有没有办法从不扩展Activity类的类调用`overridePendingTransition`？

Question

我正在使用另一个类在后台运行一些东西,同时显示主要活动,并将该活动的上下文传递给此背景类.我正在从这个后台类开始另一个活动,但是我无法在overridePendingTransition这里调用,因为对于类型BackgroundClass,"方法overridePendingTransition(int,int)是未定义的."

public class GetUPC extends AsyncTask<Void, Void, Void> 
{       
    @Override
    protected void onPreExecute() 
    {
        ...
    }
    @Override
    protected Void doInBackground(Void... arg0) 
    {
        ...


                    boolean dairy;
                    if(theDairy.equals("N"))
                    {
                        //milk test
                        dairy=true;
                    }
                    else
                    {
                        dairy=false;
                    }



                    //depending on if there is a warning it will either display the warning screen or skip it
                    if(dairy)
                    {
                        Intent intent_warn = new Intent(context, WarningScreen.class);

                        intent_warn.putExtra("Name", str_name);
                        intent_warn.putExtra("Size", str_size);
                        intent_warn.putExtra("Price", str_price);
                        intent_warn.putExtra("Carbs", str_carbs);
                        intent_warn.putExtra("Protein", str_protein);
                        intent_warn.putExtra("Fiber", str_fiber);
                        intent_warn.putExtra("Sugar", str_sugar);
                        intent_warn.putExtra("SatFat", str_satFat);
                        intent_warn.putExtra("TotFat", str_totFat);
                        intent_warn.putExtra("Cholesterol", str_cholesterol);
                        intent_warn.putExtra("Sodium", str_sodium);
                        intent_warn.putExtra("Potassium", str_potassium);
                        intent_warn.putExtra("Calories", str_calories);
                        intent_warn.putExtra("Warning", "Contains Dairy");
                        intent_warn.putExtra("WarningRed", true);
                        Log.e("Warning",intent_warn.getExtras().getString("Warning"));

                        context.startActivity(intent_warn);
                        overridePendingTransition(R.layout.fade_in, R.layout.fade_out);  //THIS PART ISN'T WORKING//
                    }
                    else
                    {
                        Intent intent_menu = new Intent(context, DisplayScreen.class);
                        intent_menu.putExtra("Name", str_name);
                        intent_menu.putExtra("Size", str_size);
                        intent_menu.putExtra("Price", str_price);
                        intent_menu.putExtra("Carbs", str_carbs);
                        intent_menu.putExtra("Protein", str_protein);
                        intent_menu.putExtra("Fiber", str_fiber);
                        intent_menu.putExtra("Sugar", str_sugar);
                        intent_menu.putExtra("SatFat", str_satFat);
                        intent_menu.putExtra("TotFat", str_totFat);
                        intent_menu.putExtra("Cholesterol", str_cholesterol);
                        intent_menu.putExtra("Sodium", str_sodium);
                        intent_menu.putExtra("Potassium", str_potassium);
                        intent_menu.putExtra("Calories", str_calories);
                        intent_menu.putExtra("Warning",  "Contains no allergens");
                        intent_menu.putExtra("WarningRed", false);
                        Log.e("Warning",intent_menu.getExtras().getString("Warning"));

                        context.startActivity(intent_menu);
                    }


                    Log.e("KYLE_DATA_UPCH",str_name+" "+str_price+""+str_size);
                } 
            }
                catch (JSONException e) 
                {
                    e.printStackTrace();
                }

            } 
            else 
            {
                Log.e("ServiceHandler", "Couldn't get any data from the url");
                _errorCode=3;
            }

            return null;
        }
    @Override
    protected void onPostExecute(Void result) 
    {
        ...
    }



}

Answer 1

所以我实际上能够通过调用overridePendingTransition上下文来解决问题,并将其转换为Activity.

((Activity) context).overridePendingTransition(R.layout.fade_in, R.layout.fade_out);

我意识到这不是最好的做法,并且可能会因为更复杂的应用程序而变得混乱,但就我们的目的而言,我认为这是可以的.我想最终调查@bariscan Kayaoglu的解决方案,因为它似乎更强大.

Answer 2

只是为Tims回答添加一些安全性,在投射之前检查上下文是否是Activity的一个实例:

if (context instanceof Activity) {
  ((Activity) context).overridePendingTransition(R.layout.fade_in, R.layout.fade_out);
}

这只是确保你调用一个真正存在的方法.你也可以使用try/catch,但我认为这就足够了

Answer 3

我认为这不是一个好主意。由于您的类是异步任务，因此您选择的活动可能不是活动活动，因为您的异步任务将在后台运行。但如果您考虑内存泄漏和空指针，您可以将活动发送到构造函数。