如何让活动返回按钮返回到片段？

Question

当有人按下Activity的返回按钮时，我希望能获取特定的Fragment，但它不起作用。请帮助我解决这个问题。

这是我的Activity代码：

TopicDisplay.java

package androidthirst.company.abhi.totalenglish;

import android.content.Intent;
import android.content.res.Resources;
import android.graphics.Color;
import android.support.v7.app.ActionBar;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.support.v7.widget.Toolbar;
import android.view.View;
import android.webkit.WebView;

public class TopicDisplay extends AppCompatActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_topic_display);
        String data = getIntent().getExtras().getString("first");
        Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar1);

        toolbar.setTitle(data);
        toolbar.setTitleTextColor(Color.WHITE);
        setSupportActionBar(toolbar);
        toolbar.setNavigationIcon(R.mipmap.ic_arrow_back_black_36dp);

        WebView tabViewing = (WebView) findViewById(R.id.webView);

        tabViewing.loadUrl(getIntent().getDataString());
    }

}

我想从Activity返回到我的Fragment代码

package androidthirst.company.abhi.totalenglish;

import android.app.Activity;
import android.content.Intent;
import android.content.res.Resources;
import android.graphics.Color;
import android.net.Uri;
import android.os.Bundle;
import android.support.v4.app.Fragment;
import android.support.v4.app.ListFragment;
import android.support.v7.widget.Toolbar;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.webkit.WebView;
import android.webkit.WebViewClient;
import android.widget.AdapterView;
import android.widget.ArrayAdapter;
import android.widget.ListView;


public class Tab1Fragment extends Fragment {
    ListView listView;
    String[] image1;
    String[] mainTopic;
    String[] mainDescription;

    public void onBackPressed() {
        if (getFragmentManager().getBackStackEntryCount() > 0) {
            getFragmentManager().popBackStack();
        } else {
            getActivity().onBackPressed();
        }
    }


    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
                             Bundle savedInstanceState) {
        // Inflate the layout for this fragment
        View view = inflater.inflate(R.layout.fragment_tab1, container, false);



        Resources res = getResources();
        mainTopic = res.getStringArray(R.array.MainTopic);
        mainDescription = res.getStringArray(R.array.DescriptionContent);
        listView = (ListView) view.findViewById(R.id.listView);
        MyAdapter myAdapter = new MyAdapter(getActivity(), mainTopic, image1, mainDescription);
        listView.setAdapter(myAdapter);

//        toolbar.setTitleTextColor(Color.WHITE);


        listView.setOnItemClickListener(new AdapterView.OnItemClickListener() {
            @Override
            public void onItemClick(AdapterView<?> parent, View view, int position, long id) {

