Question

我的第二个片段（Test2）只显示你好世界。

我的问题是每当我在第一个片段（((Test)getActivity()).display(a);）中调用Test1函数时，它会抛出NullPointerException。

我无法检测为什么会抛出NullPointerException，我已经尝试过实现它仍然没有工作的界面方法，给出了同样的错误。

我的主要活动

public class Test extends Activity implements Test1.OnFragmentInteractionListener,Test2.OnFragmentInteractionListener {
private GraphicalView show;
Intent intent;
int i;
static int a[]=new int[4];
String str;
FragmentManager manager=getFragmentManager();
FragmentTransaction transaction=manager.beginTransaction();
FragmentTransaction transaction1=manager.beginTransaction();
@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    overridePendingTransition(R.anim.fadein, R.anim.fadeout);
    ActionBar bar = getActionBar();
    bar.hide();
    // bar.setBackgroundDrawable(new ColorDrawable(Color.parseColor("#3385FF")));
    setContentView(R.layout.activity_bar_report);
    intent=getIntent();
    a=intent.getIntArrayExtra("Data");
    display(a);

}

public void display(int a[])
{  Test1 test1 = new Test1();
    if(TempValues.F_Id==0) {
        test1.newInstance(a);
        transaction.replace(android.R.id.content, test1);
    }
    else if(TempValues.F_Id==1)
    {  Test2 test2 = new Test2();
    transaction.replace(android.R.id.content, test2);
}
    transaction.commit();

}

My 1st Fragment（Test1）

public class Test1 extends Fragment {
private OnFragmentInteractionListener mListener;
private GraphicalView show;
Intent intent;
int i;
static int a[]=new int[4];static String str;
static Bundle args;
Test test=new Test();
public Test1() {

}
public Test1 newInstance(int a[]) {
    Test1 f = new Test1();
    // Supply index input as an argument.
     args = new Bundle();
    args.putIntArray("index", a);
    f.setArguments(args);
    return f;
}

public interface OnFragmentInteractionListener {

}
@Override
public void onAttach(Activity activity) {
    super.onAttach(activity);
    try {
        mListener = (OnFragmentInteractionListener) activity;
    } catch (ClassCastException e) {
        throw new ClassCastException(activity.toString()
                + " must implement OnFragmentInteractionListener");
    }
}

@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
                         Bundle savedInstanceState) {
    View V = inflater.inflate(R.layout.fragment_test1, container, false);
   try{

        a=args.getIntArray("index");
        int c=0;
        XYSeries series=new XYSeries("Report");
        for(i=0;i<4;i++)
        {
            series.add(c+1,a[i]);
            str+=String.valueOf(a[i]);
            c++;
        }
       TextView text=(TextView)getActivity().findViewById(R.id.text);
      text.setText(str);

