Android 如何在service和BroadCastReceiver中 启动activity和alertdialog？

一.启动activity源码:(记得要加上Intent.FLAG_ACTIVITY_NEW_TASK)

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

二.在BroadcastReceiver当中启动alertDialog总是会报错
首先加上权限：

<uses-permission android:name="android.permission.SYSTEM_ALERT_WINDOW" /> 

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