如何Android项目中创建一个View

public void setContentView(@LayoutRes int layoutResID) {
 getWindow().setContentView(layoutResID);
 initWindowDecorActionBar();
}

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) {
 attachBaseContext(context);
 mFragments.attachHost(null /*parent*/);
 mWindow = new PhoneWindow(this); // 这里创建了Window对象
 mWindow.setCallback(this);
 mWindow.setOnWindowDismissedCallback(this);
 mWindow.getLayoutInflater().setPrivateFactory(this);
 // ... 中间部分代码省略
 mWindow.setWindowManager(
   (WindowManager)context.getSystemService(Context.WINDOW_SERVICE),
   mToken, mComponent.flattenToString(),
   (info.flags & ActivityInfo.FLAG_HARDWARE_ACCELERATED) != 0);
 if (mParent != null) {
  mWindow.setContainer(mParent.getWindow());
 }
 mWindowManager = mWindow.getWindowManager();
 mCurrentConfig = config;
}

@Override
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)) {
  // ...
 } else {
  mLayoutInflater.inflate(layoutResID, mContentParent);
 }
 // ...
}

protected ViewGroup generateLayout(DecorView decor) {
 // ...
 View in = mLayoutInflater.inflate(layoutResource, null); // layoutResource是根据对当前显示View的Activity的theme属性值来决定由系统加载对应的布局文件
 decor.addView(in, new ViewGroup.LayoutParams(MATCH_PARENT, MATCH_PARENT));
 mContentRoot = (ViewGroup) in;
 
 ViewGroup contentParent = (ViewGroup)findViewById(ID_ANDROID_CONTENT);
 if (contentParent == null) {
 throw new RuntimeException("Window couldn't find content container view");
 }
 // ...
 return contentParent;
}

XmlResourceParser loadXmlResourceParser(int id, String type)
  throws NotFoundException {
 synchronized (mAccessLock) {
  TypedValue value = mTmpValue;
  if (value == null) {
   mTmpValue = value = new TypedValue();
  }
  getValue(id, value, true);
  if (value.type == TypedValue.TYPE_STRING) {
   return loadXmlResourceParser(value.string.toString(), id,
     value.assetCookie, type);
  }
  throw new NotFoundException(
    "Resource ID #0x" + Integer.toHexString(id) + " type #0x"
    + Integer.toHexString(value.type) + " is not valid");
 }
}
XmlResourceParser loadXmlResourceParser(String file, int id,
  int assetCookie, String type) throws NotFoundException {
 if (id != 0) {
  // ...
  // These may be compiled...
  synchronized (mCachedXmlBlockIds) {
   // First see if this block is in our cache.
   final int num = mCachedXmlBlockIds.length;
   for (int i=0; i<num; i++) {
    if (mCachedXmlBlockIds[i] == id) {
     //System.out.println("**** REUSING XML BLOCK! id="
     //     + id + ", index=" + i);
     return mCachedXmlBlocks[i].newParser();
    }
   }
   // Not in the cache, create a new block and put it at
   // the next slot in the cache.
   XmlBlock block = mAssets.openXmlBlockAsset(
     assetCookie, file);
   if (block != null) {
    int pos = mLastCachedXmlBlockIndex+1;
    if (pos >= num) pos = 0;
    mLastCachedXmlBlockIndex = pos;
    XmlBlock oldBlock = mCachedXmlBlocks[pos];
    if (oldBlock != null) {
     oldBlock.close();
    }
    mCachedXmlBlockIds[pos] = id;
    mCachedXmlBlocks[pos] = block;
    //System.out.println("**** CACHING NEW XML BLOCK! id="
    //     + id + ", index=" + pos);
    return block.newParser();
   }
  }
  // ...
 }
 // ...
}

public View inflate(XmlPullParser parser, @Nullable ViewGroup root, boolean attachToRoot) {
 synchronized (mConstructorArgs) {
 final Context inflaterContext = mContext;
 final AttributeSet attrs = Xml.asAttributeSet(parser);
 Context lastContext = (Context) mConstructorArgs[0];
 View result = root;
 // ...
 
 // Temp is the root view that was found in the xml
 final View temp = createViewFromTag(root, name, inflaterContext, attrs); // 这里将布局文件中的名称反射成具体的View类对象
 ViewGroup.LayoutParams params = null;
 if (root != null) {
  // Create layout params that match root, if supplied
  params = root.generateLayoutParams(attrs); // 这里将尺寸转换成了LayoutParams
  if (!attachToRoot) {
   // Set the layout params for temp if we are not
   // attaching. (If we are, we use addView, below)
   temp.setLayoutParams(params);
  }
 }
 // Inflate all children under temp against its context.
 rInflateChildren(parser, temp, attrs, true);
 // 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); // 将布局文件中根的View添加到mContentParent中
 }
  
 // ...
 return result;
}

public LayoutParams(Context c, AttributeSet attrs) {
 TypedArray a = c.obtainStyledAttributes(attrs, R.styleable.ViewGroup_Layout);
 setBaseAttributes(a,
   R.styleable.ViewGroup_Layout_layout_width,
   R.styleable.ViewGroup_Layout_layout_height);
 a.recycle();
}
 
protected void setBaseAttributes(TypedArray a, int widthAttr, int heightAttr) {
 width = a.getLayoutDimension(widthAttr, "layout_width");
 height = a.getLayoutDimension(heightAttr, "layout_height");
}

View createViewFromTag(View parent, String name, Context context, AttributeSet attrs,
  boolean ignoreThemeAttr) {
 if (name.equals("view")) {
  name = attrs.getAttributeValue(null, "class");
 }
 
 // Apply a theme wrapper, if allowed and one is specified.
 if (!ignoreThemeAttr) {
  final TypedArray ta = context.obtainStyledAttributes(attrs, ATTRS_THEME);
  final int themeResId = ta.getResourceId(0, 0);
  if (themeResId != 0) {
   context = new ContextThemeWrapper(context, themeResId);
  }
  ta.recycle();
 }
 // ...
 View view;
 if (mFactory2 != null) {
  view = mFactory2.onCreateView(parent, name, context, attrs);
 } else if (mFactory != null) {
  view = mFactory.onCreateView(name, context, attrs);
 } else {
  view = null;
 }
 if (view == null && mPrivateFactory != null) {
  view = mPrivateFactory.onCreateView(parent, name, context, attrs);
 }
 if (view == null) {
  final Object lastContext = mConstructorArgs[0];
  mConstructorArgs[0] = context;
  try {
   if (-1 == name.indexOf('.')) {
    view = onCreateView(parent, name, attrs);
   } else {
    view = createView(name, null, attrs);
   }
  } finally {
   mConstructorArgs[0] = lastContext;
  }
 }
 return view;
 
 // ...
}

if (name.equals("view")) {
 name = attrs.getAttributeValue(null, "class");
}

public class MainActivity extends AppCompatActivity {
 @Override
 protected void onCreate(Bundle savedInstanceState) {
  super.onCreate(savedInstanceState);
  setContentView(R.layout.activity_main);
  LayoutInflater inflater = getLayoutInflater();
  LayoutInflater inflater1 = LayoutInflater.from(this);
  Field f = null;
  try {
   f = LayoutInflater.class.getDeclaredField("mPrivateFactory");
   f.setAccessible(true);
  } catch (NoSuchFieldException e) {
   e.printStackTrace();
  }
 Log.d("may", "the same object: " + (inflater == inflater1));
  Log.d("may", "inflater factory: " + inflater.getFactory() + ", factory2: " + inflater.getFactory2());
  Log.d("may", "inflater1 factory: " + inflater1.getFactory() + ", factory2: " + inflater1.getFactory2());
  if (f != null) {
   try {
    Log.d("may", "inflater mPrivateFactory: " + f.get(inflater));
    Log.d("may", "inflater1 mPrivateFactory: " + f.get(inflater1));
   } catch (IllegalAccessException e) {
    e.printStackTrace();
   }
  }
 }
}

// 当前Activiy继承的是android.support.v7.app.AppCompatActivity
the same object: true
inflater factory: android.support.v4.view.LayoutInflaterCompatHC$FactoryWrapperHC{android.support.v7.app.AppCompatDelegateImplV14@41fdf0b0}, factory2: android.support.v4.view.LayoutInflaterCompatHC$FactoryWrapperHC{android.support.v7.app.AppCompatDelegateImplV14@41fdf0b0}
inflater1 factory: android.support.v4.view.LayoutInflaterCompatHC$FactoryWrapperHC{android.support.v7.app.AppCompatDelegateImplV14@41fdf0b0}, factory2: android.support.v4.view.LayoutInflaterCompatHC$FactoryWrapperHC{android.support.v7.app.AppCompatDelegateImplV14@41fdf0b0}
inflater mPrivateFactory: com.jacpy.sb.MainActivity@41fd9e70
inflater1 mPrivateFactory: com.jacpy.sb.MainActivity@41fd9e70
// 当前Activity继承的是android.app.Activity
the same object: true
inflater factory: null, factory2: null
inflater1 factory: null, factory2: null
inflater mPrivateFactory: com.jacpy.sb.MainActivity@41fd9a28
inflater1 mPrivateFactory: com.jacpy.sb.MainActivity@41fd9a28

public final View createView(String name, String prefix, AttributeSet attrs)
  throws ClassNotFoundException, InflateException {
 Constructor<&#63; extends View> constructor = sConstructorMap.get(name);
 Class<&#63; extends View> clazz = null;
 // ...
 // Class not found in the cache, see if it's real, and try to add it
 clazz = mContext.getClassLoader().loadClass(
   prefix != null &#63; (prefix + name) : name).asSubclass(View.class); // prefix传的值是android.view.
 
 // ...
 
 constructor = clazz.getConstructor(mConstructorSignature); // Class<&#63;>[] mConstructorSignature = new Class[] {
   Context.class, AttributeSet.class};
 constructor.setAccessible(true);
 sConstructorMap.put(name, constructor);
 // ...
 Object[] args = mConstructorArgs;
 args[1] = attrs; // 这个值是XmlBlock.Parser对象
 final View view = constructor.newInstance(args);
 if (view instanceof ViewStub) {
  // Use the same context when inflating ViewStub later.
  final ViewStub viewStub = (ViewStub) view;
  viewStub.setLayoutInflater(cloneInContext((Context) args[0]));
 }
 return view;
}