[Android] 轉-LayoutInflater丟失View的LayoutParams

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原文地址：http://lmbj.net/blog/layoutinflater-and-layoutparams/

 

View view = inflater.inflate(R.layout.item, null);

在使用類似以上方法擷取view時會遇到的一個問題就是布局檔案中定義的LayoutParams被忽略了。以下三個stackoverflow問題就是這樣:

http://stackoverflow.com/questions/5288435/layout-params-of-loaded-view-are-ignored

http://stackoverflow.com/questions/5026926/making-sense-of-layoutinflater

http://stackoverflow.com/questions/2738670/layoutinflater-ignoring-parameters

都說這樣使用就可以了：

View view = inflater.inflate( R.layout.item /* resource id */, parent /* parent */,false /*attachToRoot*/);

至此問題已經解決了，但是三個問題都沒有提到為什麼要這樣調用才行。

感興趣的我們到源碼裡來找答案，LayoutInflater的inflate方法，最後都是調用的同一個方法：

public View inflate(XmlPullParser parser, ViewGroup root, boolean attachToRoot)

原因自然在這個方法裡，大概意思就是只有ViewGroup root不為空白才會讀取View的LayoutParams。attachToRoot = true的時候，會把View添加到root中。而大多情況不希望被addView到root中，自然要賦值為flase，這樣就是上面的解決方案了。

可以參看LayoutInflater的inflate方法相關的源碼：

    /**     * Inflate a new view hierarchy from the specified xml resource. Throws     * {@link InflateException} if there is an error.     *     * @param resource ID for an XML layout resource to load (e.g.,     *        <code>R.layout.main_page</code>)     * @param root Optional view to be the parent of the generated hierarchy.     * @return The root View of the inflated hierarchy. If root was supplied,     *         this is the root View; otherwise it is the root of the inflated     *         XML file.     */    public View inflate(int resource, ViewGroup root) { return inflate(resource, root, root != null); } /** * Inflate a new view hierarchy from the specified xml node. Throws * {@link InflateException} if there is an error. * * <p> * <em><strong>Important</strong></em>&nbsp;&nbsp;&nbsp;For performance * reasons, view inflation relies heavily on pre-processing of XML files * that is done at build time. Therefore, it is not currently possible to * use LayoutInflater with an XmlPullParser over a plain XML file at runtime. * * @param parser XML dom node containing the description of the view * hierarchy. * @param root Optional view to be the parent of the generated hierarchy. * @return The root View of the inflated hierarchy. If root was supplied, * this is the root View; otherwise it is the root of the inflated * XML file. */ public View inflate(XmlPullParser parser, ViewGroup root) { return inflate(parser, root, root != null); } /** * Inflate a new view hierarchy from the specified xml resource. Throws * {@link InflateException} if there is an error. * * @param resource ID for an XML layout resource to load (e.g., * <code>R.layout.main_page</code>) * @param root Optional view to be the parent of the generated hierarchy (if * <em>attachToRoot</em> is true), or else simply an object that * provides a set of LayoutParams values for root of the returned * hierarchy (if <em>attachToRoot</em> is false.) * @param attachToRoot Whether the inflated hierarchy should be attached to * the root parameter? If false, root is only used to create the * correct subclass of LayoutParams for the root view in the XML. * @return The root View of the inflated hierarchy. If root was supplied and * attachToRoot is true, this is root; otherwise it is the root of * the inflated XML file. */ public View inflate(int resource, ViewGroup root, boolean attachToRoot) { if (DEBUG) System.out.println("INFLATING from resource: " + resource); XmlResourceParser parser = getContext().getResources().getLayout(resource); try { return inflate(parser, root, attachToRoot); } finally { parser.close(); } } /** * Inflate a new view hierarchy from the specified XML node. Throws * {@link InflateException} if there is an error. * <p> * <em><strong>Important</strong></em>&nbsp;&nbsp;&nbsp;For performance * reasons, view inflation relies heavily on pre-processing of XML files * that is done at build time. Therefore, it is not currently possible to * use LayoutInflater with an XmlPullParser over a plain XML file at runtime. * * @param parser XML dom node containing the description of the view * hierarchy. * @param root Optional view to be the parent of the generated hierarchy (if * <em>attachToRoot</em> is true), or else simply an object that * provides a set of LayoutParams values for root of the returned * hierarchy (if <em>attachToRoot</em> is false.) * @param attachToRoot Whether the inflated hierarchy should be attached to * the root parameter? If false, root is only used to create the * correct subclass of LayoutParams for the root view in the XML. * @return The root View of the inflated hierarchy. If root was supplied and * attachToRoot is true, this is root; otherwise it is the root of * the inflated XML file. */ public View inflate(XmlPullParser parser, ViewGroup root, boolean attachToRoot) { synchronized (mConstructorArgs) { final AttributeSet attrs = Xml.asAttributeSet(parser); mConstructorArgs[0] = mContext; View result = root; try { // Look for the root node. int type; while ((type = parser.next()) != XmlPullParser.START_TAG && type != XmlPullParser.END_DOCUMENT) { // Empty } if (type != XmlPullParser.START_TAG) { throw new InflateException(parser.getPositionDescription() + ": No start tag found!"); } final String name = parser.getName(); if (DEBUG) { System.out.println("**************************"); System.out.println("Creating root view: " + name); System.out.println("**************************"); } if (TAG_MERGE.equals(name)) { if (root == null || !attachToRoot) { throw new InflateException("<merge /> can be used only with a valid " + "ViewGroup root and attachToRoot=true"); } rInflate(parser, root, attrs); } else { // Temp is the root view that was found in the xml View temp = createViewFromTag(name, attrs); ViewGroup.LayoutParams params = null; if (root != null) { if (DEBUG) { System.out.println("Creating params from root: " + root); } // Create layout params that match root, if supplied params = root.generateLayoutParams(attrs); if (!attachToRoot) { // Set the layout params for temp if we are not // attaching. (If we are, we use addView, below) temp.setLayoutParams(params); } } if (DEBUG) { System.out.println("-----> start inflating children"); } // Inflate all children under temp rInflate(parser, temp, attrs); if (DEBUG) { System.out.println("-----> done inflating children"); } // We are supposed to attach all the views we found (int temp) // to root. Do that now. if (root != null && attachToRoot) { root.addView(temp, params); } // Decide whether to return the root that was passed in or the // top view found in xml. if (root == null || !attachToRoot) { result = temp; } } } catch (XmlPullParserException e) { InflateException ex = new InflateException(e.getMessage()); ex.initCause(e); throw ex; } catch (IOException e) { InflateException ex = new InflateException( parser.getPositionDescription() + ": " + e.getMessage()); ex.initCause(e); throw ex; } return result; } }

 

 

[Android] 轉-LayoutInflater丟失View的LayoutParams