android布局控件的LayoutParams

/**
 * 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;
}

　　

getLayoutParams() view没有attched到parent的时候，会返回null。

/**
 * 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();
}

　　

setLayoutParams() 这个函数最容易引出的就是参数类型转换错误，给控件设置参数的时候，设置其父布局的参数，想想xml中的参数都是相对父布局的就比较好理解了，只有padding是自身的，layoutParams中就没有padding属性。
待我看看源码。