一般進入APP都有歡迎界面，基本都是水平滾動的，今天和大家分享一個垂直滾動的例子。
<com.example.verticallinearlayout.VerticalLinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:id="@+id/id_main_ly"
android:layout_width="match_parent"
android:layout_height="fill_parent"
android:orientation="vertical"
android:background="#fff" >
<RelativeLayout
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:background="@drawable/w02" >
<Button
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="hello" />
</RelativeLayout>
<RelativeLayout
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:background="@drawable/w03" >
<Button
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_centerInParent="true"
android:background="#fff"
android:text="hello" />
</RelativeLayout>
<RelativeLayout
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:background="@drawable/w04" >
<Button
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_centerInParent="true"
android:text="hello" />
</RelativeLayout>
<RelativeLayout
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:background="@drawable/w05" >
<Button
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_centerInParent="true"
android:text="hello" />
</RelativeLayout>
</com.example.verticallinearlayout.VerticalLinearLayout>2、主要看自定義的Layout了
package com.example.verticallinearlayout;
import android.content.Context;
import android.util.AttributeSet;
import android.util.DisplayMetrics;
import android.util.Log;
import android.view.MotionEvent;
import android.view.VelocityTracker;
import android.view.View;
import android.view.ViewGroup;
import android.view.WindowManager;
import android.widget.Scroller;
public class VerticalLinearLayout extends ViewGroup
{
/**
* 屏幕的高度
*/
private int mScreenHeight;
/**
* 手指按下時的getScrollY
*/
private int mScrollStart;
/**
* 手指擡起時的getScrollY
*/
private int mScrollEnd;
/**
* 記錄移動時的Y
*/
private int mLastY;
/**
* 滾動的輔助類
*/
private Scroller mScroller;
/**
* 是否正在滾動
*/
private boolean isScrolling;
/**
* 加速度檢測
*/
private VelocityTracker mVelocityTracker;
/**
* 記錄當前頁
*/
private int currentPage = 0;
private OnPageChangeListener mOnPageChangeListener;
public VerticalLinearLayout(Context context, AttributeSet attrs)
{
super(context, attrs);
/**
* 獲得屏幕的高度
*/
WindowManager wm = (WindowManager) context.getSystemService(Context.WINDOW_SERVICE);
DisplayMetrics outMetrics = new DisplayMetrics();
wm.getDefaultDisplay().getMetrics(outMetrics);
mScreenHeight = outMetrics.heightPixels;
// 初始化
mScroller = new Scroller(context);
}
@Override
protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec)
{
super.onMeasure(widthMeasureSpec, heightMeasureSpec);
int count = getChildCount();
for (int i = 0; i < count; ++i)
{
View childView = getChildAt(i);
measureChild(childView, widthMeasureSpec,mScreenHeight);
}
}
@Override
protected void onLayout(boolean changed, int l, int t, int r, int b)
{
if (changed)
{
int childCount = getChildCount();
// 設置主佈局的高度
MarginLayoutParams lp = (MarginLayoutParams) getLayoutParams();
lp.height = mScreenHeight * childCount;
setLayoutParams(lp);
for (int i = 0; i < childCount; i++)
{
View child = getChildAt(i);
if (child.getVisibility() != View.GONE)
{
child.layout(l, i * mScreenHeight, r, (i + 1) * mScreenHeight);// 調用每個自佈局的layout
}
}
}
}
@Override
public boolean onTouchEvent(MotionEvent event)
{
// 如果當前正在滾動，調用父類的onTouchEvent
if (isScrolling)
return super.onTouchEvent(event);
int action = event.getAction();
int y = (int) event.getY();
obtainVelocity(event);
switch (action)
{
case MotionEvent.ACTION_DOWN:
mScrollStart = getScrollY();
mLastY = y;
break;
case MotionEvent.ACTION_MOVE:
if (!mScroller.isFinished())
{
mScroller.abortAnimation();
}
int dy = mLastY - y;
// 邊界值檢查
int scrollY = getScrollY();
// 已經到達頂端，下拉多少，就往上滾動多少
