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自定义View相关

自定义View相关

作者: 寺雨九歌 | 来源:发表于2020-10-27 09:51 被阅读0次

    View#measure

    public final void measure(int widthMeasureSpec, int heightMeasureSpec) {
            boolean optical = isLayoutModeOptical(this);
            if (optical != isLayoutModeOptical(mParent)) {
                Insets insets = getOpticalInsets();
                int oWidth  = insets.left + insets.right;
                int oHeight = insets.top  + insets.bottom;
                widthMeasureSpec  = MeasureSpec.adjust(widthMeasureSpec,  optical ? -oWidth  : oWidth);
                heightMeasureSpec = MeasureSpec.adjust(heightMeasureSpec, optical ? -oHeight : oHeight);
            }
    
            // Suppress sign extension for the low bytes
            long key = (long) widthMeasureSpec << 32 | (long) heightMeasureSpec & 0xffffffffL;
            if (mMeasureCache == null) mMeasureCache = new LongSparseLongArray(2);
    
            final boolean forceLayout = (mPrivateFlags & PFLAG_FORCE_LAYOUT) == PFLAG_FORCE_LAYOUT;
    
            // Optimize layout by avoiding an extra EXACTLY pass when the view is
            // already measured as the correct size. In API 23 and below, this
            // extra pass is required to make LinearLayout re-distribute weight.
            final boolean specChanged = widthMeasureSpec != mOldWidthMeasureSpec
                    || heightMeasureSpec != mOldHeightMeasureSpec;
            final boolean isSpecExactly = MeasureSpec.getMode(widthMeasureSpec) == MeasureSpec.EXACTLY
                    && MeasureSpec.getMode(heightMeasureSpec) == MeasureSpec.EXACTLY;
            final boolean matchesSpecSize = getMeasuredWidth() == MeasureSpec.getSize(widthMeasureSpec)
                    && getMeasuredHeight() == MeasureSpec.getSize(heightMeasureSpec);
            final boolean needsLayout = specChanged
                    && (sAlwaysRemeasureExactly || !isSpecExactly || !matchesSpecSize);
    
            if (forceLayout || needsLayout) {
                // first clears the measured dimension flag
                mPrivateFlags &= ~PFLAG_MEASURED_DIMENSION_SET;
    
                resolveRtlPropertiesIfNeeded();
    
                int cacheIndex = forceLayout ? -1 : mMeasureCache.indexOfKey(key);
                if (cacheIndex < 0 || sIgnoreMeasureCache) {
                    // measure ourselves, this should set the measured dimension flag back
                    onMeasure(widthMeasureSpec, heightMeasureSpec);
                    mPrivateFlags3 &= ~PFLAG3_MEASURE_NEEDED_BEFORE_LAYOUT;
                } else {
                    long value = mMeasureCache.valueAt(cacheIndex);
                    // Casting a long to int drops the high 32 bits, no mask needed
                    setMeasuredDimensionRaw((int) (value >> 32), (int) value);
                    mPrivateFlags3 |= PFLAG3_MEASURE_NEEDED_BEFORE_LAYOUT;
                }
    
                // flag not set, setMeasuredDimension() was not invoked, we raise
                // an exception to warn the developer
                if ((mPrivateFlags & PFLAG_MEASURED_DIMENSION_SET) != PFLAG_MEASURED_DIMENSION_SET) {
                    throw new IllegalStateException("View with id " + getId() + ": "
                            + getClass().getName() + "#onMeasure() did not set the"
                            + " measured dimension by calling"
                            + " setMeasuredDimension()");
                }
    
                mPrivateFlags |= PFLAG_LAYOUT_REQUIRED;
            }
    
            mOldWidthMeasureSpec = widthMeasureSpec;
            mOldHeightMeasureSpec = heightMeasureSpec;
    
            mMeasureCache.put(key, ((long) mMeasuredWidth) << 32 |
                    (long) mMeasuredHeight & 0xffffffffL); // suppress sign extension
        }
    
    1. isLayoutModeOptical(Object)
      光学边界( Optical bounds):
      Optical bounds describe where a widget appears to be. They sit inside the clip bounds which need to cover a larger area to allow other effects, such as shadows and glows, to be drawn.
      光学边界描述小部件的位置。它们位于剪辑范围内,需要覆盖更大的区域,以便绘制其他效果,如阴影和发光。

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