如何从类中调用片段答案

【问题标题】：How to call a fragment from a class如何从类中调用片段
【发布时间】：2019-12-30 20:01:39
【问题描述】：

我只想从这个类中调用片段。实际上，我的应用程序中有很多片段，必须一次又一次地调用它们。所以我想创建一个类和一个函数来加载一个片段，所以每当我需要调用一个片段时，我都可以使用这个类的函数。但我无法在此处获取 getSupportFragmentManager()。我尝试通过将类扩展为片段，但随后它产生空异常。也可以通过 Appcompactactivity 扩展并使用 getSupportFragmentManager(); 但也会通过说活动被破坏来给出错误。那么有人有解决方案从一个简单的类中调用一个片段吗？

public class CompletedandPendingScreensLoader {


public void pendingscreenLoader(int serialnumber){
    Fragment frag = null;

    switch (serialnumber){
        case 1:
            frag = new LessonOne();
            break;

        case 2:
            frag = new LessonTwo();
            break;
        case 3:
            frag = new LessonThree();
            break;
        case 4:
            frag = new LessonFour();
            break;
        case 5:
            frag = new LessonFive();
            break;

    }
    if (frag != null) {
        Bundle bundle = new Bundle();
        bundle.putString("pending","pen");
        frag.setArguments(bundle);
        FragmentTransaction transaction = getFragmentManager().beginTransaction();
        transaction.replace(R.id.frame, frag).addToBackStack(null); // replace a Fragment with Frame Layout
        transaction.commit(); // commit the changes

    }

}



public void completedscreenLoader(int serialnumber){
    Fragment frag = null;

    switch (serialnumber){
        case 1:
            frag = new LessonOne();
            break;

        case 2:
            frag = new LessonTwo();
            break;
        case 3:
            frag = new LessonThree();
            break;
        case 4:
            frag = new LessonFour();
            break;
        case 5:
            frag = new LessonFive();
            break;

    }
    if (frag != null) {
        Bundle bundle = new Bundle();
        bundle.putString("completed","yes");
        frag.setArguments(bundle);
        FragmentTransaction transaction = getFragmentManager().beginTransaction();
        transaction.replace(R.id.frame, frag).addToBackStack(null); // replace a Fragment with Frame Layout
        transaction.commit(); // commit the changes

    }

}

public void simpleScreenLoader( int serialnumber){

    Fragment frag = null;

    switch (serialnumber){
        case 1:
            frag = new LessonOne();
            break;
        case 2:
            frag = new LessonTwo();
            break;
        case 3:
            frag = new LessonThree();
            break;
        case 4:
            frag = new LessonFour();
            break;
        case 5:
            frag = new LessonFive();
            break;

    }
    if (frag != null) {
        FragmentTransaction transaction = getFragmentManager.beginTransaction();
        transaction.replace(R.id.frame, new LessonTwo()).addToBackStack(null); // replace a Fragment with Frame Layout
        transaction.commit();






    }
}

【问题讨论】：

标签： android android-fragments fragment android-fragmentactivity fragmentmanager

【解决方案1】：

我相信你会在某个时候从一些 activity 或 fragment 调用这个类，如果是这样，那么使用修改后的构造函数它将打开片段。否则，如果没有来自活动或片段的 FragmentManager 的 reference，您将无法做到这一点。

  public class CompletedandPendingScreensLoader {
    private FragmentManager fragmentManager = null;

    //when ever you start your class just start using this constructor 
    CompletedandPendingScreensLoader(FragmentManager fragmentManager){
       this.fragmentManager = fragmentManager
    }


    public void pendingscreenLoader(int serialnumber){
        Fragment frag = null;

        switch (serialnumber){
            case 1:
                frag = new LessonOne();
                break;

            case 2:
                frag = new LessonTwo();
                break;
            case 3:
                frag = new LessonThree();
                break;
            case 4:
                frag = new LessonFour();
                break;
            case 5:
                frag = new LessonFive();
                break;

        }
        if (frag != null) {
            Bundle bundle = new Bundle();
            bundle.putString("pending","pen");
            frag.setArguments(bundle);
            FragmentTransaction transaction = fragmentManager.beginTransaction();
            transaction.replace(R.id.frame, frag).addToBackStack(null); // replace a Fragment with Frame Layout
            transaction.commit(); // commit the changes

        }

    }



    public void completedscreenLoader(int serialnumber){
        Fragment frag = null;

        switch (serialnumber){
            case 1:
                frag = new LessonOne();
                break;

            case 2:
                frag = new LessonTwo();
                break;
            case 3:
                frag = new LessonThree();
                break;
            case 4:
                frag = new LessonFour();
                break;
            case 5:
                frag = new LessonFive();
                break;

