今天讲一下我开发“微读”阅读软件中实现的一个类似android主界面的滑屏控件，这个滑屏在微读的主界面和看书时左右滑平翻页中都有用到，在具体的应用效果如下：
下载到手机中体验一下
微读软件：点击下载
新浪微博：@easy微读
直接效果图 ，更多内容可以参看：我的android阅读软件“微读”-做最简单的手机阅读软件
实现思路，刚开始的时候我是用ViewFlipper控件来做非常的简单但是实现不了拖拽移动屏幕的效果，最终放弃决定自定义一个控件实现这样效果。
接下来我详细的解说一下我开发时写的这个实验demo，软件中用的滑屏就是由这样的代码实现的。
首先新建一个控件类TouchPageView并且继承自ViewGroup，左右滑动换屏我的实现是在TouchPageView添加3个子view分别代表看不到的左边屏幕、可以看到的中间屏幕、看不到的右边屏幕，这样在滑屏时候就可以通过不断调整这3个view的位置实现连续不间断滑屏换屏，下面的实验中我分别把3个view设置成红色、绿色、黄色这样切换的时候可以看到明显效果，这3个view在TouchPageView的构造方法中调用init方法进行初始化：
private void init()
{
views= new ArrayList<LinearLayout>();
view1=new LinearLayout(context);
view1.setBackgroundColor(Color.YELLOW);
this.addView(view1);
TextView tv=new TextView(context);
tv.setText("测试");
view1.addView(tv);
views.add(view1);
view2=new LinearLayout(context);
view2.setBackgroundColor(Color.RED);
this.addView(view2);
views.add(view2);
view3=new LinearLayout(context);
view3.setBackgroundColor(Color.GREEN);
this.addView(view3);
views.add(view3);
final ViewConfiguration configuration = ViewConfiguration.get(getContext());
mMaximumVelocity = configuration.getScaledMaximumFlingVelocity();
}
接下来的实现是关键，重写onLayout方法对3个view的显示位置布局进行控制，通过下面的这个方法，把3个view进行水平一个跟着一个进行布局显示。
@Override
protected void onLayout(boolean changed, int l, int t, int r, int b) {
int childLeft = -1;
final int count = views.size();
//水平从左到右放置
for (int i = 0; i < count; i++) {
final View child =views.get(i);
if (child.getVisibility() != View.GONE) {
final int childWidth = child.getMeasuredWidth();
if(childLeft==-1)
{
childLeft=-childWidth;
}
child.layout(childLeft, 0, childLeft + childWidth, child.getMeasuredHeight());
childLeft += childWidth;
}
}
}
3个view位置放置好之后，接下来的实现实现手指在屏幕拖拽滑动时让3个view跟着手指的位置进行变化显示，这个肯定是在onTouchEvent方法中实现了，分别在MotionEvent.ACTION_DOWN、MotionEvent.ACTION_MOVE、MotionEvent.ACTION_UP三个手指状态中进行控制，在下面的实现中还采用了VelocityTracker的方法对手指的滑动速度进行跟踪，这样根据滑动速度决定屏幕往哪个方向换屏，关键的代码如下：
@Override
public boolean onTouchEvent(MotionEvent ev){
if(!lock)
{
if (mVelocityTracker == null) {
mVelocityTracker = VelocityTracker.obtain();
}
mVelocityTracker.addMovement(ev);
final int action = ev.getAction();
final float x = ev.getX();
final float y = ev.getY();
switch (action) {
case MotionEvent.ACTION_DOWN://按下去
if(touchState==TOUCH_STATE_REST)
{
//记录按下去的的x坐标
lastMotionX = x;
touchState=TOUCH_STATE_MOVING;
isMoved=false;
}
break;
case MotionEvent.ACTION_MOVE://拖动时
if(touchState==TOUCH_STATE_MOVING)
{
float offsetX=x-lastMotionX;
float offsetY=y-lastMotionY;
if(isMoved)
{
lastMotionX=x;
lastMotionY=y;
final int count = views.size();
//水平从左到右放置
for (int i = 0; i < count; i++) {
final View child =views.get(i);
if (child.getVisibility() != View.GONE) {
final int childWidth = child.getMeasuredWidth();
int childLeft = child.getLeft()+(int)offsetX;
child.layout(childLeft, 0, childLeft + childWidth, child.getMeasuredHeight());
childLeft += childWidth;
}
}
}
else if(Math.abs(offsetX)>TOUCH_SLOP||Math.abs(offsetY)>TOUCH_SLOP)
{
//移动超过阈值，则表示移动了
isMoved=true;
removeCallbacks(mLongPressRunnable);
}
}
break;
case MotionEvent.ACTION_UP://放开时
//释放了
removeCallbacks(mLongPressRunnable);
if(isMoved)
{
if(touchState==TOUCH_STATE_MOVING)
{
touchState=TOUCH_STATE_SLOWING;
int sign=0;
final VelocityTracker velocityTracker = mVelocityTracker;
//计算当前速度
velocityTracker.computeCurrentVelocity(1000, mMaximumVelocity);
//x方向的速度
int velocityX = (int) velocityTracker.getXVelocity();
if(velocityX > SNAP_VELOCITY)//足够的能力向左
{
sign=1;
Log.e("enough to move left", "true");
}
else if (velocityX < -SNAP_VELOCITY)//足够的能力向右
{
sign=-1;
Log.e("enough to move right", "right");
}
else
{
sign=0;
}
moveToFitView(sign);
if (mVelocityTracker != null) {
mVelocityTracker.recycle();
mVelocityTracker = null;
}
}
}
break;
}
}
return true;
}
完成手指滑的功能后，最后在手指离开屏幕的时候，让3个view滑动到合适的位置，保证当前屏幕只能看到一个完整的view另外2个view不可见，并且在滑动的过程中为了达到比较自然的效果，采用减速滑动的实现，这里是用了Handler进行间隔的减速移动效果，这样滑动起来比较舒服，其实最好的效果应该加入阻尼效果，就是让view一定程度的冲过屏幕边界然后在回弹，经过几次这样的缓减至速度为零然后最终停止，这个可以由各位自己去实现，并不难写。
int offset=0;
private void moveToFitView(int sign)
{
boolean b=swapView(sign);
if(true)
{
View view1=views.get(1);
int left=view1.getLeft();
//int offset=0;
if(left!=0)
{
offset=-1*left;
}
moveView();
}
}
FlipAnimationHandler mAnimationHandler;
int ovv=40;
private void moveView()
{
final int count = views.size();
if(offset!=0)
{
int ov=0;
if(offset>0)
{
ov=ovv;
}
else
{
ov=-1*ovv;
}
ovv=ovv-3;
if(ovv<1)
{
ovv=3;
}
if(Math.abs(offset)<Math.abs(ov))
{
ov=offset;
offset=0;
}
else
{
offset=offset-ov;
}
//水平从左到右放置
for (int i = 0; i < count; i++) {
final View child =views.get(i);
final int childWidth = child.getMeasuredWidth();
int childLeft = child.getLeft()+ov;
child.layout(childLeft, 0, childLeft + childWidth, child.getMeasuredHeight());
childLeft += childWidth;
}
if(mAnimationHandler==null)
{
mAnimationHandler = new FlipAnimationHandler();
}
mAnimationHandler.sleep(1);
}
else
{
ovv=40;
touchState=TOUCH_STATE_REST;
}
}
class FlipAnimationHandler extends Handler {
@Override
public void handleMessage(Message msg) {
TouchPageView.this.moveView();
}
public void sleep(long millis) {
this.removeMessages(0);
sendMessageDelayed(obtainMessage(0), millis);
}
}
整个自定义控件核心的思路和代码就上面这些了，实现效果请参看我的微读效果。
完整的代码：
package xx.weidu;
import java.util.ArrayList;
import java.util.List;
import android.content.Context;
import android.graphics.Canvas;
import android.graphics.Color;
import android.os.Handler;
import android.os.Message;
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.LinearLayout;
import android.widget.TextView;
public class TouchPageView extends ViewGroup{
private LinearLayout view1;
private LinearLayout view2;
private LinearLayout view3;
//速度跟踪
private VelocityTracker mVelocityTracker;
private int mMaximumVelocity;
//手势临界速度，当速度超过这个时切换到下一屏
private static final int SNAP_VELOCITY = 100;
//停止状态
private final static int TOUCH_STATE_REST = 0;
//滚动状态
private final static int TOUCH_STATE_MOVING = 1;
//减速停止状态
private final static int TOUCH_STATE_SLOWING = 2;
//当前触摸状态
private int touchState = TOUCH_STATE_REST;
private boolean lock=false;
private float lastMotionX;
private float lastMotionY;
private Context context;
private List<LinearLayout> views;
//是否移动了
private boolean isMoved;
//长按的runnable
private Runnable mLongPressRunnable;
//移动的阈值
private static final int TOUCH_SLOP=10;
public int width;
public int height;
