前两天在面试当中被问到有没有做过加载高清大图，当时确实没有做过，听面试官提到可以动态加载图片的显示区域。回来后在网上找到了一篇鸿洋大神的博文悔啊-_-!为什么早点没有看到。废话不多说代码如下：
一、BitmapRegionDecoder
BitmapRegionDecoder主要用于显示图片的某一块矩形区域，所以可以利用它来完成大图片的动态区域显示。
- 简单用法：
- BitmapRegionDecoder提供了一系列的newInstance方法来构造对象，支持传入文件路径，文件描述符，文件的inputstrem等。
例如：
- BitmapRegionDecoder提供了一系列的newInstance方法来构造对象，支持传入文件路径，文件描述符，文件的inputstrem等。
BitmapRegionDecoder bitmapRegionDecoder = BitmapRegionDecoder
.newInstance(is, false);
- BitmapRegionDecoder.decodeRegion()方法，通过传入矩形区域即可显示图片的指定区域。
Bitmap bitmap = bitmapRegionDecoder.decodeRegion(rect, options);
参数一为矩形区域，参数二为BitmapFactory.Options。
- 一个简单的使用例子：
// load Assets image
try {
InputStream is = getAssets().open("qm.jpg");
BitmapFactory.Options tmpOptions = new BitmapFactory.Options();
tmpOptions.inJustDecodeBounds = true;
BitmapFactory.decodeStream(is, null, tmpOptions);
int width = tmpOptions.outWidth;
int height = tmpOptions.outHeight;
// 设置显示图片的中心区域
BitmapRegionDecoder bitmapRegionDecoder = BitmapRegionDecoder
.newInstance(is, false);
BitmapFactory.Options options = new BitmapFactory.Options();
options.inJustDecodeBounds = true;
// JPG图片没有Aphla通道使用该颜色模式更加节省内存
options.inPreferredConfig = Bitmap.Config.RGB_565;
// 设置显示区域的矩形大小
Rect rect = new Rect(
width / 2 - 100, height / 2 - 100,
width / 2 + 100, height / 2 + 100);
// 通过BitmapRegionDecoder来解析显示区域的图像
Bitmap bitmap = bitmapRegionDecoder.decodeRegion(rect, options);
mShow.setImageBitmap(bitmap);
} catch (IOException e) {
e.printStackTrace();
}
一个简单的使用例子，整体自定义View的设计思想，即是通过滑动时获得的坐标不断设置矩形区域的偏移坐标，然后不断绘制View来完成动态显示大图的效果。具体代码大家可以自行参考鸿洋大神的博客，我这里将我注释的代码分享给大家。
二、LargeImageView
- 首先手势检测的两个类：BaseGestureDetector、MoveGestureDetector。
public abstract class BaseGestureDetector {
protected boolean mGestureInProgress;
protected MotionEvent mPreMotionEvent;
protected MotionEvent mCurrentMotionEvent;
protected Context mContext;
public BaseGestureDetector(Context context) {
mContext = context;
}
public boolean onTouchEvent(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;
}
}
这里有一个关于抽象类的构造方法需要提一下，具体说明大家可以自行移至这里,结论即是抽象类的子类在创建对象时，也会跟非抽象类的子类一样，都会默认调用父类的无参构造方法。
public class MoveGestureDetector extends BaseGestureDetector {
private PointF mCurrentPointer;
private PointF mPrePointer;
//仅仅为了减少创建内存
private PointF mDeltaPointer = new PointF();
//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);
// Log.e("TAG", mPrePointer.toString() + " , " + mCurrentPointer);
boolean mSkipThisMoveEvent = prev.getPointerCount() != event.getPointerCount();
// Log.e("TAG", "mSkipThisMoveEvent = " + mSkipThisMoveEvent);
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 < count; i++)
{
x += event.getX(i);
y += event.getY(i);
}
x /= count;
y /= count;
return new PointF(x, y);
}
public float getMoveX()
{
return mExtenalPointer.x;
}
public float getMoveY()
{
return mExtenalPointer.y;
}
public interface OnMoveGestureListener
{
public boolean onMoveBegin(MoveGestureDetector detector);
public boolean onMove(MoveGestureDetector detector);
public void onMoveEnd(MoveGestureDetector detector);
}
public static class SimpleMoveGestureDetector implements OnMoveGestureListener
{
@Override
public boolean onMoveBegin(MoveGestureDetector detector)
{
return true;
}
@Override
public boolean onMove(MoveGestureDetector detector)
