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如果根布局控件调用此方法：
private void setHeight(RelativeLayout rl_root) {
ViewGroup.LayoutParams params = rl_root.getLayoutParams();
params.height = UtilMethod.dip2pxForAppself(mContext, 64);
rl_root.setLayoutParams(params);
}
会报错：空指针(NopointerException)
其实api解释已经很清楚了：
/**
* 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;
}所以：要想用此方法，不能把使用对象设置成根布局！This method may return null if this View is not attached to a parent
* ViewGroup
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转播
