replace - 在 ViewPager 中正确替换片段

Question

我正在尝试替换 View 中的片段，但还没有成功。

我有以下类(class)。首先是我的 PagerAdapter:

package com.example.tab1;

import android.os.Bundle;
import android.support.v4.app.Fragment;
import android.support.v4.app.FragmentManager;
import android.support.v4.app.FragmentPagerAdapter;
public class SectionsPagerAdapter extends FragmentPagerAdapter {

static final int NUM_ITEMS = 3;
private final FragmentManager mFragmentManager;
private Fragment mFragmentAtPos0;

public SectionsPagerAdapter(FragmentManager fm) {
    super(fm);
    mFragmentManager = fm;
}

@Override
public Fragment getItem(int position) {

     Bundle args = new Bundle();


     mFragmentAtPos0= new testFragment();
     args.putInt(testFragment.ARG_SECTION_NUMBER, position + 1);
     mFragmentAtPos0.setArguments(args);

     return mFragmentAtPos0;
}

@Override
public int getItemPosition(Object object) {


    return 0;

}

@Override
// liefert die Anzahl der Tabs
public int getCount() {
    return NUM_ITEMS;
}

@Override

public CharSequence getPageTitle(int position) {
    switch (position) {
    case 0:

        // return getString(R.string.title_section1).toUpperCase();
        // return
        // Resources.getSystem().getString(R.string.title_section1).toUpperCase();

        return "Suche".toUpperCase();
    case 1:
        // return getString(R.string.title_section2).toUpperCase();
        // return
        // Resources.getSystem().getString(R.string.title_section2).toUpperCase();
        return "Ergebnis".toUpperCase();
    case 2:

        // return
        // Resources.getSystem().getString(R.string.title_section3).toUpperCase();
        return "Optionen".toUpperCase();
    }
    return null;
}

}

其次是我的 DatePickerFragment:

package com.example.tab1;

import android.os.Bundle;
import android.support.v4.app.DialogFragment;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;

public class DatePickerFragment extends DialogFragment {

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

      public static DatePickerFragment newInstance() {
          DatePickerFragment f = new DatePickerFragment();
          return f;
      }

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
        //Log.d("DEBUG", "onCreateView");
        return inflater.inflate(R.layout.datepickerfrag, container, false);

    }

}

最后是我的 MainActivity，我在其中激活了方法 onClickSearch 中的更改，这是我的第一个 Fragment 中的一个接口(interface)的方法，在应用程序启动时显示。

package com.example.tab1;

import android.app.ActionBar;
import android.app.FragmentTransaction;
import android.os.Bundle;
import android.support.v4.app.Fragment;
import android.support.v4.app.FragmentActivity;
import android.support.v4.view.ViewPager;
import android.view.Menu;

public class MainActivity extends FragmentActivity implements
        ActionBar.TabListener,testFragment.ButtonListenerS{

    /**
     * The {@link android.support.v4.view.PagerAdapter} that will provide
     * fragments for each of the sections. We use a
     * {@link android.support.v4.app.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}.
     */
    SectionsPagerAdapter mSectionsPagerAdapter;

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




    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        // Create the adapter that will return a fragment for each of the three
        // primary sections
        // of the app.
        mSectionsPagerAdapter = new SectionsPagerAdapter(
                getSupportFragmentManager());

        // Set up the action bar.
        final ActionBar actionBar = getActionBar();
        actionBar.setNavigationMode(ActionBar.NAVIGATION_MODE_TABS);


        // Set up the ViewPager with the sections adapter.
        mViewPager = (ViewPager) findViewById(R.id.pager);
        mViewPager.setAdapter(mSectionsPagerAdapter);

        // When swiping between different sections, select the corresponding
        // tab.
        // We can also use ActionBar.Tab#select() to do this if we have a
        // reference to the
        // Tab.
        mViewPager.setOnPageChangeListener(new ViewPager.SimpleOnPageChangeListener() {
                    @Override
                    public void onPageSelected(int position) {
                        actionBar.setSelectedNavigationItem(position);
                    }
                });

        // For each of the sections in the app, add a tab to the action bar.
        for (int i = 0; i < mSectionsPagerAdapter.getCount(); i++) {
            // Create a tab with text corresponding to the page title defined by
            // the adapter.
            // Also specify this Activity object, which implements the
            // TabListener interface, as the
            // listener for when this tab is selected.
            actionBar.addTab(actionBar.newTab()
                    .setText(mSectionsPagerAdapter.getPageTitle(i))
                    .setTabListener(this));
        }

        actionBar.selectTab(actionBar.getTabAt(0));
    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        getMenuInflater().inflate(R.menu.activity_main, menu);
        return true;
    }


    /*
     * Implementierung des "Suchbuttons" (non-Javadoc)
     * Interaktion zwischen testFragment und MainActivity
     */
    public void OnclickSearchS() {



          android.support.v4.app.FragmentTransaction ft = getSupportFragmentManager().beginTransaction();
          ft.replace(R.id.pager,DatePickerFragment.newInstance());
          ft.commit();
        //mViewPager.setCurrentItem(1);
    }



    public void onTabUnselected(ActionBar.Tab tab,
            FragmentTransaction fragmentTransaction) {
    }

    public void onTabSelected(ActionBar.Tab tab,
            FragmentTransaction fragmentTransaction) {
        // When the given tab is selected, switch to the corresponding page in
        // the ViewPager.
        mViewPager.setCurrentItem(tab.getPosition());
    }

    public void onTabReselected(ActionBar.Tab tab,
            FragmentTransaction fragmentTransaction) {
    }

