Function in fragment makes emulator crash

2019-02-24 19:25发布

站内文章 / Java
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问题:

Error occurs when I place a function inside onCreateView in menu1_Fragment.java. Sorry in advance as I will be placing my logs in as well so it might make my post a bit big so I will tell you the layout. I am new sorry for the loads of questions.

The code works perfectly if I just don't put the function setClick() inside my fragment. quick note the function basically makes my image in menu1_layout.xml a 3 way button aka start stop reset where when you reset, it pops up a toast of exact time you got

1) menu1_Fragment.java

public class menu1_Fragment extends Fragment {
    Chronometer mChronometer;
    int loop = 0;
    double startTime;
    double millis;

    View rootview;
    @Nullable
    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
        rootview = inflater.inflate(R.layout.menu1_layout, container, false);
        setClick();
        return rootview;
    }



    Button button;
    public void setClick() {


        mChronometer = (Chronometer) getActivity().findViewById(R.id.aChronometer);

        button = (Button) getActivity().findViewById(R.id.stopWatch);
        button.setOnClickListener(mStartListener);

        button = (Button) getActivity().findViewById(R.id.stopWatch);
        button.setOnClickListener(mStartListener);

        button = (Button) getActivity().findViewById(R.id.stopWatch);
        button.setOnClickListener(mStartListener);
    }

    View.OnClickListener mStartListener = new View.OnClickListener() {
        public void onClick(View v) {
            if (loop == 0) {
                mChronometer.setBase(SystemClock.elapsedRealtime());
                mChronometer.start();
                startTime = System.currentTimeMillis();
                loop++;
            } else if (loop == 1) {
                mChronometer.stop();
                millis = System.currentTimeMillis()-startTime;
                loop++;
            } else if (loop == 2) {
                mChronometer.setBase(SystemClock.elapsedRealtime());
                Context context = getActivity().getApplicationContext();
                CharSequence text = "Your Time is: " + (millis/1000);
                int duration = Toast.LENGTH_SHORT;

                Toast toast = Toast.makeText(context, text, duration);
                toast.show();
                loop = 0;
            }
        }
    };
}

