在Android应用中，一般TabActivity和若干个Tab选项卡（TabWidget）。如果选项卡的数量超过了5个，就不适合放到一个屏幕中，这样可以让这些选项卡滑动起来。
滑动的选项卡的实现有好几种方式，在这些方式中，最简单也是我最满意的还是在原生的TabActivity上修改，将上面的选项卡改为可滑动的状态。这样既有新的滑动的效果，也保留了原有TabActivity的各项功能。
实现Tab可滑动基本的思路就是把上面的TabWidget放到一个HorizontalScrollView中，让TabWidget滑动起来。不过如果仅仅修改XML还是会产生问题，就是没有办法控制每个选项卡的宽度。所以还是需要在程序中设置每个选项卡的宽度。例如：
[java]
// 设置窗口的宽度
DisplayMetrics dm = new DisplayMetrics();
getWindowManager().getDefaultDisplay().getMetrics(dm);
int screenWidth = dm.widthPixels;
if (count < 4) {
for (int i = 0; i < count; i++) {
// 设置每个选项卡的宽度
tabWidget.getChildTabViewAt(i).setMinimumWidth(screenWidth / 4);
}
}
自定义TabActivity主界面的XML：
[html]
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:orientation="vertical" android:layout_width="fill_parent"
android:layout_height="fill_parent">
<TabHost android:id="@android:id/tabhost" android:layout_width="fill_parent"
android:layout_height="fill_parent">
<LinearLayout android:orientation="vertical"
android:layout_width="fill_parent" android:layout_height="fill_parent">
<HorizontalScrollView android:layout_height="wrap_content"
android:layout_width="fill_parent" android:scrollbars="none">
<TabWidget android:id="@android:id/tabs"
android:layout_width="fill_parent" android:layout_height="60dp" />
</HorizontalScrollView>
<FrameLayout android:id="@android:id/tabcontent"
android:layout_width="fill_parent" android:layout_height="wrap_content"
android:layout_weight="1" />
</LinearLayout>
</TabHost>
</LinearLayout>
效果图如下
上面的tab是可以滑动的,屏幕左右滑动,tab也会切换
[java]
package com.xu81.testflip;
import java.util.Vector;
import android.content.Context;
import android.util.AttributeSet;
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 Scroller mScroller;
private VelocityTracker mVelocityTracker;
private int mCurScreen;
private int mDefaultScreen = 0;
private static final int TOUCH_STATE_REST = 0;
private static final int TOUCH_STATE_SCROLLING = 1;
private static final int SNAP_VELOCITY = 500;
private int mTouchState = TOUCH_STATE_REST;
private int mTouchSlop;
private float mLastMotionX;
private int sensitivity = 30;
private boolean spring;
private Vector<LayoutChangeListener> listeners;
public ScrollLayout(Context context, AttributeSet attrs) {
super(context, attrs);
// TODO Auto-generated constructor stub
mScroller = new Scroller(context);
mCurScreen = mDefaultScreen;
mTouchSlop = ViewConfiguration.get(getContext()).getScaledTouchSlop();
listeners = new Vector<LayoutChangeListener>();
}
public void addChangeListener(LayoutChangeListener listener) {
listeners.add(listener);
}
@Override
protected void onLayout(boolean changed, int l, int t, int r, int b) {
// TODO Auto-generated method stub
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) {
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 canmCurScreen 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);
}
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
int lastIndex = mCurScreen;
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
}
for (LayoutChangeListener listener : listeners)
listener.doChange(lastIndex, whichScreen);
}
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() {
// TODO Auto-generated method stub
if (mScroller.computeScrollOffset()) {
scrollTo(mScroller.getCurrX(), mScroller.getCurrY());
postInvalidate();
}
}
public boolean isSpring() {
return spring;
}
public void setSpring(boolean spring) {
this.spring = spring;
}
@Override
public boolean onTouchEvent(MotionEvent event) {
// TODO Auto-generated method stub
if (mVelocityTracker == null)
mVelocityTracker = VelocityTracker.obtain();
mVelocityTracker.addMovement(event);
final int action = event.getAction();
final float x = event.getX();
switch (action) {
case MotionEvent.ACTION_DOWN:
if (!mScroller.isFinished())
mScroller.abortAnimation();
mLastMotionX = x;
break;
case MotionEvent.ACTION_MOVE:
int deltaX = (int) (mLastMotionX - x);
if (Math.abs(deltaX) > sensitivity) {
// 左滑动为正数、右为负数
if (spring) {
scrollBy(deltaX, 0);
mLastMotionX = x;
} else {
final int childCount = getChildCount();
boolean max = mCurScreen < childCount - 1;
boolean min = mCurScreen > 0;
boolean canMove = deltaX > 0 ? (max ? true : false)
: (min ? true : false);
if (canMove) {
scrollBy(deltaX, 0);
mLastMotionX = x;
}
}
}
break;
case MotionEvent.ACTION_UP:
final VelocityTracker velocityTracker = mVelocityTracker;
velocityTracker.computeCurrentVelocity(1000);
int velocityX = (int) velocityTracker.getXVelocity();
if (velocityX > SNAP_VELOCITY && mCurScreen > 0) {
// Fling enough to move left
snapToScreen(mCurScreen - 1);
} else if (velocityX < -SNAP_VELOCITY
&& mCurScreen < getChildCount() - 1) {
// Fling enough to move 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) {
// TODO Auto-generated method stub
final int action = ev.getAction();
if ((action == MotionEvent.ACTION_MOVE)
&& (mTouchState != TOUCH_STATE_REST))
return true;
final float x = ev.getX();
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;
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;
}
}
作者：shimiso
