一、自定义的空间通过继承ViewGroup来实现
二、scrollview的基础条件
1、基础条件scrollview需要的有:容器的大小,可视界面的大小,每个item的大小
这里定义一个item为整个view的大小,所以在initView的时候进行获取屏幕的高度
WindowManager wm = (WindowManager) context.getSystemService(Context.WINDOW_SERVICE);
DisplayMetrics dm = new DisplayMetrics();
wm.getDefaultDisplay().getMetrics(dm);
mScreenHeight = dm.heightPixels;
这里的mScreenHeight保存了屏幕的高度
关于每个item的尺寸测量,则需要在onMeasure中执行,如下所示
@Override
protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
super.onMeasure(widthMeasureSpec, heightMeasureSpec);
int count = getChildCount();
for (int i = 0; i < count; ++i) {
View childView = getChildAt(i);
measureChild(childView, widthMeasureSpec, heightMeasureSpec);
}
}
这里将宽和高的测量设置到了ViewGroup的子项,即每个scrollview的item
容器里面有多个item了,但是每个item该如何排列则需要在layout中进行设置(注意:scrollview并不会帮你讲每个item的位置设置好)
@Override
protected void onLayout(boolean b, int l, int i1, int i2, int i3) {
int childCount = getChildCount();
MarginLayoutParams lp = (MarginLayoutParams)getLayoutParams();
lp.height = childCount * mScreenHeight;
setLayoutParams(lp); // 要设置scrollview的容器的高度,注意这里不是view的高度,而是所有容器排列在一起的高度
for (int i = 0; i < childCount; ++i) {
View child = getChildAt(i);
if (child.getVisibility() != View.GONE) {
child.layout(l, i * mScreenHeight, i2, (i + 1) * mScreenHeight); // 这里每个item从上往下进行排列,每个item占据一个mScreenHeight的高度
}
}
}
2、容器的内容
这里只是基础的操作,所以用最简单的xml来设置,如下的配置所示
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical">
<com.agiledeveloper.systemwidget.MyScrollView
android:layout_width="match_parent"
android:layout_height="match_parent">
<ImageView
android:id="@+id/imageView"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:scaleType="fitXY"
android:src="@drawable/test1" />
<ImageView
android:id="@+id/imageView2"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:scaleType="fitXY"
android:src="@drawable/test2" />
<ImageView
android:id="@+id/imageView3"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:scaleType="fitXY"
android:src="@drawable/test3" />
<ImageView
android:id="@+id/imageView4"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:scaleType="fitXY"
android:src="@drawable/test4" />
</com.agiledeveloper.systemwidget.MyScrollView>
</LinearLayout>
View Code
到这里scrollview已经能够跑起来了,但是咱们如果要加点回弹的效果则需要做额外的操作
三、Scroller的使用
我们在上面initView函数中增加mScroller = new Scroller(context);
这里mScroller是用来记录和设置当前的滚动位置和状态(注意:scroller只是记录和设置没有参与渲染操作)类似于MVC的model
Scroller的几个比较常用的函数是:
startScroll(int startX, int startY, int dx, int dy) 将当前的scroller的滑动从(startX, startY)滑动到 (startX+dx, startY+dy) (注意:跟具体的ScrollView没啥关系,只是一个记录数据的动作,具体要滚动要调用scrollview的scrollTo或者scrollBy)
isFinished()和abortAnimation() 这里的isFinished判断是否完成动画的滑动,abortAnimation是停止动画的滑动,直接将最终的位置设置进来,具体可以看abortAnimation的源代码
public void abortAnimation() {
mCurrX = mFinalX;
mCurrY = mFinalY;
mFinished = true;
}
computeScrollOffset() 该函数是判断当前的滚动动画是否还在继续
四、computeScroll的继承
我们打算让滚动有回弹的效果可以重写computeScroll,具体代码如下所示
@Override
public void computeScroll() {
super.computeScroll();
if (mScroller.computeScrollOffset()) {
scrollTo(0, mScroller.getCurrY());
postInvalidate();
}
}
这里判断当前如果动画会在继续就调用scrollTo滚动到mScroller当前的指定位置
关于computeScroll和mScroller的说明可以看这篇文章https://www.freesion.com/article/7912960070/
五、完整的代码如下所示:
package com.agiledeveloper.systemwidget;
import android.content.Context;
import android.os.Debug;
import android.util.AttributeSet;
import android.util.DisplayMetrics;
import android.view.MotionEvent;
import android.view.View;
import android.view.ViewGroup;
import android.view.WindowManager;
import android.widget.Scroller;
public class MyScrollView extends ViewGroup {
public MyScrollView(Context context) {
super(context);
initView(context);
}
public MyScrollView(Context context, AttributeSet attrs) {
super(context, attrs);
initView(context);
}
public MyScrollView(Context context, AttributeSet attrs, int defStyleAttr) {
super(context, attrs, defStyleAttr);
initView(context);
}
public MyScrollView(Context context, AttributeSet attrs, int defStyleAttr, int defStyleRes) {
super(context, attrs, defStyleAttr, defStyleRes);
initView(context);
}
private int mScreenHeight;
private Scroller mScroller;
private void initView(Context context) {
WindowManager wm = (WindowManager) context.getSystemService(Context.WINDOW_SERVICE);
DisplayMetrics dm = new DisplayMetrics();
wm.getDefaultDisplay().getMetrics(dm);
mScreenHeight = dm.heightPixels;
mScroller = new Scroller(context);
}
@Override
protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
super.onMeasure(widthMeasureSpec, heightMeasureSpec);
int count = getChildCount();
for (int i = 0; i < count; ++i) {
View childView = getChildAt(i);
measureChild(childView, widthMeasureSpec, heightMeasureSpec);
}
}
@Override
protected void onLayout(boolean b, int l, int i1, int i2, int i3) {
int childCount = getChildCount();
MarginLayoutParams lp = (MarginLayoutParams)getLayoutParams();
lp.height = childCount * mScreenHeight;
setLayoutParams(lp);
for (int i = 0; i < childCount; ++i) {
View child = getChildAt(i);
if (child.getVisibility() != View.GONE) {
child.layout(l, i * mScreenHeight, i2, (i + 1) * mScreenHeight);
}
}
}
private int mLastY = 0;
private int mStartY = 0;
@Override
public boolean onTouchEvent(MotionEvent event) {
int y = (int)event.getY();
switch (event.getAction()) {
case MotionEvent.ACTION_DOWN:
mLastY = y;
mStartY = getScrollY();
break;
case MotionEvent.ACTION_MOVE:
if (!mScroller.isFinished()) {
mScroller.abortAnimation();
}
int dy = mLastY - y;
if (getScrollY() < 0) {
dy = 0;
}
if (getScrollY() > (getChildCount() - 1) * mScreenHeight) {
dy = 0;
}
scrollBy(0, dy);
mLastY = y;
break;
case MotionEvent.ACTION_UP:
int dScrollY = checkAlignment();
if (dScrollY > 0) {
if (dScrollY < mScreenHeight / 3) {
mScroller.startScroll(0, getScrollY(), 0, -dScrollY);
} else {
mScroller.startScroll(0, getScrollY(), 0, mScreenHeight - dScrollY);
}
} else {
if (-dScrollY < mScreenHeight / 3) {
mScroller.startScroll(0, getScrollY(), 0, -dScrollY);
} else {
mScroller.startScroll(0, getScrollY(), 0, -mScreenHeight - dScrollY);
}
}
break;
}
postInvalidate();
return true;
}
private int checkAlignment() {
int mEnd = getScrollY();
boolean isUp = (mEnd - mStartY) > 0? true : false;
int lastPrev = mEnd % mScreenHeight;
int lastNext = mScreenHeight - lastPrev;
if (isUp) {
return lastPrev;
} else {
return -lastNext;
}
}
@Override
public void computeScroll() {
super.computeScroll();
if (mScroller.computeScrollOffset()) {
scrollTo(0, mScroller.getCurrY());
postInvalidate();
}
}
}
View Code