android - 在 fragment 选项卡中插入 ListView 后应用程序崩溃

Question

我找到了一个代码来实现带 fragment 的选项卡。我试图将 ListView 放入 fragment 中，但应用程序因以下错误而崩溃。你能看看代码并指导我吗？谢谢。

01-18 11:44:49.130: E/AndroidRuntime(1908): FATAL EXCEPTION: main
01-18 11:44:49.130: E/AndroidRuntime(1908): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.abe/com.example.abe.TabsFragmentActivity}: java.lang.NullPointerException
01-18 11:44:49.130: E/AndroidRuntime(1908):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2059)
01-18 11:44:49.130: E/AndroidRuntime(1908):     at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2084)
01-18 11:44:49.130: E/AndroidRuntime(1908):     at android.app.ActivityThread.access$600(ActivityThread.java:130)
01-18 11:44:49.130: E/AndroidRuntime(1908):     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1195)
01-18 11:44:49.130: E/AndroidRuntime(1908):     at android.os.Handler.dispatchMessage(Handler.java:99)
01-18 11:44:49.130: E/AndroidRuntime(1908):     at android.os.Looper.loop(Looper.java:137)
01-18 11:44:49.130: E/AndroidRuntime(1908):     at android.app.ActivityThread.main(ActivityThread.java:4745)
01-18 11:44:49.130: E/AndroidRuntime(1908):     at java.lang.reflect.Method.invokeNative(Native Method)
01-18 11:44:49.130: E/AndroidRuntime(1908):     at java.lang.reflect.Method.invoke(Method.java:511)
01-18 11:44:49.130: E/AndroidRuntime(1908):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:786)
01-18 11:44:49.130: E/AndroidRuntime(1908):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553)
01-18 11:44:49.130: E/AndroidRuntime(1908):     at dalvik.system.NativeStart.main(Native Method)
01-18 11:44:49.130: E/AndroidRuntime(1908): Caused by: java.lang.NullPointerException
01-18 11:44:49.130: E/AndroidRuntime(1908):     at com.example.abe.Tab1Fragment.onCreateView(Tab1Fragment.java:44)
01-18 11:44:49.130: E/AndroidRuntime(1908):     at android.support.v4.app.Fragment.performCreateView(Fragment.java:1460)
01-18 11:44:49.130: E/AndroidRuntime(1908):     at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:911)
01-18 11:44:49.130: E/AndroidRuntime(1908):     at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1088)
01-18 11:44:49.130: E/AndroidRuntime(1908):     at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1070)
01-18 11:44:49.130: E/AndroidRuntime(1908):     at android.support.v4.app.FragmentManagerImpl.dispatchActivityCreated(FragmentManager.java:1861)
01-18 11:44:49.130: E/AndroidRuntime(1908):     at android.support.v4.app.FragmentActivity.onStart(FragmentActivity.java:547)
01-18 11:44:49.130: E/AndroidRuntime(1908):     at android.app.Instrumentation.callActivityOnStart(Instrumentation.java:1163)
01-18 11:44:49.130: E/AndroidRuntime(1908):     at android.app.Activity.performStart(Activity.java:5018)
01-18 11:44:49.130: E/AndroidRuntime(1908):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2032)
01-18 11:44:49.130: E/AndroidRuntime(1908):     ... 11 more

TABFRAGMENTACTIVITY 类:

import java.util.HashMap;
import android.content.Context;
import android.os.Bundle;
import android.support.v4.app.Fragment;
import android.support.v4.app.FragmentActivity;
import android.support.v4.app.FragmentTransaction;
import android.view.View;
import android.widget.TabHost;
import android.widget.TabHost.TabContentFactory;
public class TabsFragmentActivity extends FragmentActivity implements TabHost.OnTabChangeListener {

    private TabHost mTabHost;
    private HashMap<String, TabInfo> mapTabInfo = new HashMap<String, TabsFragmentActivity.TabInfo>();
    private TabInfo mLastTab = null;
    private class TabInfo {
        private String tag;
    private Class<?> clss;
    private Bundle args;
    private Fragment fragment;
    TabInfo(String tag, Class<?> clazz, Bundle args) {
        this.tag = tag;
        this.clss = clazz;
        this.args = args;
    }

    }
    class TabFactory implements TabContentFactory {

        private final Context mContext;
    public TabFactory(Context context) 
    {
        mContext = context;
    }
    public View createTabContent(String tag) 
    {
        View v = new View(mContext);
        v.setMinimumWidth(0);
        v.setMinimumHeight(0);
        return v;
    }

