111

flutter_monisuo/lib/ui/pages/trade/trade_page.dart

@@ -107,7 +107,9 @@ class _TradePageState extends State<TradePage>
     final amount = double.tryParse(_amountController.text) ?? 0;
     final price = _selectedCoin?.price ?? 0;
     if (price <= 0 || amount <= 0) return '0';
-    return (amount / price).toStringAsFixed(6);
+    // 向下截斷到4位小數，避免回算超出金額
+    final qty = amount / price;
+    return ((qty * 10000).truncateToDouble() / 10000).toStringAsFixed(4);
   }
 
   @override
@@ -207,7 +209,10 @@ class _TradePageState extends State<TradePage>
     final max = double.tryParse(_maxAmount) ?? 0;
     final value = max * pct;
     // 向下截斷到2位小數，避免四捨五入超出可用餘額
-    _amountController.text = ((value * 100).truncateToDouble() / 100).toStringAsFixed(2);
+    // 向下截斷到2位小數，再減0.01作為安全緩衝，避免精度問題導致餘額不足
+    final truncated = ((value * 100).truncateToDouble() / 100);
+    final safe = truncated > 0.01 ? truncated - 0.01 : truncated;
+    _amountController.text = safe.toStringAsFixed(2);
     setState(() {});
   }