上一节(
自定义初学5——自定义View显示图片
)
已经说了如何自定义View显示图片。做android时,加载图片是避免不了的,加载网络图片还需要异步加载,最烦人的就服务器托管网是经常出现OOM,为了避免这样的问题,我们一般这样解决:
- 根据图片控件的大小对图片进行压缩显示。
- 如果图片数量非常多,则会使用LruCache等缓存机制,将所有图片占据的内容维持在一个范围内。
有时加载图片还会遇到特殊情况——就是单个图片非常巨大,还不允许压缩。那么对于这种需求,该如何做呢?
首先不压缩,按照原图尺寸加载,那么屏幕肯定是不够大的,并且考虑到内存的情况,不可能一次性整图加载到内存中,所以肯定是局部加载,而有一个类很好的完成了这个功能,这就是BitmapRegionDecoder
先看下官方的API
写个简单的例子:
public class MainActivity extends Activity {
private ImageView mImageView;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
mImageView = (ImageView) findViewById(R.id.imageView1);
try {
InputStream inputStream = getAssets().open("dog.jpg");
// 获得图片的宽、高
BitmapFactory.Options tmpOptions = new BitmapFactory.Options();
// tmpOptions.inJustDecodeBounds = true;// 如果设置为true,解码器将返回null
// 设置显示图片的中心区域
BitmapRegionDecoder bitmapRegionDecoder = BitmapRegionDecoder
.newInstance(inputStream, false);
BitmapFactory.Options options = new BitmapFactory.Options();
options.inPreferredConfig = Bitmap.Config.ARGB_8888;
//用给定的Rect和options创建位图
Bitmap bitmap = bitmapRegionDecoder.decodeRegion(new Rect(0, 0,
600, 600), options);
mImageView.setImageBitmap(bitmap);
} catch (IOException e) {
e.printStackTrace();
}
}
}
效果如下:
很明显,BitmapRegionDecoder的功能就是加载图片的部分区域,现在大概原理就清楚了,我们需要定义一个View,然后利用去BitmapRegionDecoder显示一个图片的局部,然后利用手势检测,能够移动图片,好了,开始实现吧。梳理一下我们的View:
- 提供一个设置图片的入口
- 重写onTouchEvent,在里面根据用户移动的手势,去更新显示区域的参数
- 每次更新区域参数后,调用invalidate,onDraw里面去regionDecoder.decodeRegion拿到bitmap,去draw
自定义LargeImageView
public class LargeImageView extends View {
private BitmapRegionDecoder mDecoder;
/**
* 图片的宽度和高度
*/
private int mImageWidth, mImageHeight;
/**
* 绘制的区域
*/
private volatile Rect mRect = new Rect();
private MoveGestureDetector mDetector;
private static final BitmapFactory.Options options = new BitmapFactory.Options();
static {
options.inPreferredConfig = Bitmap.Config.ARGB_8888;
}
public void setInputStream(InputStream is) {
try {
mDecoder = BitmapRegionDecoder.newInstance(is, false);
BitmapFactory.Options tmpOptions = new BitmapFactory.Options();
// 获取图片的宽高
tmpOptions.inJustDecodeBounds = true;
BitmapFactory.decodeStream(is, null, tmpOptions);
mImageWidth = tmpOptions.outWidth;
mImageHeight = tmpOptions.outHeight;
requestLayout();
invalidate();
} catch (IOException e) {
e.printStackTrace();
} finally {
try {
if (is != null)
is.close();
} catch (Exception e) {
}
}
}
public void init() {
mDetector = new MoveGestureDetector(getContext(),
new MoveGestureDetector.SimpleMoveGestureDetector() {
@Override
public boolean onMove(MoveGestureDetector detector) {
int moveX = (int) detector.getMoveX();
int moveY = (int) detector.getMoveY();
if (mImageWidth > getWidth()) {
mRect.offset(-moveX, 0);
checkWidth();
invalidate();
}
if (mImageHeight > getHeight()) {
mRect.offset(0, -moveY);
checkHeight();
invalidate();
}
return true;
}
});
}
private void checkWidth() {
Rect rect = mRect;
int imageWidth = mImageWidth;
if (rect.right > imageWidth) {
rect.right = imageWidth;
rect.left = imageWidth - getWidth();
}
if (rect.left imageHeight) {
rect.bottom = imageHeight;
rect.top = imageHeight - getHeight();
}
if (rect.top
手势检测抽象类BaseGestureDetector
public abstract class BaseGestureDetector {
protected boolean mGestureInProgress;
pro服务器托管网tected MotionEvent mPreMotionEvent;
protected MotionEvent mCurrentMotionEvent;
protected Context mContext;
public BaseGestureDetector(Context context)
{
mContext = context;
}
public boolean onToucEvent(MotionEvent event)
{
if (!mGestureInProgress)
{
handleStartProgressEvent(event);
} else
{
handleInProgressEvent(event);
}
return true;
}
protected abstract void handleInProgressEvent(MotionEvent event);
protected abstract void handleStartProgressEvent(MotionEvent event);
protected abstract void updateStateByEvent(MotionEvent event);
protected void resetState()
{
if (mPreMotionEvent != null)
{
mPreMotionEvent.recycle();
mPreMotionEvent = null;
}
if (mCurrentMotionEvent != null)
{
mCurrentMotionEvent.recycle();
mCurrentMotionEvent = null;
}
mGestureInProgress = false;
}
}
手势检测实现类
public class MoveGestureDetector extends BaseGestureDetector {
private PointF mCurrentPointer;
private PointF mPrePointer;
// 用于记录最终结果,并返回
private PointF mExtenalPointer = new PointF();
private OnMoveGestureListener mListenter;
public MoveGestureDetector(Context context, OnMoveGestureListener listener) {
super(context);
mListenter = listener;
}
@Override
protected void handleInProgressEvent(MotionEvent event) {
int actionCode = event.getAction() & MotionEvent.ACTION_MASK;
switch (actionCode) {
case MotionEvent.ACTION_CANCEL:
case MotionEvent.ACTION_UP:
mListenter.onMoveEnd(this);
resetState();
break;
case MotionEvent.ACTION_MOVE:
updateStateByEvent(event);
boolean update = mListenter.onMove(this);
if (update) {
mPreMotionEvent.recycle();
mPreMotionEvent = MotionEvent.obtain(event);
}
break;
}
}
@Override
protected void handleStartProgressEvent(MotionEvent event) {
int actionCode = event.getAction() & MotionEvent.ACTION_MASK;
switch (actionCode) {
case MotionEvent.ACTION_DOWN:
resetState();// 防止没有接收到CANCEL or UP ,保险起见
mPreMotionEvent = MotionEvent.obtain(event);
updateStateByEvent(event);
break;
case MotionEvent.ACTION_MOVE:
mGestureInProgress = mListenter.onMoveBegin(this);
break;
}
}
protected void updateStateByEvent(MotionEvent event) {
final MotionEvent prev = mPreMotionEvent;
mPrePointer = caculateFocalPointer(prev);
mCurrentPointer = caculateFocalPointer(event);
boolean mSkipThisMoveEvent = prev.getPointerCount() != event
.getPointerCount();
mExtenalPointer.x = mSkipThisMoveEvent ? 0 : mCurrentPointer.x
- mPrePointer.x;
mExtenalPointer.y = mSkipThisMoveEvent ? 0 : mCurrentPointer.y
- mPrePointer.y;
}
/**
* 根据event计算多指中心点
*
* @param event
* @return
*/
private PointF caculateFocalPointer(MotionEvent event) {
final int count = event.getPointerCount();
float x = 0, y = 0;
for (int i = 0; i
用法不说了,看效果吧:
这只是简单的实现,我们当然还可以实现更多的功能了,我就抛砖引玉吧
源代码 参考:
http://www.itstrike.cn/Question/904dfdaa-5cec-4d3c-bbc3-a7cc2e6172d8.html
服务器托管,北京服务器托管,服务器租用 http://www.fwqtg.net
机房租用,北京机房租用,IDC机房托管, http://www.fwqtg.net
相关推荐: #yyds干货盘点# LeetCode程序员面试金典:困雨水(二)
1.简述: 给你一个的矩阵,其中的值均服务器托管网为非负整数,代表二维高度图每个单元的高度,请计算图中形状最多能接多少体积的雨水。m x n 示例 1: 输入: heightMap = [[1,4,3,1,3,2],[3,2,1,3,2,4],[2,3,3,2…