                switch (position) {
                    case 0:
                        Intent i0 = new Intent(getActivity().getApplicationContext(), TopicDisplay.class);
                        getActivity().overridePendingTransition(0, 0);
                        i0.putExtra("first", "Active Passive");
                        Uri uri0 = Uri.parse("file:///android_asset/ActivePassive.html");
                        i0.setData(uri0);
                        startActivity(i0);
                        break;
                    case 1:
                        Intent i1 = new Intent(getActivity().getApplicationContext(), TopicDisplay.class);
                        getActivity().overridePendingTransition(0, 0);
                        i1.putExtra("first", "Adjective");
                        Uri uri1 = Uri.parse("file:///android_asset/Adjective.html");
                        i1.setData(uri1);
                        startActivity(i1);
                        break;
                    case 2:
                        Intent i2 = new Intent(getActivity().getApplicationContext(), TopicDisplay.class);
                        i2.putExtra("first", "Adverb");
                        Uri uri2 = Uri.parse("file:///android_asset/adverb.html");
                        i2.setData(uri2);
                        startActivity(i2);
                        break;
                    case 3:
                        Intent i3 = new Intent(getActivity().getApplicationContext(), TopicDisplay.class);
                        i3.putExtra("first", "Article");
                        Uri uri3 = Uri.parse("file:///android_asset/article.html");
                        i3.setData(uri3);
                        startActivity(i3);
                        break;
                    case 4:
                        Intent i4 = new Intent(getActivity().getApplicationContext(), TopicDisplay.class);
                        i4.putExtra("first", "Clause");
                        Uri uri4 = Uri.parse("file:///android_asset/clause.html");
                        i4.setData(uri4);
                        startActivity(i4);
                        break;
                    case 5:
                        Intent i5 = new Intent(getActivity().getApplicationContext(), TopicDisplay.class);
                        Uri uri5 = Uri.parse("file:///android_asset/conjunction.html");
                        i5.putExtra("first", "Conjunction");
                        i5.setData(uri5);
                        startActivity(i5);
                        break;
                    case 6:
                        Intent i6 = new Intent(getActivity().getApplicationContext(), TopicDisplay.class);
                        i6.putExtra("first", "Degree");
                        Uri uri6 = Uri.parse("file:///android_asset/degree.html");
                        i6.setData(uri6);
                        startActivity(i6);
                        break;
                    case 7:
                        Intent i7 = new Intent(getActivity().getApplicationContext(), TopicDisplay.class);
                        i7.putExtra("first", "Determiner");
                        Uri uri7 = Uri.parse("file:///android_asset/determiner.html");
                        i7.setData(uri7);
                        startActivity(i7);
                        break;
                    case 8:
                        Intent i8 = new Intent(getActivity().getApplicationContext(), TopicDisplay.class);
                        i8.putExtra("first", "Direct Indirect");
                        Uri uri8 = Uri.parse("file:///android_asset/direct.html");
                        i8.setData(uri8);
                        startActivity(i8);
                        break;
                    case 9:
                        Intent i9 = new Intent(getActivity().getApplicationContext(), TopicDisplay.class);
                        i9.putExtra("first", "Figur of Speech");
                        Uri uri9 = Uri.parse("file:///android_asset/figur.html");
                        i9.setData(uri9);
                        startActivity(i9);
                        break;
                    case 10:
                        Intent i10 = new Intent(getActivity().getApplicationContext(), TopicDisplay.class);
                        i10.putExtra("first", "Gender");
                        Uri uri10 = Uri.parse("file:///android_asset/gender.html");
                        i10.setData(uri10);
                        startActivity(i10);
                        break;
                    case 11:
                        Intent i11 = new Intent(getActivity().getApplicationContext(), TopicDisplay.class);
                        i11.putExtra("first", "Hymonyms");
                        Uri uri11 = Uri.parse("file:///android_asset/homonyms.html");
                        i11.setData(uri11);
                        startActivity(i11);
                        break;
                    case 12:
                        Intent i12 = new Intent(getActivity().getApplicationContext(), TopicDisplay.class);
                        i12.putExtra("first", "Idoms");
                        Uri uri12 = Uri.parse("file:///android_asset/idoms.html");
                        i12.setData(uri12);
                        startActivity(i12);
                        break;
                    case 13:
                        Intent i13 = new Intent(getActivity().getApplicationContext(), TopicDisplay.class);
                        i13.putExtra("first", "Noun");
                        Uri uri13 = Uri.parse("file:///android_asset/noun.html");
                        i13.setData(uri13);
                        startActivity(i13);
                        break;
                    case 14:
                        Intent i14 = new Intent(getActivity().getApplicationContext(), TopicDisplay.class);
                        i14.putExtra("first", "Plural");
                        Uri uri14 = Uri.parse("file:///android_asset/plural.html");
                        i14.setData(uri14);
                        startActivity(i14);
                        break;
                    case 15:
                        Intent i15 = new Intent(getActivity().getApplicationContext(), TopicDisplay.class);
                        i15.putExtra("first", "Preposition");
                        Uri uri15 = Uri.parse("file:///android_asset/preposition.html");
                        i15.setData(uri15);
                        startActivity(i15);
                        break;
                    case 16:
                        Intent i16 = new Intent(getActivity().getApplicationContext(), TopicDisplay.class);
                        i16.putExtra("first", "Pronoun");
                        Uri uri16 = Uri.parse("file:///android_asset/pronoun.html");
                        i16.setData(uri16);
                        startActivity(i16);
                        break;
                    case 17:
                        Intent i17 = new Intent(getActivity().getApplicationContext(), TopicDisplay.class);
                        i17.putExtra("first", "Verbs");
                        Uri uri17 = Uri.parse("file:///android_asset/verbs.html");
                        i17.setData(uri17);
                        startActivity(i17);
                        break;


                }

            }
        });


        return view;


    }

}

- user5138430

Answer 1

在onBackPressed()中调用getActivity().onBackPressed()并没有实际意义，你可能会轻易地陷入一个无限循环。

你可能想要在else块中调用super.onBackPressed()：

@Override
public void onBackPressed() {
    if (getFragmentManager().getBackStackEntryCount() > 0) {
        getFragmentManager().popBackStack();
    } else {
        super.onBackPressed();
    }
}

通过使用super关键字，您调用超类的onBackPressed()方法（如果返回堆栈为空）。

- earthw0rmjim

---

如果后退栈为空，则调用 getActivity().onBackPressed() 将再次调用此特定的 onBackPressed()。后退栈仍将为空，因此它将再次调用此 onBackPressed()，如此循环下去。调用 super.onBackPressed() 将调用超类（Activity）的 onBackPressed()，其中包含默认的 onBackPressed() 功能。 - earthw0rmjim