Question

编辑：这是我所遵循的教程，以及它对应的YouTube视频：

http://easyway2in.blogspot.ae/2014/10/android-swipe-views-with-tabs.html

https://www.youtube.com/watch?v=Xu2yoIqTsj4

这是我在Android应用程序中使用选项卡的第一次体验，我似乎遇到了一个我似乎无法修复的错误。

这是错误：

10-29 21:46:50.928  27935-27935/tabs.ibettergetagoodgradeforthisorillbepissed.sciencefair.beta.mmmeds.com.mmmedstabbeta E/AndroidRuntime﹕ FATAL EXCEPTION: main
    Process: tabs.ibettergetagoodgradeforthisorillbepissed.sciencefair.beta.mmmeds.com.mmmedstabbeta, PID: 27935
    java.lang.NullPointerException
            at android.support.v4.app.BackStackRecord.doAddOp(BackStackRecord.java:394)
            at android.support.v4.app.BackStackRecord.add(BackStackRecord.java:389)
            at android.support.v4.app.FragmentPagerAdapter.instantiateItem(FragmentPagerAdapter.java:99)
            at android.support.v4.view.ViewPager.addNewItem(ViewPager.java:832)
            at android.support.v4.view.ViewPager.populate(ViewPager.java:1048)
            at android.support.v4.view.ViewPager.setCurrentItemInternal(ViewPager.java:550)
            at android.support.v4.view.ViewPager.setCurrentItemInternal(ViewPager.java:509)
            at android.support.v4.view.ViewPager.setCurrentItem(ViewPager.java:490)
            at tabs.ibettergetagoodgradeforthisorillbepissed.sciencefair.beta.mmmeds.com.mmmedstabbeta.MainActivity.onTabSelected(MainActivity.java:61)
            at com.android.internal.app.ActionBarImpl.selectTab(ActionBarImpl.java:577)
            at com.android.internal.app.ActionBarImpl$TabImpl.select(ActionBarImpl.java:1105)
            at com.android.internal.widget.ScrollingTabContainerView$TabClickListener.onClick(ScrollingTabContainerView.java:547)
            at android.view.View.performClick(View.java:4438)
            at android.view.View$PerformClick.run(View.java:18422)
            at android.os.Handler.handleCallback(Handler.java:733)
            at android.os.Handler.dispatchMessage(Handler.java:95)
            at android.os.Looper.loop(Looper.java:136)
            at android.app.ActivityThread.main(ActivityThread.java:5034)
            at java.lang.reflect.Method.invokeNative(Native Method)
            at java.lang.reflect.Method.invoke(Method.java:515)
            at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1270)
            at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1086)
            at de.robv.android.xposed.XposedBridge.main(XposedBridge.java:132)
            at dalvik.system.NativeStart.main(Native Method)

这是我的主要课程

    package tabs.ibettergetagoodgradeforthisorillbepissed.sciencefair.beta.mmmeds.com.mmmedstabbeta;

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


public class MainActivity extends FragmentActivity implements ActionBar.TabListener{


    ActionBar actionbar;
    ViewPager viewpager;
    FragmentPageAdapter ft;


    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        viewpager = (ViewPager) findViewById(R.id.pager);
        ft = new FragmentPageAdapter(getSupportFragmentManager());
        actionbar = getActionBar();
        viewpager.setAdapter(ft);
        actionbar.setNavigationMode(ActionBar.NAVIGATION_MODE_TABS);
        actionbar.addTab(actionbar.newTab().setText("Add Medication").setTabListener(this));
        actionbar.addTab(actionbar.newTab().setText("View Medication").setTabListener(this));
        viewpager.setOnPageChangeListener(new ViewPager.OnPageChangeListener() {


            @Override
            public void onPageSelected(int arg0) {
                actionbar.setSelectedNavigationItem(arg0);
            }
            @Override


            public void onPageScrolled(int arg0, float arg1, int arg2) {
                // TODO Auto-generated method stub
            }


            @Override
            public void onPageScrollStateChanged(int arg0) {
                // TODO Auto-generated method stub
            }
        });
    }


    @Override
    public void onTabReselected(Tab tab, FragmentTransaction ft) {
        // TODO Auto-generated method stub
    }


    @Override
    public void onTabSelected(Tab tab, FragmentTransaction ft) {
        viewpager.setCurrentItem(tab.getPosition());
    }


    @Override
    public void onTabUnselected(Tab tab, FragmentTransaction ft) {
        // TODO Auto-generated method stub
    }
}

我的主要活动XML：

<android.support.v4.view.ViewPager
xmlns:android="http://schemas.android.com/apk/res/android"
android:id="@+id/pager"
android:layout_width="match_parent"
android:layout_height="match_parent"
>

我的FragmentPageAdapter类：

    package tabs.ibettergetagoodgradeforthisorillbepissed.sciencefair.beta.mmmeds.com.mmmedstabbeta;

import android.support.v4.app.Fragment;
import android.support.v4.app.FragmentManager;
import android.support.v4.app.FragmentPagerAdapter;


public class FragmentPageAdapter extends FragmentPagerAdapter {
    public FragmentPageAdapter(FragmentManager fm) {
        super(fm);
    }
    @Override
    public Fragment getItem(int arg0) {
        // TODO Auto-generated method stub
        switch (arg0) {
            case 0:
                return new AddMedFragment();
            case 1:
                return new ViewMedFragment();
            default:
                break;
        }
        return null;
    }
    @Override
    public int getCount() {
        // TODO Auto-generated method stub
        return 3;
    }
}

以及其中一个显示片段的示例（它们现在完全相同）：

    package tabs.ibettergetagoodgradeforthisorillbepissed.sciencefair.beta.mmmeds.com.mmmedstabbeta;

/**
 * Created by WindowsSucks on 10/29/2014.
 */

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

public class AddMedFragment extends Fragment {

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
                             Bundle savedInstanceState) {
        // TODO Auto-generated method stub
        return inflater.inflate(R.layout.add_med_layout, container,false);
    }
}

以及相应的XML：

    <?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    >
    <TextView
        android:id="@+id/textView1"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_alignParentTop="true"
        android:layout_centerHorizontal="true"
        android:layout_marginTop="42dp"
        android:text="Welcome to Add Med page"
        android:textAppearance="?android:attr/textAppearanceLarge" />
</RelativeLayout>

非常感谢你们

Answer 1

我能够通过更改FragmentPageAdapter类的getCount（）方法来解决这个问题。它设置为返回3（如上所示），但只应设置为返回2，因为这是我当前设置的选项卡数。

代码：

   package tabs.ibettergetagoodgradeforthisorillbepissed.sciencefair.beta.mmmeds.com.mmmedstabbeta;

import android.support.v4.app.Fragment;
import android.support.v4.app.FragmentManager;
import android.support.v4.app.FragmentPagerAdapter;
public class FragmentPageAdapter extends FragmentPagerAdapter {
    public FragmentPageAdapter(FragmentManager fm) {
        super(fm);
    }
    @Override
    public Fragment getItem(int arg0) {
        // TODO Auto-generated method stub
        switch (arg0) {
            case 0:
                return new AddMedFragment();
            case 1:
                return new ViewMedFragment();
            default:
                break;
        }
        return null;
    }
    @Override
    public int getCount() {
        // TODO Auto-generated method stub
        return 2;
    }
}

应用程序强制在滑动或单击选项卡时关闭

1 个答案: