABLE_NAME +" group by Semester", null);（虽然 0 现在是学期）

SQL查询未更新

1 个答案:

备注