        XYMultipleSeriesDataset multipleSeriesDataset=new XYMultipleSeriesDataset();
        multipleSeriesDataset.addSeries(series);
        XYSeriesRenderer renderer=new XYSeriesRenderer();
        renderer.setChartValuesTextSize(40);
        renderer.setChartValuesTextAlign(Paint.Align.CENTER);
        renderer.setLineWidth(4);
        renderer.setDisplayChartValues(true);
        renderer.setDisplayChartValuesDistance(1);
        XYMultipleSeriesRenderer multipleSeriesRenderer=new XYMultipleSeriesRenderer();
        multipleSeriesRenderer.addSeriesRenderer(renderer);
        multipleSeriesRenderer.setBarSpacing(1);
        multipleSeriesRenderer.setMarginsColor(Color.argb(0x00, 0xff, 0x00, 0x00));
        multipleSeriesRenderer.setZoomEnabled(false, false);
        multipleSeriesRenderer.setScale(1);
        multipleSeriesRenderer.setXAxisMin(0);
        multipleSeriesRenderer.setYAxisMin(0);
        multipleSeriesRenderer.setXAxisMax(5);
        multipleSeriesRenderer.setPanLimits(new double[]{0.0,4.0,0.0,Double.MAX_VALUE});
        multipleSeriesRenderer.setLabelsTextSize(20);
        multipleSeriesRenderer.setXLabelsColor(Color.BLACK);
        multipleSeriesRenderer.setYLabelsColor(0,Color.BLACK);
        multipleSeriesRenderer.setXLabels(0);
        multipleSeriesRenderer.addXTextLabel(1, "Order \nBooking");
        multipleSeriesRenderer.addXTextLabel(2, "Display/\nCounter Share");
        multipleSeriesRenderer.addXTextLabel(3,"Hygiene \nAudit");
        multipleSeriesRenderer.addXTextLabel(4,"VoC");
        multipleSeriesRenderer.setXLabelsAlign(Paint.Align.CENTER);
        show= ChartFactory.getBarChartView(getActivity(), multipleSeriesDataset, multipleSeriesRenderer, BarChart.Type.DEFAULT);
        multipleSeriesRenderer.setClickEnabled(true);
        multipleSeriesRenderer.setSelectableBuffer(10);
        show.setOnClickListener(new View.OnClickListener()
                                {   @Override
                                    public void onClick(View v)
                                    {   String str="";
                                        SeriesSelection select=show.getCurrentSeriesAndPoint();
                                        if(select.getXValue()==1) {
                                            TempValues.F_Id = 1;
                                            str = String.valueOf(TempValues.F_Id);
                                            ((Test)getActivity()).display(a);

                                            int i = (int) select.getValue();
                                            Toast.makeText(getActivity(), str + String.valueOf(i), Toast.LENGTH_LONG).show();
                                        }
                                    }
                                });
     LinearLayout layout=(LinearLayout)getActivity().findViewById(R.id.BarChart);
      layout.addView(show);


    }catch (Exception e){TextView text=(TextView)getActivity().findViewById(R.id.text);
       text.setText(e.toString());
      }

    return inflater.inflate(R.layout.fragment_test1, container, false);

}

这是我的logCat

02-26 14:19:56.583  30591-30591/com.example.administrator.edge E/AndroidRuntime﹕ FATAL EXCEPTION: main
Process: com.example.administrator.edge, PID: 30591
java.lang.NullPointerException
        at com.example.administrator.edge.Test1$1.onClick(Test1.java:123)
        at android.view.View.performClick(View.java:4470)
        at android.view.View$PerformClick.run(View.java:18599)
        at android.os.Handler.handleCallback(Handler.java:733)
        at android.os.Handler.dispatchMessage(Handler.java:95)
        at android.os.Looper.loop(Looper.java:157)
        at android.app.ActivityThread.main(ActivityThread.java:5633)
        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:896)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:712)
        at dalvik.system.NativeStart.main(Native Method)

Answer 1

您传递给事务的Test1实例不是您设置参数的实例。 newInstance()方法返回带有参数的实例，但它被丢弃。这意味着在事务实例中，args中的onCreateView()为空，并且当您调用NullPointerException方法时，它会抛出getIntArray()。按如下方式更改display()方法：

public void display(int a[])
{
    if(TempValues.F_Id==0) {
        Test1 test1 = Test1.newInstance(a);
        transaction.replace(android.R.id.content, test1);
    }
    ...     
}

此外，newInstance()方法应该是静态的：

public static Test1 newInstance(int a[])

Answer 2

1。 Diplay方法错误。

test1.newInstance(a);

执行此操作将返回Test1的新实例，该实例使用您作为参数传递的数组，但该实例与test1变量引用的实例不同。将newInstance方法设为静态，并将其命名为：

Test1.newInstance(a);

2。请勿在{{1}}内拨打getActvity()。原因是因为框架不能保证在onCreateView调用Activity时完全创建onCreateView。您可以使用Fragment回调。出于同样的原因，这并不能保证每次都有效：

onActivityCreated

由于您不知道TextView text=(TextView)getActivity().findViewById(R.id.text); text.setText(str);是否确实已完全创建，因此在Activity上调用findViewById可能会返回Activity，从而在此之后立即生成NullPointerException，当你拨打null时。

从fragment调用父活动的方法，抛出空指针异常

2 个答案: