Question

我正在试图找出为什么我的图像在CustomPagerAdapter mResources类中没有出现一旦VerticalViewPager小部件出现 - 在开始时没有任何内容，在垂直滑动期间什么也没有。

我已经在这里呆了几天但是不能破解它。没有帮助ViewPager / Adapters上的文档不是很清楚。

使用 - Nexus 6 AVD，minSdkVersion = 19

当我尝试向上滚动（从底部单击并一直向上滑动到顶部）时，我会收到此错误消息...

*AndroidRuntime: FATAL EXCEPTION: main
Process: sparktic.com.verticalviewpager, PID: 19242
java.lang.IllegalStateException: The specified child already has a parent. You must call removeView() on the child's parent first.
at android.view.ViewGroup.addViewInner(ViewGroup.java:3562)*

AFAIK我正在正确添加和删除pager_item。

java / MainActivity.java

package sparktic.com.verticalviewpager;

import android.content.Context;
import android.support.v4.view.PagerAdapter;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;

import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.ImageView;
import android.widget.LinearLayout;

public class MainActivity extends AppCompatActivity
{
    VerticalViewPager mPager;

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

        mPager = findViewById(R.id.viewpager);

        CustomPagerAdapter adapter = new CustomPagerAdapter(this);
        mPager.setAdapter(adapter);
    }

    class CustomPagerAdapter extends PagerAdapter
    {
        Context mContext;
        public LayoutInflater mLayoutInflater;   

        int[] mResources = {
                R.drawable.first,  // Dload: https://i.imgur.com/suvAa9x.jpg
                R.drawable.second, // Dload: https://i.imgur.com/c2f0Hvy.jpg
                R.drawable.third   // Dload: https://i.imgur.com/0GAs8qp.jpg
        };

        public CustomPagerAdapter(Context context)
        {
            mContext = context;
            mLayoutInflater = (LayoutInflater) mContext.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
        }

        @Override
        public int getCount()
        {
            return mResources.length;
        }

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

        @Override
        public Object instantiateItem(ViewGroup container, int position)
        {
            View itemView = mLayoutInflater.inflate(R.layout.pager_item, container, false);

            ImageView imageView = (ImageView) itemView.findViewById(R.id.imageView);
            imageView.setImageResource(mResources[position]);

            container.addView(imageView);

            return itemView;
        }

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

layout / activity_main.xml

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context="sparktic.com.verticalviewpager.MainActivity">

    <sparktic.com.verticalviewpager.VerticalViewPager
        android:id="@+id/viewpager"
        android:layout_width="match_parent"
        android:layout_height="match_parent" />

</RelativeLayout>

layout / pager_item.xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
              android:orientation="vertical" android:layout_width="match_parent"
              android:layout_height="match_parent">

    <ImageView
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:id="@+id/imageView" />
</LinearLayout>

java / VerticalViewPager.java

package sparktic.com.verticalviewpager;

import android.content.Context;
import android.support.v4.view.ViewPager;
import android.util.AttributeSet;
import android.view.MotionEvent;
import android.view.View;

public class VerticalViewPager extends ViewPager
{

    public VerticalViewPager(Context context)
    {
        this(context, null);
    }

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

    @Override
    public boolean canScrollHorizontally(int direction)
    {
        return false;
    }

    @Override
    public boolean canScrollVertically(int direction)
    {
        return super.canScrollHorizontally(direction);
    }

    private void init()
    {
        setPageTransformer(true, new VerticalPageTransformer());
        setOverScrollMode(View.OVER_SCROLL_NEVER);
    }

    @Override
    public boolean onInterceptTouchEvent(MotionEvent ev)
    {
        final boolean toIntercept = super.onInterceptTouchEvent(flipXY(ev));
        flipXY(ev);
        return toIntercept;
    }

    @Override
    public boolean onTouchEvent(MotionEvent ev)
    {
        final boolean toHandle = super.onTouchEvent(flipXY(ev));
        flipXY(ev);
        return toHandle;
    }

    private MotionEvent flipXY(MotionEvent ev)
    {
        final float width = getWidth();
        final float height = getHeight();
        final float x = (ev.getY() / height) * width;
        final float y = (ev.getX() / width) * height;
        ev.setLocation(x, y);
        return ev;
    }

    private static final class VerticalPageTransformer implements ViewPager.PageTransformer
    {
        @Override
        public void transformPage(View view, float position)
        {
            final int pageWidth = view.getWidth();
            final int pageHeight = view.getHeight();
            if (position < -1)
            {
                view.setAlpha(0);
            }
            else if (position <= 1)
            {
                view.setAlpha(1);
                view.setTranslationX(pageWidth * -position);
                float yPosition = position * pageHeight;
                view.setTranslationY(yPosition);
            }
            else
            {
                view.setAlpha(0);
            }
        }
    }
}

Answer 1

解决了我自己的问题。万一它可以帮助别人...

问题出在“ instantiateItem ”方法中。

container.addView（ImageView的）;应该是container.addView（ itemView ）;

我仍然没有完全掌握PageAdapter覆盖范围内发生的事情，但它确实有效，所以我会接受胜利并继续前进。

PageAdapter + VerticalViewPager不能一起工作。为什么呢？

1 个答案: