java - 如何从父类(super class)到子类重用代码 Intent Intent=new Intent(context,Activity.class) ？

Question

鉴于子类具有不同的上下文以及在单击监听器后启动的不同 Activity ，父类(super class)中的代码 Intent Intent=new Intent(context,Activity.class) 如何可由其子类重用叫。是否可以？

这是父类(super class):

public class CommonPost extends AppCompatActivity {

    public void on_create(final Context context, final Class aclass) {
        post.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                CommonPost commonPost = new CommonPost();
                MyTask task = commonPost.new MyTask(context, aclass);
                if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.HONEYCOMB)
                    task.executeOnExecutor(AsyncTask.THREAD_POOL_EXECUTOR);
                else
                    task.execute();
            }
        });
    }


class MyTask extends AsyncTask<Void,Void,Void> {
          Context context;
          Class aclass;

        public MyTask(Context context,Class aclass){
             this.context=context;
             this.aclass=aclass;
        }

        @Override
        protected void onPreExecute() {
            // do something
        }

        @Override
        protected Void doInBackground(Void... voids) {
            // do something
            return null;
        }

        @Override
        protected void onPostExecute(Void aVoid) {
            Intent intent = new Intent(context, aclass);
            startActivity(intent);
        }
}

子类之一:

public class PlacementPost extends CommonPost {
            Context context=PlacementPost.this;
            Class aclass=Placements.class;

            @Override
            protected void onCreate(Bundle savedInstanceState) {
                super.onCreate(savedInstanceState);
                on_create(context,aclass);
            }
        }

当我尝试上面的代码时，出现以下错误:

java.lang.NullPointerException: Attempt to invoke virtual method 'android.app.ActivityThread$ApplicationThread android.app.ActivityThread.getApplicationThread()' on a null object reference
       at android.app.Activity.startActivityForResult(Activity.java:4266)
       at android.support.v4.app.BaseFragmentActivityJB.startActivityForResult(BaseFragmentActivityJB.java:50)



at android.support.v4.app.FragmentActivity.startActivityForResult(FragmentActivity.java:79)
   at android.app.Activity.startActivityForResult(Activity.java:4224)
   at android.support.v4.app.FragmentActivity.startActivityForResult(FragmentActivity.java:859)
   at android.app.Activity.startActivity(Activity.java:4548)
   at android.app.Activity.startActivity(Activity.java:4516)
   at studentapp.notefi.CommonPost$PlaceTask.onPostExecute(CommonPost.java:240)
   at studentapp.notefi.CommonPost$PlaceTask.onPostExecute(CommonPost.java:177)
   at android.os.AsyncTask.finish(AsyncTask.java:660)
   at android.os.AsyncTask.-wrap1(AsyncTask.java)
   at android.os.AsyncTask$InternalHandler.handleMessage(AsyncTask.java:677)
   at android.os.Handler.dispatchMessage(Handler.java:102)
   at android.os.Looper.loop(Looper.java:154)
   at android.app.ActivityThread.main(ActivityThread.java:6077)
   at java.lang.reflect.Method.invoke(Native Method)
   at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:865)
   at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:755)

我不知道我错在哪里或者我错过了什么。我只是尝试了任何逻辑上我认为正确的东西。有不对的地方请大家指正!

Answer 1

对于初学者来说，你不应该使用 new 来初始化你的 Activity，它有自己的生命周期，上下文应该是你实际开始 Intent 的类，将代码更改为

on_create

 public void on_create(final Context context, final Class aclass) {
            post.setOnClickListener(new View.OnClickListener() {
                @Override
                public void onClick(View view) {
                    MyTask task = new MyTask(stor_root, mProgress, editTextplace, post, ninfo, imageUri,
                            mstorage, mDatabase, context, aclass);
                    if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.HONEYCOMB)
                        task.executeOnExecutor(AsyncTask.THREAD_POOL_EXECUTOR);
                    else
                        task.execute();
                }
            });
        }

MyTask - 停止从子级传递上下文

class MyTask extends AsyncTask<Void,Void,Void> {
        Class aclass;

        public MyTask(Class aclass){
             this.aclass=aclass;
        }

        @Override
        protected void onPreExecute() {
            // do something
        }

        @Override
        protected Void doInBackground(Void... voids) {
            // do something
            return null;
        }

        @Override
        protected void onPostExecute(Void aVoid) {
            Intent intent = new Intent(CommonPost.this, aclass);
            startActivity(intent);
        }
}

子类

public class PlacementPost extends CommonPost {
            Context context=PlacementPost.this;
            Class aclass=Placements.class;

            @Override
            protected void onCreate(Bundle savedInstanceState) {
                super.onCreate(savedInstanceState);
                on_create(aclass);
            }
        }