android設計中，有時需要實作一組頁面進行滑動，例如在一個Activity視圖中，頂部是一個導航欄，底部是菜單欄 ，中間是3個可以滑動的區域，其功能跟android系統的Launcher的workspace相似 。
程式運作界面效果：
以下為核心代碼：
布局檔案： res/layout/main.xml：
<?xml version="1.0" encoding="UTF-8"?>
<RelativeLayout
xmlns:Android="http://schemas.android.com/apk/res/android"
Android:layout_width="fill_parent"
Android:layout_height="fill_parent"
Android:orientation="vertical">
<RelativeLayout
xmlns:Android="http://schemas.android.com/apk/res/android"
Android:id="@+id/view_top"
Android:orientation="horizontal"
Android:layout_width="fill_parent"
Android:layout_height="wrap_content"
Android:layout_alignParentTop="true"
Android:gravity="center">
<TextView
Android:text="head"
Android:textSize="15pt"
Android:layout_width="fill_parent"
Android:layout_height="wrap_content" />
<ImageView
Android:layout_width="wrap_content"
Android:layout_height="wrap_content"
Android:src="@drawable/btn_star_1"
Android:id="@+id/imageView1"
Android:layout_alignParentTop="true"
Android:layout_alignParentRight="true"></ImageView>
<TextView
Android:layout_width="wrap_content"
Android:id="@+id/textView_header"
Android:text="center page"
Android:layout_height="wrap_content"
Android:textAppearance="?android:attr/textAppearanceMedium"
Android:layout_centerVertical="true"
Android:layout_alignParentLeft="true"
Android:layout_marginLeft="78dp"></TextView>
</RelativeLayout>
<RelativeLayout
xmlns:Android="http://schemas.android.com/apk/res/android"
Android:id="@+id/view_bottom"
Android:orientation="horizontal"
Android:layout_width="fill_parent"
Android:layout_height="wrap_content"
Android:layout_alignParentBottom="true"
Android:gravity="center">
<TextView
Android:text="footer"
Android:textSize="15pt"
Android:layout_width="fill_parent"
Android:layout_height="wrap_content" />
</RelativeLayout>
<com.xxx.ScrollLayout
xmlns:Android="http://schemas.android.com/apk/res/android"
Android:id="@+id/ScrollLayoutID"
Android:layout_width="fill_parent"
Android:layout_height="fill_parent"
Android:orientation="vertical"
Android:layout_above="@id/view_bottom"
Android:layout_below="@id/view_top">
<LinearLayout
Android:background="#ffffffff"
Android:layout_width="fill_parent"
Android:layout_height="fill_parent">
<Button
Android:layout_width="wrap_content"
Android:layout_height="wrap_content"
Android:text="Left" />
</LinearLayout>
<LinearLayout
Android:background="#ffffffff"
Android:layout_width="fill_parent"
Android:layout_height="fill_parent">
<Button
Android:layout_width="wrap_content"
Android:layout_height="wrap_content"
Android:text="Center" />
</LinearLayout>
<LinearLayout
Android:background="#ffffffff"
Android:layout_width="wrap_content"
Android:layout_height="wrap_content">
<Button
Android:layout_width="wrap_content"
Android:layout_height="wrap_content"
Android:text="Right" />
</LinearLayout>
</com.xxx.ScrollLayout>
</RelativeLayout>
自定義控件 ScrollLayout.java ：
package com.xxx;
import android.content.Context;
import android.util.AttributeSet;
import android.util.Log;
import android.view.MotionEvent;
import android.view.VelocityTracker;
import android.view.View;
import android.view.ViewConfiguration;
import android.view.ViewGroup;
import android.widget.Scroller;
public class ScrollLayout extends ViewGroup {
private static final String TAG = "ScrollLayout";
private Scroller mScroller = null;
private VelocityTracker mVelocityTracker = null;