2) LOGS

10-28 16:52:26.552 2912-2912/app.z0nen.menu D/AndroidRuntime: Shutting down VM
10-28 16:52:26.552 2912-2912/app.z0nen.menu E/AndroidRuntime: FATAL EXCEPTION: main
10-28 16:52:26.552 2912-2912/app.z0nen.menu E/AndroidRuntime: Process: app.z0nen.menu, PID: 2912
10-28 16:52:26.552 2912-2912/app.z0nen.menu E/AndroidRuntime: java.lang.RuntimeException: Unable to start activity ComponentInfo{app.z0nen.menu/app.z0nen.slidemenu.MyActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.Button.setOnClickListener(android.view.View$OnClickListener)' on a null object reference
10-28 16:52:26.552 2912-2912/app.z0nen.menu E/AndroidRuntime:     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2416)
10-28 16:52:26.552 2912-2912/app.z0nen.menu E/AndroidRuntime:     at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2476)
10-28 16:52:26.552 2912-2912/app.z0nen.menu E/AndroidRuntime:     at android.app.ActivityThread.-wrap11(ActivityThread.java)
10-28 16:52:26.552 2912-2912/app.z0nen.menu E/AndroidRuntime:     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1344)
10-28 16:52:26.552 2912-2912/app.z0nen.menu E/AndroidRuntime:     at android.os.Handler.dispatchMessage(Handler.java:102)
10-28 16:52:26.552 2912-2912/app.z0nen.menu E/AndroidRuntime:     at android.os.Looper.loop(Looper.java:148)
10-28 16:52:26.552 2912-2912/app.z0nen.menu E/AndroidRuntime:     at android.app.ActivityThread.main(ActivityThread.java:5417)
10-28 16:52:26.552 2912-2912/app.z0nen.menu E/AndroidRuntime:     at java.lang.reflect.Method.invoke(Native Method)
10-28 16:52:26.552 2912-2912/app.z0nen.menu E/AndroidRuntime:     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:726)
10-28 16:52:26.552 2912-2912/app.z0nen.menu E/AndroidRuntime:     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616)
10-28 16:52:26.552 2912-2912/app.z0nen.menu E/AndroidRuntime:  Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.Button.setOnClickListener(android.view.View$OnClickListener)' on a null object reference
10-28 16:52:26.552 2912-2912/app.z0nen.menu E/AndroidRuntime:     at app.z0nen.slidemenu.menu1_Fragment.setClick(menu1_Fragment.java:39)
10-28 16:52:26.552 2912-2912/app.z0nen.menu E/AndroidRuntime:     at app.z0nen.slidemenu.menu1_Fragment.onCreateView(menu1_Fragment.java:26)
10-28 16:52:26.552 2912-2912/app.z0nen.menu E/AndroidRuntime:     at android.app.Fragment.performCreateView(Fragment.java:2220)
10-28 16:52:26.552 2912-2912/app.z0nen.menu E/AndroidRuntime:     at android.app.FragmentManagerImpl.moveToState(FragmentManager.java:973)
10-28 16:52:26.552 2912-2912/app.z0nen.menu E/AndroidRuntime:     at android.app.FragmentManagerImpl.moveToState(FragmentManager.java:1148)
10-28 16:52:26.552 2912-2912/app.z0nen.menu E/AndroidRuntime:     at android.app.BackStackRecord.run(BackStackRecord.java:793)
10-28 16:52:26.552 2912-2912/app.z0nen.menu E/AndroidRuntime:     at android.app.FragmentManagerImpl.execPendingActions(FragmentManager.java:1535)
10-28 16:52:26.552 2912-2912/app.z0nen.menu E/AndroidRuntime:     at android.app.FragmentController.execPendingActions(FragmentController.java:325)
10-28 16:52:26.552 2912-2912/app.z0nen.menu E/AndroidRuntime:     at android.app.Activity.performStart(Activity.java:6252)
10-28 16:52:26.552 2912-2912/app.z0nen.menu E/AndroidRuntime:     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2379)
10-28 16:52:26.552 2912-2912/app.z0nen.menu E/AndroidRuntime:     at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2476) 
10-28 16:52:26.552 2912-2912/app.z0nen.menu E/AndroidRuntime:     at android.app.ActivityThread.-wrap11(ActivityThread.java) 
10-28 16:52:26.552 2912-2912/app.z0nen.menu E/AndroidRuntime:     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1344) 
10-28 16:52:26.552 2912-2912/app.z0nen.menu E/AndroidRuntime:     at android.os.Handler.dispatchMessage(Handler.java:102) 
10-28 16:52:26.552 2912-2912/app.z0nen.menu E/AndroidRuntime:     at android.os.Looper.loop(Looper.java:148) 
10-28 16:52:26.552 2912-2912/app.z0nen.menu E/AndroidRuntime:     at android.app.ActivityThread.main(ActivityThread.java:5417) 
10-28 16:52:26.552 2912-2912/app.z0nen.menu E/AndroidRuntime:     at java.lang.reflect.Method.invoke(Native Method) 
10-28 16:52:26.552 2912-2912/app.z0nen.menu E/AndroidRuntime:     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:726) 
10-28 16:52:26.552 2912-2912/app.z0nen.menu E/AndroidRuntime:     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616) 
10-28 16:52:28.662 2912-2912/? I/Process: Sending signal. PID: 2912 SIG: 9

3) MyActivity.Java

public class MyActivity extends Activity
        implements NavigationDrawerFragment.NavigationDrawerCallbacks {

    /**
     * Fragment managing the behaviors, interactions and presentation of the navigation drawer.
     */
    private NavigationDrawerFragment mNavigationDrawerFragment;

    /**
     * Used to store the last screen title. For use in {@link #restoreActionBar()}.
     */
    private CharSequence mTitle;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_my);

        mNavigationDrawerFragment = (NavigationDrawerFragment)
                getFragmentManager().findFragmentById(R.id.navigation_drawer);
        mTitle = getTitle();

        // Set up the drawer.
        mNavigationDrawerFragment.setUp(
                R.id.navigation_drawer,
                (DrawerLayout) findViewById(R.id.drawer_layout));
    }

