如何将片段和AppCompatActivity扩展到同一个类？

时间：2018-02-11 09:44:33

标签： java android xml android-fragments inheritance

我有一个类。我已将Fragment扩展到此类，因为我在开发导航抽屉时使用了片段。

代码在

之下 
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");
}

}

现在我想在该类中添加一个图像滑块。我使用的代码就是这个。

@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（下图）

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，错误会消失，除了一个。就像这个（下面）

public class aboutSLFragment extends Fragment, AppCompatActivity

据我所知，我们不能继承两个班级。所以我该怎么做才能解决它？请帮我？如果有人纠正我的代码，将不胜感激。

我已经向aboutSLFragment.java添加了一个图片滑块，但是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。我已经加错了。

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");
}

}

1 个答案:

答案 0 :(得分：0)

我已经更改了你的代码。问题是：

  1. findViewById()。 Activity已经有findViewById()方法，因此您可以在Activity中调用它。但Fragment没有这种方法。在Fragment中，您必须按View.findViewById()方法查找视图，此处View将是您在onCreateView()
    2. 中充气的视图
  2. new ViewPagerAdapter(this)。要创建视图，您必须提供活动上下文。在这里，您将this传递给您的Fragment实例而非活动上下文

  3. ContextCompat.getDrawable()此方法也需要一个Context。片段中没有getApplicationContext()。您必须从Fragment调用getActivity()或getContext()才能获得活动的上下文。

    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");
 }

}

    4. 检查此代码。

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