Flutter error : “A value of type ‘Null… 继续阅读 Flutter error : “A value of type ‘Null’ can’t be assigned to a variable of type ‘Product’.”(颤振错误:“无法将“Null”类型的值分配给“Product”类型的变量。”)-flutter

The method ‘cancel’ can’t be unc… 继续阅读 The method ‘cancel’ can’t be unconditionally invoked because the receiver can be ‘null'(无法无条件调用方法“cancel”,因为接收方可以为“null”)-flutter