public TouchPageView(Context context) {
super(context);
this.context=context;
init();
}
private void init()
{
views= new ArrayList<LinearLayout>();
view1=new LinearLayout(context);
view1.setBackgroundColor(Color.YELLOW);
this.addView(view1);
TextView tv=new TextView(context);
tv.setText("测试");
view1.addView(tv);
views.add(view1);
view2=new LinearLayout(context);
view2.setBackgroundColor(Color.RED);
this.addView(view2);
views.add(view2);
view3=new LinearLayout(context);
view3.setBackgroundColor(Color.GREEN);
this.addView(view3);
views.add(view3);
final ViewConfiguration configuration = ViewConfiguration.get(getContext());
mMaximumVelocity = configuration.getScaledMaximumFlingVelocity();
}
@Override
protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec){
super.onMeasure(widthMeasureSpec, heightMeasureSpec);
final int count = views.size();
for (int i = 0; i < count; i++) {
final View child =views.get(i);
child.measure(widthMeasureSpec,heightMeasureSpec);
}
int finalWidth, finalHeight;
finalWidth = measureWidth(widthMeasureSpec);
finalHeight = measureHeight(heightMeasureSpec);
this.width=finalWidth;
this.height=finalHeight;
}
private int measureWidth(int measureSpec) {
int result = 0;
int specMode = MeasureSpec.getMode(measureSpec);
int specSize = MeasureSpec.getSize(measureSpec);
if (specMode == MeasureSpec.EXACTLY) {
result = specSize;
} else {
result = specSize;
}
return result;
}
private int measureHeight(int measureSpec) {
int result = 0;
int specMode = MeasureSpec.getMode(measureSpec);
int specSize = MeasureSpec.getSize(measureSpec);
if (specMode == MeasureSpec.EXACTLY) {
result = specSize;
} else {
result = specSize;
}
return result;
}
@Override
protected void onLayout(boolean changed, int l, int t, int r, int b) {
int childLeft = -1;
final int count = views.size();
//水平从左到右放置
for (int i = 0; i < count; i++) {
final View child =views.get(i);
if (child.getVisibility() != View.GONE) {
final int childWidth = child.getMeasuredWidth();
if(childLeft==-1)
{
childLeft=-childWidth;
}
child.layout(childLeft, 0, childLeft + childWidth, child.getMeasuredHeight());
childLeft += childWidth;
}
}
}
//绘制子元素
@Override
protected void onDraw(Canvas canvas) {
//水平从左到右放置
int count = views.size();
for (int i = 0; i < count; i++) {
View child =views.get(i);
drawChild(canvas, child, getDrawingTime());
}
}
@Override
public boolean onTouchEvent(MotionEvent ev){
if(!lock)
{
if (mVelocityTracker == null) {
mVelocityTracker = VelocityTracker.obtain();
}
mVelocityTracker.addMovement(ev);
final int action = ev.getAction();
final float x = ev.getX();
final float y = ev.getY();
switch (action) {
case MotionEvent.ACTION_DOWN://按下去
if(touchState==TOUCH_STATE_REST)
{
//记录按下去的的x坐标
lastMotionX = x;
touchState=TOUCH_STATE_MOVING;
isMoved=false;
}
break;
case MotionEvent.ACTION_MOVE://拖动时
if(touchState==TOUCH_STATE_MOVING)
{
float offsetX=x-lastMotionX;
float offsetY=y-lastMotionY;
if(isMoved)
{
lastMotionX=x;
lastMotionY=y;
final int count = views.size();
//水平从左到右放置
for (int i = 0; i < count; i++) {
final View child =views.get(i);
if (child.getVisibility() != View.GONE) {
final int childWidth = child.getMeasuredWidth();
int childLeft = child.getLeft()+(int)offsetX;
child.layout(childLeft, 0, childLeft + childWidth, child.getMeasuredHeight());
childLeft += childWidth;
}
}
}
else if(Math.abs(offsetX)>TOUCH_SLOP||Math.abs(offsetY)>TOUCH_SLOP)
{
//移动超过阈值，则表示移动了
isMoved=true;
removeCallbacks(mLongPressRunnable);
}
}
break;
case MotionEvent.ACTION_UP://放开时
//释放了
removeCallbacks(mLongPressRunnable);
if(isMoved)
{
if(touchState==TOUCH_STATE_MOVING)
{
touchState=TOUCH_STATE_SLOWING;
int sign=0;
final VelocityTracker velocityTracker = mVelocityTracker;
//计算当前速度
velocityTracker.computeCurrentVelocity(1000, mMaximumVelocity);
//x方向的速度
int velocityX = (int) velocityTracker.getXVelocity();
if(velocityX > SNAP_VELOCITY)//足够的能力向左
{
sign=1;
Log.e("enough to move left", "true");
}
else if (velocityX < -SNAP_VELOCITY)//足够的能力向右
{
sign=-1;
Log.e("enough to move right", "right");
}
else
{
sign=0;
}
moveToFitView(sign);
if (mVelocityTracker != null) {
mVelocityTracker.recycle();
mVelocityTracker = null;
}
}
}
break;
}
}
return true;
}
int offset=0;
private void moveToFitView(int sign)
{
boolean b=swapView(sign);
if(true)
{
View view1=views.get(1);
int left=view1.getLeft();
//int offset=0;
if(left!=0)
{
offset=-1*left;
}
moveView();
}
}
FlipAnimationHandler mAnimationHandler;
int ovv=40;
private void moveView()
{
final int count = views.size();
if(offset!=0)
{
int ov=0;
if(offset>0)
{
ov=ovv;
}
else
{
ov=-1*ovv;
}
ovv=ovv-3;
if(ovv<1)
{
ovv=3;
}
if(Math.abs(offset)<Math.abs(ov))
{
ov=offset;
offset=0;
}
else
{
offset=offset-ov;
}
//水平从左到右放置
for (int i = 0; i < count; i++) {
final View child =views.get(i);
final int childWidth = child.getMeasuredWidth();
int childLeft = child.getLeft()+ov;
child.layout(childLeft, 0, childLeft + childWidth, child.getMeasuredHeight());
childLeft += childWidth;
}
if(mAnimationHandler==null)
{
mAnimationHandler = new FlipAnimationHandler();
}
mAnimationHandler.sleep(1);
}
else
{
ovv=40;
touchState=TOUCH_STATE_REST;
}
}
class FlipAnimationHandler extends Handler {
@Override
public void handleMessage(Message msg) {
TouchPageView.this.moveView();
}
public void sleep(long millis) {
this.removeMessages(0);
sendMessageDelayed(obtainMessage(0), millis);
}
}
private boolean swapView(int sign)
{
boolean b=false;
if(sign==-1)//向左
{
View view0=views.get(0);
if(view0.getLeft()<=-1*view0.getMeasuredWidth())
{
swapViewIndex(sign);
View view2=views.get(1);
View view3=views.get(2);
int childWidth=view2.getMeasuredWidth();
int childLeft=view2.getLeft()+childWidth;
view3.layout(childLeft, 0, childLeft + view3.getMeasuredWidth(), view3.getMeasuredHeight());
b=true;
}
}
else if(sign==1)//向右
{
View view3=views.get(2);
if(view3.getLeft()>view3.getMeasuredWidth())
{
swapViewIndex(sign);
View view1=views.get(0);
View view2=views.get(1);
int childRight=view2.getLeft();
int childLeft=childRight-view1.getMeasuredWidth();
view1.layout(childLeft, 0, childRight, view1.getMeasuredHeight());
b=true;
}
}
return b;
}
private void swapViewIndex(int sign)
{
if(sign==-1)//向左
{
LinearLayout v=views.remove(0);
views.add(v);
}
else if(sign==1)//向右
{
LinearLayout v=views.remove(views.size()-1);
views.add(0, v);
}
}
}