Question

实现我在如何将变量从一个类传递到另一个类时找到的代码但要编译它会给我错误并且掉线，留下错误

我认为错误是在片段

中实现listview的问题

  05-11 23:20:14.697  10975-10975/com.learn2crack.tab E/AndroidRuntime﹕ FATAL EXCEPTION: main
    Process: com.learn2crack.tab, PID: 10975
    java.lang.NullPointerException
            at com.learn2crack.tab.Categoria.onCreateView(Categoria.java:53)
            at android.support.v4.app.Fragment.performCreateView(Fragment.java:1500)
            at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:938)
            at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1115)
            at android.support.v4.app.BackStackRecord.run(BackStackRecord.java:682)
            at android.support.v4.app.FragmentManagerImpl.execPendingActions(FragmentManager.java:1478)
            at android.support.v4.app.FragmentManagerImpl.executePendingTransactions(FragmentManager.java:478)
            at android.support.v4.app.FragmentStatePagerAdapter.finishUpdate(FragmentStatePagerAdapter.java:163)
            at android.support.v4.view.ViewPager.populate(ViewPager.java:1068)
            at android.support.v4.view.ViewPager.populate(ViewPager.java:914)
            at android.support.v4.view.ViewPager.onMeasure(ViewPager.java:1436)
            at android.view.View.measure(View.java:16537)
            at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5135)
            at android.widget.FrameLayout.onMeasure(FrameLayout.java:310)
            at android.view.View.measure(View.java:16537)
            at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5135)
            at com.android.internal.widget.ActionBarOverlayLayout.onMeasure(ActionBarOverlayLayout.java:327)
            at android.view.View.measure(View.java:16537)
            at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5135)
            at android.widget.FrameLayout.onMeasure(FrameLayout.java:310)
            at com.android.internal.policy.impl.PhoneWindow$DecorView.onMeasure(PhoneWindow.java:2291)
            at android.view.View.measure(View.java:16537)
            at android.view.ViewRootImpl.performMeasure(ViewRootImpl.java:1947)
            at android.view.ViewRootImpl.measureHierarchy(ViewRootImpl.java:1137)
            at android.view.ViewRootImpl.performTraversals(ViewRootImpl.java:1326)
            at android.view.ViewRootImpl.doTraversal(ViewRootImpl.java:1024)
            at android.view.ViewRootImpl$TraversalRunnable.run(ViewRootImpl.java:5796)
            at android.view.Choreographer$CallbackRecord.run(Choreographer.java:761)
            at android.view.Choreographer.doCallbacks(Choreographer.java:574)
            at android.view.Choreographer.doFrame(Choreographer.java:544)
            at android.view.Choreographer$FrameDisplayEventReceiver.run(Choreographer.java:747)
            at android.os.Handler.handleCallback(Handler.java:733)
            at android.os.Handler.dispatchMessage(Handler.java:95)
            at android.os.Looper.loop(Looper.java:136)
            at android.app.ActivityThread.main(ActivityThread.java:5102)
            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:779)
            at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:595)
            at de.robv.android.xposed.XposedBridge.main(XposedBridge.java:133)
            at dalvik.system.NativeStart.main(Native Method)

this categoria.java

代码类

 ListView Lv =(ListView) getActivity().findViewById(R.id.list_item);
        Lv.setOnItemClickListener(new OnItemClickListener() {
        // Listview on item click listener


            @Override
            public void onItemClick(AdapterView<?> parent, View view,
                                    int position, long id) {
                // getting values from selected ListItem

                String tagID = ((TextView) view.findViewById(R.id.idCAT))
                        .getText().toString();


                // Starting single contact activity
                Intent in = new Intent(getActivity(),ListaCat.class);
                //in.putExtra(TAG_title, name);
                in.putExtra(TAG_ID, tagID);
                //.putExtra(TAG_description, description);
                startActivity(in);

            }
        });

列出项目

 <LinearLayout
    android:orientation="horizontal"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent">

    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="name"
        android:id="@+id/name"
        android:textColor="#ff7900"
        android:layout_marginLeft="10dp"
        android:textSize="20dp"
        android:gravity="fill_horizontal" />

    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:id="@+id/idCAT"
        android:visibility="invisible" />
</LinearLayout>

远景

<ListView
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:id="@+id/list" />

Answer 1

我能看到的第一件事是view.findViewById(R.id.idCAT)

仅用view

替换它

ListView Lv =(ListView) getActivity().findViewById(R.id.list_item);
    Lv.setOnItemClickListener(new OnItemClickListener() {
    // Listview on item click listener


        @Override
        public void onItemClick(AdapterView<?> parent, View view,
                                int position, long id) {
            // getting values from selected ListItem

           /* String tagID = ((TextView) view)
                    .getText().toString();*/
 TextView txt = (TextView) parent.getChildAt(position - lv.firstVisiblePosition()).findViewById(R.id.list_item);
 String tagId = txt.getText().toString();


            // Starting single contact activity
            Intent in = new Intent(getActivity().getApplicationContext(),ListaCat.class);
            //in.putExtra(TAG_title, name);
            in.putExtra(TAG_ID, tagID);
            //.putExtra(TAG_description, description);
            startActivity(in);

        }
    });

您使用findViewById获得了什么？答案是view
所以你不能在视图中得到另一种观点
您必须将该视图投射到ListView

Answer 2

而不是

 Intent in = new Intent(getActivity(),ListaCat.class);

试试这个

Intent in = new Intent(getActivity().getApplicationContext(),ListaCat.class);

Answer 3

我认为问题是你的Listview没有得到xml替换的ref ListView Lv =（ListView）getActivity（）。findViewById（R.id.list_item）;到 ListView Lv =（ListView）getView（）。findViewById（R.id.list_item）; 然后检查一下。

实现应用程序崩溃意图

3 个答案: