关于 android:Action Bar 不显示


Action Bar not Displaying

我正在尝试在我的操作栏上放置一个向上按钮，但我的应用没有显示片段的操作栏。我的主要活动的片段有一个操作栏，而不是它启动的片段，所以当我调用 getActivity().getActionBar().setDisplayHomeAsUpEnabled(true) 时，应用程序会抛出一个 nullPointerException。 (下面 NPE 堆栈跟踪 1 中的堆栈跟踪)。

我已经尝试使用 getActionBar.show() 并将主题设置为 Theme.Holo.Light，如此处建议的那样。 getActionBar.show()，但这会导致应用程序崩溃并产生 nullPointerException。当我尝试使用 Theme.Holo.Light 时，它告诉我我必须使用 appcompat 主题("您需要在此活动中使用 Theme.AppCompat 主题(或后代)。")

我已经四处寻找如何修复该错误，但人们建议的 AppCompat 主题都没有解决此片段上没有操作栏的问题。任何人的建议表示赞赏。下面的代码。

不会显示操作栏的片段：

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import android.annotation.TargetApi;
import android.app.Activity;
import android.app.Fragment;
import android.app.FragmentManager;
import android.content.Intent;
import android.os.Build;
import android.os.Bundle;
import android.support.v4.app.NavUtils;
import android.text.Editable;
import android.text.TextWatcher;
import android.util.Log;
import android.view.LayoutInflater;
import android.view.MenuItem;
import android.view.View;
import android.view.ViewGroup;
import android.widget.Button;
import android.widget.CheckBox;
import android.widget.CompoundButton;
import android.widget.EditText;

import java.util.Date;
import java.util.UUID;

public class CrimeFragment extends Fragment {
public static final String EXTRA_CRIME_ID ="com.bignerdranch.android.criminalintent,crime_id";

private static final String DIALOG_DATE ="date";
private static final int REQUEST_DATE = 0;

private Crime mCrime;
private EditText mTitleField;
private Button mDateButton;
private CheckBox mSolvedCheckBox;

@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setHasOptionsMenu(true);

    UUID crimeId = (UUID)getArguments().getSerializable(EXTRA_CRIME_ID);

    mCrime = CrimeLab.get(getActivity()).getCrime(crimeId);
}

@TargetApi(11)
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup parent, Bundle savedInstanceState) {
    View v = inflater.inflate(R.layout.fragment_crime, parent, false);

    if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.HONEYCOMB) {
        if (NavUtils.getParentActivityName(getActivity()) != null)  {
            //getActivity().getActionBar().setDisplayHomeAsUpEnabled(true);
        }
    }

    mTitleField = (EditText)v.findViewById(R.id.crime_title);
    mTitleField.setText(mCrime.getTitle());
    mTitleField.addTextChangedListener(new TextWatcher() {
        @Override
        public void beforeTextChanged(CharSequence s, int start, int count, int after) {
            //This space intentionally left blank
        }

        @Override
        public void onTextChanged(CharSequence c, int start, int before, int count) {
            mCrime.setTitle(c.toString());
        }

        @Override
        public void afterTextChanged(Editable s) {
            //This space intentionally left blank
        }
    });

    mDateButton = (Button)v.findViewById(R.id.crime_date);
    updateDate();
    mDateButton.setOnClickListener(new View.OnClickListener() {
        public void onClick(View v) {
            FragmentManager fm = getActivity().getFragmentManager();
            DatePickerFragment dialog = DatePickerFragment.newInstance(mCrime.getDate());
            dialog.setTargetFragment(CrimeFragment.this, REQUEST_DATE);
            dialog.show(fm, DIALOG_DATE);
        }
    });

    mSolvedCheckBox = (CheckBox)v.findViewById(R.id.crime_solved);
    mSolvedCheckBox.setChecked(mCrime.isSolved());
    mSolvedCheckBox.setOnCheckedChangeListener(new CompoundButton.OnCheckedChangeListener() {
        @Override
        public void onCheckedChanged(CompoundButton buttonView, boolean isChecked) {
            mCrime.setSolved(isChecked);
        }
    });

    return v;
}

@Override
public void onActivityResult(int requestCode, int resultCode, Intent data)  {
    if (resultCode != Activity.RESULT_OK) return;
    if (requestCode == REQUEST_DATE)    {
        Date date = (Date)data.getSerializableExtra(DatePickerFragment.EXTRA_DATE);
        mCrime.setDate(date);
        updateDate();
    }
}

public static CrimeFragment newInstance(UUID crimeId)   {
    Bundle args = new Bundle();
    args.putSerializable(EXTRA_CRIME_ID, crimeId);

    CrimeFragment fragment = new CrimeFragment();
    fragment.setArguments(args);

    return fragment;
}

@Override
public boolean onOptionsItemSelected(MenuItem item) {
    switch(item.getItemId())    {
        case R.id.home:
            if (NavUtils.getParentActivityName(getActivity()) != null)  {
                NavUtils.navigateUpFromSameTask(getActivity());
            }
            return true;
        default:
            return super.onOptionsItemSelected(item);
    }
}

private void updateDate()   {
    mDateButton.setText(mCrime.getDate().toString());
}
}

片段 XML:

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<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical"
>

<TextView
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:text="@string/crime_title_label"
    style="?android:listSeparatorTextViewStyle"
    />

<EditText
    android:id="@+id/crime_title"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:hint="@string/crime_title_hint"
    />

<TextView
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:text="@string/crime_details_label"
    style="?android:listSeparatorTextViewStyle"
    />

<Button
    android:id="@+id/crime_date"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:layout_marginLeft="16dp"
    android:layout_marginRight="16dp"
    />

<CheckBox
    android:id="@+id/crime_solved"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:layout_marginLeft="16dp"
    android:layout_marginRight="16dp"
    android:text="@string/crime_solved_label"
    />

活动托管片段：

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import android.app.Fragment;
import android.app.FragmentManager;
import android.os.Bundle;
import android.support.v13.app.FragmentStatePagerAdapter;
import android.support.v4.app.FragmentActivity;
import android.support.v4.view.ViewPager;

import java.util.ArrayList;
import java.util.UUID;

public class CrimePagerActivity extends FragmentActivity {
private ViewPager mViewPager;
private ArrayList<Crime> mCrimes;

@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);

    mViewPager = new ViewPager(this);
    mViewPager.setId(R.id.viewpager);
    setContentView(mViewPager);

    mCrimes = CrimeLab.get(this).getCrimes();

    FragmentManager fm = getFragmentManager();
    mViewPager.setAdapter(new FragmentStatePagerAdapter(fm) {
        @Override
        public int getCount()   {
            return mCrimes.size();
        }

        @Override
        public Fragment getItem(int pos) {
            Crime crime = mCrimes.get(pos);
            return CrimeFragment.newInstance(crime.getId());
        }
    });

    UUID crimeId = (UUID)getIntent().getSerializableExtra(CrimeFragment.EXTRA_CRIME_ID);
    for (int i = 0; i < mCrimes.size(); i++)    {
        if (mCrimes.get(i).getId().equals(crimeId)) {
            mViewPager.setCurrentItem(i);
            break;
        }
    }

    mViewPager.setOnPageChangeListener(new ViewPager.OnPageChangeListener() {
        public void onPageScrollStateChanged(int state)    {}

        public void onPageScrolled(int pos, float posOffset, int posOffsetPixels)  {}

        public void onPageSelected(int pos)    {
            Crime crime = mCrimes.get(pos);
            if (crime.getTitle() != null)   {
                setTitle(crime.getTitle());
            }
        }
    });
}
}

清单：

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<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
package="com.bignerdranch.android.criminalintent">

<application
    android:allowBackup="true"
    android:icon="@mipmap/ic_launcher"
    android:label="@string/app_name"
    android:theme="@style/AppTheme">
    <activity
        android:name=".CrimeListActivity">
        <intent-filter>
           
            <category android:name="android.intent.category.LAUNCHER"   />
        </intent-filter>
    </activity>
       <activity
        android:name=".CrimePagerActivity"
        android:label="@string/app_name">
           <meta-data android:name="android.support.PARENT_ACTIVITY"
                      android:value=".CrimeListActivity"/>
    </activity>
</application>

