java - 如何从父 Activity 以编程方式生成的 fragment 中调用方法？

Question

编辑 4 好吧，我已经将示例代码更改为建议的内容，并进行了空检查。

现在在公共(public)类 MainActivity 中扩展了 AppCompatActivity 我已经

private templateFragment1 fragTest;

然后在 onCreate 中我得到了

 final FragmentManager fragMan = getFragmentManager();
    fragTest = (templateFragment1) fragMan.findFragmentByTag("1");

    onSave.setOnClickListener(new View.OnClickListener(){
        @Override
        public void onClick(View v){

            if(fragTest != null) {
                String editTestText = fragTest.editTextGetter();
                Toast.makeText(getApplicationContext(), editTestText, Toast.LENGTH_SHORT).show();
            }
        }
    });

在 templateFragment1 中我有

privateEditText text;

我已经像这样在 onCreateView 中绑定(bind)了

text = (EditText) getActivity().findViewById(R.id.editTextTest);

然后我有onCreateView下面的方法

public String editTextGetter(){
    String value1 = text.getText().toString();
    return value1;
   }

现在发生的事情..什么都没有。我点击了保存按钮，没有 Toast，也没有错误消息。所以我猜这意味着它返回 null？

编辑 3 这里有几个视频演示了该错误。

https://www.youtube.com/watch?v=w60Vljd2R4M&feature=youtu.be

https://www.youtube.com/watch?v=xqpVGBAHw0w&feature=youtu.be

我知道已经有几个与此类似的问题，但似乎没有一个问题能解决我的具体问题。

在我的主要 Activity 中，我有一个添加 fragment 实例的按钮。每次执行时，它还会为它们分配“1”、“2”等标签。只是为了看看是否可能，我只是尝试从第一个方法调用一个方法。

在我的主要 Activity 中，我有:

    // initializing button that will call the fragment's method
    Button onSave = (Button) findViewById(R.id.saveButton);


    FragmentManager fragMan = getFragmentManager();

    // calling my first created fragment
    final templateFragment1 fragTest = (templateFragment1) fragMan.findFragmentByTag("1");


    // my button that should call the frag's method and then display it as a toast
    onSave.setOnClickListener(new View.OnClickListener(){
        @Override
        public void onClick(View v){

            // here I'm assigning the fragment's method to a string
            String editTestText = fragTest.editTextGetter();

            // display as toast
            Toast.makeText(getApplicationContext(), editTestText, Toast.LENGTH_SHORT).show();

        }
    });

在我的 fragment 中:

public String editTextGetter(){
    EditText text = (EditText) getActivity().findViewById(R.id.editTextTest);
    String value1 = text.getText().toString();
    return value1;
}

如果重要的话，editTextGetter() 位于 onCreateView 方法下方。

现在发生的只是单击主 Activity 按钮后应用程序崩溃。

编辑:这是我按要求提交的代码:

addDay.setOnClickListener(new View.OnClickListener(){
        @Override
        public void onClick(View v){
            ++fragIdCount;
            FragmentManager fragmentManager = getFragmentManager();
            FragmentTransaction fragmentTransaction = fragmentManager.beginTransaction();
            String fragString = Integer.toString(fragIdCount);
            templateFragment1 frag2 = new templateFragment1();
            fragmentTransaction.add(R.id.templateFragmentLayout, frag2, fragString);
            fragmentTransaction.commit();

        }
    });

如您所见，我从 0 (fragIdCount) 开始递增一个数字，然后将其转换为字符串。然后我将其指定为 fragment 的标签。所以我试图用这个分配的标签来调用我的 fragment 。

编辑 2: 好的，伙计们，这是可以复制+粘贴到新项目中的代码。它复制了我的问题，如果你们能看一下，我将非常感激!

