看到这个控件很炫，一直想研究，拖了好几天，今天终于手打出来了。好了现在展示下成果。github地址：https://github.com/matrixxun/PullToZoomInListView
效果
pulltoview.gif
实现代码
public class PullToZoomListView extends ListView implements
AbsListView.OnScrollListener{
private static final int INVALID_VALUE = -1;
private static final String TAG = "PullToZoomListView";
int mActivePointerId = -1;
private FrameLayout mHeaderContainer;
private int mHeadHeight;//头部视图的高
private ImageView mHeaderImage;
//偏移量
float mLastMotionY = -1.0F;
float mLastScale = -1.0F;
float mMaxScale = -1.0F;
//抽象的listView
private AbsListView.OnScrollListener mOnScrollListener;
private ScalingRunnalable mScalingRunnalable;
private int mScreenHeight; //屏幕的高
private ImageView mShadow;
//定义动画变化的速率
/**
* Interpolator定义了动画变化的速率，在Animations框架当中定义了一下几种Interpolator
Ø AccelerateDecelerateInterpolator：在动画开始与结束的地方速率改变比较慢，在中间的时候速率快。
Ø AccelerateInterpolator：在动画开始的地方速率改变比较慢，然后开始加速
Ø CycleInterpolator：动画循环播放特定的次数，速率改变沿着正弦曲线
Ø DecelerateInterpolator：在动画开始的地方速率改变比较慢，然后开始减速
Ø LinearInterpolator：动画以均匀的速率改变
*/
private static final Interpolator sInterpolatar = new Interpolator(){
@Override
public float getInterpolation(float input) {
float f = input - 1.0F;
return 1.0F + f * (f*(f*(f*f)));
}
};
public PullToZoomListView(Context context) {
super(context);
init(context);
}
public PullToZoomListView(Context context, AttributeSet attrs) {
super(context, attrs);
init(context);
}
public PullToZoomListView(Context context, AttributeSet attrs, int defStyleAttr) {
super(context, attrs, defStyleAttr);
init(context);
}
private void endScraling(){
//下拉开始
if (this.mHeaderContainer.getBottom() >= this.mHeadHeight)
Log.d("mmm","endScraling");
this.mScalingRunnalable.startAnimation(200L);
}
private void init(Context paramContext){
//屏幕的像素
DisplayMetrics localDisplayMetrics = new DisplayMetrics();
///将当前窗口的一些信息放在DisplayMetrics类中，
((Activity)paramContext).getWindowManager().getDefaultDisplay()
.getMetrics(localDisplayMetrics);
//屏幕高度
this.mScreenHeight = localDisplayMetrics.heightPixels;
this.mHeaderContainer = new FrameLayout(paramContext);
this.mHeaderImage = new ImageView(paramContext);
//屏幕宽度
int i = localDisplayMetrics.widthPixels;
setHeaderViewSize(i, (int) (9.0F * (i / 16.0F)));
this.mShadow = new ImageView(paramContext);
//指定了该布局的宽和高(-1为宽,-2为高)
FrameLayout.LayoutParams localLayoutParams = new FrameLayout.LayoutParams(-1,-2);
localLayoutParams.gravity = 80;
this.mShadow.setLayoutParams(localLayoutParams);
this.mHeaderContainer.addView(this.mHeaderImage);
this.mHeaderContainer.addView(this.mShadow);
addHeaderView(this.mHeaderContainer);
//ScalingRunnalable
this.mScalingRunnalable = new ScalingRunnalable();
super.setOnScrollListener(this);
}
//第二次下拉设为0
private void onSecondaryPointerUp(MotionEvent paramMotionEvent){
int i = (paramMotionEvent.getAction()) >> 8;
if (paramMotionEvent.getPointerId(i) == this.mActivePointerId)
if (i != 0){
int j = 1;
this.mLastMotionY = paramMotionEvent.getY(0);
this.mActivePointerId = paramMotionEvent.getPointerId(0);
return;
}
}
private void reset(){
this.mActivePointerId = -1;
this.mLastMotionY = -1.0F;
this.mMaxScale = -1.0F;
this.mLastScale = -1.0F;
}
public ImageView getHeaderView(){
return this.mHeaderImage;
}
//返回true表示拦截。
public boolean onInterceptTouchEvent(MotionEvent paramMotionEvent) {
return super.onInterceptTouchEvent(paramMotionEvent);
}
// 确定View的位置
@Override
protected void onLayout(boolean changed, int l, int t, int r, int b) {
super.onLayout(changed, l, t, r, b);
if (this.mHeadHeight == 0){
this.mHeadHeight = this.mHeaderContainer.getHeight();
}
}
@Override
public void onScroll(AbsListView paramAbsListview, int firstVisibleItem, int visibleItemCount, int totalItemCount) {
float f = this.mHeadHeight - this.mHeaderContainer.getBottom();
//偏移量
Log.d("fullview", "f+" + f);
if ((f > 0.0f) && (f < this.mHeadHeight)){
int i = (int) (0.65D * f);
this.mHeaderImage.scrollTo(0 , -i);
//没有向下滑
} else if(this.mHeaderContainer.getScrollY() != 0){
this.mHeaderContainer.scrollTo(0,0);
}
if (this.mOnScrollListener != null){
this.mOnScrollListener.onScroll(paramAbsListview, firstVisibleItem,
visibleItemCount, totalItemCount);
}
}
@Override
public void onScrollStateChanged(AbsListView view, int scrollState) {
if (this.mOnScrollListener != null){
this.mOnScrollListener.onScrollStateChanged(view,
scrollState);
}
}
@Override
public boolean onTouchEvent(MotionEvent ev) {
switch (MotionEvent.ACTION_MASK & ev.getAction()){
case MotionEvent.ACTION_DOWN:
if (!this.mScalingRunnalable.mIsFinished){
//结束动画
this.mScalingRunnalable.abortAnimation();
}
this.mLastMotionY = ev.getY();
this.mActivePointerId = ev.getPointerId(0);
this.mMaxScale = (this.mScreenHeight / this.mHeadHeight);
this.mLastScale = (this.mHeaderContainer.getBottom() / this.mHeadHeight);
break;
case MotionEvent.ACTION_MOVE:
//获得指定ID的pointer在当前事件中的index。
int j = ev.findPointerIndex(this.mActivePointerId);
if (j == -1){
Log.e("pullToZoomListView", "Invalid pointerId"
+ this.mActivePointerId + "in onTouchEvent");
} else {
if (this.mLastMotionY == -1.0F)
this.mLastMotionY = ev.getY(j);
//如果底部大于图片的高
if (this.mHeaderContainer.getBottom() >= this.mHeadHeight){
//下滑
ViewGroup.LayoutParams localLayoutParams = this.mHeaderContainer.getLayoutParams();
float f = ((ev.getY(j) - this.mLastMotionY + this.mHeaderContainer.
