各位看官们大家好，上一回中咱们说的是Android中自定义View之Draw的例子，这一回咱们继续说该例子。闲话休提，言归正转。让我们一起Talk Android吧！
看官们，我们在前面章回中介绍了View的draw()函数，并且介绍了两个重载的draw()函数，以及它们的不同点。这一回中我们将介绍View的onDraw()函数，不过遗憾的是该函数是一个空函数，接下来，我们以View的直接子类TextView为例来介绍onDraw()函数的过程。下面是它的源代码：
@Override
protected void onDraw(Canvas canvas) {
restartMarqueeIfNeeded();
// Draw the background for this view
super.onDraw(canvas);
final int compoundPaddingLeft = getCompoundPaddingLeft();
final int compoundPaddingTop = getCompoundPaddingTop();
final int compoundPaddingRight = getCompoundPaddingRight();
final int compoundPaddingBottom = getCompoundPaddingBottom();
final int scrollX = mScrollX;
final int scrollY = mScrollY;
final int right = mRight;
final int left = mLeft;
final int bottom = mBottom;
final int top = mTop;
final boolean isLayoutRtl = isLayoutRtl();
final int offset = getHorizontalOffsetForDrawables();
final int leftOffset = isLayoutRtl ? 0 : offset;
final int rightOffset = isLayoutRtl ? offset : 0;
final Drawables dr = mDrawables;
if (dr != null) {
/*
* Compound, not extended, because the icon is not clipped
* if the text height is smaller.
*/
int vspace = bottom - top - compoundPaddingBottom - compoundPaddingTop;
int hspace = right - left - compoundPaddingRight - compoundPaddingLeft;
// IMPORTANT: The coordinates computed are also used in invalidateDrawable()
// Make sure to update invalidateDrawable() when changing this code.
if (dr.mShowing[Drawables.LEFT] != null) {
canvas.save();
canvas.translate(scrollX + mPaddingLeft + leftOffset,
scrollY + compoundPaddingTop + (vspace - dr.mDrawableHeightLeft) / 2);
dr.mShowing[Drawables.LEFT].draw(canvas);
canvas.restore();
}
// IMPORTANT: The coordinates computed are also used in invalidateDrawable()
// Make sure to update invalidateDrawable() when changing this code.
if (dr.mShowing[Drawables.RIGHT] != null) {
canvas.save();
canvas.translate(scrollX + right - left - mPaddingRight
- dr.mDrawableSizeRight - rightOffset,
scrollY + compoundPaddingTop + (vspace - dr.mDrawableHeightRight) / 2);
dr.mShowing[Drawables.RIGHT].draw(canvas);
canvas.restore();
}
// IMPORTANT: The coordinates computed are also used in invalidateDrawable()
// Make sure to update invalidateDrawable() when changing this code.
if (dr.mShowing[Drawables.TOP] != null) {
canvas.save();
canvas.translate(scrollX + compoundPaddingLeft
+ (hspace - dr.mDrawableWidthTop) / 2, scrollY + mPaddingTop);
dr.mShowing[Drawables.TOP].draw(canvas);
canvas.restore();
}
// IMPORTANT: The coordinates computed are also used in invalidateDrawable()
// Make sure to update invalidateDrawable() when changing this code.
if (dr.mShowing[Drawables.BOTTOM] != null) {
canvas.save();
canvas.translate(scrollX + compoundPaddingLeft
+ (hspace - dr.mDrawableWidthBottom) / 2,
scrollY + bottom - top - mPaddingBottom - dr.mDrawableSizeBottom);
dr.mShowing[Drawables.BOTTOM].draw(canvas);
canvas.restore();
}
}
int color = mCurTextColor;
if (mLayout == null) {
assumeLayout();
}
Layout layout = mLayout;
if (mHint != null && mText.length() == 0) {
if (mHintTextColor != null) {
color = mCurHintTextColor;
}
layout = mHintLayout;
}
mTextPaint.setColor(color);
mTextPaint.drawableState = getDrawableState();
canvas.save();
/* Would be faster if we didn't have to do this. Can we chop the
(displayable) text so that we don't need to do this ever?
*/
int extendedPaddingTop = getExtendedPaddingTop();
int extendedPaddingBottom = getExtendedPaddingBottom();
final int vspace = mBottom - mTop - compoundPaddingBottom - compoundPaddingTop;
final int maxScrollY = mLayout.getHeight() - vspace;
float clipLeft = compoundPaddingLeft + scrollX;
float clipTop = (scrollY == 0) ? 0 : extendedPaddingTop + scrollY;
float clipRight = right - left - getCompoundPaddingRight() + scrollX;
float clipBottom = bottom - top + scrollY
- ((scrollY == maxScrollY) ? 0 : extendedPaddingBottom);
if (mShadowRadius != 0) {
clipLeft += Math.min(0, mShadowDx - mShadowRadius);
clipRight += Math.max(0, mShadowDx + mShadowRadius);
clipTop += Math.min(0, mShadowDy - mShadowRadius);
clipBottom += Math.max(0, mShadowDy + mShadowRadius);
}
canvas.clipRect(clipLeft, clipTop, clipRight, clipBottom);
int voffsetText = 0;
int voffsetCursor = 0;
// translate in by our padding
/* shortcircuit calling getVerticaOffset() */
if ((mGravity & Gravity.VERTICAL_GRAVITY_MASK) != Gravity.TOP) {
voffsetText = getVerticalOffset(false);
voffsetCursor = getVerticalOffset(true);
}
canvas.translate(compoundPaddingLeft, extendedPaddingTop + voffsetText);
final int layoutDirection = getLayoutDirection();
final int absoluteGravity = Gravity.getAbsoluteGravity(mGravity, layoutDirection);
if (isMarqueeFadeEnabled()) {
if (!mSingleLine && getLineCount() == 1 && canMarquee()
&& (absoluteGravity & Gravity.HORIZONTAL_GRAVITY_MASK) != Gravity.LEFT) {
final int width = mRight - mLeft;
final int padding = getCompoundPaddingLeft() + getCompoundPaddingRight();
final float dx = mLayout.getLineRight(0) - (width - padding);
canvas.translate(layout.getParagraphDirection(0) * dx, 0.0f);
}
if (mMarquee != null && mMarquee.isRunning()) {
final float dx = -mMarquee.getScroll();
canvas.translate(layout.getParagraphDirection(0) * dx, 0.0f);
}
}
final int cursorOffsetVertical = voffsetCursor - voffsetText;
Path highlight = getUpdatedHighlightPath();
if (mEditor != null) {
mEditor.onDraw(canvas, layout, highlight, mHighlightPaint, cursorOffsetVertical);
} else {
layout.draw(canvas, highlight, mHighlightPaint, cursorOffsetVertical);
}
if (mMarquee != null && mMarquee.shouldDrawGhost()) {
final float dx = mMarquee.getGhostOffset();
canvas.translate(layout.getParagraphDirection(0) * dx, 0.0f);
layout.draw(canvas, highlight, mHighlightPaint, cursorOffsetVertical);
}
canvas.restore();
}
从源代码中可以看出，它会调用父类的draw()函数去绘制背景，然后依据坐标分别绘制左，右，上，下的边距，最后是绘制文字。
各位看官，关于Androd中自定义View之Draw的例子咱们就介绍到这里，欲知后面还有什么例子，且听下回分解!
