Android自定义scrollView实现顶部图片下拉放大

本文实例为大家分享了scrollView实现顶部图片下拉放大的具体代码，供大家参考，具体内容如下

之前的scrollView顶部图片下拉放大在之后的项目用到了几次，但没次都写在Activity中很麻烦，也不方便复用。这几天有空，所以重新使用自定义scrollView的方法实现这个效果。原理和之前的基本是一致的，所以也不多说了，直接上代码。

package com.example.myapplication.dropzoom; 

import android.animation.ObjectAnimator;
import android.animation.ValueAnimator;
import android.content.Context;
import android.util.AttributeSet;
import android.view.MotionEvent;
import android.view.View;
import android.view.ViewGroup;
import android.widget.ScrollView; 

/**
 * Created by Liujinhua on 2016/3/25.
 * 下拉放大scrollView
 */
public class DropZoomScrollView extends ScrollView implements View.OnTouchListener { 

  // 记录首次按下位置
  private float mFirstPosition = 0;
  // 是否正在放大
  private Boolean mScaling = false; 

  private View dropZoomView;
  private int dropZoomViewWidth;
  private int dropZoomViewHeight; 

  public DropZoomScrollView(Context context) {
    super(context);
  } 

  public DropZoomScrollView(Context context, AttributeSet attrs) {
    super(context, attrs);
  } 

  public DropZoomScrollView(Context context, AttributeSet attrs, int defStyleAttr) {
    super(context, attrs, defStyleAttr);
  } 

  @Override
  protected void onFinishInflate() {
    super.onFinishInflate();
    init();
  } 

  @Override
  protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
    super.onMeasure(widthMeasureSpec, heightMeasureSpec); 

  } 

  private void init() {
    setOverScrollMode(OVER_SCROLL_NEVER);
    if (getChildAt(0) != null) {
      ViewGroup vg = (ViewGroup) getChildAt(0);
      if (vg.getChildAt(0) != null) {
        dropZoomView = vg.getChildAt(0);
        setOnTouchListener(this); 

      }
    }
  } 

  @Override
  public boolean onTouch(View v, MotionEvent event) {
    if (dropZoomViewWidth <= 0 || dropZoomViewHeight <= 0) {
      dropZoomViewWidth = dropZoomView.getMeasuredWidth();
      dropZoomViewHeight = dropZoomView.getMeasuredHeight();
    }
    switch (event.getAction()) {
      case MotionEvent.ACTION_UP:
        //手指离开后恢复图片
        mScaling = false;
        replyImage();
        break;
      case MotionEvent.ACTION_MOVE:
        if (!mScaling) {
          if (getScrollY() == 0) {
            mFirstPosition = event.getY();// 滚动到顶部时记录位置，否则正常返回
          } else {
            break;
          }
        }
        int distance = (int) ((event.getY() - mFirstPosition) * 0.6); // 滚动距离乘以一个系数
        if (distance < 0) { // 当前位置比记录位置要小，正常返回
          break;
        } 

        // 处理放大
        mScaling = true;
        setZoom(1 + distance);
        return true; // 返回true表示已经完成触摸事件，不再处理
    }
    return false;
  } 

  // 回弹动画 (使用了属性动画)
  public void replyImage() {
    final float distance = dropZoomView.getMeasuredWidth() - dropZoomViewWidth; 

    // 设置动画
    ValueAnimator anim = ObjectAnimator.ofFloat(0.0F, 1.0F).setDuration((long) (distance * 0.7)); 

    anim.addUpdateListener(new ValueAnimator.AnimatorUpdateListener() {
      @Override
      public void onAnimationUpdate(ValueAnimator animation) {
        float cVal = (Float) animation.getAnimatedValue();
        setZoom(distance - ((distance) * cVal));
      }
    });
    anim.start(); 

  } 

  //缩放
  public void setZoom(float s) {
    if (dropZoomViewHeight <= 0 || dropZoomViewWidth <= 0) {
      return;
    }
    ViewGroup.LayoutParams lp = dropZoomView.getLayoutParams();
    lp.width = (int) (dropZoomViewWidth + s);
    lp.height = (int) (dropZoomViewHeight * ((dropZoomViewWidth + s) / dropZoomViewWidth));
    dropZoomView.setLayoutParams(lp);
  }
} 

使用的时候也十分的简单

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
  android:layout_width="match_parent"
  android:layout_height="match_parent"
  android:orientation="vertical"> 

  <com.example.myapplication.dropzoom.DropZoomScrollView
    android:layout_width="match_parent"
    android:layout_height="match_parent"> 

    <LinearLayout
      android:layout_width="match_parent"
      android:layout_height="wrap_content"
      android:orientation="vertical"> 

      <ImageView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_gravity="center"
        android:src="@drawable/bg" /> 

      <ImageView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_gravity="center"
        android:src="@drawable/home_bg" /> 

      <ImageView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_gravity="center"
        android:src="@drawable/home_bg" /> 

      <ImageView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_gravity="center"
        android:src="@drawable/home_bg" /> 

      <ImageView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_gravity="center"
        android:src="@drawable/home_bg" />
    </LinearLayout>
  </com.example.myapplication.dropzoom.DropZoomScrollView>
</LinearLayout> 

以上就是本文的全部内容，希望对大家的学习有所帮助，也希望大家多多支持我们。