getBottom()) / this.mHeadHeight - this.mLastScale)
/2.0F + this.mLastScale;
if ((this.mLastScale <= 1.0D) && (f < this.mLastScale)){
//初始化param的高，没有改变还是原来样子
localLayoutParams.height = this.mHeadHeight;
this.mHeaderContainer.setLayoutParams(localLayoutParams);
return super.onTouchEvent(ev);
}
this.mLastScale = Math.min(Math.max(f, 1.0F),this.mMaxScale);
//高度乘偏移量 为 拉伸的图片高度
localLayoutParams.height = (int)((this.mHeadHeight * this.mLastScale));
if (localLayoutParams.height < this.mScreenHeight)
this.mHeaderContainer.setLayoutParams(localLayoutParams);
this.mLastMotionY = ev.getY(j);
return true;
}
this.mLastMotionY = ev.getY(j);
}
break;
case MotionEvent.ACTION_UP:
reset();
//初始化 开始恢复动画
endScraling();
break;
//当屏幕上已经有一个点被按住,此时再按下其他点时触发。
case MotionEvent.ACTION_POINTER_DOWN:
onSecondaryPointerUp(ev);
this.mLastMotionY = ev.getY(ev.findPointerIndex(this.mActivePointerId));
break;
case MotionEvent.ACTION_POINTER_UP:
}
return super.onTouchEvent(ev);
}
//设置头部的大小
public void setHeaderViewSize(int paramInt1, int paramInt2){
Object localObject = this.mHeaderContainer.getLayoutParams();
if (localObject == null){
//如果没有的话，设置listview的宽高
localObject = new AbsListView.LayoutParams(paramInt1, paramInt2);
((ViewGroup.LayoutParams)localObject).width = paramInt1;
((ViewGroup.LayoutParams)localObject).height = paramInt2;
//这里代码有点乱
this.mHeaderContainer.setLayoutParams((ViewGroup.LayoutParams)localObject);
this.mHeadHeight = paramInt2;
}
}
public void setOnScrollListener(
AbsListView.OnScrollListener paramOnScrollListener
){
this.mOnScrollListener = paramOnScrollListener;
}
public void setShadow(int paramInt){
this.mShadow.setBackgroundResource(paramInt);
}
//启用一个动画来使HeaderView平滑的恢复到放大之前的状态。
class ScalingRunnalable implements Runnable{
long mDuration; //持续时间
boolean mIsFinished = true; //是否结束
float mScale; //测量规模
long mStartTime; //开始时间
ScalingRunnalable(){}
public void abortAnimation(){
this.mIsFinished = true;
}
public boolean isFinished(){
return this.mIsFinished;
}
@Override
public void run() {
float f2;
ViewGroup.LayoutParams locallayoutParams;
if ((!this.mIsFinished) && (this.mScale > 1.0D)){
float f1 = ((float) SystemClock.currentThreadTimeMillis() - (float) this.mStartTime)
/this.mDuration;
//每次执行run的时候mHeadContainer的高度改变了多少
//偏移量-超出的值（速度快慢）
f2 = this.mScale - (this.mScale - 1.0F)
* PullToZoomListView.sInterpolatar.getInterpolation(f1);
//设计控件的布局
locallayoutParams = PullToZoomListView.this.mHeaderContainer.getLayoutParams();
//当超过高度的时候，开始变形
if (f2 > 1.0F){
//设置图片的布局的 高度
locallayoutParams.height = PullToZoomListView.this.mHeadHeight;
locallayoutParams.height = (int)(f2* PullToZoomListView.this.mHeadHeight);
//设置变化
PullToZoomListView.this.mHeaderContainer.setLayoutParams(locallayoutParams);
PullToZoomListView.this.post(this);
return;
}
this.mIsFinished = true;
}
}
public void startAnimation(long paramLong){
this.mStartTime = SystemClock.currentThreadTimeMillis();
this.mDuration = paramLong;
//mLastScale是根据垂直偏移计算出来的
this.mScale = ((float) (PullToZoomListView.this.mHeaderContainer.getBottom())/PullToZoomListView.this.mHeadHeight);
this.mIsFinished = false;
//post调用ScalingRunnalable的run方法，而ScalingRunnalable run方法中再次调用了post，就这样不断的更新UI，直到达到一定的条件退出这个循环
PullToZoomListView.this.post(this);
}
}
}
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