Android中滑屏初探 ---- scrollTo 以及 scrollBy方法使用说明 - qinjuning、lets go - 博客频道 - CSDN.NET
今天给大家介绍下Android中滑屏功能的一个基本实现过程以及原理初探,最后给大家重点讲解View视图中scrollTo 与
scrollBy这两个函数的区别 。
首先 ,我们必须明白在Android View视图是没有边界的,Canvas是没有边界的,只不过我们通过绘制特定的View时对
Canvas对象进行了一定的操作,例如 : translate(平移)、clipRect(剪切)等,以便达到我们的对该Canvas对象绘制的要求 ,
我们可以将这种无边界的视图称为“视图坐标”-----它不受物理屏幕限制。通常我们所理解的一个Layout布局文件只是该视
图的显示区域,超过了这个显示区域将不能显示到父视图的区域中 ,对应的,我们可以将这种有边界的视图称为“布局坐标”
------ 父视图给子视图分配的布局(layout)大小。而且, 一个视图的在屏幕的起始坐标位于视图坐标起始处,如下图所示。
这么来说吧 ,世界本是无边无界的,可是我们的眼睛我们的心约束了我们所看到的“世界” 。
如下所示:
黑色框框表示该子视图的布局坐标, 褐色框框表示该子视图的视图坐标--该坐标是无限的,超过了父视图给子视图
规定的区域后,不再显示该超出内容。
那么下面的问题就是:如何将我们的视图的任意坐标能显示到该视图的中心坐标上呢? 由于该布局位置是只能显示特定的
一块视图内容 ,因此我们需要通过scrollTo()或者scrollBy()方法将我们期望的视图“滚动”至布局坐标上。
在View.java中提供了了如下两个变量以及相应的属性方法去读取滚动值 ,如下: View.java类中
- /**
- * The offset, in pixels, by which the content of this view is scrolled
- * horizontally.
- * {@hide}
- */
- protected int mScrollX; //该视图内容相当于视图起始坐标的偏移量 , X轴 方向
- /**
- * The offset, in pixels, by which the content of this view is scrolled
- * vertically.
- * {@hide}
- */
- protected int mScrollY; //该视图内容相当于视图起始坐标的偏移量 , Y轴方向
- /**
- * Return the scrolled left position of this view. This is the left edge of
- * the displayed part of your view. You do not need to draw any pixels
- * farther left, since those are outside of the frame of your view on
- * screen.
- *
- * @return The left edge of the displayed part of your view, in pixels.
- */
- public final int getScrollX() {
- return mScrollX;
- }
- /**
- * Return the scrolled top position of this view. This is the top edge of
- * the displayed part of your view. You do not need to draw any pixels above
- * it, since those are outside of the frame of your view on screen.
- *
- * @return The top edge of the displayed part of your view, in pixels.
- */
- public final int getScrollY() {
- return mScrollY;
- }
/** * The offset, in pixels, by which the content of this view is scrolled * horizontally. * {@hide} */ protected int mScrollX; //该视图内容相当于视图起始坐标的偏移量 , X轴 方向 /** * The offset, in pixels, by which the content of this view is scrolled * vertically. * {@hide} */ protected int mScrollY; //该视图内容相当于视图起始坐标的偏移量 , Y轴方向 /** * Return the scrolled left position of this view. This is the left edge of * the displayed part of your view. You do not need to draw any pixels * farther left, since those are outside of the frame of your view on * screen. * * @return The left edge of the displayed part of your view, in pixels. */ public final int getScrollX() { return mScrollX; } /** * Return the scrolled top position of this view. This is the top edge of * the displayed part of your view. You do not need to draw any pixels above * it, since those are outside of the frame of your view on screen. * * @return The top edge of the displayed part of your view, in pixels. */ public final int getScrollY() { return mScrollY; }
注意,所谓的“by which the content of this view is scrolled”表示该偏移量只针对于该View中onDraw()方法里的
具体内容实现,而不针对绘制背景图片等 。具体原因可参考<Android中View绘制流程以及invalidate()等相关方法分析>
提示:下文中提到的当前视图内容是在绘制在布局坐标处的内容。
public void scrollTo(int x, int y)
说明:在当前视图内容偏移至(x , y)坐标处,即显示(可视)区域位于(x , y)坐标处。
方法原型为: View.java类中
- /**
- * Set the scrolled position of your view. This will cause a call to
- * {@link #onScrollChanged(int, int, int, int)} and the view will be
- * invalidated.
- * @param x the x position to scroll to
- * @param y the y position to scroll to
- */
- public void scrollTo(int x, int y) {
- //偏移位置发生了改变
- if (mScrollX != x || mScrollY != y) {
- int oldX = mScrollX;
- int oldY = mScrollY;
- mScrollX = x; //赋新值,保存当前便宜量
- mScrollY = y;
- //回调onScrollChanged方法
- onScrollChanged(mScrollX, mScrollY, oldX, oldY);
- if (!awakenScrollBars()) {
- invalidate(); //一般都引起重绘
- }
- }
- }
/** * Set the scrolled position of your view. This will cause a call to * {@link #onScrollChanged(int, int, int, int)} and the view will be * invalidated. * @param x the x position to scroll to * @param y the y position to scroll to */ public void scrollTo(int x, int y) { //偏移位置发生了改变 if (mScrollX != x || mScrollY != y) { int oldX = mScrollX; int oldY = mScrollY; mScrollX = x; //赋新值,保存当前便宜量 mScrollY = y; //回调onScrollChanged方法 onScrollChanged(mScrollX, mScrollY, oldX, oldY); if (!awakenScrollBars()) { invalidate(); //一般都引起重绘 } } }public void scrollBy(int x, int y)
说明:在当前视图内容继续偏移(x , y)个单位,显示(可视)区域也跟着偏移(x,y)个单位。
方法原型为: View.java类中
- /**
- * Move the scrolled position of your view. This will cause a call to
- * {@link #onScrollChanged(int, int, int, int)} and the view will be
- * invalidated.
- * @param x the amount of pixels to scroll by horizontally
- * @param y the amount of pixels to scroll by vertically
- */
- // 看出原因了吧 。。 mScrollX 与 mScrollY 代表我们当前偏移的位置 , 在当前位置继续偏移(x ,y)个单位
- public void scrollBy(int x, int y) {
- scrollTo(mScrollX + x, mScrollY + y);
- }
/** * Move the scrolled position of your view. This will cause a call to * {@link #onScrollChanged(int, int, int, int)} and the view will be * invalidated. * @param x the amount of pixels to scroll by horizontally * @param y the amount of pixels to scroll by vertically */ // 看出原因了吧 。。 mScrollX 与 mScrollY 代表我们当前偏移的位置 , 在当前位置继续偏移(x ,y)个单位 public void scrollBy(int x, int y) { scrollTo(mScrollX + x, mScrollY + y); }
第一个小Demo非常简单 ,大家重点理解与掌握scrollTo() 与 scrollBy()函数的用法和区别。
第二个小Demo则有了Launcher的模样,能够左右切换屏幕 。实现功能如下: 采用了一个自定义ViewGroup,该ViewGroup
对象包含了3个LinearLayout子视图,并且以一定的布局坐标(由layout()方法指定)显示在ViewGroup上。 接下来,即可调用该
ViewGroup对象的scrollTo或者scrollBy()方法切换指定视图内容了,即切换屏幕。 呵呵 ,挺好玩的吧 。
如果对View绘制流程不懂的,可以参考我的这篇博客<Android中View绘制流程以及invalidate()等相关方法分析> 。
截图如下:
自定义ViewGroup如下:
- //自定义ViewGroup , 包含了三个LinearLayout控件,存放在不同的布局位置,通过scrollBy或者scrollTo方法切换
- public class MultiViewGroup extends ViewGroup {
- private Context mContext;
- private static String TAG = "MultiViewGroup";
- public MultiViewGroup(Context context) {
- super(context);
- mContext = context;
- init();
- }
- public MultiViewGroup(Context context, AttributeSet attrs) {
- super(context, attrs);
- mContext = context;
- init();
- }
- private void init() {
- // 初始化3个 LinearLayout控件
- LinearLayout oneLL = new LinearLayout(mContext);
- oneLL.setBackgroundColor(Color.RED);
- addView(oneLL);
- LinearLayout twoLL = new LinearLayout(mContext);
- twoLL.setBackgroundColor(Color.YELLOW);
- addView(twoLL);
- LinearLayout threeLL = new LinearLayout(mContext);
- threeLL.setBackgroundColor(Color.BLUE);
- addView(threeLL);
- }
- // measure过程
- @Override
- protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
- Log.i(TAG, "--- start onMeasure --");
- // 设置该ViewGroup的大小
- int width = MeasureSpec.getSize(widthMeasureSpec);
- int height = MeasureSpec.getSize(heightMeasureSpec);
- setMeasuredDimension(width, height);
- int childCount = getChildCount();
- Log.i(TAG, "--- onMeasure childCount is -->" + childCount);
- for (int i = 0; i < childCount; i++) {
- View child = getChildAt(i);
- // 设置每个子视图的大小 , 即全屏
- child.measure(MultiScreenActivity.screenWidth, MultiScreenActivity.scrrenHeight);
- }
- }
- // layout过程
- @Override
- protected void onLayout(boolean changed, int l, int t, int r, int b) {
- // TODO Auto-generated method stub
- Log.i(TAG, "--- start onLayout --");
- int startLeft = 0; // 每个子视图的起始布局坐标
- int startTop = 10; // 间距设置为10px 相当于 android:marginTop= "10px"
- int childCount = getChildCount();
- Log.i(TAG, "--- onLayout childCount is -->" + childCount);
- for (int i = 0; i < childCount; i++) {
- View child = getChildAt(i);
- child.layout(startLeft, startTop,
- startLeft + MultiScreenActivity.screenWidth,
- startTop + MultiScreenActivity.scrrenHeight);
- startLeft = startLeft + MultiScreenActivity.screenWidth ; //校准每个子View的起始布局位置
- //三个子视图的在屏幕中的分布如下 [0 , 320] / [320,640] / [640,960]
- }
- }
- }
//自定义ViewGroup , 包含了三个LinearLayout控件,存放在不同的布局位置,通过scrollBy或者scrollTo方法切换 public class MultiViewGroup extends ViewGroup { private Context mContext; private static String TAG = "MultiViewGroup"; public MultiViewGroup(Context context) { super(context); mContext = context; init(); } public MultiViewGroup(Context context, AttributeSet attrs) { super(context, attrs); mContext = context; init(); } private void init() { // 初始化3个 LinearLayout控件 LinearLayout oneLL = new LinearLayout(mContext); oneLL.setBackgroundColor(Color.RED); addView(oneLL); LinearLayout twoLL = new LinearLayout(mContext); twoLL.setBackgroundColor(Color.YELLOW); addView(twoLL); LinearLayout threeLL = new LinearLayout(mContext); threeLL.setBackgroundColor(Color.BLUE); addView(threeLL); } // measure过程 @Override protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) { Log.i(TAG, "--- start onMeasure --"); // 设置该ViewGroup的大小 int width = MeasureSpec.getSize(widthMeasureSpec); int height = MeasureSpec.getSize(heightMeasureSpec); setMeasuredDimension(width, height); int childCount = getChildCount(); Log.i(TAG, "--- onMeasure childCount is -->" + childCount); for (int i = 0; i < childCount; i++) { View child = getChildAt(i); // 设置每个子视图的大小 , 即全屏 child.measure(MultiScreenActivity.screenWidth, MultiScreenActivity.scrrenHeight); } } // layout过程 @Override protected void onLayout(boolean changed, int l, int t, int r, int b) { // TODO Auto-generated method stub Log.i(TAG, "--- start onLayout --"); int startLeft = 0; // 每个子视图的起始布局坐标 int startTop = 10; // 间距设置为10px 相当于 android:marginTop= "10px" int childCount = getChildCount(); Log.i(TAG, "--- onLayout childCount is -->" + childCount); for (int i = 0; i < childCount; i++) { View child = getChildAt(i); child.layout(startLeft, startTop, startLeft + MultiScreenActivity.screenWidth, startTop + MultiScreenActivity.scrrenHeight); startLeft = startLeft + MultiScreenActivity.screenWidth ; //校准每个子View的起始布局位置 //三个子视图的在屏幕中的分布如下 [0 , 320] / [320,640] / [640,960] } } }
PS :大家可以分别给这几个LinearLayout试着添加几个子View,例如TextView, Button等。
至于Launcher上滑屏功能的实现,我尝试着去掌握,可能天资愚钝吧,对Scoller类很是感冒,现今还没有掌握好,不过在此
给大家推荐几个不错的学习资源 。 以后有需要的话,还是采用拿来主义吧。 囧
1、 Scoller类介绍:android 中文 api (64) —— Scroller
2、相关资源汇总:http://blog.csdn.net/dellheng/article/details/7164275
示例源代码位于: http://download.csdn.net/detail/qinjuning/4054840
补充(收回上面一段话,- -):关于如何实现触摸滑屏---- 仿Launcher滑屏以及Scoller类的使用,请参阅我的
另外一篇博文: 《 Android中滑屏实现----手把手教你如何实现触摸滑屏以及Scroller类详解》