Question

我有一个包含2个不同片段的ViewPager，当我在onResume方法getActivity()之间滑动时，总是返回null。

public class ViewPagerAdapter extends FragmentPagerAdapter {
    public static final int PAGE_RECORD = 0;
    public static final int PAGE_CAPTURE = 1;
    public static final int PAGE_PICK = 2;
    private Context context;

    public ViewPagerAdapter(FragmentManager fm, Context context) {
        super(fm);
        this.context = context;
    }

    @Override
    public Fragment getItem(int type) {

        switch(type){
            case 0:
                return new RecordFragment();
            case 1:
                return new CaptureFragment();
        }

        return new Fragment();
    }

    @Override
    public int getCount() {
        return 2;
    }

    pager = (ViewPager) findViewById(R.id.pager);
        pager_adapter = new ViewPagerAdapter(getSupportFragmentManager(), this);
        pager.setAdapter(pager_adapter);

        OnPageChangeListener pageChangeListener = new OnPageChangeListener() {

            int currentPosition = 0;

            @Override
            public void onPageSelected(int newPosition) {

                FragmentLifecycle fragmentToShow = (FragmentLifecycle)pager_adapter.getItem(newPosition);
                fragmentToShow.onResumeFragment();

                FragmentLifecycle fragmentToHide = (FragmentLifecycle)pager_adapter.getItem(currentPosition);
                fragmentToHide.onPauseFragment();

                currentPosition = newPosition;
            }

            @Override
            public void onPageScrolled(int arg0, float arg1, int arg2) { }

            public void onPageScrollStateChanged(int arg0) { }
        };

        pager.setOnPageChangeListener(pageChangeListener);

和

public class CaptureFragment extends Fragment implements OnClickListener, FragmentLifecycle {

    private static final String TAG = "CaptureFragment";
    private ResizableCameraPreview mPreview;
    private RelativeLayout mLayout;
    private int camera_id = 0;
    private ImageButton record_btn;
    private ImageView flash_btn;
    public ImageView done_btn;
    private ImageView rotate_camera;
    private ImageView delete_btn;
    private TextView text;


    public CaptureFragment() {
    }

    @Override
    public void onAttach(Activity activity) {
        super.onAttach(activity);

        MainGifActivity.capture_fragment = this;
        setRetainInstance(true);
        Log.i(TAG, "onAttach");
    }

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        Log.i(TAG, "onCreate");
    }

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

        Log.i(TAG, "onCreateView");
        View view = inflater.inflate(R.layout.fragment_record, null);

        mLayout = (RelativeLayout) view.findViewById(R.id.layout);
        text = (TextView) view.findViewById(R.id.count_text);
        text.setText(""
                + (TakenPictures.FRAMES_COUNT - TakenPictures.photos.size()));

        delete_btn = (ImageView) view.findViewById(R.id.delete);
        done_btn = (ImageView) view.findViewById(R.id.done_btn);
        record_btn = (ImageButton) view.findViewById(R.id.record_btn);
        rotate_camera = (ImageView) view.findViewById(R.id.rotate_btn);
        flash_btn = (ImageView) view.findViewById(R.id.flash_btn);

        delete_btn.setOnClickListener(this);
        record_btn.setOnClickListener(this);
        flash_btn.setOnClickListener(this);
        done_btn.setOnClickListener(this);
        rotate_camera.setOnClickListener(this);

        return view;
    }

    @Override
    public void onResume() {
        super.onResume();
        Log.i(TAG, "onResume " + getActivity()); //null

    }

    @Override
    public void onPause() {
        super.onPause();
        Log.i(TAG, "onPause");
        if(mPreview == null)
            return;
        mPreview.isPause = true;
        mPreview.stop();
        mLayout.removeView(mPreview);
        mPreview = null;
    }


    public void forcePause(){
        mPreview.isPause = true;
        mPreview.stop();
        mLayout.removeView(mPreview);
        mPreview = null;
    }

    private void createCameraPreview() {
        mPreview = new ResizableCameraPreview(MainGifActivity.capture_fragment.getActivity(), camera_id,
                CameraPreview.LayoutMode.FitToParent, false, mLayout, 1, done_btn);
        LayoutParams previewLayoutParams = new LayoutParams(
                LayoutParams.WRAP_CONTENT, LayoutParams.WRAP_CONTENT);
        previewLayoutParams.addRule(RelativeLayout.CENTER_HORIZONTAL);
        mLayout.addView(mPreview, 0, previewLayoutParams);
    }

    @Override
    public void onClick(View v) {

        switch (v.getId()) {
        case R.id.done_btn:

            if (TakenPictures.photos.size() == 0)
                Toast.makeText(getActivity(), "No frames recorded",
                        Toast.LENGTH_SHORT).show();
            else {
                startActivity(new Intent(getActivity(), EditGifActivity.class));
                getActivity().finish();
            }
            mPreview.isRecording = false;
            mPreview.isInterrupted = true;
            break;

        case R.id.record_btn:

            synchronized (mPreview) {
                if (mPreview == null)
                    return;
                if (mPreview.isRecording) {
                    if (mPreview.isPause) {
                        if (mPreview.isOutOfMemory) {
                            Toast.makeText(getActivity(),
                                    "Is out of memory, please click done",
                                    Toast.LENGTH_SHORT).show();
                            break;
                        }
                        mPreview.isPause = false;
                    } else
                        mPreview.isPause = true;
                } else {
                    mPreview.isRecording = true;
                    // TimeCounterTask time_counter = new TimeCounterTask();
                    // time_counter.execute(System.currentTimeMillis());
                }
            }
            break;

        case R.id.rotate_btn:

            boolean did_r = false;
            boolean did_p = false;
            if (mPreview.isRecording)
                did_r = true;
            if (mPreview.isPause)
                did_p = true;

            synchronized (mPreview.mCamera) {
                mPreview.isRotated = true;
                camera_id = ((camera_id == 0) ? 1 : 0);
                mPreview.stop();
                mLayout.removeView(mPreview);
                createCameraPreview();

                mPreview.isRecording = did_r;
                mPreview.isPause = did_p;
            }
            break;

        case R.id.flash_btn:

            mPreview.turnFlash();
            break;

        case R.id.delete:
            synchronized (TakenPictures.photos) {
                TakenPictures.photos.clear();
            }
            text.setText("Time: "
                    + ((TakenPictures.FRAMES_COUNT - TakenPictures.photos
                            .size())));
        }
    }

    @Override
    public void onPauseFragment() {
        Log.i(TAG, "onPauseFragment()");
        //Toast.makeText(getActivity(), "onPauseFragment():" + TAG, Toast.LENGTH_SHORT).show(); 
    }

    @Override
    public void onResumeFragment() {
        onResume();

        getActivity(); // always null

        //Toast.makeText(getActivity(), "onResumeFragment():" + TAG, Toast.LENGTH_SHORT).show();
    }
}

请帮我刷一下如何活动;

Answer 1

您可以使用全局“上下文”变量，并可能将其转换为主要活动。您在类构造函数中设置了上下文，那么为什么不使用它而不是getActivitiy（）？

Answer 2

宣布这样的全球活动：

YourActivityName activity;    
     @Override
        public void onCreate(Bundle savedInstanceState) {            
           activity = (YourActivityName) getActivity();       
        }

然后你可以在任何你想要的地方使用变量activity，它不会为空。

带有片段的ViewPager：刷卡后getActivity返回null onResume

2 个答案: