转自:http://www.ithao123.cn/content-10951307.html
[摘要:我们正在讲一个界说好的结构文件(xml)文件减载到界里上揭示出去的时间,平常会用到LayoutInflater的inflate方式,仔细的同砚会发明那个方式有四种重载,分离是: public View ]
我们在讲一个定义好的布局文件(xml)文件加载到界面上展现出来的时候,通常会用到LayoutInflater的inflate方法,细心的同学会发现这个方法有四种重载,分别是:
public View inflate(@LayoutRes int resource, @Nullable ViewGroup root);
public View inflate(XmlPullParser parser, @Nullable ViewGroup root);
public View inflate(@LayoutRes int resource, @Nullable ViewGroup root, boolean attachToRoot);
public View inflate(XmlPullParser parser, @Nullable ViewGroup root, boolean attachToRoot);下面是Android Studio下查看到的源码即相关方法的参数说明:
/** * 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(@LayoutRes int resource, @Nullable 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> 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, @Nullable 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(@LayoutRes int resource, @Nullable ViewGroup root, boolean attachToRoot) { final Resources res = getContext().getResources(); if (DEBUG) { Log.d(TAG, "INFLATING from resource: \"" + res.getResourceName(resource) + "\" (" + Integer.toHexString(resource) + ")"); } final XmlResourceParser parser = res.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> 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, @Nullable ViewGroup root, boolean attachToRoot) { synchronized (mConstructorArgs) { Trace.traceBegin(Trace.TRACE_TAG_VIEW, "inflate"); final Context inflaterContext = mContext; final AttributeSet attrs = Xml.asAttributeSet(parser); Context lastContext = (Context) mConstructorArgs[0]; mConstructorArgs[0] = inflaterContext; 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, inflaterContext, attrs, false); } else { // Temp is the root view that was found in the xml final View temp = createViewFromTag(root, name, inflaterContext, 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 against its context. rInflateChildren(parser, temp, attrs, true); 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 (Exception e) { InflateException ex = new InflateException( parser.getPositionDescription() + ": " + e.getMessage()); ex.initCause(e); throw ex; } finally { // Don't retain static reference on context. mConstructorArgs[0] = lastContext; mConstructorArgs[1] = null; } Trace.traceEnd(Trace.TRACE_TAG_VIEW); return result; } }
根据以上源码我们会发现,重载的四个方法归根结底最后调用的都是这个方法:
public View inflate(XmlPullParser parser, @Nullable ViewGroup root, boolean attachToRoot)
该方法和以下方法的区别在于下面的方法根据提供的resource来获得相应的parser,然后再调用上面的方法。
public View inflate(@LayoutRes int resource, @Nullable ViewGroup root, boolean attachToRoot)
所以我们主要来分析这个方法。参数详解:
第一个参数:int resource,表示需要加载布局文件的id,意思是需要将这个布局文件中加载到Activity中来操作;
第二个参数:ViewGroup root,表示需要附加到resource资源文件的根控件。说明:调用inflate方法后会得到一个View对象,root参数就是接收该 View对象的容器;
第三个参数:boolean attachToRoot, 表示是否把inflate得到的View对象添加到root中,该参数为false时,表示不直接添加到root中;该参数为true时,表示直接添加到root中;
下面同过具体代码来说明:
activity_main.xml
<?xml version="1.0" encoding="utf-8"?> <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android" android:layout_width="fill_parent" android:layout_height="fill_parent" android:orientation="vertical"> <TextView android:layout_width="fill_parent" android:layout_height="wrap_content" android:text="@string/hello" /> <FrameLayout android:id="@+id/fl_container" android:layout_width="match_parent" android:layout_height="wrap_content"> </FrameLayout> </LinearLayout>
inflate_view_layout.xml
<?xml version="1.0" encoding="utf-8"?> <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android" android:layout_width="match_parent" android:layout_height="match_parent" android:orientation="vertical"> <CheckBox android:id="@+id/checkBox1" android:layout_width="wrap_content" android:layout_height="wrap_content" android:text="@string/checkBox" /> </LinearLayout>
package com.rainmonth.inflatemethoddemo; import android.support.v7.app.AppCompatActivity; import android.os.Bundle; import android.text.Layout; import android.view.LayoutInflater; import android.view.View; import android.widget.FrameLayout; public class MainActivity extends AppCompatActivity { @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_main); FrameLayout frameLayout = (FrameLayout) findViewById(R.id.fl_container); // 第三个参数设置为false View inflateView = LayoutInflater.from(this).inflate(R.layout.inflate_view_layout, frameLayout, false); // 第三个参数设置为true,默认为true // View inflateView = LayoutInflater.from(this).inflate(R.layout.inflate_view_layout, frameLayout, true); } }
第三个参数为false时的运行结果如下:
此时,inflateView 对应的布局内容并未呈现出来。
第三个参数为true时的运行结果如下:
此时inflateView对应的布局内容呈现出来了。由此可见第三个参数的作用就是是否把inflate出来的参数加入到root容器中,false时不添加;true时添加。
为了验证结论,我们在第三个参数为false时在添加一下代码:
frameLayout.addView(inflateView);我们发现其现实结果同第三个参数设置为true时是一样的,所以我们的结论得到了验证。