我要评论前言
最近tv开发需要加载的图片很长，大小也很大，并且还不允许压缩。比如显示：世界地图、清明上河图、微博长图、海报、活动照片等。
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，那么就需要用到一个类：
bitmapregiondecoder
其次，既然屏幕显示不完，那么最起码要添加一个上下左右拖动的手势，让用户可以拖动查看。
实现方式有很多：
1.bitmapregiondecoder：
分片加载，使用系统bitmapregiondecoder去加载本地的图片，调用bitmapregiondecoder.decoderegion解析图片的矩形区域，返回bitmap，最终显示在imageview上。这种方案需要手动处理滑动、缩放手势，网络图片还要处理缓存策略等问题。实现方式比较繁琐也不是很推荐。
2.subsamplingscaleimageview
一款封装 bitmapregiondecoder的三方库，已经处理了滑动，缩放手势。我们可以考虑选择这个库来进行加载长图，但是官方上的demo示例加载的长图均为本地图片。这可能并不符合我们的网络场景需求，所以对于网络图片，我们还要考虑不同的加载框架，
3.glide+subsamplingscaleimageview混合加载渲染
对于图片加载框架，glide当然是首选，我们使用glide进行网络图片的下载和缓存管理，filetarget作为桥梁，subsamplingscaleimageview进行本地资源图片的分片加载，看起来很靠谱，那么一起来实现吧。
4.自定义longimageview，结合bitmapregiondecoder使用
本文采取的第四种方式，代码如下：
public class longimageview extends appcompatimageview {
private string tag = getclass().getsimplename();
private int mtargety = 0;
private int scrolldistance = 0;
private int imgwidth = 0, imgheight = 0;
private bitmap imgbitmap = null;
private bitmap holderbitmap;
private bitmapregiondecoder bitmapregiondecoder;
private boolean isscrolling = false;
private float starty = -1;
private int mstarttargety = -1;
private bitmapfactory.options scaleoptions = new bitmapfactory.options();
public bitmap bitmap;
public static final string event_prop_url = "url";
public static final string event_prop_bitmap_width = "resourcewidth";
public static final string event_prop_bitmap_height = "resourceheight";
public longimageview(context context) {
super(context);
init();
}
public longimageview(context context, @nullable attributeset attrs) {
super(context, attrs);
init();
}
public longimageview(context context, @nullable attributeset attrs, int defstyleattr) {
super(context, attrs, defstyleattr);
init();
}
private void init() {
//遥控器按键事件
setonkeylistener(new onkeylistener() {
@override
public boolean onkey(view v, int keycode, keyevent event) {
scrolldistance = scrolldistance <= 0 ? getheight() : scrolldistance;
if (event.getaction() == keyevent.action_down && !isscrolling) {
switch (event.getkeycode()) {
case keyevent.keycode_dpad_up:
scrollby(0 - viewheight2imageheight(scrolldistance));
break;
case keyevent.keycode_dpad_down:
scrollby(viewheight2imageheight(scrolldistance));
break;
}
}
return false;
}
});
//响应鼠标拖拽(手指也可以)
setontouchlistener(new ontouchlistener() {
@override
public boolean ontouch(view v, motionevent event) {
switch (event.getaction()) {
case motionevent.action_down:
log.e(tag, " touch down");
starty = event.getrawy();
mstarttargety = mtargety;
break;
case motionevent.action_move:
float currenty = event.getrawy();
mtargety = mstarttargety + (int) (viewheight2imageheight((int) (starty - currenty)) * 1f);
mtargety = math.max(0, math.min(mtargety, imgheight - viewheight2imageheight(getheight())));
log.e(tag, " touch move " + mtargety);
invalidate();
break;
case motionevent.action_up:
log.e(tag, " touch up");
starty = -1;
break;
}
return true;
}
});
}
private void startscroll(int targety) {
targety = math.max(0, math.min(targety, imgheight - viewheight2imageheight(getheight())));
valueanimator valueanimator = valueanimator.ofint(mtargety, targety);
valueanimator.addupdatelistener(new valueanimator.animatorupdatelistener() {
@override
public void onanimationupdate(valueanimator animation) {
mtargety = (int) animation.getanimatedvalue();
invalidate();
}
});
