Question

因为你可以在onCreate方法中看到我在＆＃34;片段＆＃34;中的第0个片段上调用getView。名单。它返回null。我已经尝试在代码中放置一个计时器并让它每秒运行一次并检查视图是否为空。在计时器的第二个刻度上，视图不为空。基本上

MainActivity.java

package com.axinite.standapp;

import android.graphics.Color;
import android.os.CountDownTimer;
import android.os.Handler;
import android.support.annotation.Nullable;
import android.support.design.widget.TabLayout;
import android.support.design.widget.FloatingActionButton;
import android.support.design.widget.Snackbar;
import android.support.v7.app.AppCompatActivity;
import android.support.v7.widget.Toolbar;

import android.support.v4.app.Fragment;
import android.support.v4.app.FragmentManager;
import android.support.v4.app.FragmentPagerAdapter;
import android.support.v4.view.ViewPager;
import android.os.Bundle;
import android.util.Log;
import android.view.LayoutInflater;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.view.ViewGroup;

import android.view.ViewParent;
import android.widget.EditText;
import android.widget.NumberPicker;
import android.widget.RelativeLayout;
import android.widget.TextView;
import android.widget.Toast;

import java.util.ArrayList;
import java.util.List;
import java.util.Timer;
import java.util.TimerTask;
import java.util.Vector;

public class MainActivity extends AppCompatActivity {

    int i = 0;

    /**
     * The {@link android.support.v4.view.PagerAdapter} that will provide
     * fragments for each of the sections. We use a
     * {@link FragmentPagerAdapter} derivative, which will keep every
     * loaded fragment in memory. If this becomes too memory intensive, it
     * may be best to switch to a
     * {@link android.support.v4.app.FragmentStatePagerAdapter}.
     */
    private SectionsPagerAdapter mSectionsPagerAdapter;

    /**
     * The {@link ViewPager} that will host the section contents.
     */
    private ViewPager mViewPager;

    int standUpSeconds = 4000;

    List<android.support.v4.app.Fragment> fragments = new Vector<android.support.v4.app.Fragment>();

    NumberPicker SUPickerH;
    NumberPicker SUPickerM;
    NumberPicker SUPickerS;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);

        setSupportActionBar(toolbar);
        fragments.add(Fragment.instantiate(this, BlankFragment.class.getName()));

        mSectionsPagerAdapter = new SectionsPagerAdapter(getSupportFragmentManager(), fragments);
        mViewPager = (ViewPager) findViewById(R.id.container);
        mViewPager.setAdapter(mSectionsPagerAdapter);
        final TabLayout tabLayout = (TabLayout) findViewById(R.id.tabs);
        tabLayout.setupWithViewPager(mViewPager);
        tabLayout.setSelectedTabIndicatorColor(Color.WHITE);
        FloatingActionButton fab = (FloatingActionButton) findViewById(R.id.fab);
        fab.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                Snackbar.make(view, "Replace with your own action", Snackbar.LENGTH_LONG)
                        .setAction("Action", null).show();
            }
        });
        final int[] ICONS = new int[] {
                R.drawable.walking,
                R.drawable.iris
        };
        for (int i=0; i < tabLayout.getTabCount(); i++)
        {
            tabLayout.getTabAt(i).setIcon(getDrawable(ICONS[i]));
        }//endfor)
        View view = ((BlankFragment) fragments.get(0)).getView();
        if(view != null) {
            TextView tv = (TextView) view.findViewById(R.id.glupost);
            tv.setText("dasdas");
            //Toast.makeText(getApplicationContext(), ((Fragment) fragments.get(0)).toString(), Toast.LENGTH_SHORT).show();
        }
    }

    void Setup() {



    }


    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        // Inflate the menu; this adds items to the action bar if it is present.
        getMenuInflater().inflate(R.menu.menu_main, menu);
        return true;
    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        // Handle action bar item clicks here. The action bar will
        // automatically handle clicks on the Home/Up button, so long
        // as you specify a parent activity in AndroidManifest.xml.
        int id = item.getItemId();

        //noinspection SimplifiableIfStatement
        if (id == R.id.action_settings) {
            return true;
        }

        return super.onOptionsItemSelected(item);
    }


    /**
     * A {@link FragmentPagerAdapter} that returns a fragment corresponding to
     * one of the sections/tabs/pages.
     */
    public class SectionsPagerAdapter extends FragmentPagerAdapter {
        List<Fragment> fragments;
        public SectionsPagerAdapter(FragmentManager fm, List<Fragment> fragments) {
            super(fm);
            this.fragments = fragments;
        }

        @Override
        public Fragment getItem(int position) {
            return fragments.get(position);
        }

        @Override
        public int getCount() {
            // Show 3 total pages.
            return fragments.size();
        }

        @Override
        public CharSequence getPageTitle(int position) {

            return "";
        }
    }
}

BlankFragment.java

    package com.axinite.standapp;

import android.app.Activity;
import android.net.Uri;
import android.os.Bundle;
import android.support.v4.app.Fragment;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;


