(源码阅读)我们经常用的setContentView()，到底做了什么。

既然是源码阅读，那我们就果断上源码吧，首先就是Activity下的setContentView().嘿嘿，首先来看下一张比较经典的图，可能这里话的比较丑~~hhh

/**
 * Set the activity content from a layout resource.  The resource will be
 * inflated, adding all top-level views to the activity.
 *
 * @param layoutResID Resource ID to be inflated.
 *
 * @see #setContentView(android.view.View)
 * @see #setContentView(android.view.View, android.view.ViewGroup.LayoutParams)
 */
public void setContentView(@LayoutRes int layoutResID) {
    getWindow().setContentView(layoutResID);
    initWindowDecorActionBar();
}

我们可以看到有用就只有，getWindow().setContentView()，这行代码了，点进去之后发现又是一个抽象方法。

当我们看到的抽象发现确实比较的头疼，不知道从哪里去找。不过，这里我window对象调用的setContentView()，所以我们通过mWindow找到mWindow = new PhoneWindow().这么一行代码，我们来到PhoneWindow这个类找到setContentView();

public void setContentView(int layoutResID) {
    // Note: FEATURE_CONTENT_TRANSITIONS may be set in the process of installing the window
    // decor, when theme attributes and the like are crystalized. Do not check the feature
    // before this happens.
    if (mContentParent == null) {
        installDecor();
    } else if (!hasFeature(FEATURE_CONTENT_TRANSITIONS)) {
        mContentParent.removeAllViews();
    }

    if (hasFeature(FEATURE_CONTENT_TRANSITIONS)) {
        final Scene newScene = Scene.getSceneForLayout(mContentParent, layoutResID,
                getContext());
        transitionTo(newScene);
    } else {
        mLayoutInflater.inflate(layoutResID, mContentParent);
    }
    mContentParent.requestApplyInsets();
    final Callback cb = getCallback();
    if (cb != null && !isDestroyed()) {
        cb.onContentChanged();
    }
}

先从上面来看，判断了是否为空，执行了installDecor();

private void installDecor() {
    if (mDecor == null) {
        mDecor = generateDecor();     //方法一
        mDecor.setDescendantFocusability(ViewGroup.FOCUS_AFTER_DESCENDANTS);
        mDecor.setIsRootNamespace(true);
        if (!mInvalidatePanelMenuPosted && mInvalidatePanelMenuFeatures != 0) {
            mDecor.postOnAnimation(mInvalidatePanelMenuRunnable);
        }
    }
    if (mContentParent == null) {
        mContentParent = generateLayout(mDecor);    //方法二

              .............................


    }
}

installDecore()方法太长了，这里也只是截了一部分的，中间的一部分省略了，这里只有重要的俩个方法了。

protected DecorView generateDecor() {
    return new DecorView(getContext(), -1);
}

我们可以看到第一个方法，也只是new了一个DecorView()。那么我们来看第二个。%>_<%这也是一个巨长的方法。

protected ViewGroup generateLayout(DecorView decor) {
    // Apply data from current theme.

    TypedArray a = getWindowStyle();

   ...................................
    
    
    // Inflate the window decor.

