mBuilder = new AlertDialog.Builder(context);
mBuilder.setView(layoutView);
dialog = mBuilder.create();
dialog.show();
Window dialogWindow = dialog.getWindow();
dialogWindow.setBackgroundDrawableResource(android.R.color.transparent);
dialogWindow.setGravity(Gravity.BOTTOM);
WindowManager.LayoutParams lp = dialogWindow.getAttributes();
lp.width = WindowManager.LayoutParams.MATCH_PARENT;
lp.height = WindowManager.LayoutParams.WRAP_CONTENT;
lp.y = 0;
dialogWindow.setAttributes(lp);
设置dialog为屏幕宽度必须在show之后设置
