如何将片段和 AppCompatActivity 扩展到同一个类？答案

【问题标题】：How to extend both fragment and AppCompatActivity to a same class?如何将片段和 AppCompatActivity 扩展到同一个类？
【发布时间】：2018-07-21 15:52:52
【问题描述】：

我有一个类。我已经将 Fragment 扩展到这个类，因为我在开发 Navigation Drawer 时使用了 Fragment。

代码如下

public class aboutSLFragment extends Fragment  {

public aboutSLFragment() {
    // Required empty public constructor
}

@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
                         Bundle savedInstanceState) {
    // Inflate the layout for this fragment
    return inflater.inflate(R.layout.fragment_about_sl, container, false);
}

@Override
public void onViewCreated(View view, @Nullable Bundle savedInstanceState) {
    super.onViewCreated(view, savedInstanceState);
    //you can set the title for your toolbar here for different fragments different titles
    getActivity().setTitle("About Sri Lanka");
}

}

现在我想为该类添加一个图像滑块。我使用的代码是这样的。

@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);

    viewPager = (ViewPager) findViewById(R.id.viewPager);

    sliderDotspanel = (LinearLayout) findViewById(R.id.SliderDots);

    ViewPagerAdapter viewPagerAdapter = new ViewPagerAdapter(this);

    viewPager.setAdapter(viewPagerAdapter);

    dotscount = viewPagerAdapter.getCount();
    dots = new ImageView[dotscount];

    for(int i = 0; i < dotscount; i++){

        dots[i] = new ImageView(this);
        dots[i].setImageDrawable(ContextCompat.getDrawable(getApplicationContext(), R.drawable.non_active_dot));

        LinearLayout.LayoutParams params = new LinearLayout.LayoutParams(LinearLayout.LayoutParams.WRAP_CONTENT, LinearLayout.LayoutParams.WRAP_CONTENT);

        params.setMargins(8, 0, 8, 0);

        sliderDotspanel.addView(dots[i], params);

    }

    dots[0].setImageDrawable(ContextCompat.getDrawable(getApplicationContext(), R.drawable.active_dot));

    viewPager.addOnPageChangeListener(new ViewPager.OnPageChangeListener() {
        @Override
        public void onPageScrolled(int position, float positionOffset, int positionOffsetPixels) {

        }

        @Override
        public void onPageSelected(int position) {

            for(int i = 0; i< dotscount; i++){
                dots[i].setImageDrawable(ContextCompat.getDrawable(getApplicationContext(), R.drawable.non_active_dot));
            }

            dots[position].setImageDrawable(ContextCompat.getDrawable(getApplicationContext(), R.drawable.active_dot));

        }

        @Override
        public void onPageScrollStateChanged(int state) {

        }
    });

}

当我将此图像滑块代码添加到 aboutSLFragment 类时，代码将如下所示（下）

public class aboutSLFragment extends Fragment  {

ViewPager viewPager;
LinearLayout sliderDotspanel;
private int dotscount;
private ImageView[] dots;


public aboutSLFragment() {
    // Required empty public constructor
}

@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);

    viewPager = (ViewPager) findViewById(R.id.viewPager);

    sliderDotspanel = (LinearLayout) findViewById(R.id.SliderDots);

    ViewPagerAdapter viewPagerAdapter = new ViewPagerAdapter(this);

    viewPager.setAdapter(viewPagerAdapter);

    dotscount = viewPagerAdapter.getCount();
    dots = new ImageView[dotscount];

    for(int i = 0; i < dotscount; i++){

        dots[i] = new ImageView(this);
        dots[i].setImageDrawable(ContextCompat.getDrawable(getApplicationContext(), R.drawable.non_active_dot));

        LinearLayout.LayoutParams params = new LinearLayout.LayoutParams(LinearLayout.LayoutParams.WRAP_CONTENT, LinearLayout.LayoutParams.WRAP_CONTENT);

        params.setMargins(8, 0, 8, 0);

        sliderDotspanel.addView(dots[i], params);

    }

    dots[0].setImageDrawable(ContextCompat.getDrawable(getApplicationContext(), R.drawable.active_dot));

    viewPager.addOnPageChangeListener(new ViewPager.OnPageChangeListener() {
        @Override
        public void onPageScrolled(int position, float positionOffset, int positionOffsetPixels) {

        }

        @Override
        public void onPageSelected(int position) {

            for(int i = 0; i< dotscount; i++){
                dots[i].setImageDrawable(ContextCompat.getDrawable(getApplicationContext(), R.drawable.non_active_dot));
            }

            dots[position].setImageDrawable(ContextCompat.getDrawable(getApplicationContext(), R.drawable.active_dot));

        }

        @Override
        public void onPageScrollStateChanged(int state) {

        }
    });

}


@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
                         Bundle savedInstanceState) {
    // Inflate the layout for this fragment
    return inflater.inflate(R.layout.fragment_about_sl, container, false);
}

@Override
public void onViewCreated(View view, @Nullable Bundle savedInstanceState) {
    super.onViewCreated(view, savedInstanceState);
    //you can set the title for your toolbar here for different fragments different titles
    getActivity().setTitle("About Sri Lanka");
}

}

但这会产生一大堆错误。但是当我扩展 AppCompatActivity 类时，错误消失了，除了一个。像这样（下）

public class aboutSLFragment extends Fragment, AppCompatActivity

据我所知，我们不能继承两个类。那么我应该怎么做才能解决它？请帮我？如果有人更正我的代码，将不胜感激。

我在 aboutSLFragment.java 中添加了一个图像滑块，但有一些我无法修复的错误。我是 android 新手，所以请有人告诉我如何修复错误。我已将错误加粗。

public class aboutSLFragment extends Fragment{

ViewPager viewPager;
LinearLayout sliderDotspanel;
private int dotscount;
private ImageView[] dots;


public aboutSLFragment() {
    // Required empty public constructor
}


@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
                         Bundle savedInstanceState) {

    viewPager = (ViewPager) **findViewById**(R.id.viewPager);

    sliderDotspanel = (LinearLayout) **findViewById**(R.id.SliderDots);

    ViewPagerAdapter viewPagerAdapter = new ViewPagerAdapter(**this**);

    viewPager.setAdapter(viewPagerAdapter);

    dotscount = viewPagerAdapter.getCount();
    dots = new ImageView[dotscount];

    for(int i = 0; i < dotscount; i++){

        dots[i] = new ImageView(**this**);
        dots[i].setImageDrawable(ContextCompat.getDrawable(**getApplicationContext()**, R.drawable.non_active_dot));

        LinearLayout.LayoutParams params = new LinearLayout.LayoutParams(LinearLayout.LayoutParams.WRAP_CONTENT, LinearLayout.LayoutParams.WRAP_CONTENT);

        params.setMargins(8, 0, 8, 0);

        sliderDotspanel.addView(dots[i], params);

    }

    dots[0].setImageDrawable(ContextCompat.getDrawable(**getApplicationContext()**, R.drawable.active_dot));

    viewPager.addOnPageChangeListener(new ViewPager.OnPageChangeListener() {
        @Override
        public void onPageScrolled(int position, float positionOffset, int positionOffsetPixels) {

        }

        @Override
        public void onPageSelected(int position) {

            for(int i = 0; i< dotscount; i++){
                dots[i].setImageDrawable(ContextCompat.getDrawable(**getApplicationContext()**, R.drawable.non_active_dot));
            }

            dots[position].setImageDrawable(ContextCompat.getDrawable(**getApplicationContext()**, R.drawable.active_dot));

        }

        @Override
        public void onPageScrollStateChanged(int state) {

        }
    });

    // Inflate the layout for this fragment
    return inflater.inflate(R.layout.fragment_about_sl, container, false);
}

@Override
public void onViewCreated(View view, @Nullable Bundle savedInstanceState) {
    super.onViewCreated(view, savedInstanceState);
    //you can set the title for your toolbar here for different fragments different titles
    getActivity().setTitle("About Sri Lanka");
}

}

【问题讨论】：

不可能Java不支持多个inheritance
我现在不可能。我问我该怎么办？
在onCreateView() 中设置您的ViewPager 并发布您的Logcat（如果有）
你好阿布优素福我添加了图像滑块，但有一些我无法解决的错误。请我是安卓新手，你能检查并告诉我如何解决。我加粗了错误。有一个看
我已经编辑了您的代码。发布错误消息有助于快速找到问题。希望下次您发布带有一些错误消息的代码

标签： java android xml android-fragments inheritance

【解决方案1】：

我已更改您的代码。问题是：

findViewById()。 Activity 已经有 findViewById() 方法，所以你可以在 Activity 中调用它。但是Fragment 没有这个方法。在Fragment 中，您必须通过View.findViewById() 方法找到一个视图，这里View 将是您在onCreateView() 中膨胀的视图
new ViewPagerAdapter(this)。要创建视图，您必须提供活动上下文。在这里，您传递 this 它是您的 Fragment 实例而不是 Activity Context

ContextCompat.getDrawable() 这个方法也需要一个上下文。 getApplicationContext() 在 Fragment 中不可用。您必须从 Fragment 调用 getActivity() 或 getContext() 才能获取 Activity 的上下文。

public class aboutSLFragment extends Fragment{

ViewPager viewPager;
LinearLayout sliderDotspanel;
private int dotscount;
private ImageView[] dots;

public aboutSLFragment() {
  // Required empty public constructor
}

@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
                     Bundle savedInstanceState) {

View rootView = inflater.inflate(R.layout.fragment_about_sl, container, false);
viewPager = (ViewPager) rootView .findViewById(R.id.viewPager);

sliderDotspanel = (LinearLayout)rootView.findViewById(R.id.SliderDots);

ViewPagerAdapter viewPagerAdapter = new ViewPagerAdapter(getContext());

viewPager.setAdapter(viewPagerAdapter);

dotscount = viewPagerAdapter.getCount();
dots = new ImageView[dotscount];

for(int i = 0; i < dotscount; i++){

    dots[i] = new ImageView(getContext());
    dots[i].setImageDrawable(ContextCompat.getDrawable(getContext(), R.drawable.non_active_dot));

    LinearLayout.LayoutParams params = new LinearLayout.LayoutParams(LinearLayout.LayoutParams.WRAP_CONTENT, LinearLayout.LayoutParams.WRAP_CONTENT);

    params.setMargins(8, 0, 8, 0);

    sliderDotspanel.addView(dots[i], params);

}

dots[0].setImageDrawable(ContextCompat.getDrawable(getContext(), R.drawable.active_dot));

viewPager.addOnPageChangeListener(new ViewPager.OnPageChangeListener() {
    @Override
    public void onPageScrolled(int position, float positionOffset, int positionOffsetPixels) {

    }

    @Override
    public void onPageSelected(int position) {

        for(int i = 0; i< dotscount; i++){
            dots[i].setImageDrawable(ContextCompat.getDrawable(getContext(), R.drawable.non_active_dot));
        }

        dots[position].setImageDrawable(ContextCompat.getDrawable(getContext(), R.drawable.active_dot));

    }

    @Override
    public void onPageScrollStateChanged(int state) {

    }
});

 // Inflate the layout for this fragment
 return rootView;
}

@Override
public void onViewCreated(View view, @Nullable Bundle savedInstanceState) {
  super.onViewCreated(view, savedInstanceState);
  //you can set the title for your toolbar here for different fragments different titles
  getActivity().setTitle("About Sri Lanka");
 }

}

检查此代码。

【讨论】：