valueanimator.addlistener(new animator.animatorlistener() {
@override
public void onanimationstart(animator animation) {
isscrolling = true;
}
@override
public void onanimationend(animator animation) {
isscrolling = false;
}
@override
public void onanimationcancel(animator animation) {
isscrolling = false;
}
@override
public void onanimationrepeat(animator animation) {
}
});
valueanimator.setinterpolator(new linearinterpolator());
//设置滑动速度
valueanimator.setduration(10);
valueanimator.start();
}
/**
* 根据inputstream 生成 bitmapregiondecoder
*
* @param imgstream
*/
public void setimagestream(inputstream imgstream) {
try {
bitmapfactory.options options = new bitmapfactory.options();
options.injustdecodebounds = true;
bitmapfactory.decodestream(imgstream, new rect(0, 0, 0, 0), options);
imgwidth = options.outwidth;
imgheight = options.outheight;
//寻找最佳的缩放比例
int viewheight2imageheight = viewheight2imageheight(getheight());
//设置缩放比例
int scale = getscalevalue(imgwidth, viewheight2imageheight, 1);
scaleoptions.insamplesize = scale;
} catch (exception e) {
e.printstacktrace();
}
try {
bitmapregiondecoder = bitmapregiondecoder.newinstance(imgstream, false);
} catch (exception e) {
e.printstacktrace();
}
}
/**
* 根据图片文件 生成 bitmapregiondecoder
*
* @param imgfile
*/
public void setimagefile(file imgfile) {
try {
bitmapfactory.options options = new bitmapfactory.options();
options.injustdecodebounds = true;
bitmapfactory.decodefile(imgfile.getabsolutepath(), options);
imgwidth = options.outwidth;
imgheight = options.outheight;
//寻找最佳的缩放比例
int viewheight2imageheight = viewheight2imageheight(getheight());
int scale = getscalevalue(imgwidth, viewheight2imageheight, 1);
scaleoptions.insamplesize = scale;
} catch (exception e) {
e.printstacktrace();
}
try {
bitmapregiondecoder = bitmapregiondecoder.newinstance(imgfile.getabsolutepath(), false);
} catch (exception e) {
e.printstacktrace();
}
}
private int getscalevalue(int imgwidth, int imgheight, int scalevalue) {
long memory = runtime.getruntime().maxmemory() / 4;
if (memory > 0) {
if (imgwidth * imgheight * 4 > memory) {
scalevalue += 1;
return getscalevalue(imgwidth, imgheight, scalevalue);
}
}
return scalevalue;
}
/**
* 根据图片id 生成 bitmapregiondecoder
*
* @param resourceid
*/
@suppresslint("resourcetype")
public void setimageresource(int resourceid) {
inputstream imgstream = getresources().openrawresource(resourceid);
setimagestream(imgstream);
}
/**
* 设置占位图
*
* @param holderid
*/
public void setplaceholder(int holderid) {
holderbitmap = bitmapfactory.decoderesource(getresources(), holderid);
}
/**
* 滑动到具体的位置
*
* @param targety
*/
private void scrollto(int targety) {
startscroll(targety);
}
/**
* 设置相对于当前，继续滑动的距离。小于0 向上滑动，大于0向下滑动
*
* @param distance
*/
private void scrollby(int distance) {
startscroll(mtargety + distance);
}
/**
* 设置每次滑动的距离
*
* @param scrolldistance
*/
public void setscrolldistance(int scrolldistance) {
this.scrolldistance = scrolldistance;
}
@override
protected void ondraw(canvas canvas) {
log.e(getclass().getsimplename(), "draw start " + getwidth() + " " + getheight());
canvas.save();
int sr = canvas.savelayer(0, 0, getwidth(), getheight(), null, canvas.all_save_flag);
paint paint = new paint();
paint.setantialias(true);
if (bitmapregiondecoder != null) {
int targetheight = viewheight2imageheight(getheight());//根据控件的高度获取需要在原始图片上截取的高度
log.e(getclass().getsimplename(), "targetheight " + targetheight);
