Android ImageView设置图片原理（上）
2014-04-16 10:15
615 查看
本文来自http://blog.csdn.net/liuxian13183/ ，引用必须注明出处！
首先关于图片加载到ImageView上，我们来讨论几个问题：
如下：
imageView.setImageResource(resId);获得图片资源运行在主线程
[html] view
plaincopyprint?
This does Bitmap reading and decoding on the UI
* thread, which can cause a latency hiccup. If that's a concern,
* consider using {@link #setImageDrawable(android.graphics.drawable.Drawable)} or
* {@link #setImageBitmap(android.graphics.Bitmap)} and
* {@link android.graphics.BitmapFactory} instead.</p>
*
* @param resId the resource identifier of the the drawable
*
* @attr ref android.R.styleable#ImageView_src
*/
@android.view.RemotableViewMethod
public void setImageResource(int resId) {
if (mUri != null || mResource != resId) {
updateDrawable(null);
mResource = resId;
mUri = null;
resolveUri();
requestLayout();
invalidate();
}
}
[html] view
plaincopyprint?
private void resolveUri() {
if (mDrawable != null) {
return;
}
Resources rsrc = getResources();
if (rsrc == null) {
return;
}
Drawable d = null;
if (mResource != 0) {
try {
d = rsrc.getDrawable(mResource);
} catch (Exception e) {
Log.w("ImageView", "Unable to find resource: " + mResource, e);
// Don't try again.
mUri = null;
}
} else if (mUri != null) {
从源码上看，mResource不为空，而mUri不为空，所以下面的方法咱们只贴出来一部分，可以看到，图片drawable值是通过Resource对象在UI线程中完成。方法上面的解释也可佐证，同时引出下面两个问题，由于SetImageResource会使UI线程延迟，所以可以考虑下面两种做法
imageView.setImageDrawable(drawable);获得图片资源运行在子线程
[html] view
plaincopyprint?
/**
* Sets a drawable as the content of this ImageView.
*
* @param drawable The drawable to set
*/
public void setImageDrawable(Drawable drawable) {
if (mDrawable != drawable) {
mResource = 0;
mUri = null;
int oldWidth = mDrawableWidth;
int oldHeight = mDrawableHeight;
updateDrawable(drawable);
if (oldWidth != mDrawableWidth || oldHeight != mDrawableHeight) {
requestLayout();
}
invalidate();
}
}
[html] view
plaincopyprint?
private void updateDrawable(Drawable d) {
if (mDrawable != null) {
mDrawable.setCallback(null);
unscheduleDrawable(mDrawable);
}
mDrawable = d;
if (d != null) {
d.setCallback(this);
if (d.isStateful()) {
d.setState(getDrawableState());
}
d.setLevel(mLevel);
mDrawableWidth = d.getIntrinsicWidth();
mDrawableHeight = d.getIntrinsicHeight();
applyColorMod();
configureBounds();
} else {
mDrawableWidth = mDrawableHeight = -1;
}
}
从源码上看，只需要把获得的值，解析一下，刷新到UI线程即可，所以Drawable对象可以在子线程中获取。
imageView.setImageBitmap(bm);获得图片资源可以运行在子线程，且可以改变图片大小
[html] view
plaincopyprint?
/**
* Sets a Bitmap as the content of this ImageView.
*
* @param bm The bitmap to set
*/
@android.view.RemotableViewMethod
public void setImageBitmap(Bitmap bm) {
// if this is used frequently, may handle bitmaps explicitly
// to reduce the intermediate drawable object
setImageDrawable(new BitmapDrawable(mContext.getResources(), bm));
}
[html] view
plaincopyprint?
/**
* Create drawable from a bitmap, setting initial target density based on
* the display metrics of the resources.
