QQ space stretchable head

Source code introduction: Imitating QQ space with stretchable header, classic and easy to use, worth a try.

Source code effect:

Source code snippet:

 package com.example.tz_demo_6_27; 
  
 import android.content.Context;
 import android.util.AttributeSet;
 import android.view.MotionEvent;
 import android.view.View;
 import android.view.animation.Animation;
 import android.view.animation.Transformation;
 import android.widget.ImageView;
 import android.widget.ImageView.ScaleType;
 import android.widget.ListView; 
  
 public   class ParallaxListView extends ListView { 
  
 private ImageView mImageView;
 // Initial height  
 private   int mImageViewHeight = - 1 ;
 //***Stretch height  
 private   int mDrawableMaxHeight = - 1 ; 
  
 public ParallaxListView(Context context, AttributeSet attrs) {
 super (context, attrs); 
  
 } 
  
 /**
 * Set the stretched image
 *
 * @param imageView
 */  
 public   void setParallaxImageView(ImageView imageView) {
 this .mImageView = imageView;
 // Set the telescopic type -- center fill  
 this .mImageView.setScaleType(ScaleType.CENTER_CROP);
 } 
  
 /**
 * Initialize the initial height of the loaded image
 *
 */  
 public   void setViewBounds() {
 if (mImageViewHeight == - 1 ) {
            mImageViewHeight = mImageView.getHeight();
 if (mImageViewHeight < 0 ) {
                mImageViewHeight = getContext().getResources()
                        .getDimensionPixelSize(R.dimen.size_default);
 }
 } 
  
 } 
  
 /**
 * Callback when sliding too far
 */  
 @Override  
 protected   boolean overScrollBy( int deltaX, int deltaY, int scrollX,
 int scrollY, int scrollRangeX, int scrollRangeY,
 int maxOverScrollX, int maxOverScrollY, boolean isTouchEvent) {
 // Control the height of ImageView to continue to increase  
 boolean isCollapse = resizeOverScrollBy(deltaY); 
  
 // return true: When you pull down to a certain place on the border, you will no longer pull down  
 return isCollapse ? true : super .overScrollBy(deltaX, deltaY, scrollX,
                scrollY, scrollRangeX, scrollRangeY, maxOverScrollX,
                maxOverScrollY, isTouchEvent);
 } 
  
 /**
 * Listen for ListView sliding
 */  
 @Override  
 protected   void onScrollChanged( int l, int t, int oldl, int oldt) {
 super .onScrollChanged(l, t, oldl, oldt);
 // Get the parent control of ImageView  
        View header = (View) mImageView.getParent();
 if (header.getTop() < 0 && mImageView.getHeight() > mImageViewHeight) {
 // Reduce the height of ImageView -- cannot exceed the original height of the image  
            mImageView.getLayoutParams().height = Math.max(
                    mImageView.getHeight() + header.getTop(), mImageViewHeight);
 // The height of the container where the ImageView is located also needs to change: getTop--->0  
            header.layout(header.getLeft(), 0 , header.getRight(),
                    header.getHeight());
            mImageView.requestLayout();
 } 
  
 } 
      
  
 private   boolean resizeOverScrollBy( int deltaY) {
 // During the pull-down process, constantly control the height of ImageView  
 /**
 * deltaY: is the distance slid per millisecond when exceeding the sliding limit -- Increment (- for pull-down transition, + for pull-up transition) Size: Determined by the user's sliding speed General sliding speed
 * -50~50
 */  
 if (deltaY < 0 ) {
 // Pull down transition, continuously increase the height of ImageView, deltay is a negative number, increasing the height is subtracting  
            mImageView.getLayoutParams().height = mImageView.getHeight()
 - deltaY;
 // View re-adjusts width and height  
            mImageView.requestLayout(); // onMeasure-->onLayout  
 } else {
 // Pull up transition, continuously reduce the height of ImageView, deltay is a positive number, reduce the height or subtract  
 if (mImageView.getHeight()>mImageViewHeight) {
                mImageView.getLayoutParams().height = Math.max(
                        mImageView.getHeight() - deltaY, mImageViewHeight);
 // View re-adjusts width and height  
                mImageView.requestLayout(); // onMeasure-->onLayout  
 } 
              
 } 
  
 return   false ;
 } 
      
 /**
 * Listen for touch -- release your hand
 */  
 @Override  
 public   boolean onTouchEvent(MotionEvent ev) {
 // judge  
 if (ev.getAction()== MotionEvent.ACTION_UP) {
 // Start the rebound animation  
            ResetAnimation animation= new ResetAnimation(mImageView,mImageViewHeight);
            animation.setDuration( 300 );
            mImageView.startAnimation(animation);
 } 
          
 return   super .onTouchEvent(ev);
 } 
      
 public   class ResetAnimation extends Animation{ 
          
          
          
 private ImageView mView; 
          
 private   int targetHeight;
 // Height before animation execution  
 private   int originalHeight;
 // Height difference  
 private   int extraHeight; 
  
 public ResetAnimation(ImageView mImageView, int targetHeight) {
 this .mView=mImageView;
 this .targetHeight=targetHeight;
 this .originalHeight=mImageView.getHeight();
            extraHeight=originalHeight-targetHeight;
 } 
          
 /**
 * This method will be called back when the animation is continuously executed
 * interpolatedTime: range is 0
         * 0ms-------------->300ms
 * Current image height ---> height before animation execution - height difference * interpolatedTime
         * extraHeight------>0
 */  
 @Override  
 protected   void applyTransformation( float interpolatedTime,
                Transformation t) { 
              
            mView.getLayoutParams().height=( int ) (originalHeight-extraHeight*interpolatedTime);
            mView.requestLayout();
 super .applyTransformation(interpolatedTime, t);
 }
 } 
  
 }

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