Question

我正在使用滑动标签创建地址簿应用程序，即＆＃34; ViewPager＆＃34;。当我运行应用程序时，它崩溃了。我收到错误，我不明白。请有人可以帮助我吗？感谢。

这是我的Fragm.java Fragment类。

package com.rufflez.viewpagerexample;

import android.database.Cursor;
import android.net.Uri;
import android.os.Bundle;
import android.provider.ContactsContract;
import android.support.v4.app.Fragment;
import android.support.v4.widget.CursorAdapter;
import android.support.v4.widget.SimpleCursorAdapter;  
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.ListView;

public class Fragm extends Fragment{
private CursorAdapter mAdapter;
public ListView listView;
public Cursor cursor;


public static final String[] FROM = { ContactsContract.Contacts.DISPLAY_NAME_PRIMARY, ContactsContract.Contacts.PHOTO_THUMBNAIL_URI };
private static final int[] TO = { R.id.text_name, R.id.contact_thumbnail };

int layout = R.layout.contact_list_item;

private android.content.Context context = getActivity();
public View view;
public static Uri uri;

// columns requested from the database
    private static final String[] PROJECTION = {
        ContactsContract.Contacts._ID,
        ContactsContract.Contacts.PHOTO_THUMBNAIL_URI,
        ContactsContract.Contacts.DISPLAY_NAME_PRIMARY,
        ContactsContract.Contacts.HAS_PHONE_NUMBER,
        ContactsContract.Contacts.IN_VISIBLE_GROUP
    };

    // this goes in the CursorLoader parameter list, it filters
    // out only those contacts who have a phone number
    private static final String SELECTION = 
            ContactsContract.Contacts.HAS_PHONE_NUMBER + "='1'";

    // Empty public constructor, required by the system
    public Fragm() {}

public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState){

    View view =  inflater.inflate(R.layout.contact_list_view,
            container, true);
    listView = (ListView) view.findViewById(R.id.list); 

    Cursor c = null; // there is no cursor yet
    int flags = 0;
    mAdapter = new SimpleCursorAdapter(context, layout, c, FROM, TO, flags);

    return view;
}
}

这是我的TestFragmentAdapter.java类

package com.rufflez.viewpagerexample;

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

import com.viewpagerindicator.IconPagerAdapter;

public class TestFragmentAdapter extends FragmentPagerAdapter implements      IconPagerAdapter{
protected static final String[] CONTENT = new String[] {
    "This", "Is", "A", "Test"   
};

private int mCount = CONTENT.length;

public TestFragmentAdapter(FragmentManager fm) {
    super(fm);
}

@Override
public int getIconResId(int index) {
    // TODO Auto-generated method stub
    return 0;
}

@Override
public Fragment getItem(int position) {
    Fragment fragment = new Fragment1();
    switch(position){
    case 0:
        fragment = new Fragment1();
        break;
    case 1:
        fragment = new Fragm();
        break;
    case 2:
        fragment = new Fragment3();
        break;
    case 3:
        fragment = new Fragment4();
        break;
    }
    return fragment;
}

@Override
public int getCount() {
    return mCount;
}

@Override
public CharSequence getPageTitle(int position){
    String title = "";
    switch(position){
    case 0:
        title = "Fragment 1";
        break;
    case 1:
        title = "Fragment 2";
        break;
    case 2:
        title = "Fragment 3";
        break;
    case 3:
        title = "Fragment 4";
        break;
    }

    return title;
}

public void setCount(int count){
    if (count > 0 && count < 10){
        mCount = count;
        notifyDataSetChanged();
    }
}