分辨率/样式：

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<resources>

<!-- Base application theme. -->
<style name="AppTheme" parent="Theme.AppCompat.Light.DarkActionBar">
    <!-- Customize your theme here. -->
</style>

NPE 堆栈跟踪 1:

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Process: com.bignerdranch.android.criminalintent, PID: 24448
java.lang.NullPointerException
        at com.bignerdranch.android.criminalintent.CrimeFragment.onCreateView(CrimeFragment.java:57)
        at android.app.Fragment.performCreateView(Fragment.java:1700)
        at android.app.FragmentManagerImpl.moveToState(FragmentManager.java:890)
        at android.app.FragmentManagerImpl.moveToState(FragmentManager.java:1062)
        at android.app.BackStackRecord.run(BackStackRecord.java:684)
        at android.app.FragmentManagerImpl.execPendingActions(FragmentManager.java:1453)
        at android.app.FragmentManagerImpl.executePendingTransactions(FragmentManager.java:479)
        at android.support.v13.app.FragmentStatePagerAdapter.finishUpdate(FragmentStatePagerAdapter.java:167)
        at android.support.v4.view.ViewPager.populate(ViewPager.java:1073)
        at android.support.v4.view.ViewPager.populate(ViewPager.java:919)
        at android.support.v4.view.ViewPager.onMeasure(ViewPager.java:1441)
        at android.view.View.measure(View.java:17495)
        at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5363)
        at android.widget.FrameLayout.onMeasure(FrameLayout.java:310)
        at android.view.View.measure(View.java:17495)
        at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5363)
        at android.widget.LinearLayout.measureChildBeforeLayout(LinearLayout.java:1410)
        at android.widget.LinearLayout.measureVertical(LinearLayout.java:695)
        at android.widget.LinearLayout.onMeasure(LinearLayout.java:588)
        at android.view.View.measure(View.java:17495)
        at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5363)
        at android.widget.FrameLayout.onMeasure(FrameLayout.java:310)
        at com.android.internal.policy.impl.PhoneWindow$DecorView.onMeasure(PhoneWindow.java:2548)
        at android.view.View.measure(View.java:17495)
        at android.view.ViewRootImpl.performMeasure(ViewRootImpl.java:2285)
        at android.view.ViewRootImpl.measureHierarchy(ViewRootImpl.java:1396)
        at android.view.ViewRootImpl.performTraversals(ViewRootImpl.java:1595)
        at android.view.ViewRootImpl.doTraversal(ViewRootImpl.java:1254)
        at android.view.ViewRootImpl$TraversalRunnable.run(ViewRootImpl.java:6632)
        at android.view.Choreographer$CallbackRecord.run(Choreographer.java:814)
        at android.view.Choreographer.doCallbacks(Choreographer.java:614)
        at android.view.Choreographer.doFrame(Choreographer.java:584)
        at android.view.Choreographer$FrameDisplayEventReceiver.run(Choreographer.java:800)
        at android.os.Handler.handleCallback(Handler.java:733)
        at android.os.Handler.dispatchMessage(Handler.java:95)
        at android.os.Looper.loop(Looper.java:146)
        at android.app.ActivityThread.main(ActivityThread.java:5487)
        at java.lang.reflect.Method.invokeNative(Native Method)
        at java.lang.reflect.Method.invoke(Method.java:515)
        at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1283)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1099)
        at dalvik.system.NativeStart.main(Native Method)
相关讨论

CrimePagerActivity 可能想扩展 ActionBarActivity 而不是 FragmentActivity。

when I call
getActivity().getActionBar().setDisplayHomeAsUpEnabled(true), the app
throws a nullPointerException.

当你调用这个函数并说你自己的 Fragment 中有 ActionBar 而不是你的 Activity 时，你怎么能运行这个命令。

I've tried using getActionBar.show() and setting the theme to Theme.Holo.Light, as suggested here. getActionBar.show()

那个例子已经过时，不再有 Holo Theme 或 ActionBar。现在有 Toolbar。