java - fragment 中的函数使模拟器崩溃

Question

当我在 menu1_Fragment.java 的 onCreateView 中放置一个函数时发生错误。提前抱歉，因为我也会将我的日志放入其中，所以这可能会使我的帖子有点大，所以我会告诉你布局。我很抱歉提出了这么多问题。

如果我不将函数 setClick() 放入 fragment 中，代码将完美运行。快速注意该功能基本上使我在 menu1_layout.xml 中的图像成为一个 3 向按钮，也称为开始停止重置，当您重置时，它会弹出您得到的准确时间的 toast

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) 日志

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>

Answer 1

您不能使用 onCreateView() 中的 getActivity()，因为 fragment 的 Activity 尚未创建。在调用 onActivityCreated() 之前，您不应该使用 getActivity()，或者更好的是，使用您膨胀的 rootview 来执行您的 findViewByID() 调用。

此外，您还对按钮进行了三次初始化。你应该摆脱其中两个:)