*/
public BitmapDrawable(Resources res, Bitmap bitmap) {
this(new BitmapState(bitmap), res);
mBitmapState.mTargetDensity = mTargetDensity;
}
[html] view
plaincopyprint?
private BitmapDrawable(BitmapState state, Resources res) {
mBitmapState = state;
if (res != null) {
mTargetDensity = res.getDisplayMetrics().densityDpi;
} else {
mTargetDensity = state.mTargetDensity;
}
setBitmap(state != null ? state.mBitmap : null);
}
[html] view
plaincopyprint?
private void setBitmap(Bitmap bitmap) {
if (bitmap != mBitmap) {
mBitmap = bitmap;
if (bitmap != null) {
computeBitmapSize();
} else {
mBitmapWidth = mBitmapHeight = -1;
}
invalidateSelf();
}
}
SetImageBitmap同理，其实是通过BitmapDrawable获得一个Drawable对象，同setImageDrawable。值可以在子线程获得，在主界面刷新。
与此同时，有两个方法出现频率比较高，requestLayout和invalidate方法。
requestLayout：
[html] view
plaincopyprint?
/**
* Call this when something has changed which has invalidated the
* layout of this view. This will schedule a layout pass of the view
* tree.
*/
public void requestLayout() {
if (ViewDebug.TRACE_HIERARCHY) {
ViewDebug.trace(this, ViewDebug.HierarchyTraceType.REQUEST_LAYOUT);
}
mPrivateFlags |= FORCE_LAYOUT;
mPrivateFlags |= INVALIDATED;
if (mParent != null) {
if (mLayoutParams != null) {
mLayoutParams.resolveWithDirection(getResolvedLayoutDirection());
}
if (!mParent.isLayoutRequested()) {
mParent.requestLayout();
}
}
}
[html] view
plaincopyprint?
* To intiate a layout, call {@link #requestLayout}. This method is typically
* called by a view on itself when it believes that is can no longer fit within
* its current bounds.
最主要的是这句，主要是当前View已经放不用所存放的值时，需要重新计算宽高
Invalidate()：
[html] view
plaincopyprint?
/**
* Invalidate the whole view. If the view is visible,
* {@link #onDraw(android.graphics.Canvas)} will be called at some point in
* the future. This must be called from a UI thread. To call from a non-UI thread,
* call {@link #postInvalidate()}.
*/
public void invalidate() {
invalidate(true);
}
[html] view
plaincopyprint?
/**
* This is where the invalidate() work actually happens. A full invalidate()
* causes the drawing cache to be invalidated, but this function can be called with
* invalidateCache set to false to skip that invalidation step for cases that do not
* need it (for example, a component that remains at the same dimensions with the same
* content).
*
* @param invalidateCache Whether the drawing cache for this view should be invalidated as
* well. This is usually true for a full invalidate, but may be set to false if the
* View's contents or dimensions have not changed.
*/
void invalidate(boolean invalidateCache) {
if (ViewDebug.TRACE_HIERARCHY) {
ViewDebug.trace(this, ViewDebug.HierarchyTraceType.INVALIDATE);
}
if (skipInvalidate()) {
return;
}
if ((mPrivateFlags & (DRAWN | HAS_BOUNDS)) == (DRAWN | HAS_BOUNDS) ||
(invalidateCache && (mPrivateFlags & DRAWING_CACHE_VALID) == DRAWING_CACHE_VALID) ||
(mPrivateFlags & INVALIDATED) != INVALIDATED || isOpaque() != mLastIsOpaque) {
mLastIsOpaque = isOpaque();
mPrivateFlags &= ~DRAWN;
mPrivateFlags |= DIRTY;
if (invalidateCache) {
mPrivateFlags |= INVALIDATED;
mPrivateFlags &= ~DRAWING_CACHE_VALID;
}
final AttachInfo ai = mAttachInfo;
final ViewParent p = mParent;
//noinspection PointlessBooleanExpression,ConstantConditions
if (!HardwareRenderer.RENDER_DIRTY_REGIONS) {
if (p != null && ai != null && ai.mHardwareAccelerated) {
// fast-track for GL-enabled applications; just invalidate the whole hierarchy
// with a null dirty rect, which tells the ViewAncestor to redraw everything
p.invalidateChild(this, null);
return;
}
}
if (p != null && ai != null) {
final Rect r = ai.mTmpInvalRect;
r.set(0, 0, mRight - mLeft, mBottom - mTop);
// Don't call invalidate -- we don't want to internally scroll
// our own bounds
p.invalidateChild(this, r);
}
}
}
把计算宽高、实际宽高、布局等刷新进来
[html] view
plaincopyprint?
If either {@link #requestLayout()} or {@link #invalidate()} were called,
* the framework will take care of measuring, laying out, and drawing the tree
* as appropriate.
