为何信号始终为FASLE

Params Numeric FastLength(12); Numeric SlowLength(26); Numeric MACDLength(9);Vars Numeric MACDDiff; Numeric AvgMACD; Numeric MACDValue; Series<Bool> upcross(False); Events OnBar(ArrayRef<Integer> indexs) { MACDDiff = XAverage( Close, FastLength ) - XAverage( Close, SlowLength ) ; AvgMACD = XAverage(MACDDiff,MACDLength); if (CrossOver(MACDDiff,AvgMACD)) { upcross=True; }Else { upcross=upcross[1]; } if (CrossUnder(MACDDiff,AvgMACD)) { upcross=false; }Else { upcross=upcross[1]; }　 Commentary(\"upcross = \" + IIFString(upcross,\"True\",\"False\")); }//为何向上突破成功，但信号始终为false?