转载

自定义控件之重写ScrollView实现图片下拉放大

前言

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

效果

自定义控件之重写ScrollView实现图片下拉放大

实现思路

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

代码

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);      } } 

重要点,从上往下

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

最主要的地方,事件拦截

    @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);     } 

详细说明

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

最后说两句

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。

原文  http://www.raye.wang/2016/06/13/zi-ding-yi-kong-jian-zhi-zhong-xie-scrollviewshi-xian/
正文到此结束
Loading...