/**
 * A simple {@link Fragment} subclass.
 * Activities that contain this fragment must implement the
 * {@link BlankFragment.OnFragmentInteractionListener} interface
 * to handle interaction events.
 * Use the {@link BlankFragment#newInstance} factory method to
 * create an instance of this fragment.
 */
public class BlankFragment extends Fragment {

    protected View mView;
    // TODO: Rename parameter arguments, choose names that match
    // the fragment initialization parameters, e.g. ARG_ITEM_NUMBER
    private static final String ARG_PARAM1 = "param1";
    private static final String ARG_PARAM2 = "param2";

    // TODO: Rename and change types of parameters
    private String mParam1;
    private String mParam2;

    private OnFragmentInteractionListener mListener;

    /**
     * Use this factory method to create a new instance of
     * this fragment using the provided parameters.
     *
     * @param param1 Parameter 1.
     * @param param2 Parameter 2.
     * @return A new instance of fragment BlankFragment.
     */
    // TODO: Rename and change types and number of parameters
    public static BlankFragment newInstance(String param1, String param2) {
        BlankFragment fragment = new BlankFragment();
        Bundle args = new Bundle();
        args.putString(ARG_PARAM1, param1);
        args.putString(ARG_PARAM2, param2);
        fragment.setArguments(args);
        return fragment;
    }

    public BlankFragment() {
        // Required empty public constructor
    }

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        if (getArguments() != null) {
            mParam1 = getArguments().getString(ARG_PARAM1);
            mParam2 = getArguments().getString(ARG_PARAM2);
        }
    }

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
                             Bundle savedInstanceState) {
        // Inflate the layout for this fragment
        View view = inflater.inflate(R.layout.fragment_blank, container, false);
        mView = view;
        return view;
    }

    // TODO: Rename method, update argument and hook method into UI event
    public void onButtonPressed(Uri uri) {
        if (mListener != null) {
            mListener.onFragmentInteraction(uri);
        }
    }

    @Override
    public void onAttach(Activity activity) {
        super.onAttach(activity);
        try {
            mListener = (OnFragmentInteractionListener) activity;
        } catch (ClassCastException e) {

        }
    }

    @Override
    public void onDetach() {
        super.onDetach();
        mListener = null;
    }

    /**
     * This interface must be implemented by activities that contain this
     * fragment to allow an interaction in this fragment to be communicated
     * to the activity and potentially other fragments contained in that
     * activity.
     * <p/>
     * See the Android Training lesson <a href=
     * "http://developer.android.com/training/basics/fragments/communicating.html"
     * >Communicating with Other Fragments</a> for more information.
     */
    public interface OnFragmentInteractionListener {
        // TODO: Update argument type and name
        public void onFragmentInteraction(Uri uri);
    }

}

Answer 1

Activity与Fragment进行通信的典型方法如下：

MyFragment frag = (MyFragment) getFragmentManager().findFragmentById(R.id.container_of_fragment);
frag.getMyTextView().setText("New text");

或（通常首选的IMO）

MyFragment frag = (MyFragment) getFragmentManager().findFragmentByTag("fragment_tag_string_value");
frag.getMyTextView().setText("New text");

然而，ViewPager使这变得更加困难，因为容器的“id”是ViewPager本身，其中包含多个片段。另外，没有内置的适配器机制（我知道）将标签设置为片段。

我可以想到两种避免这种情况的方法。首先，您可以使用Android API中的EventBus，例如GreenRobot's EventBus或LocalBroadcastManager。 GreenRobot的EventBus也是回答this类似问题的推荐技巧。

另一种方法是利用Fragment始终引用其主机Activity的事实，这意味着Fragment可以通过Activity请求来自interface的文本Fragment，将其返回public class MainActivity implements FragmentOne.Callbacks { //... @Override public String requestTextViewString() { return "Text to send to Fragment" }：

FragmentOne

在您假设的public class FragmentOne extends Fragment { private Callbacks mCallback; private TextView mTextView; public interface Callbacks { String requestTextViewString(); } @Override public void onAttach(Activity activity) { if (activity instanceof Callbacks) { mCallback = (Callbacks) activity; } } /* *Later in your Fragment, when you want to get text from your MainActivity * i.e. in onCreateView() */ mTextView.setText(mCallback.requestTextViewString());：

中

Fragment

修改：另请注意，尝试从onCreate() Activity NullPointerException访问Fragment可能会导致Fragment 。 This图表显示了彼此并存的生命周期。这不应该是一个问题，因为newInstance()的“设置”生命周期事件中所需的任何内容都可以作为public class FragmentOne extends Fragment { private static final String KEY = "text_for_text_view_key"; public static FragmentOne newInstance(String textForTextView) { Bundle args = new Bundle(); FragmentOne frag = new FragmentOne(); args.putString(KEY, textForTextView); frag.setArguments(args); return frag; } //And when required... mTextView.setText(getArguments().getString(KEY));的{{1}}方法中的参数传递：

var options = allBindingsAccessor().dateTimePickerOptions || { locale: 'da', format: 'DD-MM-YYYY' };
$(element).datetimepicker(options);

在片段上调用getView将返回null

1 个答案: