让Android后台运行，不用service

今天因项目需求，让Android后台运行，在网上查找了哈资料，找到了一种比较简单的方式，不用service，模拟home键，该代码只能在启动程序中使用，其他activity会报空异常。贴上代码

//后台运行
    private void mainservice(){
    	PackageManager pm = getPackageManager();  
	 	ResolveInfo homeInfo = pm.resolveActivity(new Intent(Intent.ACTION_MAIN)  .addCategory(Intent.CATEGORY_HOME), 0);
        ActivityInfo ai = homeInfo.activityInfo;  
        Intent startIntent = new Intent(Intent.ACTION_MAIN);  
        startIntent.addCategory(Intent.CATEGORY_LAUNCHER);  
        startIntent.setComponent(new ComponentName(ai.packageName,  
                ai.name));  
        startActivitySafely(startIntent);
    }
  //后台运行
  	 private void startActivitySafely(Intent intent){
  		 intent.addFlags(Intent.FLAG_ACTIVITY_NEW_TASK);
  		 try{
  			 startActivity(intent);
  		 }catch (ActivityNotFoundException e) {  
  		        Toast.makeText(this, "未发现该activity",  
  		                Toast.LENGTH_SHORT).show();  
  		 } catch (SecurityException e) {  
  			 Toast.makeText(this, "SecurityException",  
  		                Toast.LENGTH_SHORT).show(); 
  		 }
  	 }