实习杂记（25）：View基类里面的LayoutParams

在源码里面:

LayoutParams 是ViewGroup类里面的静态内部类，

同时MarginLayoutParams extends LayoutParams 也作为ViewGroup类里面的静态内部类

然后在各个视图如：LinearLayout,RelativeLayout,AbsoluteLayout,AbsListView,ViewPager，Gallery等类里面都会去重载上面两个参数基类

而在视图View基类里面关于参数是这样的：

首先是申明：用的当然是基类，

    /**
     * The layout parameters associated with this view and used by the parent
     * {@link android.view.ViewGroup} to determine how this view should be
     * laid out.
     * {@hide}
     */
    protected ViewGroup.LayoutParams mLayoutParams;

其次是get,这个大家都不陌生：

    /**
     * Get the LayoutParams associated with this view. All views should have
     * layout parameters. These supply parameters to the <i>parent</i> of this
     * view specifying how it should be arranged. There are many subclasses of
     * ViewGroup.LayoutParams, and these correspond to the different subclasses
     * of ViewGroup that are responsible for arranging their children.
     *
     * This method may return null if this View is not attached to a parent
     * ViewGroup or {@link #setLayoutParams(android.view.ViewGroup.LayoutParams)}
     * was not invoked successfully. When a View is attached to a parent
     * ViewGroup, this method must not return null.
     *
     * @return The LayoutParams associated with this view, or null if no
     *         parameters have been set yet
     */
    @ViewDebug.ExportedProperty(deepExport = true, prefix = "layout_")
    public ViewGroup.LayoutParams getLayoutParams() {
        return mLayoutParams;
    }

然后是set函数：这个函数里面他调用了requestLayout方法，走View的 measure，layout，draw过程了

    /**
     * Set the layout parameters associated with this view. These supply
     * parameters to the <i>parent</i> of this view specifying how it should be
     * arranged. There are many subclasses of ViewGroup.LayoutParams, and these
     * correspond to the different subclasses of ViewGroup that are responsible
     * for arranging their children.
     *
     * @param params The layout parameters for this view, cannot be null
     */
    public void setLayoutParams(ViewGroup.LayoutParams params) {
        if (params == null) {
            throw new NullPointerException("Layout parameters cannot be null");
        }
        mLayoutParams = params;
        resolveLayoutParams();
        if (mParent instanceof ViewGroup) {
            ((ViewGroup) mParent).onSetLayoutParams(this, params);
        }
        requestLayout();
    }

确定方向：

    /**
     * Resolve the layout parameters depending on the resolved layout direction
     *
     * @hide
     */
    public void resolveLayoutParams() {
        if (mLayoutParams != null) {
            mLayoutParams.resolveLayoutDirection(getLayoutDirection());
        }
    }

然后在打印里面有输出当前View的参数信息，debug

平常我们调用的就是上面的get和set函数，得到LayoutParams对象，然后就可以去调用它自己的相关设置函数，主要是宽高，左右上下边距（margin），

下面四个函数是通用的：

    public static void setHeightParams(View view,int dp){
    	LayoutParams lp=(LayoutParams)view.getLayoutParams(); 
    	lp.height=dp;
    	view.setLayoutParams(lp);
    }
    
    public static void setWidthParams(View view,int dp){
    	LayoutParams lp=(LayoutParams)view.getLayoutParams(); 
    	lp.width=dp;
    	view.setLayoutParams(lp);
    }
    
    public static void setLeftMarginParams(View view,int dp){
    	MarginLayoutParams lp=(MarginLayoutParams)view.getLayoutParams(); 
    	lp.leftMargin=dp;
    	view.setLayoutParams(lp);
    }
    
    public static void setRightMarginParams(View view,int dp){
    	MarginLayoutParams lp=(MarginLayoutParams)view.getLayoutParams(); 
    	lp.rightMargin=dp;
    	view.setLayoutParams(lp);
    }

当然如果去改变RelativeLayout相关的边距参数，这个只能用它自己的派生子类去做这件事，比如：toLeftof

但是我发现，动态的去改变这些参数好像是不行的，没有这样的函数可以调用，具体的那些参数可以动态的改变，

自己写个方法，看看提示就知道了，

    /**
     * Per-child layout information associated with RelativeLayout.
     *
     * @attr ref android.R.styleable#RelativeLayout_Layout_layout_alignWithParentIfMissing
     * @attr ref android.R.styleable#RelativeLayout_Layout_layout_toLeftOf
     * @attr ref android.R.styleable#RelativeLayout_Layout_layout_toRightOf
     * @attr ref android.R.styleable#RelativeLayout_Layout_layout_above
     * @attr ref android.R.styleable#RelativeLayout_Layout_layout_below
     * @attr ref android.R.styleable#RelativeLayout_Layout_layout_alignBaseline
     * @attr ref android.R.styleable#RelativeLayout_Layout_layout_alignLeft
     * @attr ref android.R.styleable#RelativeLayout_Layout_layout_alignTop
     * @attr ref android.R.styleable#RelativeLayout_Layout_layout_alignRight
     * @attr ref android.R.styleable#RelativeLayout_Layout_layout_alignBottom
     * @attr ref android.R.styleable#RelativeLayout_Layout_layout_alignParentLeft
     * @attr ref android.R.styleable#RelativeLayout_Layout_layout_alignParentTop
     * @attr ref android.R.styleable#RelativeLayout_Layout_layout_alignParentRight
     * @attr ref android.R.styleable#RelativeLayout_Layout_layout_alignParentBottom
     * @attr ref android.R.styleable#RelativeLayout_Layout_layout_centerInParent
     * @attr ref android.R.styleable#RelativeLayout_Layout_layout_centerHorizontal
     * @attr ref android.R.styleable#RelativeLayout_Layout_layout_centerVertical
     * @attr ref android.R.styleable#RelativeLayout_Layout_layout_toStartOf
     * @attr ref android.R.styleable#RelativeLayout_Layout_layout_toEndOf
     * @attr ref android.R.styleable#RelativeLayout_Layout_layout_alignStart
     * @attr ref android.R.styleable#RelativeLayout_Layout_layout_alignEnd
     * @attr ref android.R.styleable#RelativeLayout_Layout_layout_alignParentStart
     * @attr ref android.R.styleable#RelativeLayout_Layout_layout_alignParentEnd
     */
    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;