为什么不是每个人都使用 ViewGroup.LayoutParams 而不是 LinearLayout.LayoutParams？

Question

因为它可以与Relative 或Linear 布局一起使用。因此，如果我们稍后从 RelativeLayout 更改为 LinearLayout，它可能会很有用。

看来LinearLayout.LayoutParams 不是从ViewGroup.LayoutParams 继承的函数。

那么有什么理由我们应该使用LinearLayout.LayoutParams 而不是另一个？使用这个LinearLayout.LayoutParams 比普通的东西有什么特定的布局类型优势吗？

Answer 1

LinearLayout需要使用LinearLayout.LayoutParams，RelativeLayout需要使用RelativeLayout.LayoutParams，否则会崩溃。虽然MATCH_PARENT 和WRAP_CONTENT 的常量相同，但特定的布局参数会向布局参数添加附加信息，例如在RelativeLayout 中，RelativeLayout.LayoutParams 存储您指定为centerInParent 或@ 的规则987654328@ 或toRightOf 等。如果你给它一个LinearLayout.LayoutParams，它就会崩溃。

例如，这是 LinearLayout.LayoutParams

    public static class LayoutParams extends ViewGroup.MarginLayoutParams {
        @ViewDebug.ExportedProperty(category = "layout")
        public float weight;

这是RelativeLayout.LayoutParams

public static class LayoutParams extends ViewGroup.MarginLayoutParams {
        @ViewDebug.ExportedProperty(category = "layout", resolveId = true, indexMapping = {
            @ViewDebug.IntToString(from = ABOVE,               to = "above"),
            @ViewDebug.IntToString(from = ALIGN_BASELINE,      to = "alignBaseline"),
            @ViewDebug.IntToString(from = ALIGN_BOTTOM,        to = "alignBottom"),
            @ViewDebug.IntToString(from = ALIGN_LEFT,          to = "alignLeft"),
            @ViewDebug.IntToString(from = ALIGN_PARENT_BOTTOM, to = "alignParentBottom"),
            @ViewDebug.IntToString(from = ALIGN_PARENT_LEFT,   to = "alignParentLeft"),
            @ViewDebug.IntToString(from = ALIGN_PARENT_RIGHT,  to = "alignParentRight"),
            @ViewDebug.IntToString(from = ALIGN_PARENT_TOP,    to = "alignParentTop"),
            @ViewDebug.IntToString(from = ALIGN_RIGHT,         to = "alignRight"),
            @ViewDebug.IntToString(from = ALIGN_TOP,           to = "alignTop"),
            @ViewDebug.IntToString(from = BELOW,               to = "below"),
            @ViewDebug.IntToString(from = CENTER_HORIZONTAL,   to = "centerHorizontal"),
            @ViewDebug.IntToString(from = CENTER_IN_PARENT,    to = "center"),
            @ViewDebug.IntToString(from = CENTER_VERTICAL,     to = "centerVertical"),
            @ViewDebug.IntToString(from = LEFT_OF,             to = "leftOf"),
            @ViewDebug.IntToString(from = RIGHT_OF,            to = "rightOf"),
            @ViewDebug.IntToString(from = ALIGN_START,         to = "alignStart"),
            @ViewDebug.IntToString(from = ALIGN_END,           to = "alignEnd"),
            @ViewDebug.IntToString(from = ALIGN_PARENT_START,  to = "alignParentStart"),
            @ViewDebug.IntToString(from = ALIGN_PARENT_END,    to = "alignParentEnd"),
            @ViewDebug.IntToString(from = START_OF,            to = "startOf"),
            @ViewDebug.IntToString(from = END_OF,              to = "endOf")
        }, mapping = {
            @ViewDebug.IntToString(from = TRUE, to = "true"),
            @ViewDebug.IntToString(from = 0,    to = "false/NO_ID")
        })

        private int[] mRules = new int[VERB_COUNT];
        private int[] mInitialRules = new int[VERB_COUNT];

        private int mLeft, mTop, mRight, mBottom;

        private boolean mRulesChanged = false;
        private boolean mIsRtlCompatibilityMode = false;

        /**
         * When true, uses the parent as the anchor if the anchor doesn't exist or if
         * the anchor's visibility is GONE.
         */
        @ViewDebug.ExportedProperty(category = "layout")
        public boolean alignWithParent;

Answer 2

那么有什么理由我们应该使用 LinearLayout.LayoutParams 而不是另一个

LinearLayout 需要 LinearLayout.LayoutParams，您可以通过阅读 the source code for LinearLayout 看到。如果您提供其他内容，例如ViewGroup.LayoutParams，则当LinearLayout 代码尝试将ViewGroup.LayoutParams 转换为LinearLayout.LayoutParams 时，您将在运行时崩溃并出现ClassCastException。