android Realizes Long Graph Loading Effect
- 2021-11-13 02:36:59
- OfStack
Long graph loading requires a key class BitmapRegionDecoder, bitmap memory reuse will be used for loading long pictures. For example, the size of view is 440*654, and the width and height of pictures are 440*12000. At this time, it is necessary to obtain the width and height of pictures, compare them with the width and height of view, and obtain a reduction ratio, then you will get a width ratio and a height ratio. Use a large ratio as a scaling factor, and then slide the long pictures with gestures
import android.content.Context;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.graphics.BitmapRegionDecoder;
import android.graphics.Canvas;
import android.graphics.Matrix;
import android.graphics.Rect;
import android.support.annotation.Nullable;
import android.util.AttributeSet;
import android.util.Log;
import android.view.GestureDetector;
import android.view.MotionEvent;
import android.view.View;
import android.widget.Scroller;
import java.io.IOException;
import java.io.InputStream;
public class BigView extends View implements GestureDetector.OnGestureListener, View.OnTouchListener {
private static final String TAG = "BigView";
private Scroller mScroller;
private GestureDetector mGestureDetector;
private BitmapFactory.Options mOptions;
private Rect mRect;
private int mImageWidth;
private int mImageHeight;
private BitmapRegionDecoder mDecoder;
private int mViewWidth;
private int mViewHeight;
private float mScale;
private Bitmap bitmap;
public BigView(Context context) {
this(context, null, 0);
}
public BigView(Context context, @Nullable AttributeSet attrs) {
this(context, attrs, 0);
}
public BigView(Context context, @Nullable AttributeSet attrs, int defStyleAttr) {
super(context, attrs, defStyleAttr);
//指定要加载的矩形区域
mRect = new Rect();
//解码图片的配置
mOptions = new BitmapFactory.Options();
//手势
mGestureDetector = new GestureDetector(context, this);
setOnTouchListener(this);
// 滑动帮助
mScroller = new Scroller(context);
}
/**
* 由使用者输入1张图片 输入流
*
* @param is
*/
public void setImage(InputStream is) {
//先读取原图片的 宽、高
mOptions.inJustDecodeBounds = true;
BitmapFactory.decodeStream(is, null, mOptions);
mImageWidth = mOptions.outWidth;
mImageHeight = mOptions.outHeight;
//复用 内存复用
mOptions.inMutable = true;
//设置像素格式为 rgb565
mOptions.inPreferredConfig = Bitmap.Config.RGB_565;
mOptions.inJustDecodeBounds = false;
//创建区域解码器 用于区域解码图片
try {
mDecoder = BitmapRegionDecoder.newInstance(is, false);
} catch (IOException e) {
e.printStackTrace();
}
requestLayout();
}
/**
* 测量 view的大小
*
* @param widthMeasureSpec
* @param heightMeasureSpec
*/
@Override
protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
super.onMeasure(widthMeasureSpec, heightMeasureSpec);
//获得测量的view的大小
mViewWidth = getMeasuredWidth();
mViewHeight = getMeasuredHeight();
//如果解码器是null 表示没有设置过要现实的图片
if (null == mDecoder) {
return;
}
//确定要加载的图片的区域
mRect.left = 0;
mRect.top = 0;
mRect.right = mImageWidth;
// Log.e(TAG,"缩放因子="+(mViewWidth*1.0f/mImageWidth*1.0f));
// Log.e(TAG,"缩放因子="+(mViewHeight*1.0f/mImageHeight*1.0f));
//获得缩放因子
mScale = mViewWidth / (float) mImageWidth;
// 需要加载的高 * 缩放因子 = 视图view的高
// x * mScale = mViewHeight
mRect.bottom = (int) (mViewHeight / mScale);
Log.e(TAG,"l="+mRect.left);
Log.e(TAG,"t="+mRect.top);
Log.e(TAG,"r="+mRect.right);
Log.e(TAG,"b="+mRect.bottom);
}
/**
* 把图片画上去
*
* @param canvas
*/
@Override
protected void onDraw(Canvas canvas) {
super.onDraw(canvas);
// 如果解码器是null 表示没有设置过要现实的图片
if (null == mDecoder) {
return;
}
//复用上1张bitmap
Log.e(TAG,"复用上1张bitmap="+bitmap);
mOptions.inBitmap = bitmap;
//解码指定区域
bitmap = mDecoder.decodeRegion(mRect, mOptions);
//使用矩阵 对图片进行 缩放
Matrix matrix = new Matrix();
matrix.setScale(mScale, mScale);
//画出来
canvas.drawBitmap(bitmap, matrix, null);
}
/**
* 手指按下屏幕的回调
* @param e
* @return
*/
@Override
public boolean onDown(MotionEvent e) {
//如果滑动还没有停止 强制停止
if (!mScroller.isFinished()){
mScroller.forceFinished(true);
}
//继续接收后续事件
return true;
}
@Override
public void onShowPress(MotionEvent e) {
}
@Override
public boolean onSingleTapUp(MotionEvent e) {
return false;
}
@Override
public void onLongPress(MotionEvent e) {
}
/**
* 手指 不离开屏幕 拖动
* @param e1 手指按下去 的事件 -- 获取开始的坐标
* @param e2 当前手势事件 -- 获取当前的坐标
* @param distanceX x轴 方向移动的距离
* @param distanceY y方向移动的距离
* @return
*/
@Override
public boolean onScroll(MotionEvent e1, MotionEvent e2, float distanceX, float distanceY) {
// 手指从下往上 图片也要往上 distanceY是负数, top 和 bottom 在减
// 手指从上往下 图片也要往下 distanceY是正数, top 和 bottom 在加
//改变加载图片的区域
mRect.offset(0, (int) distanceY);
//bottom大于图片高了， 或者 top小于0了
if (mRect.bottom > mImageHeight){
mRect.bottom = mImageHeight;
mRect.top = mImageHeight-(int) (mViewHeight / mScale);
}
if (mRect.top < 0){
mRect.top = 0;
mRect.bottom = (int) (mViewHeight / mScale);
}
//重绘
invalidate();
return false;
}
/**
* 手指离开屏幕 滑动 惯性
* @param e1
* @param e2
* @param velocityX 速度 每秒x方向 移动的像素
* @param velocityY y
* @return
*/
@Override
public boolean onFling(MotionEvent e1, MotionEvent e2, float velocityX, float velocityY) {
/**
* startX: 滑动开始的x坐标
* startY: 滑动开始的y坐标
* 两个速度
* minX: x方向的最小值
* max 最大
* y
*/
//计算器
mScroller.fling(0,mRect.top,
0,(int)-velocityY,
0,0,0,
mImageHeight - (int) (mViewHeight / mScale));
return false;
}
//获取计算结果并且重绘
@Override
public void computeScroll() {
//已经计算结束 return
if (mScroller.isFinished()){
return;
}
//true 表示当前动画未结束
if (mScroller.computeScrollOffset()){
//
mRect.top = mScroller.getCurrY();
mRect.bottom = mRect.top+ (int) (mViewHeight / mScale);
invalidate();
}
}
@Override
public boolean onTouch(View v, MotionEvent event) {
//交由手势处理
return mGestureDetector.onTouchEvent(event);
}
}
If it is the key 2 points of interview, the first one should say this class, and the second one should know that memory reuse is used.