{
return false;
}
@Override
public void onMoveEnd(MoveGestureDetector detector)
{
}
}
}
关于这两个检测手势移动的类我还没有研究，各位同学可以自行研究。
- 最后自定义View的代码如下：
public class LargeImageView extends View {
private BitmapRegionDecoder mDecoder;
/**
* 图片的宽高
*/
private int mImageWidth,mImageHeight;
/**
* 矩形显示的区域（volatile修饰的对象线程安全）
*/
private volatile Rect mRect = new Rect();
/**
* 手势检测
*/
private MoveGestureDetector mDetector;
private static final BitmapFactory.Options options =
new BitmapFactory.Options();
static {
options.inPreferredConfig = Bitmap.Config.RGB_565;
}
public LargeImageView(Context context, AttributeSet attrs) {
super(context, attrs);
init();
}
public void setInputStream(InputStream is) {
try {
mDecoder = BitmapRegionDecoder.newInstance(is, false);
BitmapFactory.Options tmpOptions = new BitmapFactory.Options();
tmpOptions.inJustDecodeBounds = true;
BitmapFactory.decodeStream(is, null, tmpOptions);
mImageWidth = tmpOptions.outWidth;
mImageHeight = tmpOptions.outHeight;
// Log.d("xns", "width:" + mImageWidth + " ,height:" + mImageHeight);
// 重新布局View
requestLayout();
invalidate();
} catch (IOException e) {
e.printStackTrace();
} finally {
try {
if (is != null) {
is.close();
}
} catch (IOException e) {
e.printStackTrace();
}
}
}
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();
// 只要图片在X或Y方向上大于View的宽高才进行矩形区域的偏移
if (mImageWidth > getWidth()) {
mRect.offset(-moveX, 0);
checkWidth();
// 偏移后重新绘制显示图片
invalidate();
}
if (mImageHeight > getHeight())
{
mRect.offset(0, -moveY);
checkHeight();
invalidate();
}
return true;
}
});
}
private void checkHeight() {
Rect rect = mRect;
int imageHeight = mImageHeight;
if (rect.bottom > imageHeight)
{
rect.bottom = imageHeight;
rect.top = imageHeight - getHeight();
}
if (rect.top < 0)
{
rect.top = 0;
rect.bottom = getHeight();
}
}
private void checkWidth() {
Rect rect = mRect;
int imageWidth = mImageWidth;
if (rect.right > imageWidth) {
rect.right = imageWidth;
rect.left = imageWidth - getWidth();
}
if (rect.left < 0) {
rect.left = 0;
rect.right = getWidth();
}
}
@Override
public boolean onTouchEvent(MotionEvent event) {
//Log.d("xns", "x:" + event.getX() + " ,y:" + event.getY());
mDetector.onTouchEvent(event);
return true;
}
@Override
protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
super.onMeasure(widthMeasureSpec, heightMeasureSpec);
int width = getMeasuredWidth();
int height = getMeasuredHeight();
int imageWidth = mImageWidth;
int imageHeight = mImageHeight;
// 默认显示图片中心区域
mRect.left = imageWidth / 2 - width / 2;
mRect.top = imageHeight / 2 - height / 2;
mRect.right = mRect.left + width;
mRect.bottom = mRect.top + height;
}
@Override
protected void onDraw(Canvas canvas) {
Bitmap bitmap = mDecoder.decodeRegion(mRect, options);
canvas.drawBitmap(bitmap, 0, 0, null);
}
}
- 使用代码如下：
public class MainActivity extends AppCompatActivity {
private static final String TAG = "MainActivity";
private LargeImageView mLIv;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
mLIv = (LargeImageView) findViewById(R.id.iv_large);
// load Assets image
try {
InputStream is = getAssets().open("qm.jpg");
// 调用自定义大图加载View
mLIv.setInputStream(is);
} catch (IOException e) {
e.printStackTrace();
}
}
}
写在最后
最近找工作找的很烦躁，最后写给自己的寄语，以此激励自己一下，静心思考，勇往直前。
