Oracle Forms计算器退格按钮实现代码咨询

Hey there, let's get that backspace button working for your Oracle Forms calculator. I've tackled this exact scenario before, so here's a solid, easy-to-implement solution:

1. Create the Trigger #

First, open up your Forms Builder and locate your backspace button. Right-click the button, select Triggers, then create a new WHEN-BUTTON-PRESSED trigger. This is where we'll add the logic to remove the last character from your calculator's display item.

2. Core Backspace Logic #

Paste this PL/SQL code into the trigger, making sure to replace BLOCK_NAME and DISPLAY_ITEM with the actual names of your data block and the item that shows the calculator's current value:

DECLARE
    v_current_display VARCHAR2(100); -- Adjust length based on your display's max input
BEGIN
    -- Grab the current value from the display item
    v_current_display := :BLOCK_NAME.DISPLAY_ITEM;
    
    -- Only backspace if there's something to remove
    IF LENGTH(v_current_display) > 0 THEN
        -- Trim off the last character
        :BLOCK_NAME.DISPLAY_ITEM := SUBSTR(v_current_display, 1, LENGTH(v_current_display) - 1);
    END IF;
END;

3. Optional Enhancements #

Depending on your calculator's functionality, you might want to add these tweaks:

Handle Decimal Points Gracefully #

If you want to make sure deleting a decimal point works as expected (instead of just removing any last character), use this adjusted code:

DECLARE
    v_current_display VARCHAR2(100);
BEGIN
    v_current_display := :BLOCK_NAME.DISPLAY_ITEM;
    
    IF LENGTH(v_current_display) > 0 THEN
        -- If last character is a decimal, remove it
        IF SUBSTR(v_current_display, -1, 1) = '.' THEN
            :BLOCK_NAME.DISPLAY_ITEM := SUBSTR(v_current_display, 1, LENGTH(v_current_display) - 1);
        ELSE
            -- Otherwise remove the last digit/character
            :BLOCK_NAME.DISPLAY_ITEM := SUBSTR(v_current_display, 1, LENGTH(v_current_display) - 1);
        END IF;
    END IF;
END;

Avoid Leaving a Lone Minus Sign #

If your calculator supports negative numbers, add a check to clear the display instead of leaving just a - when backspacing a negative number with one digit:

DECLARE
    v_current_display VARCHAR2(100);
BEGIN
    v_current_display := :BLOCK_NAME.DISPLAY_ITEM;
    
    IF LENGTH(v_current_display) = 1 AND v_current_display = '-' THEN
        -- Clear the display if only the minus sign remains
        :BLOCK_NAME.DISPLAY_ITEM := '';
    ELSIF LENGTH(v_current_display) > 0 THEN
        :BLOCK_NAME.DISPLAY_ITEM := SUBSTR(v_current_display, 1, LENGTH(v_current_display) - 1);
    END IF;
END;

That's it! Test the button out, and it should remove the last character from your calculator's display every time you click it.

内容的提问来源于stack exchange，提问作者Ramiz Tariq