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Android中Window添加View的底層原理

時間:2016-03-03 10:17:20      閱讀:345      評論:0      收藏:0      [點我收藏+]

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一,WIndow和windowManager

Window是一個抽象類,它的具體實現是PhoneWindow,創建一個window很簡單,只需要創建一個windowManager即可,window具體實現在windowManagerService中,windowManager和windowManagerService的交互是一個IPC的過程。
下面是用windowManager的例子:
 mFloatingButton = new Button(this);
            mFloatingButton.setText( "window");
            mLayoutParams = new WindowManager.LayoutParams(
                    LayoutParams. WRAP_CONTENT, LayoutParams.WRAP_CONTENT, 0, 0,
                    PixelFormat. TRANSPARENT);
            mLayoutParams. flags = LayoutParams.FLAG_NOT_TOUCH_MODAL
                    | LayoutParams. FLAG_NOT_FOCUSABLE
                    | LayoutParams. FLAG_SHOW_WHEN_LOCKED;
            mLayoutParams. type = LayoutParams. TYPE_SYSTEM_ERROR;
            mLayoutParams. gravity = Gravity. LEFT | Gravity. TOP;
            mLayoutParams. x = 100;
            mLayoutParams. y = 300;
            mFloatingButton.setOnTouchListener( this);
             mWindowManager.addView( mFloatingButton, mLayoutParams); 

flags和type兩個屬性很重要,下面對一些屬性進行介紹,首先是flags:
FLAG_NOT_TOUCH_MODAL表示不需要獲取焦點,也不需要接收各種輸入,最終事件直接傳遞給下層具有焦點的window。
FLAG_NOT_FOCUSABLE:在此window外的區域單擊事件傳遞到底層window中。當前的區域則自己處理,這個一般都要設置,很重要。
FLAG_SHOW_WHEN_LOCKED :開啟可以讓window顯示在鎖屏界面上。
再來看下type這個參數:
window有三種類型:應用window,子window,系統window。應用類對應一個Activity,子Window不能單獨存在,需要附屬在父Window上,比如常用的Dialog。系統Window是需要聲明權限再創建的window,如toast等。
window有z-ordered屬性,層級越大,越在頂層。應用window層級1-99,子window1000-1999,系統2000-2999。這此層級對應著windowManager的type參數。系統層級常用的有兩個TYPE_SYSTEM_OVERLAY或者TYPE_SYSTEM_ERROR。比如想用TYPE_SYSTEM_ERROR,只需
mLayoutParams.type = LayoutParams.TYPE_SYSTEM_ERROR。還要添加權限<uses-permission andorid:name="android.permission.SYSTEM_ALERT_WINDOW"/>。
有了對window的基本認識之后,我們來看下它底層如何實現加載View的。

二,window的創建。

其實Window的創建跟之前我寫的一篇博客LayoutInflater源碼分析有點相似。Window的創建是在Activity創建的attach方法中,通過PolicyManager的makeNewWindow方法。Activity中實現了Window的Callback接口,因此當window狀態改變時就會回調Activity方法。如onAttachedToWindow等。PolicyManager的真正實現類是Policy,看下它的代碼:
 public Window makeNewWindow(Context context) {
        return new PhoneWindow(context);
    }
到此Window創建完成。
下面分析view是如何附屬到window上的。看Activity的setContentView方法。
public void setContentView(int layoutResID) {
        getWindow().setContentView(layoutResID);
        initWindowDecorActionBar();
    }
兩部分,設置內容和設置ActionBar。window的具體實現是PhoneWindow,看它的setContent。
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);
        }
        final Callback cb = getCallback();
        if (cb != null && !isDestroyed()) {
            cb.onContentChanged();
        }
   } 
看到了吧,又是分析它。
這里分三步執行:
1.如果沒有DecorView,在installDecor中的generateDecor()創建DecorView。之前就分析過,這次就不再分析它了。
2.將View添加到decorview中的mContentParent中。
3.回調Activity的onContentChanged接口。
經過以上操作,DecorView創建了,但還沒有正式添加到Window中。在ActivityResumeActivity中首先會調用Activity的onResume,再調用Activity的makeVisible,makeVisible中真正添加view ,代碼如下:
  void makeVisible() {
        if (!mWindowAdded) {
            ViewManager wm = getWindowManager();
            wm.addView(mDecor, getWindow().getAttributes());
            mWindowAdded = true;
        }
        mDecor.setVisibility(View.VISIBLE);
    }
通過上面的addView方法將View添加到Window

三,Window操作View內部機制

1.window的添加

一個window對應一個view和一個viewRootImpl,window和view通過ViewRootImpl來建立聯系,它并不存在,實體是view。只能通過 windowManager來操作它。
windowManager的實現類是windowManagerImpl。它并沒有直接實現三大操作,而是委托給WindowManagerGlobal。addView的實現分為以下幾步:
1.檢查參數是否合法。
if (view == null) {
            throw new IllegalArgumentException("view must not be null");
        }
        if (display == null) {
            throw new IllegalArgumentException("display must not be null");
        }
        if (!(params instanceof WindowManager.LayoutParams)) {
            throw new IllegalArgumentException("Params must be WindowManager.LayoutParams");
        }

        final WindowManager.LayoutParams wparams = (WindowManager.LayoutParams)params;
        if (parentWindow != null) {
            parentWindow.adjustLayoutParamsForSubWindow(wparams);
        } else {
            // If there's no parent and we're running on L or above (or in the
            // system context), assume we want hardware acceleration.
            final Context context = view.getContext();
            if (context != null
                    && context.getApplicationInfo().targetSdkVersion >= Build.VERSION_CODES.LOLLIPOP) {
                wparams.flags |= WindowManager.LayoutParams.FLAG_HARDWARE_ACCELERATED;
            }
        }

2.創建ViewRootImpl并將View添加到列表中。

 root = new ViewRootImpl(view.getContext(), display);

            view.setLayoutParams(wparams);

            mViews.add(view);
            mRoots.add(root);
            mParams.add(wparams);
3.通過ViewRootImpl來更新界面并完成window的添加過程 。
root.setView(view, wparams, panelParentView);
上面的root就是ViewRootImpl,setView中通過requestLayout()來完成異步刷新,看下requestLayout:
 public void requestLayout() {
        if (!mHandlingLayoutInLayoutRequest) {
            checkThread();
            mLayoutRequested = true;
            scheduleTraversals();
        }
    }
接下來通過WindowSession來完成window添加過程,WindowSession是一個Binder對象,真正的實現類是 Session,window的添加是一次IPC調用。
 try {
                    mOrigWindowType = mWindowAttributes.type;
                    mAttachInfo.mRecomputeGlobalAttributes = true;
                    collectViewAttributes();
                    res = mWindowSession.addToDisplay(mWindow, mSeq, mWindowAttributes,
                            getHostVisibility(), mDisplay.getDisplayId(),
                            mAttachInfo.mContentInsets, mAttachInfo.mStableInsets, mInputChannel);
                } catch (RemoteException e) {
                    mAdded = false;
                    mView = null;
                    mAttachInfo.mRootView = null;
                    mInputChannel = null;
                    mFallbackEventHandler.setView(null);
                    unscheduleTraversals();
                    setAccessibilityFocus(null, null);
                    throw new RuntimeException("Adding window failed", e);
}
在Session內部會通過WindowManagerService來實現Window的添加。
  public int addToDisplay(IWindow window, int seq, WindowManager.LayoutParams attrs,
            int viewVisibility, int displayId, Rect outContentInsets, Rect outStableInsets,
            InputChannel outInputChannel) {
        return mService.addWindow(this, window, seq, attrs, viewVisibility, displayId,
                outContentInsets, outStableInsets, outInputChannel);
    }
在WindowManagerService內部會為每一個應用保留一個單獨的session。

2.window的刪除

看下WindowManagerGlobal的removeView:
public void removeView(View view, boolean immediate) {
        if (view == null) {
            throw new IllegalArgumentException("view must not be null");
        }

        synchronized (mLock) {
            int index = findViewLocked(view, true);
            View curView = mRoots.get(index).getView();
            removeViewLocked(index, immediate);
            if (curView == view) {
                return;
            }

            throw new IllegalStateException("Calling with view " + view
                    + " but the ViewAncestor is attached to " + curView);
        }
    }

首先調用findViewLocked來查找刪除view的索引,這個過程就是建立數組遍歷。然后再調用removeViewLocked來做進一步的刪除。
private void removeViewLocked(int index, boolean immediate) {
        ViewRootImpl root = mRoots.get(index);
        View view = root.getView();

        if (view != null) {
            InputMethodManager imm = InputMethodManager.getInstance();
            if (imm != null) {
                imm.windowDismissed(mViews.get(index).getWindowToken());
            }
        }
        boolean deferred = root.die(immediate);
        if (view != null) {
            view.assignParent(null);
            if (deferred) {
                mDyingViews.add(view);
            }
        }
    }
真正刪除操作是viewRootImpl來完成的。windowManager提供了兩種刪除接口,removeViewImmediate,removeView。它們分別表示異步刪除和同步刪除。具體的刪除操作由ViewRootImpl的die來完成。
boolean die(boolean immediate) {
        // Make sure we do execute immediately if we are in the middle of a traversal or the damage
        // done by dispatchDetachedFromWindow will cause havoc on return.
        if (immediate && !mIsInTraversal) {
            doDie();
            return false;
        }

        if (!mIsDrawing) {
            destroyHardwareRenderer();
        } else {
            Log.e(TAG, "Attempting to destroy the window while drawing!\n" +
                    "  window=" + this + ", title=" + mWindowAttributes.getTitle());
        }
        mHandler.sendEmptyMessage(MSG_DIE);
        return true;
    }
由上可知如果是removeViewImmediate,立即調用doDie,如果是removeView,用handler發送消息,ViewRootImpl中的Handler會處理消息并調用doDie。重點看下doDie:
void doDie() {
        checkThread();
        if (LOCAL_LOGV) Log.v(TAG, "DIE in " + this + " of " + mSurface);
        synchronized (this) {
            if (mRemoved) {
                return;
            }
            mRemoved = true;
            if (mAdded) {
                dispatchDetachedFromWindow();
            }

            if (mAdded && !mFirst) {
                destroyHardwareRenderer();

                if (mView != null) {
                    int viewVisibility = mView.getVisibility();
                    boolean viewVisibilityChanged = mViewVisibility != viewVisibility;
                    if (mWindowAttributesChanged || viewVisibilityChanged) {
                        // If layout params have been changed, first give them
                        // to the window manager to make sure it has the correct
                        // animation info.
                        try {
                            if ((relayoutWindow(mWindowAttributes, viewVisibility, false)
                                    & WindowManagerGlobal.RELAYOUT_RES_FIRST_TIME) != 0) {
                                mWindowSession.finishDrawing(mWindow);
                            }
                        } catch (RemoteException e) {
                        }
                    }

                    mSurface.release();
                }
            }

            mAdded = false;
        }
        WindowManagerGlobal.getInstance().doRemoveView(this);
    }
主要做四件事:
1.垃圾回收相關工作,比如清數據,回調等。
2.通過Session的remove方法刪除Window,最終調用WindowManagerService的removeWindow

3.調用dispathDetachedFromWindow,在內部會調用onDetachedFromWindow()和onDetachedFromWindowInternal()。當view移除時會調用onDetachedFromWindow,它用于作一些資源回收。
4.通過doRemoveView刷新數據,刪除相關數據,如在mRoot,mDyingViews中刪除對象等。
void doRemoveView(ViewRootImpl root) {
        synchronized (mLock) {
            final int index = mRoots.indexOf(root);
            if (index >= 0) {
                mRoots.remove(index);
                mParams.remove(index);
                final View view = mViews.remove(index);
                mDyingViews.remove(view);
            }
        }
        if (HardwareRenderer.sTrimForeground && HardwareRenderer.isAvailable()) {
            doTrimForeground();
        }
    }

3.更新window

看下WindowManagerGlobal中的updateViewLayout。
 public void updateViewLayout(View view, ViewGroup.LayoutParams params) {
        if (view == null) {
            throw new IllegalArgumentException("view must not be null");
        }
        if (!(params instanceof WindowManager.LayoutParams)) {
            throw new IllegalArgumentException("Params must be WindowManager.LayoutParams");
        }

        final WindowManager.LayoutParams wparams = (WindowManager.LayoutParams)params;

        view.setLayoutParams(wparams);

        synchronized (mLock) {
            int index = findViewLocked(view, true);
            ViewRootImpl root = mRoots.get(index);
            mParams.remove(index);
            mParams.add(index, wparams);
            root.setLayoutParams(wparams, false);
        }
    }
通過viewRootImpl的setLayoutParams更新viewRootImpl的layoutParams,接著scheduleTraversals對view重新布局,包括測量,布局,重繪,此外它還會通過WindowSession來更新window。這個過程由WindowManagerService實現。這跟上面類似,就不再重復。到此Window底層源碼就分析完啦。



















Android中Window添加View的底層原理

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原文地址:http://blog.csdn.net/u014486880/article/details/50785919

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