Invalidate

正常刷新

/**
     * 使整个视图无效。如果视图可见，
     * {@link #onDraw(android.graphics.Canvas)} 调用此方法后将在后续的UI刷新里调用onDraw(android.graphics.Canvas)方法
     * <p>
     * 必须从UI线程调用此方法。要从非UI线程调用，请调用{@link #postInvalidate()}.*/
    public void invalidate() {
        invalidate(true);
    }

    /**
     * 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.
     * @hide
     */
    public void invalidate(boolean invalidateCache) {
        invalidateInternal(0, 0, mRight - mLeft, mBottom - mTop, invalidateCache, true);
    }

一些解释

1.首先invalidate() 也是调用 invalidate(boolean invalidateCache) 这个方法的,只有设置为true时才会让这个View刷新

2.上面的注释已经说了invalidate()的刷新是必需在UI线程的

设置布局位置,重新调整View的刷新位置

/**
     * Mark the area defined by dirty as needing to be drawn. If the view is
     * visible, {@link #onDraw(android.graphics.Canvas)} will be called at some
     * point in the future.
     * <p>
     * This must be called from a UI thread. To call from a non-UI thread, call
     * {@link #postInvalidate()}.
     * <p>
     * <b>WARNING:</b> In API 19 and below, this method may be destructive to
     * {@code dirty}.
     *
     * @param dirty the rectangle representing the bounds of the dirty region
     *
     * @deprecated The switch to hardware accelerated rendering in API 14 reduced
     * the importance of the dirty rectangle. In API 21 the given rectangle is
     * ignored entirely in favor of an internally-calculated area instead.
     * Because of this, clients are encouraged to just call {@link #invalidate()}.
     */
    @Deprecated
    public void invalidate(Rect dirty) {
        final int scrollX = mScrollX;
        final int scrollY = mScrollY;
        invalidateInternal(dirty.left - scrollX, dirty.top - scrollY,
                dirty.right - scrollX, dirty.bottom - scrollY, true, false);
    }

    /**
     * Mark the area defined by the rect (l,t,r,b) as needing to be drawn. The
     * coordinates of the dirty rect are relative to the view. If the view is
     * visible, {@link #onDraw(android.graphics.Canvas)} will be called at some
     * point in the future.
     * <p>
     * This must be called from a UI thread. To call from a non-UI thread, call
     * {@link #postInvalidate()}.
     *
     * @param l the left position of the dirty region
     * @param t the top position of the dirty region
     * @param r the right position of the dirty region
     * @param b the bottom position of the dirty region
     *
     * @deprecated The switch to hardware accelerated rendering in API 14 reduced
     * the importance of the dirty rectangle. In API 21 the given rectangle is
     * ignored entirely in favor of an internally-calculated area instead.
     * Because of this, clients are encouraged to just call {@link #invalidate()}.
     */
    @Deprecated
    public void invalidate(int l, int t, int r, int b) {
        final int scrollX = mScrollX;
        final int scrollY = mScrollY;
        invalidateInternal(l - scrollX, t - scrollY, r - scrollX, b - scrollY, true, false);
    }

postInvalidate

这个方法可以非UI线程中调用

正常刷新

/**
     * <p>导致在事件循环的后续循环中发生无效。使用此选项使非UI线程中的View无效</p>
     *
     * <p>仅当此视图附加到窗口时，才能从UI线程*外部调用此方法。</p>
     *
     * @see #invalidate()
     * @see #postInvalidateDelayed(long)
     */
    public void postInvalidate() {
        postInvalidateDelayed(0);
    }

改变位置后刷新

/**
     * <p>Cause an invalidate of the specified area 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>
     *
     * @param left The left coordinate of the rectangle to invalidate.
     * @param top The top coordinate of the rectangle to invalidate.
     * @param right The right coordinate of the rectangle to invalidate.
     * @param bottom The bottom coordinate of the rectangle to invalidate.
     *
     * @see #invalidate(int, int, int, int)
     * @see #invalidate(Rect)
     * @see #postInvalidateDelayed(long, int, int, int, int)
     */
    public void postInvalidate(int left, int top, int right, int bottom) {
        postInvalidateDelayed(0, left, top, right, bottom);
    }

延迟刷新

/**
     * <p>导致在事件*循环的后续循环中发生无效。等待指定的时间。</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
     *
     * @see #invalidate()
     * @see #postInvalidate()
     */
    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
        final AttachInfo attachInfo = mAttachInfo;
        if (attachInfo != null) {
            attachInfo.mViewRootImpl.dispatchInvalidateDelayed(this, delayMilliseconds);
        }
    }

改变位置,并且延迟刷新

/**
     * <p>Cause an invalidate of the specified area 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
     * @param left The left coordinate of the rectangle to invalidate.
     * @param top The top coordinate of the rectangle to invalidate.
     * @param right The right coordinate of the rectangle to invalidate.
     * @param bottom The bottom coordinate of the rectangle to invalidate.
     *
     * @see #invalidate(int, int, int, int)
     * @see #invalidate(Rect)
     * @see #postInvalidate(int, int, int, int)
     */
    public void postInvalidateDelayed(long delayMilliseconds, int left, int top,
            int right, int bottom) {

        // We try only with the AttachInfo because there‘s no point in invalidating
        // if we are not attached to our window
        final AttachInfo attachInfo = mAttachInfo;
        if (attachInfo != null) {
            final AttachInfo.InvalidateInfo info = AttachInfo.InvalidateInfo.obtain();
            info.target = this;
            info.left = left;
            info.top = top;
            info.right = right;
            info.bottom = bottom;

            attachInfo.mViewRootImpl.dispatchInvalidateRectDelayed(info, delayMilliseconds);
        }
    }

end

原文地址：https://www.cnblogs.com/guanxinjing/p/11558790.html