添加CycleViewPager

可以无限循环的ViewPager

Android/代码/可以循环滑动的ViewPager.md

@@ -0,0 +1,136 @@
+# 可以循环滑动的ViewPager
+
+## 说明
+
+> Android自带的ViewPager是有边界的，不可以循环滑动。此代码通过自定义ViewPager，实现了无限循环左右滑动。
+>
+> 不需要了解原理，使用方法和自带ViewPager一样
+
+## CycleViewPager
+
+```java
+import android.content.Context;
+import android.database.DataSetObserver;
+import android.support.v4.view.PagerAdapter;
+import android.support.v4.view.ViewPager;
+import android.util.AttributeSet;
+import android.view.View;
+import android.view.ViewGroup;
+
+public class CycleViewPager extends ViewPager {
+
+    private InnerPagerAdapter mAdapter;
+
+    public CycleViewPager(Context context) {
+        super(context);
+        setOnPageChangeListener(null);
+    }
+
+    public CycleViewPager(Context context, AttributeSet attrs) {
+        super(context, attrs);
+        setOnPageChangeListener(null);
+    }
+
+    @Override
+    public void setAdapter(PagerAdapter arg0) {
+        mAdapter = new InnerPagerAdapter(arg0);
+        super.setAdapter(mAdapter);
+        setCurrentItem(1);
+    }
+
+    @Override
+    public void setOnPageChangeListener(OnPageChangeListener listener) {
+        super.setOnPageChangeListener(new InnerOnPageChangeListener(listener));
+    }
+
+    private class InnerOnPageChangeListener implements OnPageChangeListener {
+
+        private OnPageChangeListener listener;
+        private int position;
+
+        public InnerOnPageChangeListener(OnPageChangeListener listener) {
+            this.listener = listener;
+        }
+
+        @Override
+        public void onPageScrollStateChanged(int arg0) {
+            if (null != listener) {
+                listener.onPageScrollStateChanged(arg0);
+            }
+            if (arg0 == ViewPager.SCROLL_STATE_IDLE) {
+                if (position == mAdapter.getCount() - 1) {
+                    setCurrentItem(1, false);
+                } else if (position == 0) {
+                    setCurrentItem(mAdapter.getCount() - 2, false);
+                }
+            }
+        }
+
+        @Override
+        public void onPageScrolled(int arg0, float arg1, int arg2) {
+            if (null != listener) {
+                listener.onPageScrolled(arg0, arg1, arg2);
+            }
+        }
+
+        @Override
+        public void onPageSelected(int arg0) {
+            position = arg0;
+            if (null != listener) {
+                listener.onPageSelected(arg0);
+            }
+        }
+    }
+
+    private class InnerPagerAdapter extends PagerAdapter {
+
+        private PagerAdapter adapter;
+
+        public InnerPagerAdapter(PagerAdapter adapter) {
+            this.adapter = adapter;
+            adapter.registerDataSetObserver(new DataSetObserver() {
+
+                @Override
+                public void onChanged() {
+                    notifyDataSetChanged();
+                }
+
+                @Override
+                public void onInvalidated() {
+                    notifyDataSetChanged();
+                }
+
+            });
+        }
+
+        @Override
+        public int getCount() {
+            return adapter.getCount() + 2;
+        }
+
+        @Override
+        public boolean isViewFromObject(View arg0, Object arg1) {
+            return adapter.isViewFromObject(arg0, arg1);
+        }
+
+        @Override
+        public Object instantiateItem(ViewGroup container, int position) {
+            if (position == 0) {
+                position = adapter.getCount() - 1;
+            } else if (position == adapter.getCount() + 1) {
+                position = 0;
+            } else {
+                position -= 1;
+            }
+            return adapter.instantiateItem(container, position);
+        }
+
+        @Override
+        public void destroyItem(ViewGroup container, int position, Object object) {
+            adapter.destroyItem(container, position, object);
+        }
+
+    }
+}
+```
+