Android：无法从 Activity 更新 Fragment 中的文本视图。空指针异常

Question

我正在尝试从另一个 activity 更新片段中的文本视图。但是在调用 setText 方法时我得到了一个 NUllPointerException。我尝试了以下方法，但仍然得到 NPE。 1. 尝试在 activity 中使用 FindViewbyId 访问片段 textview。 2. 尝试使用片段中的方法并从 activity 调用它并将值作为参数传递

FragHome Activity

public class FragHome extends AppCompatActivity implements TabLayout.OnTabSelectedListener {

Handler bluetoothIn;
private static TextView tmpF, humF, CoF;
String tempGL, HumGL, coGL, devname;
double dblTemp, dblCo;
final int handlerState = 0; // used to identify handler message
private BluetoothAdapter btAdapter = null;
private TabLayout tabLayout;
private ViewPager viewPager;

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

    //Adding toolbar to the activity
    Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
    setSupportActionBar(toolbar);
    //Initializing the tablayout
    tabLayout = (TabLayout) findViewById(R.id.tabLayout);
    //Initializing viewPager
    viewPager = (ViewPager) findViewById(R.id.pager);
    //Adding the tabs using addTab() method
    tabLayout.addTab(tabLayout.newTab().setText("Temperature"));
    tabLayout.addTab(tabLayout.newTab().setText("Humidity"));
    tabLayout.addTab(tabLayout.newTab().setText("CO"));
    tabLayout.setTabGravity(TabLayout.GRAVITY_FILL);

    //Creating our pager adapter
    Pager adapter = new Pager(getSupportFragmentManager(), tabLayout.getTabCount());

    //Adding adapter to pager
    viewPager.setAdapter(adapter);
    viewPager.setOnPageChangeListener(new TabLayout.TabLayoutOnPageChangeListener(tabLayout));
    //Adding onTabSelectedListener to swipe views
    tabLayout.setOnTabSelectedListener(this);

    bluetoothIn=new Handler() {

        String readMessage;
        String[] values = new String[]{""};

        public void handleMessage(android.os.Message msg) {

            if (msg.what == handlerState) {

                readMessage = (String) msg.obj;
                values = readMessage.split("#");
                for (int j = 0; j < values.length; j++) {

                    int rem = j % 3;

                    if (rem == 0) {

                        tmpF.setText(values[j] + " C");
                        tempGL = String.valueOf(values[j]);

                        try {
                            dblTemp = Double.parseDouble(tempGL);
                        } catch (NumberFormatException e) {
                            e.printStackTrace();
                        }

                    } else if (rem == 1) {

                        CoF.setText(values[j] + " ppm");
                        coGL = values[j];
                        try {
                            dblCo = Double.parseDouble(coGL);
                        } catch (NumberFormatException e) {
                            e.printStackTrace();
                        }

                    } else if (rem == 2) {
                        humF.setText(values[j] + " %");
                        HumGL = values[j];
                    }
                }
            }
        }
    };

    btAdapter=BluetoothAdapter.getDefaultAdapter(); // get Bluetooth
}

@Override
public void onTabSelected(TabLayout.Tab tab) {
    // mViewPager.setCurrentItem(tab.getPosition());

}

@Override
public void onTabUnselected(TabLayout.Tab tab) {

}

@Override
public void onTabReselected(TabLayout.Tab tab) {

}
}

寻呼机

  public class Pager extends FragmentStatePagerAdapter {

//integer to count number of tabs
int tabCount;

//Constructor to the class
public Pager(FragmentManager fm, int tabCount) {
    super(fm);
    //Initializing tab count
    this.tabCount= tabCount;
}

//Overriding method getItem
@Override
public Fragment getItem(int position) {
    //Returning the current tabs
    switch (position) {
        case 0:
            Tab1 tab1 = new Tab1();
            return tab1;
        case 1:
            Tab2 tab2 = new Tab2();
            return tab2;
        case 2:
            Tab3 tab3 = new Tab3();
            return tab3;
        default:
            return null;
    }
}

//Overriden method getCount to get the number of tabs
@Override
public int getCount() {
    return tabCount;
}
}

选项卡 1

public class OneFragment extends Fragment {

View view;
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
    view = inflater.inflate(R.layout.fragment_one, container, false);
    return view;

}
}

fragment_one.xml

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
tools:context="shinil.tablayout.OneFragment"
android:id="@+id/rltnvnv">

<TextView
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:text="Temperature"
    android:textSize="40dp"
    android:textStyle="bold"
    android:id="@+id/textviewtemp"
    android:layout_centerInParent="true"/>

 </RelativeLayout>

frag_home.xml

 LinearLayout
android:id="@+id/main_layout"
android:orientation="vertical"
xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
tools:context=".MainActivity">

<!-- our toolbar -->
<android.support.v7.widget.Toolbar
    android:id="@+id/toolbar"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:background="?attr/colorPrimary"
    android:minHeight="?attr/actionBarSize"
    android:theme="@style/ThemeOverlay.AppCompat.Dark.ActionBar"
    app:popupTheme="@style/ThemeOverlay.AppCompat.Light"/>

<!-- our tablayout to display tabs  -->
<android.support.design.widget.TabLayout
    android:id="@+id/tabLayout"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:background="?attr/colorPrimary"

    android:minHeight="?attr/actionBarSize"
    android:theme="@style/ThemeOverlay.AppCompat.Dark.ActionBar"/>

<!-- View pager to swipe views -->
<android.support.v4.view.ViewPager
    android:id="@+id/pager"
    android:layout_width="match_parent"
    android:layout_height="fill_parent"/>

  </LinearLayout>

当我尝试从 activity 设置文本时出现 NPE。请帮忙

Answer 1

使用以下回调：

片段Class：

public class FragmentOne extends Fragment {


private ViewCallback mCallback;

 public FragmentOne(ViewCallback mCallback) {
    this.mCallback = mCallback;
}

@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
    view = inflater.inflate(R.layout.fragment_one, container, false);
    mCallback.updateTextView((TextView) view.findViewById(R.id.fragmentTextView));
    return view;
}

public interface ViewCallback {
    void updateTextView(TextView view);
}
}

下面是Activity class:

public class MainCallbackActivity extends Activity implements CallbackFragment.ViewCallback {

public TextView textView;

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

    FragmentOne fragment = new FragmentOne(this);
    getFragmentManager().beginTransaction().add(R.id.frameLayout, fragment).commit();

}

@Override
protected void onResume() {
    super.onResume();
    if (textView != null)
        textView.setText("Updating Fragment TextView in Activity..!!");
}

@Override
public void updateTextView(TextView view) {
    this.textView = view;
}
}

在您的 activity class 中实施回调。.然后更新文本视图。

Android：无法从 Activity 更新 Fragment 中的文本视图。空指针异常

Android: Can't update textview in Fragment from Activity. NullPointerException

android

android-fragments

nullpointerexception

textview

settext