    @Override
    public void onNavigationDrawerItemSelected(int position) {

        Fragment objFragment = null;

        switch (position) {
            case 0:
                objFragment = new menu1_Fragment();
                break;
            case 1:
                objFragment = new menu2_Fragment();
                break;
        }
        // update the main content by replacing fragments
        FragmentManager fragmentManager = getFragmentManager();
        fragmentManager.beginTransaction()
                .replace(R.id.container, objFragment)
                .commit();
    }

    public void onSectionAttached(int number) {
        switch (number) {
            case 1:
                mTitle = getString(R.string.title_section1);
                break;
            case 2:
                mTitle = getString(R.string.title_section2);
                break;
        }
    }

    public void restoreActionBar() {
        ActionBar actionBar = getActionBar();
        actionBar.setNavigationMode(ActionBar.NAVIGATION_MODE_STANDARD);
        actionBar.setDisplayShowTitleEnabled(true);
        actionBar.setTitle(mTitle);
    }


    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        if (!mNavigationDrawerFragment.isDrawerOpen()) {
            // Only show items in the action bar relevant to this screen
            // if the drawer is not showing. Otherwise, let the drawer
            // decide what to show in the action bar.
            getMenuInflater().inflate(R.menu.my, menu);
            restoreActionBar();
            return true;
        }
        return super.onCreateOptionsMenu(menu);
    }

    @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 placeholder fragment containing a simple view.
     */
    public static class PlaceholderFragment extends Fragment {
        /**
         * The fragment argument representing the section number for this
         * fragment.
         */
        private static final String ARG_SECTION_NUMBER = "section_number";

        /**
         * Returns a new instance of this fragment for the given section
         * number.
         */
        public static PlaceholderFragment newInstance(int sectionNumber) {
            PlaceholderFragment fragment = new PlaceholderFragment();
            Bundle args = new Bundle();
            args.putInt(ARG_SECTION_NUMBER, sectionNumber);
            fragment.setArguments(args);
            return fragment;
        }

        public PlaceholderFragment() {
        }

        @Override
        public View onCreateView(LayoutInflater inflater, ViewGroup container,
                Bundle savedInstanceState) {
            View rootView = inflater.inflate(R.layout.fragment_my, container, false);
            return rootView;
        }

        @Override
        public void onAttach(Activity activity) {
            super.onAttach(activity);
            ((MyActivity) activity).onSectionAttached(
                    getArguments().getInt(ARG_SECTION_NUMBER));
        }
    }

}

4) Menu1_layout.xml

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent" android:layout_height="match_parent"
    android:gravity="center_horizontal">

    <Chronometer
        android:id="@+id/aChronometer"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:textSize="40sp"
        android:textColor="#111111"
        android:layout_marginTop="27dp"
        android:layout_below="@+id/stopWatch"
        android:layout_centerHorizontal="true" />

    <Button
        android:id="@+id/stopWatch"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:background="@drawable/stopwatch2"
        android:layout_marginTop="38dp"
        android:layout_alignParentTop="true"
        android:layout_centerHorizontal="true" />

</RelativeLayout>

回答1:

You can't use getActivity() from onCreateView() as the fragment's activity has not been created yet. You should use not use getActivity() until onActivityCreated() is called, or better yet, use the rootview you inflated to do your findViewByID() calls.

Also, you are initializing your button three times. You should get rid on two of them :)



回答2:

Change 

button = (Button) getActivity().findViewById(R.id.stopWatch);

to this:

button = (Button) findViewById(R.id.stopWatch);

Your button is inside your fragment's layout, not the activity's.

EDIT:

Make your button a member variable, so that you could access it from the onCreateView & setClick methods:

private Button mButton;

And we need to save a reference of your button in the onCreateView method to this: (rootview is your fragment's inflated layout)

@Nullable
    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
        rootview = inflater.inflate(R.layout.menu1_layout, container, false);
        mButton = rootview.findViewById(R.id.stopWatch);
        setClick();
        return rootview;
    }

and in the setClick method put this instead :

mButton.setOnClickListener(mStartListener);


标签： java android android-fragments crash fragment
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