35

我想允许用户ViewPager只从右向左滑动。因此，一旦他通过了一页，他就无法再回到它了。如何才能做到这一点？

我试过这个解决方案：

public class CustomViewPager extends ViewPager {

float lastX = 0;

boolean lockScroll = false;

public CustomViewPager(Context context, AttributeSet attrs) {
    super(context, attrs);
}

public CustomViewPager(Context context) {
    super(context);
}

@Override
public boolean onTouchEvent(MotionEvent ev) {

    switch (ev.getAction()) {
    case MotionEvent.ACTION_DOWN:
        lastX = ev.getX();
        lockScroll = false;
        return super.onTouchEvent(ev);
    case MotionEvent.ACTION_MOVE:

        if (lastX > ev.getX()) {
            lockScroll = false;
        } else {
            lockScroll = true;
        }

        lastX = ev.getX();
        break;
    }

    lastX = ev.getX();

    if(lockScroll) {
        return false;
    } else {
        return super.onTouchEvent(ev);
    }
}
}

但它仍然让我无法向另一个方向滑动。

4

4 回答 4

78

您还错过了一个事件：onInterceptTouchEvent。它必须包含与 onTouchEvent 相同的逻辑。

我的完整解决方案基于此 答案。它将允许您在需要的任何时间启用/禁用任何方向的分页。

1.创建枚举

 public enum SwipeDirection {
    ALL, LEFT, RIGHT, NONE ;
}

2.扩展ViewPager（Java）

public class CustomViewPager extends ViewPager {

    private float initialXValue;
    private SwipeDirection direction;

    public CustomViewPager(Context context, AttributeSet attrs) {
        super(context, attrs);
        this.direction = SwipeDirection.ALL;
    }

    @Override
    public boolean onTouchEvent(MotionEvent event) {
        if (this.isSwipeAllowed(event)) {
            return super.onTouchEvent(event);
        }

        return false;
    }

    @Override
    public boolean onInterceptTouchEvent(MotionEvent event) {
        if (this.isSwipeAllowed(event)) {
            return super.onInterceptTouchEvent(event);
        }

        return false;
    }

    private boolean isSwipeAllowed(MotionEvent event) {
        if(this.direction == SwipeDirection.ALL) return true;

        if(direction == SwipeDirection.NONE )//disable any swipe
            return false;

        if(event.getAction()==MotionEvent.ACTION_DOWN) {
            initialXValue = event.getX();
            return true;
        }

        if (event.action === MotionEvent.ACTION_MOVE) {
            val diffX = event.x - initialXValue
            if (diffX > 0 && direction === SwipeDirection.RIGHT) {
                // swipe from left to right detected
                return false
            } else if (diffX < 0 && direction === SwipeDirection.LEFT) {
                // swipe from right to left detected
                return false
            }
        }

        return true;
    }

    public void setAllowedSwipeDirection(SwipeDirection direction) {
        this.direction = direction;
    }
}

2.扩展 ViewPager（在 Kotlin 中）

enum class SwipeDirection {
    ALL, LEFT, RIGHT, NONE
}

class SingleDirectionViewPager @JvmOverloads constructor(
    context: Context,
    attrs: AttributeSet?
) : ViewPager(context, attrs) {

    private var initialXValue = 0f
    private var direction: SwipeDirection = SwipeDirection.ALL

    override fun onTouchEvent(event: MotionEvent): Boolean =
        if (isSwipeAllowed(event)) {
            super.onTouchEvent(event)
        } else {
            false
        }

    override fun onInterceptTouchEvent(event: MotionEvent): Boolean =
        if (isSwipeAllowed(event)) {
            super.onInterceptTouchEvent(event)
        } else {
            false
        }

    private fun isSwipeAllowed(event: MotionEvent): Boolean {
        if (direction == SwipeDirection.ALL) {
            return true
        }

        if (direction == SwipeDirection.NONE) {
            return false
        }

        if (event.action == MotionEvent.ACTION_DOWN) {
            initialXValue = event.x
            return true
        }

        if (event.action == MotionEvent.ACTION_MOVE) {
            val diffX = event.x - initialXValue

            if (diffX > 0 && direction === SwipeDirection.RIGHT) {
                // swipe from left to right detected
                return false
            } else if (diffX < 0 && direction === SwipeDirection.LEFT) {
                // swipe from right to left detected
                return false
            }
        }

        return true
    }

    fun setAllowedSwipeDirection(direction: SwipeDirection) {
        this.direction = direction
    }
}

3.在布局中使用 viewPager

 <package_name.customviewpager 
     android:id="@+id/customViewPager" 
     android:layout_height="match_parent" 
     android:layout_width="match_parent" />

