Android仿微博加载长图滚动查看效果

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); 
  } 
 
}