LayoutInflater之inflate()简单分析

//方法1
LayoutInflater inflater_1 = getLayoutInflater(); // 调用Activity的getLayoutInflater()
//方法2
LayoutInflater inflater_2 = (LayoutInflater) mContext.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
//方法3
LayoutInflater inflater_3 = LayoutInflater.from(mContext);

frameworks\base\core\java\android\app\Activity.java

@NonNull
public LayoutInflater getLayoutInflater() {
    return getWindow().getLayoutInflater();
}

public Window getWindow() {
    return mWindow;
}

final void attach(Context context, ActivityThread aThread,
            Instrumentation instr, IBinder token, int ident,
            Application application, Intent intent, ActivityInfo info,
            CharSequence title, Activity parent, String id,
            NonConfigurationInstances lastNonConfigurationInstances,
            Configuration config, String referrer, IVoiceInteractor voiceInteractor,
            Window window, ActivityConfigCallback activityConfigCallback) {
    attachBaseContext(context);
    mFragments.attachHost(null /*parent*/);
    //初始化mWindow
    mWindow = new PhoneWindow(this, window, activityConfigCallback);
    //略
}

public PhoneWindow(Context context) {
    super(context);
    mLayoutInflater = LayoutInflater.from(context);
}
​
public PhoneWindow(Context context, Window preservedWindow,
        ActivityConfigCallback activityConfigCallback) {
    this(context);
    //略
}

@Override
public LayoutInflater getLayoutInflater() {
    return mLayoutInflater;
}

mLayoutInflater = LayoutInflater.from(context);

\frameworks\base\core\java\android\view\LayoutInflater.java

public static LayoutInflater from(Context context) {
    LayoutInflater LayoutInflater =
            (LayoutInflater) context.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
    if (LayoutInflater == null) {
        throw new AssertionError("LayoutInflater not found.");
    }
    return LayoutInflater;
}

 public View inflate(XmlPullParser parser, @Nullable ViewGroup root) {
    //如果root不为null，就attachToRoot
     return inflate(parser, root, root != null);
 }

public View inflate(@LayoutRes int resource, @Nullable ViewGroup root, boolean attachToRoot) {
    final Resources res = getContext().getResources();
    final XmlResourceParser parser = res.getLayout(resource);
    try {
        //是否attachToRoot，要看参数attachToRoot
        return inflate(parser, root, attachToRoot);
    } finally {
        parser.close();
    }
}

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 {
            int type;
            while ((type = parser.next()) != XmlPullParser.START_TAG &&
                    type != XmlPullParser.END_DOCUMENT) {
            }
            if (type != XmlPullParser.START_TAG) {
                throw new InflateException(parser.getPositionDescription()
                        + ": No start tag found!");
            }
            final String name = parser.getName();
            //是否有merge
            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 {
                //一般都走这
                //创建临时View
                final View temp = createViewFromTag(root, name, inflaterContext, attrs);
                ViewGroup.LayoutParams params = null;
                //[重点]如果root不为null，才会走这
                if (root != null) {
                    params = root.generateLayoutParams(attrs);
                    //[重点]如果attachToRoot为false，表示不附加，仅仅设置LayoutParams
                    if (!attachToRoot) {
                        temp.setLayoutParams(params);
                    }
                }
                rInflateChildren(parser, temp, attrs, true);
                //如果attachToRoot为true，把temp添加到root中。
                if (root != null && attachToRoot) {
                    root.addView(temp, params);
                }
                 //root为null时，返回temp
                //attachToRoot为false时，返回时临时创建的view，否则返回root
                if (root == null || !attachToRoot) {
                    result = temp;
                }
            }
        } catch (XmlPullParserException e) {
            final InflateException ie = new InflateException(e.getMessage(), e);
            ie.setStackTrace(EMPTY_STACK_TRACE);
            throw ie;
        } catch (Exception e) {
            final InflateException ie = new InflateException(parser.getPositionDescription()
                    + ": " + e.getMessage(), e);
            ie.setStackTrace(EMPTY_STACK_TRACE);
            throw ie;
        } finally {
            mConstructorArgs[0] = lastContext;
            mConstructorArgs[1] = null;
            Trace.traceEnd(Trace.TRACE_TAG_VIEW);
        }
        return result;
    }
}

View result = root;
​
params = root.generateLayoutParams(attrs);
​
//attachToRoot为true
//附加，就添加到root中
if (root != null && attachToRoot) {
    root.addView(temp, params);
}

params = root.generateLayoutParams(attrs);
​
//attachToRoot = false
//不附加，直接设置params
if (!attachToRoot) {
    temp.setLayoutParams(params);
}
​
result = temp;

LayoutInflater.from(MediaApp.getContext()).inflate(R.layout.layout_item_media, parent, false)

LayoutInflater.from(MediaApp.getContext()).inflate(R.layout.layout_item_media, null)

 #PhoneWindow.java中
 public void setContentView(int layoutResID) {
     //略
    mLayoutInflater.inflate(layoutResID, mContentParent);
     //略
 }