private int mCurScreen = 0;
private int mDefaultScreen = 1;
private static final int TOUCH_STATE_REST = 0;
private static final int TOUCH_STATE_SCROLLING = 1;
private static final int SNAP_VELOCITY = 600;
private int mTouchState = TOUCH_STATE_REST;
private int mTouchSlop = 0;
private float mLastMotionX = 0;
private float mLastMotionY = 0;
private OnScreenChangedListener mOnScreenChangedListener;
public void setOnScreenChangedListener(OnScreenChangedListener l){
mOnScreenChangedListener = l;
}
public interface OnScreenChangedListener {
void onScreenChanged(ScrollLayout sc ,int whichScreen);
}
public ScrollLayout(Context context, AttributeSet attrs) {
this(context, attrs, 0);
}
public ScrollLayout(Context context, AttributeSet attrs, int defStyle) {
super(context, attrs, defStyle);
mScroller = new Scroller(context);
mCurScreen = mDefaultScreen;
mTouchSlop = ViewConfiguration.get(getContext()).getScaledTouchSlop();
}
@Override
protected void onLayout(boolean changed, int l, int t, int r, int b) {
// TODO Auto-generated method stub
if (changed) {
int childLeft = 0;
final int childCount = getChildCount();
for (int i=0; i<childCount; i++) {
final View childView = getChildAt(i);
if (childView.getVisibility() != View.GONE) {
final int childWidth = childView.getMeasuredWidth();
childView.layout(childLeft, 0,
childLeft+childWidth, childView.getMeasuredHeight());
childLeft += childWidth;
}
}
}
}
@Override
protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
Log.e(TAG, "onMeasure");
super.onMeasure(widthMeasureSpec, heightMeasureSpec);
final int width = MeasureSpec.getSize(widthMeasureSpec);
final int widthMode = MeasureSpec.getMode(widthMeasureSpec);
if (widthMode != MeasureSpec.EXACTLY) {
throw new IllegalStateException("ScrollLayout only can run at EXACTLY mode!");
}
final int heightMode = MeasureSpec.getMode(heightMeasureSpec);
if (heightMode != MeasureSpec.EXACTLY) {
throw new IllegalStateException("ScrollLayout only can run at EXACTLY mode!");
}
// The children are given the same width and height as the scrollLayout
final int count = getChildCount();
for (int i = 0; i < count; i++) {
getChildAt(i).measure(widthMeasureSpec, heightMeasureSpec);
}
// Log.e(TAG, "moving to screen "+mCurScreen);
scrollTo(mCurScreen * width, 0);
}
public void snapToDestination() {
final int screenWidth = getWidth();
final int destScreen = (getScrollX()+ screenWidth/2)/screenWidth;
snapToScreen(destScreen);
}
public void snapToScreen(int whichScreen) {
// get the valid layout page
whichScreen = Math.max(0, Math.min(whichScreen, getChildCount()-1));
if (getScrollX() != (whichScreen * getWidth())) {
final int delta = whichScreen*getWidth()-getScrollX();
mScroller.startScroll(getScrollX(), 0,
delta, 0, Math.abs(delta)*2);
mCurScreen = whichScreen;
invalidate(); // Redraw the layout
mOnScreenChangedListener.onScreenChanged(this, mCurScreen);
}
}
public void setToScreen(int whichScreen) {
whichScreen = Math.max(0, Math.min(whichScreen, getChildCount()-1));
mCurScreen = whichScreen;
scrollTo(whichScreen*getWidth(), 0);
}
public int getCurScreen() {
return mCurScreen;
}
@Override
public void computeScroll() {
if (mScroller.computeScrollOffset()) {
scrollTo(mScroller.getCurrX(), mScroller.getCurrY());
postInvalidate();
}
}
@Override
public boolean onTouchEvent(MotionEvent event) {
