视差特效实现思路

视差特效实现思路:

* 1.解析ontouch ACTION_Down ,Action_move ,ACTION_up 业务逻辑过于复杂

* 2,重写Listview的overScrollby方法.继承式自定义控件 根据用户下拉的距离,动态修改Headerview的高度

* a:拷贝文本资源到项目中,自定义控件继承ListView

* b:使用自定义控件,并往头部添加布局,设置适配器

* c:使用试图时,把ImageView传给我们的自定义控件

MainActivity里面的东西

public class MainActivity extends AppCompatActivity {

private ParallaListView plv ;

@Override

protected void onCreate(Bundle savedInstanceState) {

super .onCreate(savedInstanceState);

setContentView(R.layout. activity_main );

//a,view

plv = (ParallaListView) findViewById(R.id. plv );

//B.ListView添加一个头布局 listview的上拉加载下拉刷新

View headview = View. inflate ( this , R.layout. layout_head , null );

plv .addHeaderView(headview);

final ImageView iv_header = (ImageView) headview.findViewById(R.id. iv_header );

//等view界面全部绘制完毕的时候,去得到已经绘制的宽和高,查下这个方法,并做下笔记

iv_header.getViewTreeObserver().addOnGlobalLayoutListener( new ViewTreeObserver.OnGlobalLayoutListener() {

@Override

public void onGlobalLayout() {

//宽和高已经测量完毕

plv .setIv_header( iv_header );

}

});

//b.使用ListView的arrayadapter 添加文本的item

plv .setAdapter( new ArrayAdapter( this , android.R.layout. simple_list_item_1 , Cheeses. NAMES ));

}

}

继承式控件

* 1.继承ListView 覆写构造方法

* 2.覆写overScrollby方法重点关注deltaY ,isTouchEvent方法

* 3.暴露一个方法,去得到外界的ImageView ,并测量ImageView控件的高度

* 4.覆写OnTouchEvent方法

第二个类

public class ParallaListView extends ListView {

private ImageView iv_header ;

private int drawableHeight ;

private int orignalHeight ;

public ParallaListView(Context context) {

this (context, null );

}

public ParallaListView(Context context, AttributeSet attrs) {

this (context, attrs, 0 );

}

public ParallaListView(Context context, AttributeSet attrs, int defStyleAttr) {

super (context, attrs, defStyleAttr);

}

public void setIv_header(ImageView iv_header) {

this . iv_header = iv_header;

//b.获取图片的原始高度

drawableHeight = iv_header.getDrawable().getIntrinsicHeight();

//c.获取ImageView控件的原始高度,以便回弹时,回弹到原始高度

orignalHeight = iv_header.getHeight();

}

/*

A.滑动到listview两端时,才会被调用

/*

*deltay :竖直方向滑动的瞬间变化量,顶部下拉为-;顶部上拉为+;

* isTouchEvent是否是用户触摸拉动,true表示用户手指拉动,false是惯性

*

*

*/

@Override

protected boolean overScrollBy( int deltaX, int deltaY, int scrollX,

int scrollY, int scrollRangeX, int scrollRangeY,

int maxOverScrollX, int maxOverScrollY, boolean isTouchEvent) {

//A.通过Log来验证参数的作用

System. out .println( "deltaX--" + deltaX + "deltaY--" + deltaY + "scrollX--" + scrollX + "scrollY--" + scrollY + "scrollRangeX--" + scrollRangeX + "scrollRangeY--" + scrollRangeY + "maxOverScrollX--" + maxOverScrollX + "maxOverScrollY--" + maxOverScrollY + "isTouchEvent--" + isTouchEvent);

//a.顶部下拉,用户触摸的操作才执行视察效果("&"和"&&"和"|"和"||"区别)

if (deltaY < 0 && isTouchEvent) {

//a.deltaY是负值,我们要改为绝对值,累计给我们的iv_header高度

int newHeight = iv_header .getHeight() + Math. abs (deltaY);

//b.避免图片的无限放大,是图片最大不能超过图片的本身的高度

if (newHeight <= drawableHeight ) {

//把新的高度值负值给控件,改变控件的高度

iv_header .getLayoutParams(). height = newHeight;

iv_header .requestLayout();

}

}

return super .overScrollBy(deltaX, deltaY, scrollX, scrollY, scrollRangeX, scrollRangeY, maxOverScrollX, maxOverScrollY, isTouchEvent);