MainActivity.java

公共(public)类 MainActivity 扩展 AppCompatActivity {

int fragIdCount = 0;



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


    Button addDay = (Button) findViewById(R.id.addDay);
    Button removeDay = (Button) findViewById(R.id.removeDay);

// Here I'm making it so I have an instance of the fragment displayed on create
    FragmentManager fragmentManager = getFragmentManager();
    FragmentTransaction fragmentTransaction = fragmentManager.beginTransaction();
    String fragString = Integer.toString(fragIdCount);
    templateFragment1 frag2 = new templateFragment1();
    fragmentTransaction.add(R.id.templateFragmentLayout, frag2, fragString);
    fragmentTransaction.commit();


// My button that adds fragment. Obviously this can quickly generate a bunch of fragment instances
// I try to make that manageable by incrementing a fragment count to use as tags
    addDay.setOnClickListener(new View.OnClickListener(){
        @Override
        public void onClick(View v){
            ++fragIdCount;
            FragmentManager fragmentManager = getFragmentManager();
            FragmentTransaction fragmentTransaction = fragmentManager.beginTransaction();
            String fragString = Integer.toString(fragIdCount);
            templateFragment1 frag2 = new templateFragment1();
            fragmentTransaction.add(R.id.templateFragmentLayout, frag2,    fragString);
            fragmentTransaction.commit();
            fragmentManager.executePendingTransactions();

        }
    });

// remove button. same concept as the add button
    removeDay.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v){
            FragmentManager fragmentManager = getFragmentManager();
            FragmentTransaction fragmentTransaction = fragmentManager.beginTransaction();
            String fragString = Integer.toString(fragIdCount);
            //Fragment f = getFragmentManager().findFragmentByTag(fragString);
            if(fragIdCount != 0){
                fragmentTransaction.remove(fragmentManager.findFragmentByTag(fragString)).commit();
                --fragIdCount;
            }
        }
    });

// initialize Save button (which SHOULD get the value of an editText from whichever
// fragment I specify)
    Button onSave = (Button) findViewById(R.id.saveButton);

    onSave.setOnClickListener(new View.OnClickListener(){
        @Override
        public void onClick(View v){

            // Eventually I'll want to make this a for loop to perform this operation on all fragments created.
            FragmentManager fragMan = getFragmentManager();

            // this should get the fragment "1"
            templateFragment1 fragTest = (templateFragment1)   fragMan.findFragmentByTag("1");
            // and this should run the method "editTextGetter()" inside of  the previously specified fragment
            String editTestText = fragTest.editTextGetter();

            // just a quick way to show if I got the correct value, for debugging
            Toast.makeText(getApplicationContext(), editTestText, Toast.LENGTH_SHORT).show();

        }
    });

  }
}

activity_main.xml

<ScrollView
    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"
>

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
              xmlns:tools="http://schemas.android.com/tools"
              tools:context="com.liftrpoc.scheduler1.pushpulldetails"
              android:layout_height="wrap_content"
              android:layout_width="match_parent"
              android:orientation="vertical"
>

    <LinearLayout
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:id="@+id/templateFragmentLayout"
            android:orientation="vertical">


    </LinearLayout>

    <Button
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:id="@+id/addDay"
            android:text="Add Day"
    />

    <Button
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:id="@+id/removeDay"
            android:text="Remove Day"
    />


    <Button
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:id="@+id/saveButton"
            android:text="Save"
    />

</LinearLayout>

</ScrollView>

templateFragment1.java

public class templateFragment1 extends Fragment {
public templateFragment1() {
    // Required empty public constructor
}

@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
                         Bundle savedInstanceState) {
    // Inflate the layout for this fragment
    LinearLayout view = (LinearLayout)   inflater.inflate(R.layout.fragment_template_fragment1, container, false);

    // a good bit of extra code that adds it's own instanced fragments, just like in the main activity.
    // this shouldn't have anything to do with what we're trying to do  though. It doesn't touch anything else.

    return view;
}

// here's the editText method I'm trying to access from my main activity.
public String editTextGetter(){
    EditText text = (EditText) getActivity().findViewById(R.id.editTextTest);
    String value1 = text.getText().toString();
    return value1;
}

}

fragment_template_fragment1.xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
          xmlns:tools="http://schemas.android.com/tools" android:layout_width="match_parent"
          android:layout_height="wrap_content"
          android:background="#E3E3E3"
          android:orientation="vertical"
          android:id="@+id/ParentLinearLayout1"
>

<EditText
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:id="@+id/editTextTest"
/>

</LinearLay

Answer 1

使用 ArrayList 并将您制作的每个 fragment 存储在其中。然后，当您想调用 fragment 中的特定函数或获取 View 时，只需从 ArrayList 中获取所需的 fragment 即可完成您的工作。