}

这是我的Logcat错误

08-31 21:42:57.956: E/AndroidRuntime(6614): Process: com.rufflez.viewpagerexample, PID: 6614
08-31 21:42:57.956: E/AndroidRuntime(6614): java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.Object android.content.Context.getSystemService(java.lang.String)' on a null object reference
08-31 21:42:57.956: E/AndroidRuntime(6614):     at android.support.v4.widget.ResourceCursorAdapter.<init>(ResourceCursorAdapter.java:95)
08-31 21:42:57.956: E/AndroidRuntime(6614):     at android.support.v4.widget.SimpleCursorAdapter.<init>(SimpleCursorAdapter.java:89)
08-31 21:42:57.956: E/AndroidRuntime(6614):     at com.rufflez.viewpagerexample.Fragm.onCreateView(Fragm.java:55)
08-31 21:42:57.956: E/AndroidRuntime(6614):     at android.support.v4.app.Fragment.performCreateView(Fragment.java:1500)
08-31 21:42:57.956: E/AndroidRuntime(6614):     at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:938)
08-31 21:42:57.956: E/AndroidRuntime(6614):     at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1115)
08-31 21:42:57.956: E/AndroidRuntime(6614):     at android.support.v4.app.BackStackRecord.run(BackStackRecord.java:682)
08-31 21:42:57.956: E/AndroidRuntime(6614):     at android.support.v4.app.FragmentManagerImpl.execPendingActions(FragmentManager.java:1478)
08-31 21:42:57.956: E/AndroidRuntime(6614):     at android.support.v4.app.FragmentManagerImpl.executePendingTransactions(FragmentManager.java:478)
08-31 21:42:57.956: E/AndroidRuntime(6614):     at android.support.v4.app.FragmentPagerAdapter.finishUpdate(FragmentPagerAdapter.java:141)
08-31 21:42:57.956: E/AndroidRuntime(6614):     at android.support.v4.view.ViewPager.populate(ViewPager.java:1068)
08-31 21:42:57.956: E/AndroidRuntime(6614):     at android.support.v4.view.ViewPager.populate(ViewPager.java:914)
08-31 21:42:57.956: E/AndroidRuntime(6614):     at android.support.v4.view.ViewPager.onMeasure(ViewPager.java:1436)
08-31 21:42:57.956: E/AndroidRuntime(6614):     at android.view.View.measure(View.java:18580)
08-31 21:42:57.956: E/AndroidRuntime(6614):     at android.widget.LinearLayout.measureVertical(LinearLayout.java:874)
08-31 21:42:57.956: E/AndroidRuntime(6614):     at android.widget.LinearLayout.onMeasure(LinearLayout.java:612)
08-31 21:42:57.956: E/AndroidRuntime(6614):     at android.view.View.measure(View.java:18580)
08-31 21:42:57.956: E/AndroidRuntime(6614):     at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5827)
08-31 21:42:57.956: E/AndroidRuntime(6614):     at android.widget.FrameLayout.onMeasure(FrameLayout.java:430)
08-31 21:42:57.956: E/AndroidRuntime(6614):     at android.view.View.measure(View.java:18580)
08-31 21:42:57.956: E/AndroidRuntime(6614):     at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5827)
08-31 21:42:57.956: E/AndroidRuntime(6614):     at com.android.internal.widget.ActionBarOverlayLayout.onMeasure(ActionBarOverlayLayout.java:447)
08-31 21:42:57.956: E/AndroidRuntime(6614):     at android.view.View.measure(View.java:18580)
08-31 21:42:57.956: E/AndroidRuntime(6614):     at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5827)
08-31 21:42:57.956: E/AndroidRuntime(6614):     at android.widget.FrameLayout.onMeasure(FrameLayout.java:430)
08-31 21:42:57.956: E/AndroidRuntime(6614):     at com.android.internal.policy.impl.PhoneWindow$DecorView.onMeasure(PhoneWindow.java:2897)
08-31 21:42:57.956: E/AndroidRuntime(6614):     at android.view.View.measure(View.java:18580)
08-31 21:42:57.956: E/AndroidRuntime(6614):     at android.view.ViewRootImpl.performMeasure(ViewRootImpl.java:2248)
08-31 21:42:57.956: E/AndroidRuntime(6614):     at android.view.ViewRootImpl.measureHierarchy(ViewRootImpl.java:1306)
08-31 21:42:57.956: E/AndroidRuntime(6614):     at android.view.ViewRootImpl.performTraversals(ViewRootImpl.java:1548)

Answer 1

您的context为空。您需要在onAttach之后填充它。一种可能的解决方案是从onCreateView方法中设置它。

以下是有关片段和活动生命周期的一些信息的链接：https://github.com/xxv/android-lifecycle

片段上的

getActivity()只会返回onAttach和onDetach之间的活动

Answer 2

由于初始化上下文的方式，您得到一个空指针：

this

以下内容适用于某项活动：

private Context context = getActivity();

但是对于一个片段，它将在周期的早期，所以你需要在片段附加后进行。

private Context context = this;是一个很好的地方：

OnCreate()

运行包含List的片段

2 个答案: