Android ViewPager刷新解析

ViewPager刷新解析

　　原本以为PagerAdapter类似于BaseAdapter 但是使用起来发现刷新还是有区别的 解析如下

先上Demo

PagerAdapter的四大函数

　　getCount 返回要滑动的View的个数

　　isViewFromObject 从当前container中删除指定位置（position）的View

　　instantiateItem 将当前视图添加到container中 返回当前View

　　destroyItem

第一个问题 但数据源发生变化时 调用viewPagerAdapter.notifyDataSetChanged() 发现无法刷新数据

解决办法 PagerAdapter中重写getItemPosition方法

上代码

public class MainActivity extends Activity {

  private ViewPager view_pager; //预览照片的分页显示
  private ViewPagerAdapter viewPagerAdapter; //分页图片的预览器

  private ArrayList<String> fileNames = new ArrayList<String>(); //本地图片路径
  private int currentPosition; //当前选择的图片

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

    initData();
    initView();
  }

  // 获取本地所有照片路径
  private void initData() {

    fileNames.clear();
    Cursor cursor = getContentResolver().query(Media.EXTERNAL_CONTENT_URI, null, null, null, null);
    while (cursor.moveToNext()) {
      byte[] data = cursor.getBlob(cursor.getColumnIndex(Media.DATA)); //图片的保存位置的数据
      fileNames.add(new String(data, 0, data.length - 1));
    }

  }

  //初始化控件
  private void initView() {
    view_pager = (ViewPager) findViewById(R.id.view_pager);
    viewPagerAdapter = new ViewPagerAdapter(this, fileNames);
    view_pager.setAdapter(viewPagerAdapter);

    view_pager.setOnPageChangeListener(new ViewPager.OnPageChangeListener() {

      @Override
      public void onPageSelected(int i) {
        currentPosition = i;

        Log.i("mbk", "翻页后的当前页面" + currentPosition);
      }

      @Override
      public void onPageScrolled(int i, float f, int j) {
      }

      @Override
      public void onPageScrollStateChanged(int i) {
      }
    });

    Button delete = (Button)findViewById(R.id.delete);
    delete.setOnClickListener(new View.OnClickListener() {

      @Override
      public void onClick(View v) {
        if (fileNames.size() > 0) {
          fileNames.remove(currentPosition);
        }
        Log.i("mbk", "删除的当前页面" + currentPosition);
        viewPagerAdapter.notifyDataSetChanged();
      }
    });

  }

}

public class ViewPagerAdapter extends PagerAdapter{

  private Context context;
  private ArrayList<String> fileNames = new ArrayList<String>(); //本地图片路径

  public ViewPagerAdapter(Context context, ArrayList<String> fileNames) {
    super();
    this.context = context;
    this.fileNames = fileNames;
  }

  @Override
  public int getCount() {
    return fileNames.size();
  }

  @Override
  public boolean isViewFromObject(View view, Object object) {
    return view == object;
  }

  @Override
  public View instantiateItem(ViewGroup container, int position) {
    ImageView imageView = new ImageView(context);
    Glide.with(context).load(fileNames.get(position)).centerCrop().into(imageView);

    container.addView(imageView, LayoutParams.MATCH_PARENT, LayoutParams.MATCH_PARENT);
    return imageView;
  }

  @Override
  public void destroyItem(ViewGroup container, int position, Object object) {
    container.removeView((View) object);
  }

  //解决数据不刷新的问题
  @Override
  public int getItemPosition(Object object) {
      return POSITION_NONE;
  }
}

Demo见 https://github.com/huanyi0723/TestViewPager1

第二个问题 解决刷新单个页面的方法 对于控件采取setTag和findViewWithTag寻找到 再更新 同时注意position和currentPosition

上代码

public class MainActivity extends Activity {

  private ViewPager view_pager; //预览照片的分页显示
  private ViewPagerAdapter viewPagerAdapter; //分页图片的预览器

  private ArrayList<String> fileNames = new ArrayList<String>(); //本地图片路径
  private int currentPosition = 0; //当前选择的图片

  private Timer timer = new Timer(); // 定时器
  private TimerTask timerTask;
  private int progress = 0;

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

    initData();
    initView();
  }

  // 获取本地所有照片路径
  private void initData() {

    fileNames.clear();
    Cursor cursor = getContentResolver().query(Media.EXTERNAL_CONTENT_URI, null, null, null, null);
    while (cursor.moveToNext()) {
      byte[] data = cursor.getBlob(cursor.getColumnIndex(Media.DATA)); //图片的保存位置的数据
      fileNames.add(new String(data, 0, data.length - 1));
    }

  }

  //初始化控件
  private void initView() {
    view_pager = (ViewPager) findViewById(R.id.view_pager);
    viewPagerAdapter = new ViewPagerAdapter(this, fileNames, view_pager, currentPosition);
    view_pager.setAdapter(viewPagerAdapter);

    view_pager.setOnPageChangeListener(new ViewPager.OnPageChangeListener() {

      @Override
      public void onPageSelected(int i) {
        currentPosition = i;

        Log.i("mbk", "翻页后的当前页面" + currentPosition);
      }

      @Override
      public void onPageScrolled(int i, float f, int j) {
      }

      @Override
      public void onPageScrollStateChanged(int i) {
      }
    });

    Button delete = (Button)findViewById(R.id.delete);
    delete.setOnClickListener(new View.OnClickListener() {

      @Override
      public void onClick(View v) {
        if (fileNames.size() > 0) {
          fileNames.remove(currentPosition);
        }
        Log.i("mbk", "删除的当前页面" + currentPosition);
        viewPagerAdapter.notifyDataSetChanged();
      }
    });

    Button update = (Button)findViewById(R.id.update);
    update.setOnClickListener(new View.OnClickListener() {

      @Override
      public void onClick(View v) {
        initTimeTask();
      }
    });

  }

  // 定时器轮询
  private void initTimeTask() {

    timerTask = new TimerTask() {
      @Override
      public void run() {
        viewPagerAdapter.setProgress( progress , currentPosition);

        Log.i("mbk", "---------------MainActivity -----------progress--------------" + progress);
        progress++;
      }
    };

    timer.schedule(timerTask, 0, 1000);

  }

}

public class ViewPagerAdapter extends PagerAdapter {

  private Context context;
  private ArrayList<String> fileNames = new ArrayList<String>(); // 本地图片路径

  private SeekBar seekBar;
  private ViewPager view_pager;

  public ViewPagerAdapter(Context context, ArrayList<String> fileNames, ViewPager view_pager ) {
    super();
    this.context = context;
    this.fileNames = fileNames;
    this.view_pager = view_pager;
  }

  @Override
  public int getCount() {
    return fileNames.size();
  }

  @Override
  public boolean isViewFromObject(View view, Object object) {
    return view == object;
  }

  @Override
  public View instantiateItem(ViewGroup container, int position) {

    View view = LayoutInflater.from(context).inflate(R.layout.pager_adapter_item, null);
    ImageView imageView = (ImageView) view.findViewById(R.id.imageView);
    seekBar = (SeekBar) view.findViewById(R.id.seekBar);
    seekBar.setMax(100);

    seekBar.setTag("seekBar" + position);

    Log.i("mbk", "---------------ViewPagerAdapter -----------setTag--------------" + position);

    Glide.with(context).load(fileNames.get(position)).centerCrop().into(imageView);

    container.addView(view, LayoutParams.MATCH_PARENT, LayoutParams.MATCH_PARENT);
    return view;

  }

  @Override
  public void destroyItem(ViewGroup container, int position, Object object) {
    container.removeView((View) object);
  }

  // 解决数据不刷新的问题
  @Override
  public int getItemPosition(Object object) {
    return POSITION_NONE;
  }

  public void setProgress(int progress, int currentPosition) {
    seekBar =  (SeekBar) view_pager.findViewWithTag("seekBar"+currentPosition);
    seekBar.setProgress(progress);

    Log.i("mbk", "---------------ViewPagerAdapter -----------progress--------------" + progress);
  }
}

Demo见 https://github.com/huanyi0723/TestViewPager2