Question

在Android源代码中，有一个块表示什么时候不应该调用onMeasure，这意味着在满足以下条件后，如果满足以下条件，就不会调用onMeasure。

// 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.

//my understanding: parent measure mode or height/width is changed
final boolean specChanged = widthMeasureSpec != mOldWidthMeasureSpec
                || heightMeasureSpec != mOldHeightMeasureSpec;

//my understanding: parent measure mode is Exactly
final boolean isSpecExactly = MeasureSpec.getMode(widthMeasureSpec) == MeasureSpec.EXACTLY
                && MeasureSpec.getMode(heightMeasureSpec) == MeasureSpec.EXACTLY;

//my understanding: last current(child) view measurement is the same as parent measurement
final boolean matchesSpecSize = getMeasuredWidth() == MeasureSpec.getSize(widthMeasureSpec)
                && getMeasuredHeight() == MeasureSpec.getSize(heightMeasureSpec);


final boolean needsLayout = specChanged
                && (sAlwaysRemeasureExactly || !isSpecExactly || !matchesSpecSize);

据我了解，widthMeasureSpec是父级度量规范。根据源代码，如果父测量方式为Exact，并且其宽度和高度已更改，则子级不需要重新测量。

这对我来说没有意义，即使孩子是match_parent，即使父母是正确的，当其宽度或高度发生变化时，孩子也需要进行匹配和更改。我想念什么吗？

为什么在这些源代码中未调用onMeasure

0 个答案: