致命错误：无法实例化活动组件

Question

每当我点击ListView时，我一直在尝试查看项目的详细信息。但我经常收到一条错误，指出无法实例化活动。

这是我的logcat

10-29 03:01:44.516: E/AndroidRuntime(1252): FATAL EXCEPTION: main
10-29 03:01:44.516: E/AndroidRuntime(1252): Process: com.esggoa.iffi_app, PID: 1252
10-29 03:01:44.516: E/AndroidRuntime(1252): java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{com.esggoa.iffi_app/com.esggoa.iffi_app.model.SingleItemView}: java.lang.NullPointerException
10-29 03:01:44.516: E/AndroidRuntime(1252):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2121)
10-29 03:01:44.516: E/AndroidRuntime(1252):     at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2245)
10-29 03:01:44.516: E/AndroidRuntime(1252):     at android.app.ActivityThread.access$800(ActivityThread.java:135)
10-29 03:01:44.516: E/AndroidRuntime(1252):     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1196)
10-29 03:01:44.516: E/AndroidRuntime(1252):     at android.os.Handler.dispatchMessage(Handler.java:102)
10-29 03:01:44.516: E/AndroidRuntime(1252):     at android.os.Looper.loop(Looper.java:136)
10-29 03:01:44.516: E/AndroidRuntime(1252):     at android.app.ActivityThread.main(ActivityThread.java:5017)
10-29 03:01:44.516: E/AndroidRuntime(1252):     at java.lang.reflect.Method.invokeNative(Native Method)
10-29 03:01:44.516: E/AndroidRuntime(1252):     at java.lang.reflect.Method.invoke(Method.java:515)
10-29 03:01:44.516: E/AndroidRuntime(1252):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:779)
10-29 03:01:44.516: E/AndroidRuntime(1252):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:595)
10-29 03:01:44.516: E/AndroidRuntime(1252):     at dalvik.system.NativeStart.main(Native Method)
10-29 03:01:44.516: E/AndroidRuntime(1252): Caused by: java.lang.NullPointerException
10-29 03:01:44.516: E/AndroidRuntime(1252):     at com.esggoa.iffi_app.model.SingleItemView.<init>(SingleItemView.java:26)
10-29 03:01:44.516: E/AndroidRuntime(1252):     at java.lang.Class.newInstanceImpl(Native Method)
10-29 03:01:44.516: E/AndroidRuntime(1252):     at java.lang.Class.newInstance(Class.java:1208)
10-29 03:01:44.516: E/AndroidRuntime(1252):     at android.app.Instrumentation.newActivity(Instrumentation.java:1061)
10-29 03:01:44.516: E/AndroidRuntime(1252):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2112)
10-29 03:01:44.516: E/AndroidRuntime(1252):     ... 11 more

同样如上所述

Caused by: java.lang.NullPointerException
10-29 03:01:44.516: E/AndroidRuntime(1252): at com.esggoa.iffi_app.model.SingleItemView.<init>(SingleItemView.java:26)

我在

下面发布我的SingleItemView.java

public class SingleItemView extends Fragment {
    // Declare Variables
    String rank;
    String country;
    String population;
    String flag;
    String position;
    ImageLoader imageLoader = new ImageLoader(getActivity().getApplicationContext());
    private FragmentActivity fa;
    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
            Bundle savedInstanceState)
    {

        View rootView = inflater.inflate(R.layout.singleitemview, container, false);

        return rootView;

    }
    @Override
    public void onStart() {
        super.onStart();
        // Get the view from singleitemview.xml


        Intent i = new Intent(fa, SingleItemView.class);
        // Get the result of rank
        rank = i.getStringExtra("rank");
        // Get the result of country
        country = i.getStringExtra("country");
        // Get the result of population
        population = i.getStringExtra("population");
        // Get the result of flag
        flag = i.getStringExtra("flag");

        // Locate the TextViews in singleitemview.xml
        TextView txtrank = (TextView) getView().findViewById(R.id.rank);
        TextView txtcountry = (TextView) getView().findViewById(R.id.country);
        TextView txtpopulation = (TextView) getView().findViewById(R.id.population);

        // Locate the ImageView in singleitemview.xml
        ImageView imgflag = (ImageView) getView().findViewById(R.id.flag);

        // Set results to the TextViews
        txtrank.setText(rank);
        txtcountry.setText(country);
        txtpopulation.setText(population);

        // Capture position and set results to the ImageView
        // Passes flag images URL into ImageLoader.class
        imageLoader.DisplayImage(flag, imgflag);
    }
}