与此同时，我们还可以看到一个知识点postInvalidate
[html] view
plaincopyprint?
/**
* <p>Cause an invalidate to happen on a subsequent cycle through the event loop.
* Use this to invalidate the View from a non-UI thread.</p>
*
* <p>This method can be invoked from outside of the UI thread
* only when this View is attached to a window.</p>
*
* @see #invalidate()
*/
public void postInvalidate() {
postInvalidateDelayed(0);
}
[html] view
plaincopyprint?
/**
* <p>Cause an invalidate to happen on a subsequent cycle through the event
* loop. Waits for the specified amount of time.</p>
*
* <p>This method can be invoked from outside of the UI thread
* only when this View is attached to a window.</p>
*
* @param delayMilliseconds the duration in milliseconds to delay the
* invalidation by
*/
public void postInvalidateDelayed(long delayMilliseconds) {
// We try only with the AttachInfo because there's no point in invalidating
// if we are not attached to our window
AttachInfo attachInfo = mAttachInfo;
if (attachInfo != null) {
Message msg = Message.obtain();
msg.what = AttachInfo.INVALIDATE_MSG;
msg.obj = this;
attachInfo.mHandler.sendMessageDelayed(msg, delayMilliseconds);
}
}
这个刷新会排到消息队列去刷新，也就是在空闲时刷新，相对来说可以减少阻塞，此任务优先级稍低，当然我们可以加入延迟时间来相对自定义优先级。
在开发过程中，大概会遇到这样的情况，在布局的时候，需要图片的宽度或长度；或者图片太大，ImageView太小，要做图片压缩；这时就要用到接下来讲到的知识点。
BitmapFactory.Options options = new BitmapFactory.Options();
options.inJustDecodeBounds = true;//API中有说明，此时返回bitmap值为null
bitmap = BitmapFactory.decodeFile(pathName,options);
int height=options.outHeight;//获得图片的高
int width=options.outWidth;//获得图片的宽
options.inJustDecodeBounds=false;//之后设置
bitmap=BitmapFactory.decodeFile(pathName, options);
可获得正确的bitmap值。
本文来自http://blog.csdn.net/liuxian13183/ ，引用必须注明出处！
首先关于图片加载到ImageView上，我们来讨论几个问题：
如下：
imageView.setImageResource(resId);获得图片资源运行在主线程
[html] view
plaincopyprint?
This does Bitmap reading and decoding on the UI
* thread, which can cause a latency hiccup. If that's a concern,
* consider using {@link #setImageDrawable(android.graphics.drawable.Drawable)} or
* {@link #setImageBitmap(android.graphics.Bitmap)} and
* {@link android.graphics.BitmapFactory} instead.</p>
*
* @param resId the resource identifier of the the drawable
*
* @attr ref android.R.styleable#ImageView_src
*/
@android.view.RemotableViewMethod
public void setImageResource(int resId) {
if (mUri != null || mResource != resId) {
updateDrawable(null);
mResource = resId;
mUri = null;
resolveUri();
requestLayout();
invalidate();
}
}
[html] view
plaincopyprint?
private void resolveUri() {
if (mDrawable != null) {
return;
}
Resources rsrc = getResources();
if (rsrc == null) {
return;
}
Drawable d = null;
if (mResource != 0) {
try {
d = rsrc.getDrawable(mResource);
} catch (Exception e) {
Log.w("ImageView", "Unable to find resource: " + mResource, e);
// Don't try again.
mUri = null;
}
} else if (mUri != null) {
从源码上看，mResource不为空，而mUri不为空，所以下面的方法咱们只贴出来一部分，可以看到，图片drawable值是通过Resource对象在UI线程中完成。方法上面的解释也可佐证，同时引出下面两个问题，由于SetImageResource会使UI线程延迟，所以可以考虑下面两种做法
imageView.setImageDrawable(drawable);获得图片资源运行在子线程
[html] view
plaincopyprint?
/**
* Sets a drawable as the content of this ImageView.
*
* @param drawable The drawable to set
*/
public void setImageDrawable(Drawable drawable) {
if (mDrawable != drawable) {
mResource = 0;
mUri = null;
int oldWidth = mDrawableWidth;
int oldHeight = mDrawableHeight;
updateDrawable(drawable);
if (oldWidth != mDrawableWidth || oldHeight != mDrawableHeight) {
requestLayout();
}
invalidate();
}
}
[html] view
plaincopyprint?
private void updateDrawable(Drawable d) {
if (mDrawable != null) {
mDrawable.setCallback(null);
unscheduleDrawable(mDrawable);
}
mDrawable = d;
if (d != null) {
d.setCallback(this);
if (d.isStateful()) {
d.setState(getDrawableState());
}
d.setLevel(mLevel);
mDrawableWidth = d.getIntrinsicWidth();
mDrawableHeight = d.getIntrinsicHeight();
applyColorMod();
configureBounds();
} else {
mDrawableWidth = mDrawableHeight = -1;
}
}
从源码上看，只需要把获得的值，解析一下，刷新到UI线程即可，所以Drawable对象可以在子线程中获取。
imageView.setImageBitmap(bm);获得图片资源可以运行在子线程，且可以改变图片大小
[html] view
plaincopyprint?
/**
* Sets a Bitmap as the content of this ImageView.
*
* @param bm The bitmap to set
*/
@android.view.RemotableViewMethod
public void setImageBitmap(Bitmap bm) {
// if this is used frequently, may handle bitmaps explicitly
// to reduce the intermediate drawable object
setImageDrawable(new BitmapDrawable(mContext.getResources(), bm));
}
[html] view
plaincopyprint?
/**
* Create drawable from a bitmap, setting initial target density based on
* the display metrics of the resources.
*/
public BitmapDrawable(Resources res, Bitmap bitmap) {
this(new BitmapState(bitmap), res);
mBitmapState.mTargetDensity = mTargetDensity;
}
[html] view
plaincopyprint?
private BitmapDrawable(BitmapState state, Resources res) {
mBitmapState = state;
if (res != null) {
mTargetDensity = res.getDisplayMetrics().densityDpi;
} else {
mTargetDensity = state.mTargetDensity;
}
setBitmap(state != null ? state.mBitmap : null);
}
[html] view
plaincopyprint?
private void setBitmap(Bitmap bitmap) {
if (bitmap != mBitmap) {
mBitmap = bitmap;
if (bitmap != null) {
computeBitmapSize();
} else {
mBitmapWidth = mBitmapHeight = -1;
}
invalidateSelf();
}
}
SetImageBitmap同理，其实是通过BitmapDrawable获得一个Drawable对象，同setImageDrawable。值可以在子线程获得，在主界面刷新。
与此同时，有两个方法出现频率比较高，requestLayout和invalidate方法。
requestLayout：
[html] view
plaincopyprint?
/**
* Call this when something has changed which has invalidated the
* layout of this view. This will schedule a layout pass of the view
* tree.
*/
public void requestLayout() {
if (ViewDebug.TRACE_HIERARCHY) {
ViewDebug.trace(this, ViewDebug.HierarchyTraceType.REQUEST_LAYOUT);
}
mPrivateFlags |= FORCE_LAYOUT;
mPrivateFlags |= INVALIDATED;
if (mParent != null) {
if (mLayoutParams != null) {
mLayoutParams.resolveWithDirection(getResolvedLayoutDirection());
}
if (!mParent.isLayoutRequested()) {
mParent.requestLayout();
}
}
}
[html] view
plaincopyprint?
* To intiate a layout, call {@link #requestLayout}. This method is typically
* called by a view on itself when it believes that is can no longer fit within
* its current bounds.
最主要的是这句，主要是当前View已经放不用所存放的值时，需要重新计算宽高
Invalidate()：
[html] view
plaincopyprint?
/**
* Invalidate the whole view. If the view is visible,
* {@link #onDraw(android.graphics.Canvas)} will be called at some point in
* the future. This must be called from a UI thread. To call from a non-UI thread,
* call {@link #postInvalidate()}.
*/
public void invalidate() {
invalidate(true);
}
[html] view
plaincopyprint?
/**
* This is where the invalidate() work actually happens. A full invalidate()
* causes the drawing cache to be invalidated, but this function can be called with
* invalidateCache set to false to skip that invalidation step for cases that do not
* need it (for example, a component that remains at the same dimensions with the same
* content).
