switch不能与AsyncTask一起使用

Question

似乎displayView变量与void不兼容，我尝试将导航对话框添加到导航抽屉中，每次选中一个元素

public class AsyncClass extends AsyncTask<Void, String, Void> {
	    private Context context;
	    ProgressDialog dialog = new ProgressDialog(context);

	    public AsyncClass(Context cxt) {
	        context = cxt;
	    }
	    @Override
	    protected void onPreExecute() {
	        dialog.setTitle("Please wait");
	        dialog.show();
	    }
	    @Override
	    protected Void doInBackground(Void... unused) {
	    	
	    	public void displayView(int position) { /*the message here is :void is an invalid type for the variable displayView*/

	    		
	    		
	    		Fragment fragment = null;
	    		switch (position) { 
	    		
	    		case 1:
	    			fragment = new  HomeFragment();
	    			break;
	    		case 2:
	    			fragment = new  CalendarioFragment();
	    			break;
	    		case 5:
	    			fragment = new  ContactoFragment();
	    			break;
	    		case 6:
	    			fragment = new  OnclickFragment();
	    			break;
	    		default:
	    			break;
	    		}

	    		if (fragment != null) {
	    			try{
	    			FragmentManager fragmentManager = getFragmentManager();
	    			fragmentManager.beginTransaction().replace(R.id.frame_container, fragment).commit();

	    			// update selected item and tit|le, then close the drawer
	    			mDrawerList.setItemChecked(position, true);
	    			mDrawerList.setSelection(position);
	    			setTitle(navMenuTitles[position]);
	    			mDrawerLayout.closeDrawer(mDrawerList);
	    			}
	    			catch(Exception E)
	    			{
	    				Log.e("MainActivity", "Error in creating fragment");
	    			}
	    		} 
	    		else {
	    			// error in creating fragment
	    			Log.e("MainActivity", "Error in creating fragment");
	    		}
	    	}
	    	SystemClock.sleep(2000);
	        return (null);
	    }

	    @Override
	    protected void onPostExecute(Void unused) {
	        dialog.dismiss();
	    }
	}

它说“void是变量displayView的无效类型”

Answer 1

首先，Java不支持您在doInBackground()中执行的嵌套方法。这是给定错误的原因。详细检查here。

另一件事是，doInBackground()将在后台线程上运行，因此不要从那里更新UI。 AsyncTask仅用于长时间运行的操作。您可以考虑将doInBackground()代码移至相关的Activity或Fragment。