今天在设置ImageView的图片时无意遇到一些问题,区分了一下设置background和src的区别,顺便看了一下View的setBackgroundDrawable源码(ImageView继承View调用的是View的方法)。将理解的简单总结一下,以便下一次接着看~
源码:
/**
* @deprecated use {@link #setBackground(Drawable)} instead
*/
@Deprecated
public void setBackgroundDrawable(Drawable background) {
computeOpaqueFlags();
/*background为null,直接return*/
if (background == mBackground) {
return;
}
/*requestLayout初始化为false,用于最后requestLayout()方法对requestLayout变量进行判断,如果为true,就调用requestLayout()方法。
requestLayout():当view确定自身已经不再适合现有的区域时,该view本身调用这个方法要求parent view重新调用他的onMeasure onLayout来对重新设置自己位置。*/
boolean requestLayout = false;
mBackgroundResource = 0;
/*下面这一小段代码是用来判断,当view中已有内容时,清除已有内容的相关属性。其中调用unscheduleDrawable()方法在后面有介绍,主要是用来解除原有内容的相关事件,这块我也没有理解太清楚,只能理解为这样。。。*/
/*
* Regardless of whether we're setting a new background or not, we want
* to clear the previous drawable.
*/
if (mBackground != null) {
mBackground.setCallback(null);
unscheduleDrawable(mBackground);
}
/*sThreadLocal系统临时创建的矩形,用于未来扩展*/
if (background != null) {
Rect padding = sThreadLocal.get();
if (padding == null) {
padding = new Rect();
sThreadLocal.set(padding);
}
resetResolvedDrawables();
/*设置图片是从左到右还是从右到左对齐,依据父组件*/ background.setLayoutDirection(getLayoutDirection());
if (background.getPadding(padding)) {
resetResolvedPadding();
switch (background.getLayoutDirection()) {
case LAYOUT_DIRECTION_RTL:
mUserPaddingLeftInitial = padding.right;
mUserPaddingRightInitial = padding.left;
internalSetPadding(padding.right, padding.top, padding.left, padding.bottom);
break;
case LAYOUT_DIRECTION_LTR:
default:
mUserPaddingLeftInitial = padding.left;
mUserPaddingRightInitial = padding.right;
internalSetPadding(padding.left, padding.top, padding.right, padding.bottom);
}
mLeftPaddingDefined = false;
mRightPaddingDefined = false;
}
/*当原本没用内容,或者原本的内容的最小大小和新的内容的最小大小不相同时,设置 requestLayout为true,调用 requestLayout()方法*/
// Compare the minimum sizes of the old Drawable and the new. If there isn't an old or
// if it has a different minimum size, we should layout again
if (mBackground == null || mBackground.getMinimumHeight() != background.getMinimumHeight() ||
mBackground.getMinimumWidth() != background.getMinimumWidth()) {
requestLayout = true;
}
background.setCallback(this);
if (background.isStateful()) {
background.setState(getDrawableState());
}
background.setVisible(getVisibility() == VISIBLE, false);
mBackground = background;
if ((mPrivateFlags & PFLAG_SKIP_DRAW) != 0) {
mPrivateFlags &= ~PFLAG_SKIP_DRAW;
mPrivateFlags |= PFLAG_ONLY_DRAWS_BACKGROUND;
requestLayout = true;
}
} else {//新的内容为空时
/* Remove the background */
mBackground = null;
if ((mPrivateFlags & PFLAG_ONLY_DRAWS_BACKGROUND) != 0) {
/*
* This view ONLY drew the background before and we're removing
* the background, so now it won't draw anything
* (hence we SKIP_DRAW)
*/
mPrivateFlags &= ~PFLAG_ONLY_DRAWS_BACKGROUND;
mPrivateFlags |= PFLAG_SKIP_DRAW;
}
/*
* When the background is set, we try to apply its padding to this
* View. When the background is removed, we don't touch this View's
* padding. This is noted in the Javadocs. Hence, we don't need to
* requestLayout(), the invalidate() below is sufficient.
*/
// The old background's minimum size could have affected this
// View's layout, so let's requestLayout
requestLayout = true;
}
computeOpaqueFlags();
// requestLayout()方法
if (requestLayout) {
requestLayout();
}
mBackgroundSizeChanged = true;
invalidate(true);
}
以上只是为了以后学习记录,如有错误希望指出,感谢~
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