Android片段自定义适配器

Question

我在Android Fragment中使用自定义适配器有一些问题。下面是代码。但在我在活动中使用这个代码之前，一切都很好。我找不到我在使用Fragments时出错的地方。

package com.testapp.test.fragments;
import org.holoeverywhere.LayoutInflater;
import org.holoeverywhere.app.Fragment;
import com.testapp.test.R;
import android.content.Context;
import android.os.Bundle;
import android.view.View;
import android.view.ViewGroup;
import android.widget.BaseAdapter;
import android.widget.ImageView;
import android.widget.ListView;
import android.widget.TextView;
public class LawDocFragment extends Fragment{
private static LawDocFragment instance;
public static LawDocFragment getInstance() {
    if (LawDocFragment.instance == null) {
        return new LawDocFragment();
    }
    return LawDocFragment.instance;
}
public LawDocFragment() {
    LawDocFragment.instance = this;
}
@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setRetainInstance(true);
}
String[] zakonmenubig;
String[] zakonmenusmall;
Integer[] zakonmenuicon = { R.drawable.ic_menu_zakonu_pravila, 
                            R.drawable.ic_menu_zakonu_strafu, 
                            R.drawable.ic_menu_zakonu_doc,
                            R.drawable.ic_menu_zakonu_u77,
                            R.drawable.ic_menu_zakonu_u33,
                            R.drawable.ic_menu_zakonu_u400,
                            R.drawable.ic_menu_zakonu_p1103};
myAdapter zakonAdapter;
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
        Bundle savedInstanceState) {
    View LawDoc = inflater.inflate(R.layout.zakonbaza);     
    ListView zakonmenulist = (ListView)LawDoc.findViewById(R.id.zakonmenulist);     
    zakonAdapter = new myAdapter();     
    zakonmenulist.setAdapter(zakonAdapter);
    zakonmenubig = getResources().getStringArray(R.array.zakonmenubig);
    zakonmenusmall = getResources().getStringArray(R.array.zakonmenusmall);
    return LawDoc;
}
//start myAdapter
public class myAdapter extends BaseAdapter {
    private LayoutInflater mLayoutInflater;
    public myAdapter(Context ctx) {
        mLayoutInflater = LayoutInflater.from(ctx);
    }
    public int getCount() {
        return zakonmenubig.length;
    }
    public Object getItem(int position) {
        return position;
    }
    public long getItemId(int position) {
        return position;
    }
    public String getString(int position) {
        return zakonmenubig[position] + " (" + zakonmenusmall[position] + ")";
    }
    public View getView(int position, View convertView, ViewGroup parent) {
        if (convertView == null)
            convertView = mLayoutInflater.inflate(R.layout.list_zakonbaza, null);
        ImageView image = (ImageView) convertView.findViewById(R.id.icon);
        image.setImageResource(zakonmenuicon[position]);
        TextView sign = (TextView) convertView.findViewById(R.id.zakonmenuitem);
        sign.setText(zakonmenubig[position]);
        TextView date = (TextView) convertView.findViewById(R.id.zakonmenuitemsmall);
        date.setText(zakonmenusmall[position]);
        return convertView;
    }
} // end myAdapter
}

现在Eclipse显示错误"The constructor LawDocFragment.myAdapter() is undefined"在行

zakonAdapter = new myAdapter();

如果我要改成

zakonAdapter = new myAdapter(getActivity());

我将得到这个EXCEPTION

12-27 00:39:25.297: E/AndroidRuntime(652): FATAL EXCEPTION: main
12-27 00:39:25.297: E/AndroidRuntime(652): java.lang.NullPointerException
12-27 00:39:25.297: E/AndroidRuntime(652):  at com.testapp.test.fragments.fragments.LawDocFragment$myAdapter.getCount(LawDocFragment.java:72)
12-27 00:39:25.297: E/AndroidRuntime(652):  at android.widget.ListView.setAdapter(ListView.java:436)
12-27 00:39:25.297: E/AndroidRuntime(652):  at com.testapp.test.fragments.fragments.LawDocFragment.onCreateView(LawDocFragment.java:55)
12-27 00:39:25.297: E/AndroidRuntime(652):  at android.support.v4.app._HoloFragment.onCreateView(_HoloFragment.java:177)
12-27 00:39:25.297: E/AndroidRuntime(652):  at android.support.v4.app.Fragment.performCreateView(Fragment.java:1460)
12-27 00:39:25.297: E/AndroidRuntime(652):  at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:911)
12-27 00:39:25.297: E/AndroidRuntime(652):  at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1088)
12-27 00:39:25.297: E/AndroidRuntime(652):  at android.support.v4.app.BackStackRecord.run(BackStackRecord.java:682)
12-27 00:39:25.297: E/AndroidRuntime(652):  at android.support.v4.app.FragmentManagerImpl.execPendingActions(FragmentManager.java:1444)
12-27 00:39:25.297: E/AndroidRuntime(652):  at android.support.v4.app.FragmentManagerImpl$1.run(FragmentManager.java:429)
12-27 00:39:25.297: E/AndroidRuntime(652):  at android.os.Handler.handleCallback(Handler.java:587)
12-27 00:39:25.297: E/AndroidRuntime(652):  at android.os.Handler.dispatchMessage(Handler.java:92)
12-27 00:39:25.297: E/AndroidRuntime(652):  at android.os.Looper.loop(Looper.java:123)
12-27 00:39:25.297: E/AndroidRuntime(652):  at android.app.ActivityThread.main(ActivityThread.java:4627)
12-27 00:39:25.297: E/AndroidRuntime(652):  at java.lang.reflect.Method.invokeNative(Native Method)
12-27 00:39:25.297: E/AndroidRuntime(652):  at java.lang.reflect.Method.invoke(Method.java:521)
12-27 00:39:25.297: E/AndroidRuntime(652):  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:868)
12-27 00:39:25.297: E/AndroidRuntime(652):  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:626)
12-27 00:39:25.297: E/AndroidRuntime(652):  at dalvik.system.NativeStart.main(Native Method)    

在行"LawDocFragment.java:72"我有这个代码

return zakonmenubig.length;

和"LawDocFragment.java:55"行，我有

zakonmenulist.setAdapter(zakonAdapter);

我认为类myAdapter有问题，但什么…以及为什么在简单的活动中一切都很好……

我发现了这个问题，并尝试用代码工作，但仍然没有

Answer 1

问题是

1. 在显示错误时使用空白构造函数是正确的，因为在适配器类中没有这样的构造函数。因此，要么创建一个不带参数的构造函数(坏主意)，要么只是在上下文中传递。

2. 你的空指针发生了，因为

   zakonmenubig

在创建适配器时尚未定义，而是在适配器之前创建这些元素，如下所示:

zakonmenubig = getResources().getStringArray(R.array.zakonmenubig);
zakonmenusmall = getResources().getStringArray(R.array.zakonmenusmall);
ListView zakonmenulist = (ListView)LawDoc.findViewById(R.id.zakonmenulist);     
zakonAdapter = new myAdapter();     
zakonmenulist.setAdapter(zakonAdapter);

现在你的zakonmenubig将被初始化