Android仿微博加载长图滚动查看效果

本文实例为大家分享了Android加载长图片的具体代码，供大家参考，具体内容如下

解决步骤

1.将图片缩放到与控件等宽
2.判断缩放后的图片高度，如果高度大于控件高度较多（这里设置的是1.5倍），认定为长图，可滑动查看图片
                     |-如果高度小于控件高度的1.5倍，以控件高度为基准，重新缩放图片

package org.wandcf_ces.fairproject.widgets; 

import android.annotation.TargetApi;
import android.content.Context;
import android.graphics.Bitmap;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Matrix;
import android.graphics.Paint;
import android.graphics.Rect;
import android.graphics.RectF;
import android.os.Build;
import android.support.annotation.Nullable;
import android.util.AttributeSet;
import android.view.MotionEvent;
import android.view.View; 

/**
 * Created by sunrui on 2017/3/8.
 * 加载长图片
 * 解决步骤
 * 1.将图片缩放到与控件等宽
 * 2.判断缩放后的图片高度，如果高度大于控件高度较多（这里设置的是1.5倍），认定为长图，可滑动查看图片
 *           |-如果高度小于控件高度的1.5倍，以控件高度为基准，重新缩放图片
 *
 */
public class LongImageView extends View { 

  private int width, height; 

  //需要绘制的Bitmap
  private Bitmap bitmap; 

  /**
   * 需要绘制的图片的区域
   */
  private Rect srcRect; 

  /**
   * 绘制的区域
   */
  private RectF dstRectF; 

  /**
   * 画笔
   */
  private Paint paint; 

  /**
   * 是否需要滑动
   */
  private boolean isNeedSlide; 

  /**
   * 已经滑动过的距离
   */
  private float slideLength; 

  /**
   * 绘制的Bitmap
   */
  private Bitmap drawBitmap; 

  {
    srcRect = new Rect();
    dstRectF = new RectF();
    paint = new Paint();
    paint.setAntiAlias(true);
    paint.setColor(Color.BLACK);
    paint.setStrokeWidth(1.0f);
  } 

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

  public LongImageView(Context context, @Nullable AttributeSet attrs) {
    super(context, attrs);
  } 

  public LongImageView(Context context, @Nullable AttributeSet attrs, int defStyleAttr) {
    super(context, attrs, defStyleAttr);
  } 

  @TargetApi(Build.VERSION_CODES.LOLLIPOP)
  public LongImageView(Context context, @Nullable AttributeSet attrs, int defStyleAttr, int defStyleRes) {
    super(context, attrs, defStyleAttr, defStyleRes);
  } 

  /**
   * 设置Bitmap
   *
   * @param bitmap
   *     需要绘制的Bitmap
   */
  public void setBitmap(Bitmap bitmap) {
    this.bitmap = bitmap;
  } 

  @Override
  protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
    int specSize = MeasureSpec.getSize(widthMeasureSpec);
    width = getPaddingLeft() + getPaddingRight() + specSize;
    specSize = MeasureSpec.getSize(heightMeasureSpec);
    height = getPaddingTop() + getPaddingBottom() + specSize;
    if (drawBitmap == null) {
      drawBitmap = resizeImage(bitmap, width);
      if (drawBitmap.getHeight() > 1.5 * height) {
        //需要滑动
        setNeedSlide(true);
      } else {
        //不需要滑动
        setNeedSlide(false);
        srcRect.left = 0;
        srcRect.top = 0;
        srcRect.right = drawBitmap.getWidth();
        srcRect.bottom = drawBitmap.getHeight();
        if (drawBitmap.getHeight() > height) {
          drawBitmap = resizeImageH(drawBitmap, height - 20);
        } else {
          float space = (height - drawBitmap.getHeight());
          dstRectF.left = 0;
          dstRectF.top = space;
          dstRectF.right = width;
          dstRectF.bottom = height - space;
        }
      }
    }
    setMeasuredDimension(width, height);
  } 

  @Override
  protected void onDraw(Canvas canvas) {
    canvas.drawBitmap(drawBitmap, (width - drawBitmap.getWidth()) / 2, slideLength, paint);
  } 

  /**
   * 设置是否需要滑动
   *
   * @param needSlide
   *     true or false
   */
  public void setNeedSlide(boolean needSlide) {
    isNeedSlide = needSlide;
  } 

  /**
   * 触摸操作的坐标
   */
  private float lastX;
  private float lastY; 

  @Override
  public boolean onTouchEvent(MotionEvent event) {
    if (!isNeedSlide) {
      return super.onTouchEvent(event);
    }
    int action = event.getAction();
    switch (action) {
      case MotionEvent.ACTION_DOWN:
        //按下
        lastX = event.getX();
        lastY = event.getY();
        break;
      case MotionEvent.ACTION_MOVE:
        float moveX = event.getX();
        if (moveX - lastX > 50) {
          //判断为左右滑动
          return super.onTouchEvent(event);
        }
        float moveY = event.getY();
        float distance = moveY - lastY;
        lastY = moveY;
        slideLength += distance;
        if (slideLength >= 0) {
          slideLength = 0;
        }
        if (slideLength <= (-1) * (drawBitmap.getHeight() - height)) {
          slideLength = (-1) * (drawBitmap.getHeight() - height);
        }
        postInvalidate();
        break;
      default:
        break;
    }
    return true;
  } 

  public Bitmap resizeImage(Bitmap bitmap, int w) {
    int width = bitmap.getWidth();
    int height = bitmap.getHeight();
    float scaleWidth = ((float) w) / width;
    Matrix matrix = new Matrix();
    matrix.postScale(scaleWidth, scaleWidth);
    return Bitmap.createBitmap(bitmap, 0, 0, width,
        height, matrix, true);
  } 

  public Bitmap resizeImageH(Bitmap bitmap, int h) {
    int width = bitmap.getWidth();
    int height = bitmap.getHeight();
    float scaleWidth = ((float) h) / height;
    Matrix matrix = new Matrix();
    matrix.postScale(scaleWidth, scaleWidth);
    return Bitmap.createBitmap(bitmap, 0, 0, width,
        height, matrix, true);
  } 

} 

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