感谢任何帮助

10-29 05:20:12.075: E/AndroidRuntime(1108): FATAL EXCEPTION: main
10-29 05:20:12.075: E/AndroidRuntime(1108): Process: com.esggoa.iffi_app, PID: 1108
10-29 05:20:12.075: E/AndroidRuntime(1108): java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{com.esggoa.iffi_app/com.esggoa.iffi_app.model.SingleItemView}: java.lang.ClassCastException: com.esggoa.iffi_app.model.SingleItemView cannot be cast to android.app.Activity
10-29 05:20:12.075: E/AndroidRuntime(1108):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2121)
10-29 05:20:12.075: E/AndroidRuntime(1108):     at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2245)
10-29 05:20:12.075: E/AndroidRuntime(1108):     at android.app.ActivityThread.access$800(ActivityThread.java:135)
10-29 05:20:12.075: E/AndroidRuntime(1108):     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1196)
10-29 05:20:12.075: E/AndroidRuntime(1108):     at android.os.Handler.dispatchMessage(Handler.java:102)
10-29 05:20:12.075: E/AndroidRuntime(1108):     at android.os.Looper.loop(Looper.java:136)
10-29 05:20:12.075: E/AndroidRuntime(1108):     at android.app.ActivityThread.main(ActivityThread.java:5017)
10-29 05:20:12.075: E/AndroidRuntime(1108):     at java.lang.reflect.Method.invokeNative(Native Method)
10-29 05:20:12.075: E/AndroidRuntime(1108):     at java.lang.reflect.Method.invoke(Method.java:515)
10-29 05:20:12.075: E/AndroidRuntime(1108):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:779)
10-29 05:20:12.075: E/AndroidRuntime(1108):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:595)
10-29 05:20:12.075: E/AndroidRuntime(1108):     at dalvik.system.NativeStart.main(Native Method)
10-29 05:20:12.075: E/AndroidRuntime(1108): Caused by: java.lang.ClassCastException: com.esggoa.iffi_app.model.SingleItemView cannot be cast to android.app.Activity
10-29 05:20:12.075: E/AndroidRuntime(1108):     at android.app.Instrumentation.newActivity(Instrumentation.java:1061)
10-29 05:20:12.075: E/AndroidRuntime(1108):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2112)
10-29 05:20:12.075: E/AndroidRuntime(1108):     ... 11 more

Answer 1

您无法在View的开头使用Fragment Context。只需更改此行

即可

ImageLoader imageLoader = new ImageLoader(getActivity().getApplicationContext());

到

ImageLoader imageLoader;

并在ImageLoader方法中初始化您的onCreateView()课程。

imageLoader = new ImageLoader(getActivity());

同样SingleItemView是您的Fragment课程，因此您无法通过Intent进行调用。

 Intent i = new Intent(fa, SingleItemView.class);

Answer 2

移动views'中所有onCreateView(...)的所有初始化，并在类级别声明这些视图globally。从意图中获取信息是错误的。这样做

public class SingleItemView extends Fragment {
    // Declare Variables
    private String rank;
    private String country;
    private String population;
    private String flag;
    private String position;
    private TextView txtrank;
    private TextView txtcountry;
    private TextView txtpopulation;
    private ImageView imgflag;
    ImageLoader imageLoader;

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

        View rootView = inflater.inflate(R.layout.singleitemview, container, false);
        rank = getArguments().getString("rank");
        country = getArguments().getString("country");
        population = getArguments().getString("population");
        flag = getArguments().getString("flag");

        txtrank = (TextView) rootView.findViewById(R.id.rank);
        txtcountry = (TextView) rootView.findViewById(R.id.country);
        txtpopulation = (TextView) rootView.findViewById(R.id.population);
        imgflag = (ImageView) rootView.findViewById(R.id.flag);

        txtrank.setText(rank);
        txtcountry.setText(country);
        txtpopulation.setText(population);

        imageLoader = new ImageLoader(getActivity());
        // Capture position and set results to the ImageView
        // Passes flag images URL into ImageLoader.class
        imageLoader.DisplayImage(flag, imgflag);

        return rootView;
    }
}

Answer 3

onCreateView（）：调用以创建与片段关联的视图层次结构。  最好使用onActivityCreated（）而不是onStart（）。

private TextView txtrank;
private TextView txtcountry;
private TextView txtpopulation;
private ImageView imgflag;

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

    View rootView = inflater.inflate(R.layout.singleitemview, container, false);
    // Locate the TextViews in singleitemview.xml
    txtrank = (TextView) rootView .findViewById(R.id.rank);
    txtcountry = (TextView) rootView .findViewById(R.id.country);
    txtpopulation = (TextView)rootView .findViewById(R.id.population);

    // Locate the ImageView in singleitemview.xml
    imgflag = (ImageView) rootView .findViewById(R.id.flag);
    return rootView;

}
@Override
public void onStart() {
   //......bla bla
  // Set results to the TextViews
    txtrank.setText(rank);
    txtcountry.setText(country);
    txtpopulation.setText(population);

    // Capture position and set results to the ImageView
    // Passes flag images URL into ImageLoader.class
    imageLoader.DisplayImage(flag, imgflag);

}