今天给大家介绍一下如何实现androd主页面的左右拖动效果。实现起来很简单，就是使用ViewFlipper来将您要来回拖动的View装在一起，然后与GestureDetector手势识别类来联动，确定要显示哪个View，加上一点点动画效果即可。比如当手指向左快速滑动时跳转到上一个View，手指向右快速滑动时跳转到下一个View，本例中使用图片作为各个View的页面，实现左右快速滑动显示不同的图片。
首先来看看我们的layout，如下所示：
<linearlayout android:layout_height="fill_parent" android:layout_width="fill_parent" android:orientation="vertical" xmlns:android="http://schemas.android.com/apk/res/android">
<viewflipper android:id="@+id/flipper" android:layout_below="@+id/CockpitLayout" android:layout_height="fill_parent" android:layout_width="fill_parent">
<include android:id="@+id/firstlayout" layout="@layout/first">
<include android:id="@+id/secondlayout" layout="@layout/second">
<include android:id="@+id/thirdlayout" layout="@layout/third">
<include android:id="@+id/fourthlayout" layout="@layout/fourth">
</include></include></include></include></viewflipper>
</linearlayout>
如上所示，在ViewFlipper中放置多个layout（接下来会在不同的layout中来回滑动），ViewFlipper在同一个页面就显示其中一个layout。ViewFlipper中的四个layout很简单，我们就放置一张图片，如下所示：
<linearlayout android:gravity="center_vertical" android:layout_height="fill_parent" android:layout_width="fill_parent" xmlns:android="http://schemas.android.com/apk/res/android">
<imageview android:layout_height="wrap_content" android:layout_width="wrap_content" android:src="@drawable/v1">
</imageview></linearlayout>
接下来我们来看看Activity，我们的Activity需要实现两个接口OnGestureListener,OnTouchListener。具体的代码如下所示，代码中都有相应的注释，这里就不再详述。
package com.ideasandroid.demo;
import android.app.Activity;
import android.os.Bundle;
import android.view.GestureDetector;
import android.view.MotionEvent;
import android.view.View;
import android.view.GestureDetector.OnGestureListener;
import android.view.View.OnTouchListener;
import android.view.animation.AccelerateInterpolator;
import android.view.animation.Animation;
import android.view.animation.TranslateAnimation;
import android.widget.ViewFlipper;
public class ViewFlipperDemo extends Activity implements OnGestureListener,OnTouchListener{
private ViewFlipper mFlipper;
GestureDetector mGestureDetector;
private int mCurrentLayoutState;
private static final int FLING_MIN_DISTANCE = 100;
private static final int FLING_MIN_VELOCITY = 200;
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
mFlipper = (ViewFlipper) findViewById(R.id.flipper);
//注册一个用于手势识别的类
mGestureDetector = new GestureDetector(this);
//给mFlipper设置一个listener
mFlipper.setOnTouchListener(this);
mCurrentLayoutState = 0;
//允许长按住ViewFlipper,这样才能识别拖动等手势
mFlipper.setLongClickable(true);
}
/**
* 此方法在本例中未用到，可以指定跳转到某个页面
* @param switchTo
*/
public void switchLayoutStateTo(int switchTo) {
while (mCurrentLayoutState != switchTo) {
if (mCurrentLayoutState > switchTo) {
mCurrentLayoutState--;
mFlipper.setInAnimation(inFromLeftAnimation());
mFlipper.setOutAnimation(outToRightAnimation());
mFlipper.showPrevious();
} else {
mCurrentLayoutState++;
mFlipper.setInAnimation(inFromRightAnimation());
mFlipper.setOutAnimation(outToLeftAnimation());
