近日，遇到一個Dialog半透明背景消失的問題，背景需求是自定義Dialog實現警告提示框：

// 初始化警告彈出框
alertDialog = new EmpAlertView(context, Utils.getIdByName(context, "style", "alert_style"));
alertDialog.setCanceledOnTouchOutside(false);
LayoutInflater inflater = (LayoutInflater) context.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
layout = inflater.inflate(Utils.getIdByName(context, "layout", "alertview"), null);
layout.setLayoutParams(new LayoutParams(LayoutParams.MATCH_PARENT, LayoutParams.WRAP_CONTENT));
// 設定半透明背景
Window window = alertDialog.getWindow(); 
WindowManager.LayoutParams lp = window.getAttributes();
lp.alpha = 0.9f;
window.setAttributes(lp);
			
alertDialog.setContentView(layout);
 

當按下螢幕電源按鈕，再次點亮螢幕，發現Dialog半透明的灰暗背景消失了.....

解決方法：設定window.addFlags(WindowManager.LayoutParams.FLAG_SHOW_WHEN_LOCKED);修改後如下：

// 初始化警告彈出框
alertDialog = new EmpAlertView(context, Utils.getIdByName(context, "style", "alert_style"));
alertDialog.setCanceledOnTouchOutside(false);
LayoutInflater inflater = (LayoutInflater) context.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
layout = inflater.inflate(Utils.getIdByName(context, "layout", "alertview"), null);
layout.setLayoutParams(new LayoutParams(LayoutParams.MATCH_PARENT, LayoutParams.WRAP_CONTENT));
			
Window window = alertDialog.getWindow(); 
WindowManager.LayoutParams lp = window.getAttributes();
lp.alpha = 0.9f;
window.setAttributes(lp);
// 防止按下再重新開啟螢幕電源，原先變暗的背景變白色
window.addFlags(WindowManager.LayoutParams.FLAG_SHOW_WHEN_LOCKED);
			
alertDialog.setContentView(layout);