if (dy < 0 && scrollY + dy < 0)
{
dy = -scrollY;
}
// 已經到達底部，上拉多少，就往下滾動多少
if (dy > 0 && scrollY + dy > getHeight() - mScreenHeight)
{
dy = getHeight() - mScreenHeight - scrollY;
}
scrollBy(0, dy);
mLastY = y;
break;
case MotionEvent.ACTION_UP:
mScrollEnd = getScrollY();
int dScrollY = mScrollEnd - mScrollStart;
if (wantScrollToNext())// 往上滑動
{
if (shouldScrollToNext())
{
mScroller.startScroll(0, getScrollY(), 0, mScreenHeight - dScrollY);
} else
{
mScroller.startScroll(0, getScrollY(), 0, -dScrollY);
}
}
if (wantScrollToPre())// 往下滑動
{
if (shouldScrollToPre())
{
mScroller.startScroll(0, getScrollY(), 0, -mScreenHeight - dScrollY);
} else
{
mScroller.startScroll(0, getScrollY(), 0, -dScrollY);
}
}
isScrolling = true;
postInvalidate();
recycleVelocity();
break;
}
return true;
}
/**
* 根據滾動距離判斷是否能夠滾動到下一頁
*
* @return
*/
private boolean shouldScrollToNext()
{
return mScrollEnd - mScrollStart > mScreenHeight / 2 || Math.abs(getVelocity()) > 600;
}
/**
* 根據用戶滑動，判斷用戶的意圖是否是滾動到下一頁
*
* @return
*/
private boolean wantScrollToNext()
{
return mScrollEnd > mScrollStart;
}
/**
* 根據滾動距離判斷是否能夠滾動到上一頁
*
* @return
*/
private boolean shouldScrollToPre()
{
return -mScrollEnd + mScrollStart > mScreenHeight / 2 || Math.abs(getVelocity()) > 600;
}
/**
* 根據用戶滑動，判斷用戶的意圖是否是滾動到上一頁
*
* @return
*/
private boolean wantScrollToPre()
{
return mScrollEnd < mScrollStart;
}
@Override
public void computeScroll()
{
super.computeScroll();
if (mScroller.computeScrollOffset())
{
scrollTo(0, mScroller.getCurrY());
postInvalidate();
} else
{
int position = getScrollY() / mScreenHeight;
Log.e("xxx", position + "," + currentPage);
if (position != currentPage)
{
if (mOnPageChangeListener != null)
{
currentPage = position;
mOnPageChangeListener.onPageChange(currentPage);
}
}
isScrolling = false;
}
}
/**
* 獲取y方向的加速度
*
* @return
*/
private int getVelocity()
{
mVelocityTracker.computeCurrentVelocity(1000);
return (int) mVelocityTracker.getYVelocity();
}
/**
* 釋放資源
*/
private void recycleVelocity()
{
if (mVelocityTracker != null)
{
mVelocityTracker.recycle();
mVelocityTracker = null;
}
}
/**
* 初始化加速度檢測器
*
* @param event
*/
private void obtainVelocity(MotionEvent event)
{
if (mVelocityTracker == null)
{
mVelocityTracker = VelocityTracker.obtain();
}
mVelocityTracker.addMovement(event);
}
/**
* 設置回調接口
*
* @param onPageChangeListener
*/
public void setOnPageChangeListener(OnPageChangeListener onPageChangeListener)
{
mOnPageChangeListener = onPageChangeListener;
}
/**
* 回調接口
*
* @author zhy
*
*/
public interface OnPageChangeListener
{
void onPageChange(int currentPage);
}
}註釋還是相當詳細的，我簡單描述一下，Action_down時獲得當前的scrollY,然後Action_move時，根據移動的距離不斷scrollby就行了，當前處理了一下邊界判斷，在Action_up中再次獲得scrollY，兩個的scrollY進行對比，然後根據移動的距離與方向決定最後的動作。
3、主Activity
package com.example.verticallinearlayout;
import android.app.Activity;
import android.os.Bundle;
import android.widget.Toast;
import com.example.verticallinearlayout.VerticalLinearLayout.OnPageChangeListener;
public class MainActivity extends Activity
{
private VerticalLinearLayout mMianLayout;
@Override
protected void onCreate(Bundle savedInstanceState)
{
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
mMianLayout = (VerticalLinearLayout) findViewById(R.id.id_main_ly);
mMianLayout.setOnPageChangeListener(new OnPageChangeListener()
{
@Override
public void onPageChange(int currentPage)
{
// mMianLayout.getChildAt(currentPage);
Toast.makeText(MainActivity.this, "第"+(currentPage+1)+"頁", Toast.LENGTH_SHORT).show();
}
});
}
}
爲了提供可擴展性，還是定義了回調接口，完全可以把這個當成一個垂直的ViewPager使用。
總結下：
Scroller這個輔助類還是相當好用的，原理我簡單說一下：每次滾動時，讓Scroller進行滾動，然後調用postInvalidate方法，這個方法會引發調用onDraw方法，onDraw方法中會去調用computeScroll方法，然後我們在computScroll中判斷，Scroller的滾動是否結束，沒有的話，把當前的View滾動到現在Scroller的位置，然後繼續調用postInvalidate，這樣一個循環的過程。
