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<String>(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>