Android/SQLite:保存/检索 REAL 类型的数据 [英] Android/SQLite : Saving/Retrieving data of type REAL

问题描述

我有一个带有 REAL 字段表的 SQLDB.在我的布局中，我将其字段大小设置为仅允许 8+2 位.在我的对象中，我将该字段的数据类型用作float".

I have a SQLDB with table of field REAL. In my layout I have set its field size to allow only 8+2 digits. In my object I have used the data-type of the field as "float".

qs[0] = "CREATE TABLE " + RELATION_TABLE_NAME + "(id TEXT PRIMARY KEY, name TEXT NOT NULL, startBal REAL NOT NULL, currentBal REAL NOT NULL);";

<EditText android:text="" android:id="@+id/relCurrBalTxt" style="@style/EditTextStyle"
 android:inputType="numberDecimal" android:maxLength="11" android:hint="12345678.99" />

我在 editText 中输入了值87654321.99"并点击了保存.它填充对象

I entered value "87654321.99" in my editText and clicked save. It populates the object

// Send the data to object 
rowData.setValue(2, Float.parseFloat(sbalTxt.getText().toString()));
// In object, this is how I save it
this.setCurrentBalance( ((Float)value).floatValue() );  // value is Object type

// Saving data in ContenteValues to save to DB
// LOG Rcvd from Object while Saving CurrBal: 8.765432E7
values.put("currentBal", new Float(rowData.getValue(3).toString()));

保存时，它直接显示更新数据的表格.在表格中显示时，我使用 DecimalFormat 来确保它以正确的方式显示:

On saving, it directly show the table with the updated data. While showing it in table I use DecimalFormat to make sure it is shown in proper manner :

    field_type = r.getFieldType(field);
// Get Data
str = r.getValue(field).toString();

// Format accordingly
if(field_type.equals(DBRow.DOUBLE_TYPE) || field_type.equals(DBRow.FLOAT_TYPE)) {
        double douValue = Double.parseDouble(str);
            //NumberFormat nf = NumberFormat.getNumberInstance(Locale.ITALY);
            //DecimalFormat df = (DecimalFormat) nf;
            DecimalFormat df = new DecimalFormat();
            df.applyPattern("##,###,###.##");
            df.setGroupingUsed(true);
            str = df.format(douValue);
        //  Log.v("DF", "While Showing in Table : double = " + douValue + " String = " + str);
        } 

((TextView) tr.getChildAt(field)).setText(str);

这里显示了值:8.765432E7

HERE it showed me the value : 8.765432E7

当我再次选择该行以查看 EditText 中的值时，我看到:87654320.00

When I again selected that row to see the values in EditText I see : 87654320.00

值如何变化?在其他情况下，我也将数据保存为50009876.99"，但不知何故，它没有保存 .99，而是将其保存为 .00，即 50009876.00.

How is the value changed ? In other instance also I saved the data as "50009876.99", but somehow it doesn't save .99 and makes that as .00 i.e 50009876.00.

为什么事情不能正常工作?我哪里错了?

Why things are not working correctly ? Where am I going wrong ?

非常感谢任何帮助.

*用于在表中显示的 DecimalFromat 代码 *

        // Format accordingly
    if(field_type.equals(DBRow.DOUBLE_TYPE) || field_type.equals(DBRow.FLOAT_TYPE)) {
        /*
                      WAS USING THIS CODE TILL NOW
    DecimalFormatSymbols dfs = new DecimalFormatSymbols();  
    String decep = String.valueOf(dfs.getDecimalSeparator());
    int index = str.indexOf(decSep); 
    if (index > 0) {
       // If digits after decimal are more than 2
       if (str.substring(index+1).length() > 2) {
        str = str.substring(0, index+3);
    }
    }
    DecimalFormat df = new DecimalFormat();
            df.setGroupingUsed(true);
            str = df.format(Double.parseDouble(str));

            if (addRow)
        create_addTextView(tr, str, true); 
    else 
        ((TextView) tr.getChildAt(field)).setText(str);

            */

                 // DECIMALFORMAT CODE
            double douValue = Double.parseDouble(str);
            DecimalFormat df = new DecimalFormat();
            df.applyPattern("##,###,###.##");
            df.setGroupingUsed(true);
            str = df.format(douValue);

            if (addRow)
       create_addTextView(tr, str, true); 
    else 
      ((TextView) tr.getChildAt(field)).setText(str);

}

推荐答案

我认为您的问题是您将数字存储为 Float.Float 没有很好的精度 - 它实际上只有 23 位二进制精度，如 这里.这意味着您无法在 float 中准确存储小数点前的 7 位，甚至更糟 - 小数点前的 7 位和小数点后的几位.这意味着你错误地选择了 balance 变量的类型——你不能存储在 Float 8+2 中.我建议您将类型更改为 Double，它的精度范围要大得多.

I think your problem is that you store the numbers as Float. Float does not have very good precision - it actually has only 23 binary digits of precision as seen here. This means that you can not store accurately in float 7 digits before the decimal point or even worse - 7 digits before the point and a couple after. This means that you have incorrectly chosen the type of the balance variable - you can not store in Float 8+2. I would recommend you to change the type to Double, which has significantly larger range of precision.

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