mFlipper.showNext();
}
}
;
}
/**
* 定义从右侧进入的动画效果
* @return
*/
protected Animation inFromRightAnimation() {
Animation inFromRight = new TranslateAnimation(
Animation.RELATIVE_TO_PARENT, +1.0f,
Animation.RELATIVE_TO_PARENT, 0.0f,
Animation.RELATIVE_TO_PARENT, 0.0f,
Animation.RELATIVE_TO_PARENT, 0.0f);
inFromRight.setDuration(500);
inFromRight.setInterpolator(new AccelerateInterpolator());
return inFromRight;
}
/**
* 定义从左侧退出的动画效果
* @return
*/
protected Animation outToLeftAnimation() {
Animation outtoLeft = new TranslateAnimation(
Animation.RELATIVE_TO_PARENT, 0.0f,
Animation.RELATIVE_TO_PARENT, -1.0f,
Animation.RELATIVE_TO_PARENT, 0.0f,
Animation.RELATIVE_TO_PARENT, 0.0f);
outtoLeft.setDuration(500);
outtoLeft.setInterpolator(new AccelerateInterpolator());
return outtoLeft;
}
/**
* 定义从左侧进入的动画效果
* @return
*/
protected Animation inFromLeftAnimation() {
Animation inFromLeft = new TranslateAnimation(
Animation.RELATIVE_TO_PARENT, -1.0f,
Animation.RELATIVE_TO_PARENT, 0.0f,
Animation.RELATIVE_TO_PARENT, 0.0f,
Animation.RELATIVE_TO_PARENT, 0.0f);
inFromLeft.setDuration(500);
inFromLeft.setInterpolator(new AccelerateInterpolator());
return inFromLeft;
}
/**
* 定义从右侧退出时的动画效果
* @return
*/
protected Animation outToRightAnimation() {
Animation outtoRight = new TranslateAnimation(
Animation.RELATIVE_TO_PARENT, 0.0f,
Animation.RELATIVE_TO_PARENT, +1.0f,
Animation.RELATIVE_TO_PARENT, 0.0f,
Animation.RELATIVE_TO_PARENT, 0.0f);
outtoRight.setDuration(500);
outtoRight.setInterpolator(new AccelerateInterpolator());
return outtoRight;
}
public boolean onDown(MotionEvent e) {
// TODO Auto-generated method stub
return false;
}
/*
* 用户按下触摸屏、快速移动后松开即触发这个事件
* e1：第1个ACTION_DOWN MotionEvent
* e2：最后一个ACTION_MOVE MotionEvent
* velocityX：X轴上的移动速度，像素/秒
* velocityY：Y轴上的移动速度，像素/秒
* 触发条件 ：
* X轴的坐标位移大于FLING_MIN_DISTANCE，且移动速度大于FLING_MIN_VELOCITY个像素/秒
*/
public boolean onFling(MotionEvent e1, MotionEvent e2, float velocityX,
float velocityY) {
if (e1.getX() - e2.getX() > FLING_MIN_DISTANCE
&& Math.abs(velocityX) > FLING_MIN_VELOCITY) {
// 当像左侧滑动的时候
//设置View进入屏幕时候使用的动画
mFlipper.setInAnimation(inFromRightAnimation());
//设置View退出屏幕时候使用的动画
mFlipper.setOutAnimation(outToLeftAnimation());
mFlipper.showNext();
} else if (e2.getX() - e1.getX() > FLING_MIN_DISTANCE
&& Math.abs(velocityX) > FLING_MIN_VELOCITY) {
// 当像右侧滑动的时候
mFlipper.setInAnimation(inFromLeftAnimation());
mFlipper.setOutAnimation(outToRightAnimation());
mFlipper.showPrevious();
}
return false;
}
public void onLongPress(MotionEvent e) {
// TODO Auto-generated method stub
}
public boolean onScroll(MotionEvent e1, MotionEvent e2, float distanceX,
float distanceY) {
return false;
}
public void onShowPress(MotionEvent e) {
// TODO Auto-generated method stub
}
public boolean onSingleTapUp(MotionEvent e) {
// TODO Auto-generated method stub
return false;
}
public boolean onTouch(View v, MotionEvent event) {
// 一定要将触屏事件交给手势识别类去处理（自己处理会很麻烦的）
return mGestureDetector.onTouchEvent(event);
}
}