今天我记录一下怎么通过自定义控件来实现图片的预览的功能 -- 根据慕课网上学习的内容所写的。
包含的内容主要有:
1.图片的多指放大。
2.图片的双击放大和缩小
3.图片的滑动。
4.与ViewPager的冲突解决办法
1.概述
图片的多指放大,主要用到一个类叫做ScaleGestureDetector,这个类用来一些多指的操作;图片的双击,主要用到一个类叫做GestureDetector,这个类用来处理双击的操作;图片的缩放用到了Matrix类来处理。
2.自定义ImageView,并且完美的加载一张图片
当我们在使用ImageView时,有时候要处理图片的大小很大或者很小的情况,这时候需要我们手动将图片放大或者缩小。在处理图片的放大和缩小,我们会使用一个类叫做Matrix,这个类来帮我处理图片的缩放和移动。
有一个问题,就是在处理图片的时候,一定在ImageView加载完了的时候,因为在加载完成之前,控件的大小,我们是不知道的,所以怎么知道ImageView加载完成呢?之后需要我们监听整个视图树,视图树一旦有更新,我们便知道ImageView加载完成了。
设置监听事件和取消监听事件分别在两个方法里面:onAttachedToWindow和onDetachedFromWindow。这两个方法分别表示该控件加载到窗口和该控件从窗口上移除时。
@Override
protected void onAttachedToWindow() {
super.onAttachedToWindow();
getViewTreeObserver().addOnGlobalLayoutListener(this);
}
@RequiresApi(api = Build.VERSION_CODES.JELLY_BEAN)
@Override
protected void onDetachedFromWindow() {
super.onDetachedFromWindow();
getViewTreeObserver().removeOnGlobalLayoutListener(this);
}
@Override
public void onGlobalLayout() {
if (!mOnce) {
//获得控件的宽和高
int width = getWidth();
int height = getHeight();
Log.i("main", "width = " + width + " height = " + height);
//获得图片的宽和高
Drawable d = getDrawable();
if (d == null) {
return;
}
int dh = d.getIntrinsicHeight();
int dw = d.getIntrinsicWidth();
Log.i("main", "dw = " + dw + " dh = " + dh);
float scale = 1;
if (dw > width && dh < height) {
scale = width * 1.0f / dw;
}
if (dw < width && dh > height) {
scale = height * 1.0f / dh;
}
if ((dh > height && dw > width) || (dh < height && dw < width)) {
scale = Math.min(height * 1.0f / dh, width * 1.0f / dw);
}
int dx = (int) (width / 2 - dw/ 2);
int dy = (int) (height / 2 - dh / 2);
mInitScale = scale;
mMaxScale = 4 * scale;
mMinScale = 0.7f * scale;
mMidScale = 2 * scale;
mMatrix.postTranslate(dx, dy);
mMatrix.postScale(scale, scale, width / 2, height / 2);
setImageMatrix(mMatrix);
RectF rectF = getRectF();
Log.i("main", "width = " + rectF.width() + " height = " + rectF.height());
mOnce = true;
}
}
3.多指放大和缩小
多指的操作用到了一个类--ScaleGestureDetector。我们得定义ScaleGestureDetector类型的变量,并且在构造方法里面初始化它。初始化的时候需要我们实现OnScaleGestureListener,并且实现三个方法
public boolean onScale(ScaleGestureDetector detector); // 多指缩放时调用
public boolean onScaleBegin(ScaleGestureDetector detector); //开始缩放时调用
public void onScaleEnd(ScaleGestureDetector detector); //缩放结束时调用
要想这三个方法接受到我们的手指事件,我们还必须在onTouch方法这样写:mScaleGestureDetector.onTouchEvent(event);将事件传到ScaleGestureDetector里面去。
@Override
public boolean onScale(ScaleGestureDetector detector) {
if (getDrawable() == null) {
return true;
}
float scaleFactor = detector.getScaleFactor();
mMatrix.postScale(scaleFactor, scaleFactor, detector.getFocusX(), detector.getFocusY());
setImageMatrix(mMatrix);
checkBorderAndCenterWhenScale();
return true;
}
@Override
public boolean onScaleBegin(ScaleGestureDetector detector) {
return true;
}
@Override
public void onScaleEnd(ScaleGestureDetector detector) {
float scale = getScale();
if (scale > mMaxScale) {