        }
        if (frag != null) {
            Bundle bundle = new Bundle();
            bundle.putString("completed","yes");
            frag.setArguments(bundle);
            FragmentTransaction transaction = fragmentManager.beginTransaction();
            transaction.replace(R.id.frame, frag).addToBackStack(null); // replace a Fragment with Frame Layout
            transaction.commit(); // commit the changes

        }

    }

    public void simpleScreenLoader( int serialnumber){

        Fragment frag = null;

        switch (serialnumber){
            case 1:
                frag = new LessonOne();
                break;
            case 2:
                frag = new LessonTwo();
                break;
            case 3:
                frag = new LessonThree();
                break;
            case 4:
                frag = new LessonFour();
                break;
            case 5:
                frag = new LessonFive();
                break;

        }
        if (frag != null) {
            FragmentTransaction transaction = fragmentManager.beginTransaction();
            transaction.replace(R.id.frame, new LessonTwo()).addToBackStack(null); // replace a Fragment with Frame Layout
            transaction.commit();

        }
    }

【讨论】：

【解决方案2】：

您的类必须扩展 AppCompatActivity 类才能调用此函数，并且当您扩展该类时，您还必须覆盖活动的 onCreate() 方法，并且您拥有还要在 onCreate() 方法中为活动设置布局

public class CompletedandPendingScreensLoader {

 private AppCompatActivity myActivty;

 public CompletedandPendingScreensLoader(AppCompatAcitivity myActivty)
 {
     this.myActivity = myActivity
   }


public void pendingscreenLoader(int serialnumber){
Fragment frag = null;

switch (serialnumber){
    case 1:
        frag = new LessonOne();
        break;

    case 2:
        frag = new LessonTwo();
        break;
    case 3:
        frag = new LessonThree();
        break;
    case 4:
        frag = new LessonFour();
        break;
    case 5:
        frag = new LessonFive();
        break;

}
if (frag != null) {
    Bundle bundle = new Bundle();
    bundle.putString("pending","pen");
    frag.setArguments(bundle);
    FragmentTransaction transaction = 
    myActivity.getFragmentManager().beginTransaction();
    transaction.replace(R.id.frame, frag).addToBackStack(null); // replace a Fragment with Frame Layout
    transaction.commit(); // commit the changes

}

  }



public void completedscreenLoader(int serialnumber){
Fragment frag = null;

switch (serialnumber){
    case 1:
        frag = new LessonOne();
        break;

    case 2:
        frag = new LessonTwo();
        break;
    case 3:
        frag = new LessonThree();
        break;
    case 4:
        frag = new LessonFour();
        break;
    case 5:
        frag = new LessonFive();
        break;

}
if (frag != null) {
    Bundle bundle = new Bundle();
    bundle.putString("completed","yes");
    frag.setArguments(bundle);
    FragmentTransaction transaction = 
    myAcitvity.getFragmentManager().beginTransaction();
    transaction.replace(R.id.frame, frag).addToBackStack(null); // replace a Fragment with Frame Layout
    transaction.commit(); // commit the changes

}

}

 public void simpleScreenLoader( int serialnumber){

Fragment frag = null;

switch (serialnumber){
    case 1:
        frag = new LessonOne();
        break;
    case 2:
        frag = new LessonTwo();
        break;
    case 3:
        frag = new LessonThree();
        break;
    case 4:
        frag = new LessonFour();
        break;
    case 5:
        frag = new LessonFive();
        break;

}
if (frag != null) {
    FragmentTransaction transaction = 
     myActivity.getFragmentManager.beginTransaction();
    transaction.replace(R.id.frame, new LessonTwo()).addToBackStack(null); // replace a Fragment with Frame Layout
    transaction.commit();






}
}

【讨论】：

但我不需要那个......我只想使用这个类的功能而不使其活动。
然后你可以在你的类中创建一个 AppCompatActivity 类的实例，并在你的类的构造函数中初始化它，然后你可以从 appCompatActivity 的对象调用函数
你能用代码例子解释一下吗……因为我没听懂你
好的，我明白了...但是在片段中制作对象时要为 appcompatactivity 传递对象参数是什么？ CompletedandPendingScreensLoader screenLoader = new CompletedandPendingScreensLoader(---这里要传递什么 ---);
如果您在活动中制作此类的对象传递“this”，如果您在片段中制作this的对象传递“getActivty()”。