    /**
     * A {@link FragmentPagerAdapter} that returns a fragment corresponding to
     * one of the primary sections of the app.
     */

}

当应用程序运行时，我第一次按下按钮并没有任何 react ，当我再次这样做时，我看到一个空片段，然后出现错误:

07-30 21:20:17.800: W/dalvikvm(32553): threadid=1: thread exiting with uncaught exception (group=0x40c671f8)
07-30 21:20:17.805: E/AndroidRuntime(32553): FATAL EXCEPTION: main
07-30 21:20:17.805: E/AndroidRuntime(32553): java.lang.NullPointerException
07-30 21:20:17.805: E/AndroidRuntime(32553):    at android.support.v4.app.Fragment.setUserVisibleHint(Fragment.java:750)
07-30 21:20:17.805: E/AndroidRuntime(32553):    at android.support.v4.app.FragmentPagerAdapter.setPrimaryItem(FragmentPagerAdapter.java:130)
07-30 21:20:17.805: E/AndroidRuntime(32553):    at android.support.v4.view.ViewPager.populate(ViewPager.java:893)
07-30 21:20:17.805: E/AndroidRuntime(32553):    at android.support.v4.view.ViewPager.populate(ViewPager.java:772)
07-30 21:20:17.805: E/AndroidRuntime(32553):    at android.support.v4.view.ViewPager.completeScroll(ViewPager.java:1539)
07-30 21:20:17.805: E/AndroidRuntime(32553):    at android.support.v4.view.ViewPager.onInterceptTouchEvent(ViewPager.java:1663)
07-30 21:20:17.805: E/AndroidRuntime(32553):    at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:1631)
07-30 21:20:17.805: E/AndroidRuntime(32553):    at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:1963)
07-30 21:20:17.805: E/AndroidRuntime(32553):    at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:1690)
07-30 21:20:17.805: E/AndroidRuntime(32553):    at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:1963)
07-30 21:20:17.805: E/AndroidRuntime(32553):    at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:1690)
07-30 21:20:17.805: E/AndroidRuntime(32553):    at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:1963)
07-30 21:20:17.805: E/AndroidRuntime(32553):    at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:1690)
07-30 21:20:17.805: E/AndroidRuntime(32553):    at com.android.internal.policy.impl.PhoneWindow$DecorView.superDispatchTouchEvent(PhoneWindow.java:2063)
07-30 21:20:17.805: E/AndroidRuntime(32553):    at com.android.internal.policy.impl.PhoneWindow.superDispatchTouchEvent(PhoneWindow.java:1399)
07-30 21:20:17.805: E/AndroidRuntime(32553):    at android.app.Activity.dispatchTouchEvent(Activity.java:2364)
07-30 21:20:17.805: E/AndroidRuntime(32553):    at com.android.internal.policy.impl.PhoneWindow$DecorView.dispatchTouchEvent(PhoneWindow.java:2011)
07-30 21:20:17.805: E/AndroidRuntime(32553):    at android.view.View.dispatchPointerEvent(View.java:5861)
07-30 21:20:17.805: E/AndroidRuntime(32553):    at android.view.ViewRootImpl.deliverPointerEvent(ViewRootImpl.java:3094)
07-30 21:20:17.805: E/AndroidRuntime(32553):    at android.view.ViewRootImpl.handleMessage(ViewRootImpl.java:2614)
07-30 21:20:17.805: E/AndroidRuntime(32553):    at android.view.ViewRootImpl.processInputEvents(ViewRootImpl.java:978)
07-30 21:20:17.805: E/AndroidRuntime(32553):    at android.view.ViewRootImpl.performTraversals(ViewRootImpl.java:992)
07-30 21:20:17.805: E/AndroidRuntime(32553):    at android.view.ViewRootImpl.handleMessage(ViewRootImpl.java:2585)
07-30 21:20:17.805: E/AndroidRuntime(32553):    at android.os.Handler.dispatchMessage(Handler.java:99)
07-30 21:20:17.805: E/AndroidRuntime(32553):    at android.os.Looper.loop(Looper.java:137)
07-30 21:20:17.805: E/AndroidRuntime(32553):    at android.app.ActivityThread.main(ActivityThread.java:4507)
07-30 21:20:17.805: E/AndroidRuntime(32553):    at java.lang.reflect.Method.invokeNative(Native Method)
07-30 21:20:17.805: E/AndroidRuntime(32553):    at java.lang.reflect.Method.invoke(Method.java:511)
07-30 21:20:17.805: E/AndroidRuntime(32553):    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:790)
07-30 21:20:17.805: E/AndroidRuntime(32553):    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:557)
07-30 21:20:17.805: E/AndroidRuntime(32553):    at dalvik.system.NativeStart.main(Native Method)

我不知道，发生了什么事。

Answer 1

当我缺少 getItemId(int position) 方法重新实现时，我遇到了这个异常，该方法为默认和替换片段返回不同的(唯一)ID。见 https://stackoverflow.com/a/11974777/685292进一步解释和示例实现。