Java 从不同片段调用时返回null的片段上的getView

我有一个包含两个片段的活动。其中一个片段mainFragment是整个屏幕的大小。还有另一个片段summaryFrag，它包含在mainFragment内部的视图中。我正试图根据mainFragment中发生的操作更新summaryFrag上的文本

目标：当按下mainFragment中的按钮时，将summaryFrag中文本视图的文本设置为某物

我试图通过使用从mainFragment内部获取TextView来实现这一点

TextView TextView=（TextView）summary.getView（）.findViewById（R.id.prev\u guess\u txt）

但我得到一个空指针异常错误

FATAL EXCEPTION: main
              Process: com.example.damia.bullseyev3, PID: 6049
              java.lang.NullPointerException: Attempt to invoke virtual method 'android.view.View android.view.View.findViewById(int)' on a null object reference
                  at com.example.damia.bullseyev3.fragments.mainFragment.updatePreviousGuesses(mainFragment.java:83)
                  at com.example.damia.bullseyev3.fragments.mainFragment$1.onClick(mainFragment.java:68)
                  at android.view.View.performClick(View.java:5610)
                  at android.view.View$PerformClick.run(View.java:22260)
                  at android.os.Handler.handleCallback(Handler.java:751)
                  at android.os.Handler.dispatchMessage(Handler.java:95)
                  at android.os.Looper.loop(Looper.java:154)
                  at android.app.ActivityThread.main(ActivityThread.java:6077)
                  at java.lang.reflect.Method.invoke(Native Method)
                  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:865)
                  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:755)


mainFragment.java

@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
                         Bundle savedInstanceState) {
    View v = inflater.inflate(R.layout.fragment_main, container, false);
    scrollView = (ScrollView) v.findViewById(R.id.scroll);
    ll = (LinearLayout)v.findViewById(R.id.linearlayout);


    submitBtn = (Button)v.findViewById(R.id.submit_guess_btn);

    submitBtn.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            updatePreviousGuesses();
        }
    });

    return v;
}

public void updatePreviousGuesses(){
    //TODO add method to check if guess is valid first before updating the scrollview
    FrameLayout holder = new FrameLayout(getActivity());
    holder.setId(R.id.holder);

    summaryFrag summary = summaryFrag.newInstance("","");
    getActivity().getSupportFragmentManager().beginTransaction().add(R.id.holder, summary).commit();

    TextView textView = (TextView) summary.getView().findViewById(R.id.prev_guess_txt);
    textView.setText("test");

    ll.addView(holder, 0);
}

@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    if (getArguments() != null) {
        mParam1 = getArguments().getString(ARG_PARAM1);
        mParam2 = getArguments().getString(ARG_PARAM2);
    }
}

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

    return v;
}
}

public class MainActivity extends AppCompatActivity {

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

    FragmentManager fm = getSupportFragmentManager();
    mainFragment mainfrag = (mainFragment)fm.findFragmentById(R.id.fragment_container);

    if(mainfrag == null){
        mainfrag = mainFragment.newInstance("","");
        fm.beginTransaction().add(R.id.fragment_container, mainfrag).commit();
    }
}
}


summaryFrag.java

@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
                         Bundle savedInstanceState) {
    View v = inflater.inflate(R.layout.fragment_main, container, false);
    scrollView = (ScrollView) v.findViewById(R.id.scroll);
    ll = (LinearLayout)v.findViewById(R.id.linearlayout);


    submitBtn = (Button)v.findViewById(R.id.submit_guess_btn);

    submitBtn.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            updatePreviousGuesses();
        }
    });

    return v;
}

public void updatePreviousGuesses(){
    //TODO add method to check if guess is valid first before updating the scrollview
    FrameLayout holder = new FrameLayout(getActivity());
    holder.setId(R.id.holder);

    summaryFrag summary = summaryFrag.newInstance("","");
    getActivity().getSupportFragmentManager().beginTransaction().add(R.id.holder, summary).commit();

    TextView textView = (TextView) summary.getView().findViewById(R.id.prev_guess_txt);
    textView.setText("test");

    ll.addView(holder, 0);
}

@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    if (getArguments() != null) {
        mParam1 = getArguments().getString(ARG_PARAM1);
        mParam2 = getArguments().getString(ARG_PARAM2);
    }
}

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

    return v;
}
}

public class MainActivity extends AppCompatActivity {

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

    FragmentManager fm = getSupportFragmentManager();
    mainFragment mainfrag = (mainFragment)fm.findFragmentById(R.id.fragment_container);

    if(mainfrag == null){
        mainfrag = mainFragment.newInstance("","");
        fm.beginTransaction().add(R.id.fragment_container, mainfrag).commit();
    }
}
}

（summaryFrag目前与默认生成的片段代码没有任何更改）


MainActivity.java

@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
                         Bundle savedInstanceState) {
    View v = inflater.inflate(R.layout.fragment_main, container, false);
    scrollView = (ScrollView) v.findViewById(R.id.scroll);
    ll = (LinearLayout)v.findViewById(R.id.linearlayout);


    submitBtn = (Button)v.findViewById(R.id.submit_guess_btn);

    submitBtn.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            updatePreviousGuesses();
        }
    });

    return v;
}

public void updatePreviousGuesses(){
    //TODO add method to check if guess is valid first before updating the scrollview
    FrameLayout holder = new FrameLayout(getActivity());
    holder.setId(R.id.holder);

    summaryFrag summary = summaryFrag.newInstance("","");
    getActivity().getSupportFragmentManager().beginTransaction().add(R.id.holder, summary).commit();

    TextView textView = (TextView) summary.getView().findViewById(R.id.prev_guess_txt);
    textView.setText("test");

    ll.addView(holder, 0);
}

@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    if (getArguments() != null) {
        mParam1 = getArguments().getString(ARG_PARAM1);
        mParam2 = getArguments().getString(ARG_PARAM2);
    }
}

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

    return v;
}
}

public class MainActivity extends AppCompatActivity {

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

    FragmentManager fm = getSupportFragmentManager();
    mainFragment mainfrag = (mainFragment)fm.findFragmentById(R.id.fragment_container);

    if(mainfrag == null){
        mainfrag = mainFragment.newInstance("","");
        fm.beginTransaction().add(R.id.fragment_container, mainfrag).commit();
    }
}
}


我读过一些关于这方面的解决方案，我知道这是由于碎片化的生活方式和其他原因造成的，但我仍然试图自己解决它，但没有成功。我尝试过将一些东西移到onViewCreated，但我不知道它是如何工作的，以至于不知道什么应该移到那里，什么不应该移到那里

我对回调和所有东西都是新手，所以如果您的解决方案包括回调和所有东西，请您向初学者解释一下：）

谢谢
当您尝试在片段之间交互时，最好使用setarguments和getarguments