log.e(getclass().getsimplename(), "draw resource "
+ " " + imgwidth + " " + imgheight
+ " " + mtargety + " " + targetheight);
imgbitmap = null;
if (imgheight - mtargety >= targetheight) {//剩余区域大于 当前控件高度
imgbitmap = bitmapregiondecoder.decoderegion(new rect(0, mtargety, imgwidth, mtargety + targetheight)
, scaleoptions);
} else {//剩余区域小于 当前控件高度
imgbitmap = bitmapregiondecoder.decoderegion(new rect(0, imgheight - targetheight, imgwidth, imgheight)
, scaleoptions);
}
if (imgbitmap != null) {
//绘制需要展示的图片
canvas.drawbitmap(imgbitmap
, new rect(0, 0, imgbitmap.getwidth(), imgbitmap.getheight())
, new rect(0, 0, getwidth(), getheight())
, paint);
}
imgbitmap = null;
holderbitmap = null;
} else {
if (holderbitmap != null) {//绘制占位图
canvas.drawbitmap(holderbitmap
, new rect(0, 0, holderbitmap.getwidth(), holderbitmap.getheight())
, new rect(0, 0, getwidth(), getheight())
, paint);
}
}
canvas.restoretocount(sr);
canvas.restore();
log.e(getclass().getsimplename(), "draw end");
}
/**
* 图片高度转为相对于控件的高度
*
* @param imgheight
* @return
*/
private int imageheight2viewheight(int imgheight) {
if (this.imgheight <= 0) {
return 0;
}
return (int) (imgheight / ((float) getwidth() / imgwidth * imgheight) * getheight());
}
/**
* 控件高度转为相对于图片高度
*
* @param viewheight
* @return
*/
private int viewheight2imageheight(int viewheight) {
if (getheight() <= 0) {
return 0;
}
return (int) (viewheight / ((float) getwidth() / imgwidth * imgheight) * imgheight);
}
@override
protected void ondetachedfromwindow() {
super.ondetachedfromwindow();
//回收资源和释放内存
release();
}
public void release() {
if (imgbitmap != null && !imgbitmap.isrecycled()) {
imgbitmap.recycle();
imgbitmap = null;
}
if (holderbitmap != null && !holderbitmap.isrecycled()) {
holderbitmap.recycle();
holderbitmap = null;
}
system.gc();
}
}5.在mainactivity中的使用:
/**
* @auth: njb
* @date: 2022/11/7 0:11
* @desc:
*/
public class mainactivity extends appcompatactivity {
public string url = "https://qcloudimg-moss.cp47.ott.cibntv.net/data_center/files/2022/10/26/67a66d35-3f7c-4de8-9dfe-c706e42f44f2.jpg";
@override
protected void oncreate(@nullable bundle savedinstancestate) {
super.oncreate(savedinstancestate);
setcontentview(r.layout.activity_main);
initview();
}
private void initview() {
longimageview mimageview = findviewbyid(r.id.imageview);
mimageview.setscrolldistance((int) ((float) screenutils.getscreenheight(this) / 3 * 2));
mimageview.setfocusable(true);
try {
glide.with(this)
.load(url)
.downloadonly(new simpletarget<file>() {
@override
public void onresourceready(@nonnull file resource, @nullable transition<? super file> transition) {
mimageview.setimagefile(resource);
}
});
} catch (exception e) {
e.printstacktrace();
}
}
}6.布局文件代码：
<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.constraintlayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent"
xmlns:app="http://schemas.android.com/apk/res-auto">
<com.example.longimageview.view.longimageview
android:id="@+id/imageview"
android:layout_width="0dp"
android:layout_height="0dp"
android:focusable="true"
app:layout_constraintleft_toleftof="parent"
app:layout_constraintright_torightof="parent"
app:layout_constrainttop_totopof="parent"
app:layout_constraintbottom_tobottomof="parent"/>
</androidx.constraintlayout.widget.constraintlayout>7.实现的效果如下：
总结
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