mMatrix.postScale(mMaxScale / scale, mMaxScale / scale, detector.getFocusX(), detector.getFocusY());
}
if (scale < mMinScale) {
mMatrix.postScale(mMinScale / scale, mMinScale / scale, detector.getFocusX(), detector.getFocusY());
}
setImageMatrix(mMatrix);
checkBorderAndCenterWhenScale();
}
private float getScale() {
float[] values = new float[9];
mMatrix.getValues(values);
return values[Matrix.MSCALE_X];
}
在我们根据手指聚集的焦点缩放,会发现图片会到处乱跑。这时候还需要加入一个边界限定的函数。
private void checkBorderAndCenterWhenScale() {
//获得控件的宽和高
int width = getWidth();
int height = getHeight();
//获得图片的宽和高
Drawable d = getDrawable();
if (d == null) {
return;
}
int dh = d.getIntrinsicHeight();
int dw = d.getIntrinsicWidth();
float dx = 0;
float dy = 0;
RectF rectF = getRectF();
//放大的调整
//左右
if (rectF.width() >= width) {
//图片向右偏移了,需要向左调整
if (rectF.left > 0) {
dx = -rectF.left;
}
//图片向左偏移了,需要向右调整了
if (rectF.right < width) {
dx = width - rectF.right;
}
}
if (rectF.height() >= height) {
//图片向下偏移了,需要向上调整
if (rectF.top > 0) {
dy = -rectF.top;
}
//图片向上偏移了,需要向下调整
if (rectF.bottom < height) {
dy = height - rectF.bottom;
}
}
//缩小的调整
//左右
if (rectF.width() <= width) {
/**
*
*dx = width / 2 - (rectF.left + rectF.right) / 2
*
*/
dx = width / 2 - (rectF.left + rectF.right) / 2;
}
if (rectF.height() <= height) {
/**
* dy = height / 2 - (rectF.top + rectF.bottom) / 2
*/
dy = height / 2 - (rectF.top + rectF.bottom) / 2;
}
mMatrix.postTranslate(dx, dy);
setImageMatrix(mMatrix);
}
4.双击放大和缩小
双击放大和缩小需要一个类:GestureDetector。这个类里面含有一些双击事件处理的方法。
我们在初始化GestureDetector变量的时候,需要我们传入一个OnGestureListener接口类型的参数,我们传入SimpleOnGestureListener就行,因为这个类对很多方法进行了空实现,不能我们去写很多的代码。
mGestureDetector = new GestureDetector(context, new GestureDetector.SimpleOnGestureListener(){
@Override
public boolean onDoubleTap(MotionEvent e) {
int x = (int) e.getX();
int y = (int) e.getY();
float scale = getScale();
AutoScaleRunnable autoScaleRunnable = null;
if(scale < mInitScale)
{
//mMatrix.postScale(mInitScale / scale, mInitScale / scale, x, y);
autoScaleRunnable = new AutoScaleRunnable(x, y, mInitScale);
}
if(scale >= mInitScale && scale < mMidScale)
{
//mMatrix.postScale(mMidScale / scale, mMidScale / scale ,x, y);
autoScaleRunnable = new AutoScaleRunnable(x, y, mMidScale);
}
if(scale >= mMidScale && scale < mMaxScale)
{
//mMatrix.postScale(mMaxScale / scale, mMaxScale / scale, x, y);
autoScaleRunnable = new AutoScaleRunnable(x, y, mMaxScale);
}
if(scale == mMaxScale)
{
// mMatrix.postScale(mInitScale / scale, mInitScale / scale, x, y);
autoScaleRunnable = new AutoScaleRunnable(x, y, mInitScale);
}
//setImageMatrix(mMatrix);
postDelayed(autoScaleRunnable, 16);
return true;
}
});
同时,我们还是在onTouch里面将事件传过来。
if(mGestureDetector.onTouchEvent(event))
{
return true;
}
双击放大或者缩小,我们会发现,放大和缩小都是瞬间完成,所以我们需要实现缓慢的完成,这个需要我们调用postDelayed方法。postDelayed需要我们传入一个Runnabl,所以我们得自定义一个Runnable。
rivate class AutoScaleRunnable implements Runnable
{
private int x = 0;
private int y = 0;
private float mTargetScale = 0;
