android-invalidate()源码

/**
* 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);
}

个人理解是如果在调用这个方法时，view是可见的，则刷新他。。。重新调用onDraw()方法，重绘页面。这个方法必须在UI线程里面。如果是非UI线程可以使用postInvalidate()

下面是带参数方法的原码(太多看不懂。。。，一个View类加注释2W行，确实有点。。。)：

/**
* 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 (skipInvalidate()) {
return;
}
if ((mPrivateFlags & (PFLAG_DRAWN | PFLAG_HAS_BOUNDS)) == (PFLAG_DRAWN | PFLAG_HAS_BOUNDS) ||
(invalidateCache && (mPrivateFlags & PFLAG_DRAWING_CACHE_VALID) == PFLAG_DRAWING_CACHE_VALID) ||
(mPrivateFlags & PFLAG_INVALIDATED) != PFLAG_INVALIDATED || isOpaque() != mLastIsOpaque) {
mLastIsOpaque = isOpaque();
mPrivateFlags &= ~PFLAG_DRAWN;
mPrivateFlags |= PFLAG_DIRTY;
if (invalidateCache) {
mPrivateFlags |= PFLAG_INVALIDATED;
mPrivateFlags &= ~PFLAG_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);
}
}
}

View.java原码：点击下载链接