    int layoutResource;    //resId
    int features = getLocalFeatures();
    // System.out.println("Features: 0x" + Integer.toHexString(features));
    if ((features & (1 << FEATURE_SWIPE_TO_DISMISS)) != 0) {
        layoutResource = R.layout.screen_swipe_dismiss;
    } else if ((features & ((1 << FEATURE_LEFT_ICON) | (1 << FEATURE_RIGHT_ICON))) != 0) {
        if (mIsFloating) {
            TypedValue res = new TypedValue();
            getContext().getTheme().resolveAttribute(
                    R.attr.dialogTitleIconsDecorLayout, res, true);
            layoutResource = res.resourceId;
        } else {
            layoutResource = R.layout.screen_title_icons;
        }
        // XXX Remove this once action bar supports these features.
        removeFeature(FEATURE_ACTION_BAR);
        // System.out.println("Title Icons!");
    } else if ((features & ((1 << FEATURE_PROGRESS) | (1 << FEATURE_INDETERMINATE_PROGRESS))) != 0
            && (features & (1 << FEATURE_ACTION_BAR)) == 0) {
        // Special case for a window with only a progress bar (and title).
        // XXX Need to have a no-title version of embedded windows.
        layoutResource = R.layout.screen_progress;
        // System.out.println("Progress!");
    } else if ((features & (1 << FEATURE_CUSTOM_TITLE)) != 0) {
        // Special case for a window with a custom title.
        // If the window is floating, we need a dialog layout
        if (mIsFloating) {
            TypedValue res = new TypedValue();
            getContext().getTheme().resolveAttribute(
                    R.attr.dialogCustomTitleDecorLayout, res, true);
            layoutResource = res.resourceId;
        } else {
            layoutResource = R.layout.screen_custom_title;
        }
        // XXX Remove this once action bar supports these features.
        removeFeature(FEATURE_ACTION_BAR);
    } else if ((features & (1 << FEATURE_NO_TITLE)) == 0) {
        // If no other features and not embedded, only need a title.
        // If the window is floating, we need a dialog layout
        if (mIsFloating) {
            TypedValue res = new TypedValue();
            getContext().getTheme().resolveAttribute(
                    R.attr.dialogTitleDecorLayout, res, true);
            layoutResource = res.resourceId;
        } else if ((features & (1 << FEATURE_ACTION_BAR)) != 0) {
            layoutResource = a.getResourceId(
                    R.styleable.Window_windowActionBarFullscreenDecorLayout,
                    R.layout.screen_action_bar);
        } else {
            layoutResource = R.layout.screen_title;
        }
        // System.out.println("Title!");
    } else if ((features & (1 << FEATURE_ACTION_MODE_OVERLAY)) != 0) {
        layoutResource = R.layout.screen_simple_overlay_action_mode;
    } else {
        // Embedded, so no decoration is needed.
        layoutResource = R.layout.screen_simple;   //这个布局是Android自带的
        // System.out.println("Simple!");
    }

    mDecor.startChanging();

    View in = mLayoutInflater.inflate(layoutResource, null);   //o通过inflate去加载对应的一系列判断下来的resId
    decor.addView(in, new ViewGroup.LayoutParams(MATCH_PARENT, MATCH_PARENT));
    mContentRoot = (ViewGroup) in;

    ViewGroup contentParent = (ViewGroup)findViewById(ID_ANDROID_CONTENT);    //去拿到Android自带的一个布局文件 ，里面只有一个LinearLayout
    if (contentParent == null) {
        throw new RuntimeException("Window couldn't find content container view");
    }

    mDecor.finishChanging();

    return contentParent;     //最终将拿到的布局文件返回回去。
}

/**
 * The ID that the main layout in the XML layout file should have.
 */
public static final int ID_ANDROID_CONTENT = com.android.internal.R.id.content;

这个时候我们再回来在phoneWindow里面看到的setContentView()方法，我们发现下面去.inflate(layoutResID,mContentParent);

if (hasFeature(FEATURE_CONTENT_TRANSITIONS)) {
    final Scene newScene = Scene.getSceneForLayout(mContentParent, layoutResID,
            getContext());
    transitionTo(newScene);
} else {
    mLayoutInflater.inflate(layoutResID, mContentParent);
}
mContentParent.requestApplyInsets();
final Callback cb = getCallback();
if (cb != null && !isDestroyed()) {
    cb.onContentChanged();
}

这里其实也就是去把我们在setContentView()时，设置的resId的布局解析到我们在generateLayout方法所加载的R.id.content的布局上面。

到这里，所看的源码也基本上结束了，中间还有很多的判断或许对大家有用，需要大家去阅读。

看了一些源码之后，本人也get到一些技能了，当不会写的时候就根据Android的源码去写。

(源码阅读)我们经常用的setContentView()，到底做了什么。

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