因为公司项目要实现一个效果,在ScrollView没有向下滚动时,下拉(未重写前下拉是没有任何效果的)放大顶部的图片,当时去网上找了,记得以前见过很多这样的控件的,现在却找半天也很难找到一个,好不容易找到了2个,发现效果都和需求上面的效果有偏差,最后没有办法只能是自己写了,花费了半天时间研究出来了,同时为了记录实现思路,所以就有了此文章
拦截ScrollView的触摸滑动事件(ACTION_MOVE),记录下当前事件y轴坐标,判断当前ScrollView的Y轴滚动进度(getScrollY)是否等于0,等于0就与上次事件记录的位置进行对比,如果为正数就放大(X轴是从左往右,Y轴是从上往下,所以下拉时本次事件的Y轴会大于上次事件的Y轴),每次事件都通过设置ImageView的高度来放大图片控件(本来想用属性动画的,但是因为每个事件放大的比例非常小,所以最后就没使用,直接通过修改属性来实现),同时记录从开始到现在事件位置一共偏移了多少,当偏移量大于最大值的,就停止放大并将偏移量设置为最大值,当偏移量小于0时,则将偏移量设置为0,同时不再继续拦截事件。注意被放大的图片需要设置scaleType为centerCrop,这样当图片高度发生变化时,图片内容才会跟着大,当然其他几种模式有些模式也能跟着放大,但是具体可以自己去测试,我就不去测试了,毕竟我已经达到我要的效果了
好了,废话少说,先贴代码,再对代码进行说明
package wang.raye.library; import android.annotation.TargetApi; import android.content.Context; import android.content.res.TypedArray; import android.os.Build; import android.os.Handler; import android.os.Message; import android.util.AttributeSet; import android.util.Log; import android.view.MotionEvent; import android.view.View; import android.widget.LinearLayout; import android.widget.ScrollView; /** * 重写让ScrollView有滚动监听(23以前是没有滚动监听的) * 拦截touch事件,让其支持下拉放大图片 * Created by Raye on 2016/6/11. */ public class ZoomScrollView extends ScrollView { private View zoomView; /** 记录上次事件的Y轴*/ private float mLastMotionY; /** 记录一个滚动了多少距离,通过这个来设置缩放*/ private int allScroll = -1; /** 控件原本的高度*/ private int height = 0; /** 被放大的控件id*/ private int zoomId; /** 最大放大多少像素*/ private int maxZoom; /** 滚动监听*/ private ScrollViewListener scrollViewListener = null; private Handler handler = new Handler(){ @Override public void handleMessage(Message msg) { allScroll -= 25; if(allScroll < 0){ allScroll = 0; } LinearLayout.LayoutParams lp = (LinearLayout.LayoutParams) zoomView.getLayoutParams(); lp.height = (int) (height + allScroll/2); zoomView.setLayoutParams(lp); if(allScroll != 0){ handler.sendEmptyMessageDelayed(1,10); }else{ allScroll = -1; } } }; public ZoomScrollView(Context context) { super(context); } public ZoomScrollView(Context context, AttributeSet attrs) { super(context, attrs); init(attrs); } public ZoomScrollView(Context context, AttributeSet attrs, int defStyleAttr) { super(context, attrs, defStyleAttr); init(attrs); } @TargetApi(Build.VERSION_CODES.LOLLIPOP) public ZoomScrollView(Context context, AttributeSet attrs, int defStyleAttr, int defStyleRes) { super(context, attrs, defStyleAttr, defStyleRes); init(attrs); } @Override protected void onFinishInflate() { super.onFinishInflate(); zoomView = findViewById(zoomId); } private void init(AttributeSet attrs){ TypedArray t = getContext().obtainStyledAttributes(attrs, R.styleable.ObservableScrollView); zoomId = t.getResourceId(R.styleable.ObservableScrollView_zoomId,-1); maxZoom = t.getDimensionPixelOffset(R.styleable.ObservableScrollView_maxZoom,0); } public void setScrollViewListener(ScrollViewListener scrollViewListener) { this.scrollViewListener = scrollViewListener; } @Override public boolean dispatchTouchEvent(MotionEvent event) { if(zoomView == null || maxZoom == 0){ return super.dispatchTouchEvent(event); } final int action = event.getAction(); if (action == MotionEvent.ACTION_CANCEL || action == MotionEvent.ACTION_UP) { if(allScroll != -1){ handler.sendEmptyMessageDelayed(1,10); } return super.dispatchTouchEvent(event); } switch (action) { case MotionEvent.ACTION_MOVE: { final float y = event.getY(); final float diff, absDiff; diff = y - mLastMotionY; mLastMotionY = y; absDiff = Math.abs(diff); if(allScroll >= 0 && absDiff > 1){ allScroll += diff; if(allScroll < 0){ allScroll = 0; }else if(allScroll > maxZoom){ allScroll = maxZoom; } LinearLayout.LayoutParams lp = (LinearLayout.LayoutParams) zoomView.getLayoutParams(); lp.height = (int) (height + allScroll/2); zoomView.setLayoutParams(lp); if(allScroll == 0){ allScroll = -1; } return false; } if (isReadyForPullStart()) { if (absDiff > 0 ) { if (diff >= 1f && isReadyForPullStart()) { mLastMotionY = y; allScroll = 0; height = zoomView.getHeight(); return true; } } } break; } } return super.dispatchTouchEvent(event); } @Override public boolean onTouchEvent(MotionEvent ev) { if(allScroll != -1){ Log.i("ScrollView","onTouchEvent"); return false; } return super.onTouchEvent(ev); } /** * 返回是否可以开始放大 * @return */ protected boolean isReadyForPullStart() { return getScrollY() == 0; } @Override protected void onScrollChanged(int x, int y, int oldx, int oldy) { super.onScrollChanged(x, y, oldx, oldy); if (scrollViewListener != null) { scrollViewListener.onScrollChanged(this, x, y, oldx, oldy); } } public interface ScrollViewListener { void onScrollChanged(ZoomScrollView scrollView, int x, int y, int oldx, int oldy); } }
private Handler handler = new Handler(){ @Override public void handleMessage(Message msg) { allScroll -= 25; if(allScroll < 0){ allScroll = 0; } LinearLayout.LayoutParams lp = (LinearLayout.LayoutParams) zoomView.getLayoutParams(); lp.height = (int) (height + allScroll/2); zoomView.setLayoutParams(lp); if(allScroll != 0){ handler.sendEmptyMessageDelayed(1,10); }else{ allScroll = -1; } } };
这里是当ACTION_UP事件发生时,如果图片还在放大状态,就模拟动画效果,吧图片缩放回去,当然是可以用属性动画的,只是我之前没用属性动画,所以这里也直接用这个了
@Override protected void onFinishInflate() { super.onFinishInflate(); zoomView = findViewById(zoomId); }
这里是当控件从xml中初始化完成的生命周期方法,在这里我们找到被放大的图片控件
private void init(AttributeSet attrs){ TypedArray t = getContext().obtainStyledAttributes(attrs, R.styleable.ObservableScrollView); zoomId = t.getResourceId(R.styleable.ObservableScrollView_zoomId,-1); maxZoom = t.getDimensionPixelOffset(R.styleable.ObservableScrollView_maxZoom,0); }
这段代码相信很容易看懂,就是获取2个自定义属性,一个是被放大的图片控件id,一个是最大的放大像素
@Override public boolean dispatchTouchEvent(MotionEvent event) { if(zoomView == null || maxZoom == 0){ return super.dispatchTouchEvent(event); } final int action = event.getAction(); if (action == MotionEvent.ACTION_CANCEL || action == MotionEvent.ACTION_UP) { if(allScroll != -1){ handler.sendEmptyMessageDelayed(1,10); } return super.dispatchTouchEvent(event); } switch (action) { case MotionEvent.ACTION_MOVE: { final float y = event.getY(); final float diff, absDiff; diff = y - mLastMotionY; mLastMotionY = y; absDiff = Math.abs(diff); if(allScroll >= 0 && absDiff > 1){ allScroll += diff; if(allScroll < 0){ allScroll = 0; }else if(allScroll > maxZoom){ allScroll = maxZoom; } LinearLayout.LayoutParams lp = (LinearLayout.LayoutParams) zoomView.getLayoutParams(); lp.height = (int) (height + allScroll/2); zoomView.setLayoutParams(lp); if(allScroll == 0){ allScroll = -1; } return false; } if (isReadyForPullStart()) { if (absDiff > 0 ) { if (diff >= 1f && isReadyForPullStart()) { mLastMotionY = y; allScroll = 0; height = zoomView.getHeight(); return true; } } } break; } } return super.dispatchTouchEvent(event); }
if(zoomView == null || maxZoom == 0){ return super.dispatchTouchEvent(event); }
当控件为空和最大放大像素为0 的时候,不进行事件拦截
if (action == MotionEvent.ACTION_CANCEL || action == MotionEvent.ACTION_UP) { if(allScroll != -1){ handler.sendEmptyMessageDelayed(1,10); } return super.dispatchTouchEvent(event); }
当事件取消和手指松开时,判断当前偏移量(allScroll )是否回到了最初状态-1,如果没有说明图片没有缩放,要缩放回去
case MotionEvent.ACTION_MOVE: { final float y = event.getY(); final float diff, oppositeDiff, absDiff; diff = y - mLastMotionY; mLastMotionY = y; absDiff = Math.abs(diff); if( allScroll >= 0 && absDiff > 1){ allScroll += diff; if(allScroll < 0){ allScroll = 0; }else if(allScroll > maxZoom){ allScroll = maxZoom; } LinearLayout.LayoutParams lp = (LinearLayout.LayoutParams) zoomView.getLayoutParams(); lp.height = (int) (height + allScroll/2); zoomView.setLayoutParams(lp); if(allScroll == 0){ allScroll = -1; } return false; } if (isReadyForPullStart()) { if (absDiff > 0 ) { if (diff >= 1f && isReadyForPullStart()) { mLastMotionY = y; allScroll = 0; height = zoomView.getHeight(); return true; } } } break; }
拦截移动事件,每次记录下Y轴坐标,当滚动为0的时候,就计算与上次坐标的偏移量,大于0就开始放大,每次放大总偏移值的二分之一,因为每次放大总偏移值的效果不大好看,同时判断总偏移值是否大于最大偏移值,大于就设置总偏移值为最大值,相当于停止放大。如果小于0,就把总偏移值设置为0,并且重置偏移值的为-1,-1的时候,就不会拦截事件
@Override public boolean onTouchEvent(MotionEvent ev) { if(allScroll != -1){ Log.i("ScrollView","onTouchEvent"); return false; } return super.onTouchEvent(ev); }
重写onTouchEvent,当偏移值不是-1的时候,说明图片在进行放大或缩放,这时候不能让ScrollView滚动,所以需要把onTouchEvent拦截掉
protected boolean isReadyForPullStart() { return getScrollY() == 0; }
获取当前ScrollView的滚动位置,是0的时候才可以开始放大图片
控件中还有个监听,那个不用管,那个是为了获取滚动位置来设置标题栏透明度的,跟本文内容无关,所以就不详细说明了。当然这个自定义控件只是为了实现我项目中需求的效果,很简陋,实现方法也很简单,所以欢迎高手前来指点。