*
* @param invalidateCache Whether the drawing cache for this view should be invalidated as
* well. This is usually true for a full invalidate, but may be set to false if the
* View's contents or dimensions have not changed.
*/
void invalidate(boolean invalidateCache) {
if (ViewDebug.TRACE_HIERARCHY) {
ViewDebug.trace(this, ViewDebug.HierarchyTraceType.INVALIDATE);
}
if (skipInvalidate()) {
return;
}
if ((mPrivateFlags & (DRAWN | HAS_BOUNDS)) == (DRAWN | HAS_BOUNDS) ||
(invalidateCache && (mPrivateFlags & DRAWING_CACHE_VALID) == DRAWING_CACHE_VALID) ||
(mPrivateFlags & INVALIDATED) != INVALIDATED || isOpaque() != mLastIsOpaque) {
mLastIsOpaque = isOpaque();
mPrivateFlags &= ~DRAWN;
mPrivateFlags |= DIRTY;
if (invalidateCache) {
mPrivateFlags |= INVALIDATED;
mPrivateFlags &= ~DRAWING_CACHE_VALID;
}
final AttachInfo ai = mAttachInfo;
final ViewParent p = mParent;
//noinspection PointlessBooleanExpression,ConstantConditions
if (!HardwareRenderer.RENDER_DIRTY_REGIONS) {
if (p != null && ai != null && ai.mHardwareAccelerated) {
// fast-track for GL-enabled applications; just invalidate the whole hierarchy
// with a null dirty rect, which tells the ViewAncestor to redraw everything
p.invalidateChild(this, null);
return;
}
}
if (p != null && ai != null) {
final Rect r = ai.mTmpInvalRect;
r.set(0, 0, mRight - mLeft, mBottom - mTop);
// Don't call invalidate -- we don't want to internally scroll
// our own bounds
p.invalidateChild(this, r);
}
}
}
把计算宽高、实际宽高、布局等刷新进来
[html] view
plaincopyprint?
If either {@link #requestLayout()} or {@link #invalidate()} were called,
* the framework will take care of measuring, laying out, and drawing the tree
* as appropriate.
与此同时，我们还可以看到一个知识点postInvalidate
[html] view
plaincopyprint?
/**
* <p>Cause an invalidate to happen on a subsequent cycle through the event loop.
* Use this to invalidate the View from a non-UI thread.</p>
*
* <p>This method can be invoked from outside of the UI thread
* only when this View is attached to a window.</p>
*
* @see #invalidate()
*/
public void postInvalidate() {
postInvalidateDelayed(0);
}
[html] view
plaincopyprint?
/**
* <p>Cause an invalidate to happen on a subsequent cycle through the event
* loop. Waits for the specified amount of time.</p>
*
* <p>This method can be invoked from outside of the UI thread
* only when this View is attached to a window.</p>
*
* @param delayMilliseconds the duration in milliseconds to delay the
* invalidation by
*/
public void postInvalidateDelayed(long delayMilliseconds) {
// We try only with the AttachInfo because there's no point in invalidating
// if we are not attached to our window
AttachInfo attachInfo = mAttachInfo;
if (attachInfo != null) {
Message msg = Message.obtain();
msg.what = AttachInfo.INVALIDATE_MSG;
msg.obj = this;
attachInfo.mHandler.sendMessageDelayed(msg, delayMilliseconds);
}
}
这个刷新会排到消息队列去刷新，也就是在空闲时刷新，相对来说可以减少阻塞，此任务优先级稍低，当然我们可以加入延迟时间来相对自定义优先级。
在开发过程中，大概会遇到这样的情况，在布局的时候，需要图片的宽度或长度；或者图片太大，ImageView太小，要做图片压缩；这时就要用到接下来讲到的知识点。
BitmapFactory.Options options = new BitmapFactory.Options();
options.inJustDecodeBounds = true;//API中有说明，此时返回bitmap值为null
bitmap = BitmapFactory.decodeFile(pathName,options);
int height=options.outHeight;//获得图片的高
int width=options.outWidth;//获得图片的宽
options.inJustDecodeBounds=false;//之后设置
bitmap=BitmapFactory.decodeFile(pathName, options);
可获得正确的bitmap值。
本文来自http://blog.csdn.net/liuxian13183/ ，引用必须注明出处！
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