Service里面启动Activity和Alertdialog

Intent intent = new Intent();
intent.setFlags(Intent.FLAG_ACTIVITY_NEW_TASK); 
intent.setClass(getApplicationContext(),FileBrowserActivity.class);
startActivity(intent);

AlertDialog.Builder builder = new AlertDialog.Builder(this);
builder.setMessage("是否接受文件?")
.setPositiveButton("是", new DialogInterface.OnClickListener() {
                    @Override
                    public void onClick(DialogInterface dialog, int which) {

                    }
                }).setNegativeButton("否", new OnClickListener() {
                    @Override
                    public void onClick(DialogInterface dialog, int which) {
                    }
                });

AlertDialog ad = builder.create();
//ad.getWindow().setType(WindowManager.LayoutParams.TYPE_SYSTEM_DIALOG); //系统中关机对话框就是这个属性 
ad.getWindow().setType(WindowManager.LayoutParams.TYPE_SYSTEM_ALERT);
ad.setCanceledOnTouchOutside(false);                                   //点击外面区域不会让dialog消失
ad.show();