Android从另一个片段设置Textview

【问题标题】：Android set Textview from another fragmentAndroid从另一个片段设置Textview
【发布时间】：2016-01-27 14:30:14
【问题描述】：

我想从一个片段到另一个片段的 setText 到一个 Textview。

我该怎么做？现在我得到一个：java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.TextView.setText(java.lang.CharSequence)' on an null object reference

FragmentRonde1.java

lv1.setOnItemClickListener(new AdapterView.OnItemClickListener() {
        @Override
        public void onItemClick(AdapterView<?> parent, View view, int position, long id) {

            ListClickedFragment newFragment = new ListClickedFragment();
            FragmentTransaction transaction = getFragmentManager().beginTransaction();

            transaction.replace(R.id.fragment_container, newFragment);
            transaction.addToBackStack(null);

            transaction.commit();

            Cursor c2 = db.getIdOfSelectedItem(id);

            ListClickedFragment fragmentRonde1 = new ListClickedFragment();

            if (c2 != null) {
                c2.moveToFirst();

                // i want to set listClickedTitle from here but listClickedTitle is in ListClickedFragment
                fragmentRonde1.gettext(c2.getString(c2.getColumnIndex("title")));

            }

        }
    });

这是 ListCLickedTitle 所在片段的类：ListClickedFragment

public class ListClickedFragment extends android.support.v4.app.Fragment {

TextView tvTitle, tvDesc, tv, oop;


public ListClickedFragment() {
    // Required empty public constructor
}




@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
                         Bundle savedInstanceState) {
    // Inflate the layout for this fragment
    final View rootview2 = inflater.inflate(R.layout.fragment_list_clicked, container, false);

    tvTitle = (TextView)getActivity().findViewById(R.id.listClickedTitle);

    return rootview2;
}

public void gettext (String text) {

    tvTitle.setText(text);