}

//c.覆写触摸事件,让滑动图片重新恢复原有的样子

//触摸事件的监听

@Override

public boolean onTouchEvent(MotionEvent event) {

switch (event.getAction()) {

case MotionEvent. ACTION_UP : //松开时,回调

//把当前的头布局的高度恢复初始高度

int currentHeight = iv_header .getHeight();

//属性动画,改变高度的值,把我们当前头布局的高度,改为原始的高度

final ValueAnimator animator = ValueAnimator. ofInt (currentHeight, orignalHeight );

//动画更新的监听

animator.addUpdateListener( new ValueAnimator.AnimatorUpdateListener() {

@Override

public void onAnimationUpdate(ValueAnimator valueAnimator) {

//获取中间的值,并赋予控件新高度,可以使控件平稳回弹的效果

Integer animatedValue = (Integer) animator .getAnimatedValue();

System. out .println( "fraction" + fraction + "animatedValue" + animatedValue);

//让新的高度生效

iv_header .getLayoutParams(). height = animatedValue;

iv_header .requestLayout();

}

});

//动画的回弹效果,值越大,回弹越厉害

animator.setInterpolator( new OvershootInterpolator( 2 ));

//设置动画的执行时间,单位值毫秒

animator.setDuration( 500 );

//动画执行

animator.start();

break ;

}

return super .onTouchEvent(event);

}

}

第三个类

public class Cheeses {

public static final String[] NAMES = new String[]{ "宋江" , "卢俊义" , "吴用" ,

"公孙胜" , "关胜" , "林冲" , "秦明" , "呼延灼" , "花荣" , "柴进" , "李应" , "朱仝" , "鲁智深" ,

"武松" , "董平" , "张清" , "杨志" , "徐宁" , "索超" , "戴宗" , "刘唐" , "李逵" , "史进" , "穆弘" ,

"雷横" , "李俊" , "阮小二" , "张横" , "阮小五" , " 张顺" , "阮小七" , "杨雄" , "石秀" , "解珍" ,

" 解宝" , "燕青" , "朱武" , "黄信" , "孙立" , "宣赞" , "郝思文" , "韩滔" , "彭玘" , "单廷珪" ,

"魏定国" , "萧让" , "裴宣" , "欧鹏" , "邓飞" , " 燕顺" , "杨林" , "凌振" , "蒋敬" , "吕方" ,

"郭 盛" , "安道全" , "皇甫端" , "王英" , "扈三娘" , "鲍旭" , "樊瑞" , "孔明" , "孔亮" , "项充" ,

"李衮" , "金大坚" , "马麟" , "童威" , "童猛" , "孟康" , "侯健" , "陈达" , "杨春" , "郑天寿" ,

"陶宗旺" , "宋清" , "乐和" , "龚旺" , "丁得孙" , "穆春" , "曹正" , "宋万" , "杜迁" , "薛永" , "施恩" ,

"周通" , "李忠" , "杜兴" , "汤隆" , "邹渊" , "邹润" , "朱富" , "朱贵" , "蔡福" , "蔡庆" , "李立" ,

"李云" , "焦挺" , "石勇" , "孙新" , "顾大嫂" , "张青" , "孙二娘" , " 王定六" , "郁保四" , "白胜" ,

"时迁" , "段景柱" , "易宸锋" };

}

一共三个item布局

第一个布局

activity_main

xml version= "1.0" encoding= "utf-8" ?>

< RelativeLayout xmlns: android = "http://schemas.android.com/apk/res/android"

android :layout_width= "match_parent"

android :layout_height= "match_parent"

>

< com.zhangshixin.bwie.test0816.ParallaListView

android :id= "@+id/plv"

android :layout_width= "match_parent"

android : layout_height = "match_parent" />

RelativeLayout >

第二个布局

layout_header

xml version= "1.0" encoding= "utf-8" ?>

< LinearLayout xmlns: android = "http://schemas.android.com/apk/res/android"

android :orientation= "vertical" android :layout_width= "match_parent"

android :layout_height= "match_parent" >

< ImageView

android :id= "@+id/iv_header"

android :layout_width= "match_parent"

android :layout_height= "160dp"

android :src= "@drawable/parallax_img"

android :scaleType= "centerCrop" />

LinearLayout >

第三个布局

simple_list_item_1

xml version= "1.0" encoding= "utf-8" ?>

< LinearLayout xmlns: android = "http://schemas.android.com/apk/res/android"

android :orientation= "vertical" android :layout_width= "match_parent"

android :layout_height= "match_parent" >

LinearLayout >