    }
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.tabs_layout);
        initialiseTabHost(savedInstanceState);
        if (savedInstanceState != null) {
    mTabHost.setCurrentTabByTag(savedInstanceState.getString("tab")); //set the tab as per the saved state
    }
    }
protected void onSaveInstanceState(Bundle outState) {
    outState.putString("tab", mTabHost.getCurrentTabTag()); //save the tab selected
    super.onSaveInstanceState(outState);
}
    private void initialiseTabHost(Bundle args) {
        mTabHost = (TabHost)findViewById(android.R.id.tabhost);
    mTabHost.setup();
    TabInfo tabInfo = null;
    TabsFragmentActivity.addTab(this, this.mTabHost, this.mTabHost.newTabSpec("Tab1").setIndicator("Tab 1"), ( tabInfo = new TabInfo("Tab1", Tab1Fragment.class, args)));
    this.mapTabInfo.put(tabInfo.tag, tabInfo);
    TabsFragmentActivity.addTab(this, this.mTabHost, this.mTabHost.newTabSpec("Tab2").setIndicator("Tab 2"), ( tabInfo = new TabInfo("Tab2", Tab2Fragment.class, args)));
    this.mapTabInfo.put(tabInfo.tag, tabInfo);
    TabsFragmentActivity.addTab(this, this.mTabHost, this.mTabHost.newTabSpec("Tab3").setIndicator("Tab 3"), ( tabInfo = new TabInfo("Tab3", Tab3Fragment.class, args)));
    this.mapTabInfo.put(tabInfo.tag, tabInfo);
    this.onTabChanged("Tab1");

    mTabHost.setOnTabChangedListener(this);
    }
    private static void addTab(TabsFragmentActivity activity, TabHost tabHost, TabHost.TabSpec tabSpec, TabInfo tabInfo) {
        tabSpec.setContent(activity.new TabFactory(activity));
    String tag = tabSpec.getTag();
    tabInfo.fragment = activity.getSupportFragmentManager().findFragmentByTag(tag);
    if (tabInfo.fragment != null && !tabInfo.fragment.isDetached()) {
    FragmentTransaction ft = activity.getSupportFragmentManager().beginTransaction();
    ft.detach(tabInfo.fragment);
    ft.commit();
    activity.getSupportFragmentManager().executePendingTransactions();
    }
    tabHost.addTab(tabSpec);
    }
    public void onTabChanged(String tag) {
        TabInfo newTab = this.mapTabInfo.get(tag);
        if (mLastTab != newTab) {
            FragmentTransaction ft = this.getSupportFragmentManager().beginTransaction();
    if (mLastTab != null) {
        if (mLastTab.fragment != null) {
            ft.detach(mLastTab.fragment);
        }
    }
    if (newTab != null) {
        if (newTab.fragment == null) {
        newTab.fragment = Fragment.instantiate(this,
            newTab.clss.getName(), newTab.args);
        ft.add(R.id.realtabcontent, newTab.fragment, newTab.tag);
        } else {
        ft.attach(newTab.fragment);
        }
    }
    mLastTab = newTab;
    ft.commit();
    this.getSupportFragmentManager().executePendingTransactions();
        }
}


}

TABFRAGMENT 类 - 这是我尝试放置 ListView 的地方:

import android.annotation.TargetApi;
import android.os.Build;
import android.os.Bundle;
import android.support.v4.app.Fragment;
import android.support.v4.app.ListFragment;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.ArrayAdapter;
import android.widget.LinearLayout;
import android.widget.ListView;
public class Tab1Fragment extends ListFragment {
    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
            Bundle savedInstanceState) {
        ListView lv = (ListView)getView().findViewById(R.id.listView1);
        String android_array1[] = new String[50];
        for(int i=0;i<50;i++)
        {
            android_array1[i]="ab"+i;
        }
        ArrayAdapter<String> adapter = new ArrayAdapter<String>(getActivity().getBaseContext(), android.R.layout.simple_list_item_1, android_array1);
        lv.setAdapter(adapter);                     
        return (LinearLayout)inflater.inflate(R.layout.tab_frag1_layout, container, false);
    }
}

这是 tabfragment 类的 xml:

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout
xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:background="#FF0000"
>

<ListView
    android:id="@+id/listView1"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:layout_weight="1" >
</ListView>

</LinearLayout>  

Answer 1

注意:

如果您在 Tab1Fragment 中扩展 ListFragment那么就不需要使用

ListView lv = (ListView) root.findViewById(R.id.listView1);

只需删除它。

最后你的 onCreateView(..) 方法看起来像这样:

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

        String android_array1[] = new String[50];
        for(int i=0;i<50;i++)
        {
            android_array1[i]="ab"+i;
        }
        ArrayAdapter<String> adapter = new ArrayAdapter<String>(getActivity().getBaseContext(), android.R.layout.simple_list_item_1, android_array1);

        setListAdapter(adapter);        

        return super.onCreateView(inflater, container, savedInstanceState);
    } 

有关更多信息，请参阅此链接

http://wptrafficanalyzer.in/blog/creating-navigation-tabs-using-tabhost-and-fragments-in-android/