}
}

LOGCAT

    10-28 09:37:25.373 14349-14349/justin.drawer E/InputEventReceiver: Exception dispatching input event.
10-28 09:37:25.381 14349-14349/justin.drawer E/MessageQueue-JNI: Exception in MessageQueue callback: handleReceiveCallback
10-28 09:37:25.420 14349-14349/justin.drawer E/MessageQueue-JNI: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.TextView.setText(java.lang.CharSequence)' on a null object reference
10-28 09:37:25.420 14349-14349/justin.drawer E/MessageQueue-JNI:     at justin.drawer.ListClickedFragment.gettext(ListClickedFragment.java:40)
10-28 09:37:25.420 14349-14349/justin.drawer E/MessageQueue-JNI:     at justin.drawer.FragmentRonde1$1.onItemClick(FragmentRonde1.java:71)
10-28 09:37:25.420 14349-14349/justin.drawer E/MessageQueue-JNI:     at android.widget.AdapterView.performItemClick(AdapterView.java:310)
10-28 09:37:25.420 14349-14349/justin.drawer E/MessageQueue-JNI:     at android.widget.AbsListView.performItemClick(AbsListView.java:1145)
10-28 09:37:25.420 14349-14349/justin.drawer E/MessageQueue-JNI:     at android.widget.AbsListView$PerformClick.run(AbsListView.java:3042)
10-28 09:37:25.420 14349-14349/justin.drawer E/MessageQueue-JNI:     at android.widget.AbsListView.onTouchUp(AbsListView.java:3891)
10-28 09:37:25.420 14349-14349/justin.drawer E/MessageQueue-JNI:     at android.widget.AbsListView.onTouchEvent(AbsListView.java:3656)
10-28 09:37:25.420 14349-14349/justin.drawer E/MessageQueue-JNI:     at android.view.View.dispatchTouchEvent(View.java:9294)
10-28 09:37:25.420 14349-14349/justin.drawer E/MessageQueue-JNI:     at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:2547)
10-28 09:37:25.420 14349-14349/justin.drawer E/MessageQueue-JNI:     at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:2240)
10-28 09:37:25.420 14349-14349/justin.drawer E/MessageQueue-JNI:     at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:2553)
10-28 09:37:25.420 14349-14349/justin.drawer E/MessageQueue-JNI:     at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:2254)
10-28 09:37:25.420 14349-14349/justin.drawer E/MessageQueue-JNI:     at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:2553)
10-28 09:37:25.420 14349-14349/justin.drawer E/MessageQueue-JNI:     at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:2254)
10-28 09:37:25.420 14349-14349/justin.drawer E/MessageQueue-JNI:     at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:2553)
10-28 09:37:25.420 14349-14349/justin.drawer E/MessageQueue-JNI:     at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:2254)
10-28 09:37:25.420 14349-14349/justin.drawer E/MessageQueue-JNI:     at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:2553)
10-28 09:37:25.420 14349-14349/justin.drawer E/MessageQueue-JNI:     at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:2254)
10-28 09:37:25.420 14349-14349/justin.drawer E/MessageQueue-JNI:     at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:2553)
10-28 09:37:25.420 14349-14349/justin.drawer E/MessageQueue-JNI:     at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:2254)
10-28 09:37:25.420 14349-14349/justin.drawer E/MessageQueue-JNI:     at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:2553)
10-28 09:37:25.420 14349-14349/justin.drawer E/MessageQueue-JNI:     at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:2254)
10-28 09:37:25.420 14349-14349/justin.drawer E/MessageQueue-JNI:     at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:2553)
10-28 09:37:25.420 14349-14349/justin.drawer E/MessageQueue-JNI:     at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:2254)
10-28 09:37:25.420 14349-14349/justin.drawer E/MessageQueue-JNI:     at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:2553)
10-28 09:37:25.420 14349-14349/justin.drawer E/MessageQueue-JNI:     at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:2254)
10-28 09:37:25.420 14349-14349/justin.drawer E/MessageQueue-JNI:     at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:2553)
10-28 09:37:25.420 14349-14349/justin.drawer E/MessageQueue-JNI:     at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:2254)
10-28 09:37:25.420 14349-14349/justin.drawer E/MessageQueue-JNI:     at com.android.internal.policy.PhoneWindow$DecorView.superDispatchTouchEvent(PhoneWindow.java:2403)
10-28 09:37:25.420 14349-14349/justin.drawer E/MessageQueue-JNI:     at com.android.internal.policy.PhoneWindow.superDispatchTouchEvent(PhoneWindow.java:1737)
10-28 09:37:25.420 14349-14349/justin.drawer E/MessageQueue-JNI:     at android.app.Activity.dispatchTouchEvent(Activity.java:2765)
10-28 09:37:25.420 14349-14349/justin.drawer E/MessageQueue-JNI:     at android.support.v7.internal.view.WindowCallbackWrapper.dispatchTouchEvent(WindowCallbackWrapper.java:60)
10-28 09:37:25.420 14349-14349/justin.drawer E/MessageQueue-JNI:     at android.support.v7.internal.view.WindowCallbackWrapper.dispatchTouchEvent(WindowCallbackWrapper.java:60)
10-28 09:37:25.420 14349-14349/justin.drawer E/MessageQueue-JNI:     at com.android.internal.policy.PhoneWindow$DecorView.dispatchTouchEvent(PhoneWindow.java:2364)
10-28 09:37:25.420 14349-14349/justin.drawer E/MessageQueue-JNI:     at android.view.View.dispatchPointerEvent(View.java:9514)
10-28 09:37:25.420 14349-14349/justin.drawer E/MessageQueue-JNI:     at android.view.ViewRootImpl$ViewPostImeInputStage.processPointerEvent(ViewRootImpl.java:4230)
10-28 09:37:25.420 14349-14349/justin.drawer E/MessageQueue-JNI:     at android.view.ViewRootImpl$ViewPostImeInputStage.onProcess(ViewRootImpl.java:4096)
10-28 09:37:25.420 14349-14349/justin.drawer E/MessageQueue-JNI:     at android.view.ViewRootImpl$InputStage.deliver(ViewRootImpl.java:3642)
10-28 09:37:25.420 14349-14349/justin.drawer E/MessageQueue-JNI:     at android.view.ViewRootImpl$InputStage.onDeliverToNext(ViewRootImpl.java:3695)
10-28 09:37:25.420 14349-14349/justin.drawer E/MessageQueue-JNI:     at android.view.ViewRootImpl$InputStage.forward(ViewRootImpl.java:3661)
10-28 09:37:25.420 14349-14349/justin.drawer E/MessageQueue-JNI:     at android.view.ViewRootImpl$AsyncInputStage.forward(ViewRootImpl.java:3787)
10-28 09:37:25.420 14349-14349/justin.drawer E/MessageQueue-JNI:     at android.view.ViewRootImpl$InputStage.apply(ViewRootImpl.java:3669)
10-28 09:37:25.420 14349-14349/justin.drawer E/MessageQueue-JNI:     at android.view.ViewRootImpl$AsyncInputStage.apply(ViewRootImpl.java:3844)
10-28 09:37:25.420 14349-14349/justin.drawer E/MessageQueue-JNI:     at android.view.ViewRootImpl$InputStage.deliver(ViewRootImpl.java:3642)
10-28 09:37:25.420 14349-14349/justin.drawer E/MessageQueue-JNI:     at android.view.ViewRootImpl$InputStage.onDeliverToNext(ViewRootImpl.java:3695)
10-28 09:37:25.420 14349-14349/justin.drawer E/MessageQueue-JNI:     at android.view.ViewRootImpl$InputStage.forward(ViewRootImpl.java:3661)
10-28 09:37:25.420 14349-14349/justin.drawer E/MessageQueue-JNI:     at android.view.ViewRootImpl$InputStage.apply(ViewRootImpl.java:3669)
10-28 09:37:25.420 14349-14349/justin.drawer E/MessageQueue-JNI:     at android.view.ViewRootImpl$InputStage.deliver(ViewRootImpl.java:3642)
10-28 09:37:25.420 14349-14349/justin.drawer E/MessageQueue-JNI:     at android.view.ViewRootImpl.deliverInputEvent(ViewRootImpl.java:5922)
10-28 09:37:25.420 14349-14349/justin.drawer E/MessageQueue-JNI:     at android.view.ViewRootImpl.doProcessInputEvents(ViewRootImpl.java:5896)
10-28 09:37:25.420 14349-14349/justin.drawer E/MessageQueue-JNI:     at android.view.ViewRootImpl.enqueueInputEvent(ViewRootImpl.java:5857)
10-28 09:37:25.420 14349-14349/justin.drawer E/MessageQueue-JNI:    at android.view.ViewRootImpl$WindowInputEventReceive
10-28 09:37:25.420 14349-14349/justin.drawer D/AndroidRuntime: Shutting down VM

【问题讨论】：

  • 显然它会是空对象，尝试在片段中创建一个方法来保存文本视图，并在从另一个片段中获取片段实例后调用该方法。
  • 看看这个：stackoverflow.com/questions/17436298/… 您可以使用setArguments(Bundle) 方法将字符串传递给片段。
  • 所以我做了一个方法，但它仍然给了我一个 nullpointerEcxeption。你能看看我更新的问题吗？ @AndreiVerdes

标签： java android android-fragments android-studio nullpointerexception


【解决方案1】：

你得到一个空指针异常，因为你的视图在 onCreateView 被调用后被夸大了。 您应该在 ListClickedFrgament 的构造函数中传递一个 Bundle 或 String 参数，然后使用它来设置文本。

ListClickedFragment：

    String textToSet;
    public ListClickedFragment(String text) {
           this.textToSet = text;
    }

在 ListClickedFragment 的 OnViewCreated 方法中将此文本设置为您的 textview。

在fragmentRonde1中：

    ListClickedFragment fragmentRonde1 = new ListClickedFragment(c2.getString(c2.getColumnIndex("title")));

希望这会有所帮助。

【讨论】：

  • 那么你把 this.textToSet 放在哪里，我把 textview 和 settext 放在哪里？我还不完全明白，但我知道你要去哪里@hadi
  • 不是贾斯汀，关键是textview是一个UI组件，只有在onCreateView方法完成后才能得到它的引用。您将要做的是覆盖 ListClickedFragment 中的 onViewCreated 方法，在该方法中，您可以使用 textToSet 字符串并将其设置为您的 textview。
  • 我明白你的意思了！如果可行，我将尝试并接受作为答案！ @hadi
  • 一直在尝试，但我仍然收到 NullPointerException :( 也无法使其捆绑工作。@hadi
  • 2 分。 1. 替换这一行：tvTitle = (TextView)getActivity().findViewById(R.id.listClickedTitle);
【解决方案2】： 
tvTitle = (TextView)getActivity().findViewById(R.id.listClickedTitle);

在你的活动中找到 tvTitle 而不是片段

【讨论】：

    【解决方案3】：

    试试这个： 我在这里做了一些假设，我真的不明白为什么你有同一个片段的 2 个实例......而你没有与第二个（fragmentRonde1）进行交易......这不会显示在活动......我有点困惑，但也许这会有所帮助。

    编辑：为什么你第二次得到 NullPointerException ？因为您只调用了ListClickedFragment fragmentRonde1 的构造函数。不与它进行交易，不在某些FrameLayout 中添加/替换它不会触发onCreateView() ...视图不会被夸大，因此 TextView 将为空。

    lv1.setOnItemClickListener(new AdapterView.OnItemClickListener() {
    @Override
    public void onItemClick(AdapterView<?> parent, View view, int position, long id) {

        ListClickedFragment newFragment = ListClickedFragment.newInstance();
        FragmentTransaction transaction = getFragmentManager().beginTransaction();

        transaction.replace(R.id.fragment_container, newFragment);
        transaction.addToBackStack(null);

        transaction.commit();

        Cursor c2 = db.getIdOfSelectedItem(id);

        ListClickedFragment fragmentRonde1;

        if (c2 != null) {
            c2.moveToFirst();
            fragmentRonde1 = ListClickedFragment.newInstance(c2.getString(c2.getColumnIndex("title")));
        } else {
            fragmentRonde1 = ListClickedFragment.newInstance();
        }

    }
});

    还有这个

    public class ListClickedFragment extends android.support.v4.app.Fragment {

public static final String STRING_TAG = "some_tag_in_here";

public static ListClickedFragment newInstance() {
    return new ListClickedFragment();
}

public static ListClickedFragment newInstance(String pString) {
    ListClickedFragment listClickedFragment = newInstance();
    Bundle bundle = new Bundle();
    bundle.putString(STRING_TAG, pString);
}

TextView tvTitle;
TextView tvDesc;
TextView tv;
TextView oop;

public ListClickedFragment() {
}

@Override public View onCreateView(LayoutInflater inflater, ViewGroup container,
                                   Bundle savedInstanceState) {
    // Inflate the layout for this fragment
    final View rootview2 = inflater.inflate(R.layout.fragment_list_clicked, container, false);

    tvTitle = (TextView) getActivity().findViewById(R.id.listClickedTitle);
    if (getArguments() != null && getArguments().getString(STRING_TAG) != null) {
        tvTitle.setText(getArguments().getString(STRING_TAG));
    }
    return rootview2;
}
}

    【讨论】：

    • 如果我一两个小时后回家一定会试试这个！ @AndreiVerdes
    【解决方案4】：

    您可以使用总线实现来管理片段和活动之间的所有操作。本教程将为您提供帮助！ Tutroial...

    【讨论】：

      【解决方案5】：

      第一步

      在片段 A 中，使用 callback 访问活动。您可以从这里学习如何使用它。 Fragment Callbacks

      第 2 步

      在activity中，使用FragmentManager找到Fragment B，然后就可以访问Fragment B中的TextView

      【讨论】：

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