Android中LayoutInflater类的inflate方法的使用及注意事项

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[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>

MainActivity.java

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。