片段NullPointerException异常，改变TextView的片段的从活动文本 [英] Fragment NullPointerException, Changing fragment textView's text from activity

问题描述

我和我的Andr​​oid项目的一个问题。我使用的数据映射到我的穿着发送数据。我在磨损主要活动获取数据的DataListener。

基本上我想改变活性片段的TextView的文本。当我试图做到这一点的失败，我得到 - > NullPointerException异常。我该如何解决呢？

是不是因为我打电话mainactivity`s片段onCreate方法？

MainActivity XML：

 ＆LT; android.support.v4.view.ViewPager的xmlns：机器人=htt​​p://schemas.android.com/apk/res/android
    机器人：ID =@ + ID /寻呼机
    机器人：layout_width =match_parent
    机器人：layout_height =match_parent＆GT;＆LT; /android.support.v4.view.ViewPager>
 

Mainactivity

 公共类MainActivity扩展FragmentActivity {    @覆盖
    保护无效的onCreate（捆绑savedInstanceState）{
        super.onCreate（savedInstanceState）;
        的setContentView（R.layout.main_activity）;        viewpager =（ViewPager）findViewById（R.id.pager）;
        FragmentManager FM = getSupportFragmentManager（）;
        viewpager.setAdapter（新FragmentAdapter（FM））;        的DataListener =新DataApi。的DataListener（）{
            @TargetApi（Build.VERSION_ codeS.LOLLIPOP）
            @覆盖
            公共无效onDataChanged（DataEventBuffer dataEvents）{
                最终的ArrayList＆LT; D​​ataEvent＆GT;事件= FreezableUtils.freezeIterable（dataEvents）;
                数据映射mediaMap;
                数据映射updateMap;
                对于（DataEvent事件：事件）{
                    PutDataMa prequest putDataMa prequest =
                            PutDataMa prequest.createFromDataMapItem（DataMapItem.fromDataItem（event.getDataItem（）））;                    如果（event.getType（）== DataEvent.TYPE_CHANGED）{
                        如果（event.getDataItem（）。getUri（）的getPath（）。等于（/ mypath中））{
                            数据映射= DataMapItem.fromDataItem（event.getDataItem（））getDataMap（）;                            碎裂碎片=（MainControlScreenFragment）getSupportFragmentManager（）findFragmentById（R.id.fragmentA）。}
}
 

解决方案

请单吨执行你的片段，加入MainControlScreenFragment.class本线以上的 onCreateView（）方法

 私有静态MainControlScreenFragment实例;公共MainControlScreenFragment（）{
}/ **
 *静态方法，它返回片段的实例。如果片段为null，加载它，
 *别人创造新的片段。 Singleton模式。
 *
 * @返回
 * /
公共静态MainControlScreenFragment的getInstance（）{
    如果（例如== NULL）{
        例如=新MainControlScreenFragment（）;    }    返回实例;
}
 

在在您的活动电话 MainControlScreenFragment.getInstance（）changeTextMethod（）; 而不是 MainControlScreenFragment片段=（MainControlScreenFragment）getSupportFragmentManager（）findFragmentById （R.id.fragmentA）;

请注意，你的 changeTextMethod（）应 MainControlScreenFragment.class

声明为public

希望它能帮助！

I have a problem with my android project. I am sending data using Datamap to my wear. I have a datalistener for getting data in the wear main activity.

Basically I want to change fragment's textView's text from activity. When I am trying to do this it fails and I got -->NullPointerException. How can I fix that?

Is that because I am calling the fragment in mainactivity`s onCreate method?

MainActivity xml:

<android.support.v4.view.ViewPager xmlns:android="http://schemas.android.com/apk/res/android"
    android:id="@+id/pager"
    android:layout_width="match_parent"
    android:layout_height="match_parent" >

</android.support.v4.view.ViewPager>

Mainactivity

public class MainActivity extends FragmentActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main_activity);

        viewpager = (ViewPager) findViewById(R.id.pager);
        FragmentManager fm = getSupportFragmentManager();
        viewpager.setAdapter(new FragmentAdapter(fm));

        dataListener = new DataApi. DataListener() {
            @TargetApi(Build.VERSION_CODES.LOLLIPOP)
            @Override
            public void onDataChanged(DataEventBuffer dataEvents) {
                final ArrayList<DataEvent> events = FreezableUtils.freezeIterable(dataEvents);
                DataMap mediaMap;
                DataMap updateMap;
                for (DataEvent event : events) {
                    PutDataMapRequest putDataMapRequest =
                            PutDataMapRequest.createFromDataMapItem(DataMapItem.fromDataItem(event.getDataItem()));

                    if (event.getType() == DataEvent.TYPE_CHANGED) {
                        if (event.getDataItem().getUri().getPath().equals("/myPath")) {
                            dataMap= DataMapItem.fromDataItem(event.getDataItem()).getDataMap();

                            FragmentA fragment = (MainControlScreenFragment) getSupportFragmentManager().findFragmentById(R.id.fragmentA);

}
}

解决方案

Make single ton implementation in your fragment, add this lines in MainControlScreenFragment.class above onCreateView() method:

private static MainControlScreenFragment instance;

public MainControlScreenFragment() {
}

/**
 * Static method which return the instance of the fragment. If the fragment is null, load it,
 * else create new fragment. Singleton pattern.
 *
 * @return
 */
public static MainControlScreenFragment getInstance() {
    if (instance == null) {
        instance = new MainControlScreenFragment();

    }

    return instance;
}

After that in your activity call MainControlScreenFragment.getInstance().changeTextMethod(); instead MainControlScreenFragment fragment = (MainControlScreenFragment) getSupportFragmentManager().findFragmentById(R.id.fragmentA);

Note that your changeTextMethod() should be declared public in MainControlScreenFragment.class

Hope it help!

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