4.在代码中启用任何滑动方向。默认为全部（左右）

mViewPager.setAllowedSwipeDirection(SwipeDirection.RIGHT);
于 2015-12-03T21:37:38.977 回答
2 
package com.contacts_app.jamison.contacts__proprivacy4;

import android.content.Context;
import android.content.res.Resources;
import android.support.v4.view.ViewPager;
import android.util.AttributeSet;
import android.util.Log;
import android.view.MotionEvent;

public class ViewPager_Settings extends ViewPager
{
private final String TAG = ViewPager_Settings.class.getSimpleName();
public float startX;

public ViewPager_Settings(Context context, AttributeSet attrs) {
    super(context, attrs);
}

 ////////////////////////////////////////////////////////////////////////////////////////////////
public static int dpTOpx(double dp)
{
    return (int) (dp * Resources.getSystem().getDisplayMetrics().density);
}
public static int pxTOdp(double px)
{
    return (int) (px / Resources.getSystem().getDisplayMetrics().density);
}
////////////////////////////////////////////////////////////////////////////////////////////////

/*****DispatchTouchEvent for the View Pager to intercept and block swipes Right*****/
@Override
public boolean dispatchTouchEvent(MotionEvent ev)
{
    final int actionMasked = ev.getActionMasked() & MotionEvent.ACTION_MASK;
    //int movement_limit = pxTOdp(50);
    switch (actionMasked)
    {
        case (MotionEvent.ACTION_DOWN):
        {
            startX = ev.getX();
            Log.i(TAG, "startX: " + startX);

            /*Should always be this below*/
            return super.dispatchTouchEvent(ev);
        }
        case (MotionEvent.ACTION_MOVE):
        {
            Log.i(TAG, "ev.getX() - startX:" + (ev.getX() - startX));

            /*Switching directional changes would be a matter of flipping the  "<" sign in the line below.*/
            if (ev.getX() - startX > 0)
            {
                /*The result is that the ViewPager will not swipe from left*/
                ev.setAction(MotionEvent.ACTION_CANCEL);;
            }

            /*Should always be this below*/
            super.dispatchTouchEvent(ev);
        }
        /**The ACTION_UP case statement is only needed if you don't want to pass down the touch event 
        * to buttons that may receive the click after the swipe is blocked.*/
        /*case (MotionEvent.ACTION_UP):
        {
            //Log.i(TAG, "movement_limit: " + movement_limit);

            //(-50) may need to be changed to something more broader in scope to accompany all screen densities
            if ( (ev.getX() - startX) < (-50) )
            {
                ev.setAction(MotionEvent.ACTION_CANCEL);
            }

            //Should always be this below
            super.dispatchTouchEvent(ev);
        }*/
    }
    /*Should always be this below*/
    return super.dispatchTouchEvent(ev);
}
 ////////////////////////////////////////////////////////////////////////////////////////////////

}/*****END OF FILE*****/

不要忘记更改顶部的行以放置您的应用程序的包名称。此外，大多数（如果不是全部）注释可以深入了解代码在做什么，以防您决定要修改某些东西。

于 2017-07-29T03:58:38.387 回答
0

像这样定义你的适配器

public class MyFragmentStatePagerAdapter extends FragmentStatePagerAdapter {

    private final int totalPages = 10;
    private int currentPage = 0;

    public MyFragmentStatePagerAdapter(FragmentManager fm) {
        super(fm);
    }

    @Override
    public Fragment getItem(int position) {
        // Use whatever logic you want here to
        // to select a fragment based on
        // currentPage instead of position

        if (currentPage % 2 == 0) {
            return new Fragment1();
        } else {
            return new Fragment2();
        }
    }

    @Override
    public int getCount() {
        return currentPage == totalPages ? 1 : 2;
    }

    @Override
    public int getItemPosition(Object object){
        return PagerAdapter.POSITION_NONE;
    }

    public void nextPage() {
        currentPage++;
        notifyDataSetChanged();
    }
}

在使用视图寻呼机的片段中，执行此操作

@Override
public void onPageSelected(int arg0) {
    if (arg0 > 0) {
        pagerAdapter.nextPage();
        pager.setCurrentItem(0, false);
    }
}
于 2014-12-14T01:05:50.577 回答
-1

尝试添加（与 onTouchEvent 中相同的逻辑）

@Override
public boolean onInterceptTouchEvent(MotionEvent arg0) {
    // allow/ not allow swiping to switch between pages
    return !lockScroll ;
}
于 2014-12-16T08:29:23.920 回答