if (mVelocityTracker == null) {
mVelocityTracker = VelocityTracker.obtain();
}
mVelocityTracker.addMovement(event);
final int action = event.getAction();
final float x = event.getX();
final float y = event.getY();
switch (action) {
case MotionEvent.ACTION_DOWN:
Log.e(TAG, "event down!");
if (!mScroller.isFinished()){
mScroller.abortAnimation();
}
mLastMotionX = x;
break;
case MotionEvent.ACTION_MOVE:
int deltaX = (int)(mLastMotionX - x);
mLastMotionX = x;
scrollBy(deltaX, 0);
break;
case MotionEvent.ACTION_UP:
Log.e(TAG, "event : up");
// if (mTouchState == TOUCH_STATE_SCROLLING) {
final VelocityTracker velocityTracker = mVelocityTracker;
velocityTracker.computeCurrentVelocity(1000);
int velocityX = (int) velocityTracker.getXVelocity();
Log.e(TAG, "velocityX:"+velocityX);
if (velocityX > SNAP_VELOCITY && mCurScreen > 0) {
// Fling enough to move left
Log.e(TAG, "snap left");
snapToScreen(mCurScreen - 1);
} else if (velocityX < -SNAP_VELOCITY
&& mCurScreen < getChildCount() - 1) {
// Fling enough to move right
Log.e(TAG, "snap right");
snapToScreen(mCurScreen + 1);
} else {
snapToDestination();
}
if (mVelocityTracker != null) {
mVelocityTracker.recycle();
mVelocityTracker = null;
}
// }
mTouchState = TOUCH_STATE_REST;
break;
case MotionEvent.ACTION_CANCEL:
mTouchState = TOUCH_STATE_REST;
break;
}
return true;
}
@Override
public boolean onInterceptTouchEvent(MotionEvent ev) {
Log.e(TAG, "onInterceptTouchEvent-slop:"+mTouchSlop);
final int action = ev.getAction();
if ((action == MotionEvent.ACTION_MOVE) &&
(mTouchState != TOUCH_STATE_REST)) {
return true;
}
final float x = ev.getX();
final float y = ev.getY();
switch (action) {
case MotionEvent.ACTION_MOVE:
final int xDiff = (int)Math.abs(mLastMotionX-x);
if (xDiff>mTouchSlop) {
mTouchState = TOUCH_STATE_SCROLLING;
}
break;
case MotionEvent.ACTION_DOWN:
mLastMotionX = x;
mLastMotionY = y;
mTouchState = mScroller.isFinished()? TOUCH_STATE_REST : TOUCH_STATE_SCROLLING;
break;
case MotionEvent.ACTION_CANCEL:
case MotionEvent.ACTION_UP:
mTouchState = TOUCH_STATE_REST;
break;
}
return mTouchState != TOUCH_STATE_REST;
}
}
Main.java ：
package com.xxx;
import com.ex84.ScrollLayout.OnScreenChangedListener;
import android.app.Activity;
import android.content.res.Resources;
import android.os.Bundle;
import android.view.View;
import android.view.View.OnFocusChangeListener;
import android.widget.ImageView;
import android.widget.TextView;
public class MainActivity extends Activity implements OnScreenChangedListener {
private ImageView mImageView;
private TextView mTextView;
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
ScrollLayout scrollLayout = (ScrollLayout) findViewById(R.id.ScrollLayoutID);
int curScreen = scrollLayout.getCurScreen();
scrollLayout.setOnScreenChangedListener(this);
mImageView = (ImageView) findViewById(R.id.imageView1);
mTextView = (TextView) findViewById(R.id.textView_header);
}
@Override
public void onScreenChanged(ScrollLayout sc, int whichScreen) {
switch (whichScreen) {
case 0:
mImageView.setImageResource(R.drawable.btn_star_0);
mTextView.setText("left page");
break;
case 1:
mTextView.setText("center page");
mImageView.setImageResource(R.drawable.btn_star_1);
break;
case 2:
mTextView.setText("right page");
mImageView.setImageResource(R.drawable.btn_star_2);
break;
}
}
}