private float mTempScale = 0;
private static final float BIGGER = 1.13f;
private static final float SMALLER = 0.87f;
public AutoScaleRunnable(int x, int y, float targetScale)
{
this.x = x;
this.y = y;
this.mTargetScale = targetScale;
float scale = getScale();
if(scale > targetScale)
{
mTempScale = SMALLER;
}
if(scale < targetScale)
{
mTempScale = BIGGER;
}
}
@Override
public void run() {
mMatrix.postScale(mTempScale, mTempScale, x, y);
setImageMatrix(mMatrix);
float currentScale = getScale();
if((mTempScale > 1.0f && currentScale < mTargetScale)||(mTempScale < 1.0f && currentScale > mTargetScale))
{
postDelayed(this, 16);
}
else
{
float scale = mTargetScale / getScale();
mMatrix.postScale(scale, scale, x, y);
setImageMatrix(mMatrix);
checkBorderAndCenterWhenScale();
}
}
}
5.图片的移动
float x = 0;
float y = 0;
int pointCount = event.getPointerCount();
for (int i = 0; i < pointCount; i++) {
x += event.getX(i);
y += event.getY(i);
}
//Log.i("main", "pointCount = " + pointCount);
x /= pointCount * 1.0f;
y /= pointCount * 1.0f;
if (pointCount != mLastPointCount) {
mIsCanDrag = false;
mLastX = x;
mLastY = y;
}
mLastPointCount = pointCount;
RectF rectF = getRectF();
Log.i("main", "rectFHeight = " + rectF.height() + " rectFWidth = " + rectF.width() + "\n width = " + getWidth() + " height = " + getHeight());
switch (event.getAction()) {
case MotionEvent.ACTION_DOWN: {
if(rectF.width() > getWidth() || rectF.height() > getHeight())
{
getParent().requestDisallowInterceptTouchEvent(true);
}
break;
}
case MotionEvent.ACTION_MOVE: {
if(rectF.width() > getWidth() || rectF.height() >getHeight())
{
getParent().requestDisallowInterceptTouchEvent(true);
}
mIsCheckTopAndBottom = mIsCheckLeftAndRight = true;
float dx = x - mLastX;
float dy = y - mLastY;
if (!mIsCanDrag) {
mIsCanDrag = isMoveAction(dx, dy);
}
if (mIsCanDrag) {
if (rectF.height() <= getHeight()) {
mIsCheckTopAndBottom = false;
dy = 0;
}
if (rectF.width() <= getWidth()) {
mIsCheckLeftAndRight = false;
dx = 0;
}
mMatrix.postTranslate(dx * 1.2f, dy * 1.2f);
setImageMatrix(mMatrix);
checkBorderWhenTranslate();
}
mLastX = x;
mLastY = y;
break;
}
case MotionEvent.ACTION_UP: {
mLastPointCount = 0;
break;
}
}
在移动的时候,也需要我们进行边界的限定
private void checkBorderWhenTranslate()
{
RectF rectF = getRectF();
int deltaX = 0;
int deltaY = 0;
int height = getHeight();
int width = getWidth();
if(rectF.left > 0 && mIsCheckLeftAndRight) {
deltaX = (int) -rectF.left;
}
if(rectF.right < width && mIsCheckLeftAndRight)
{
deltaX = (int) (width - rectF.right);
}
if(rectF.top > 0 && mIsCheckTopAndBottom)
{
deltaY = (int) - rectF.top;
}
if(rectF.bottom < height && mIsCheckTopAndBottom)
{
deltaY = (int) (height - rectF.bottom);
}
mMatrix.postTranslate(deltaX, deltaY);
setImageMatrix(mMatrix);
}
5.冲突事件的处理
当我们在移动图片的时候,我们会发现ViewPager会截获子View的事件。这时候我们只需要在我们想要不被截获的时候调用此方法就行:getParent().requestDisallowInterceptTouchEvent(true);
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