Android GUI之View绘制流程
在上篇文章中,我们通过跟踪源代码,我们了解了Activity、Window、DecorView以及View之间的关系(查看文章:http://blog.csdn.net/jerehedu/article/details/47021541)。
那么整个Activity的界面究竟是怎样绘制出来的呢?既然DecorView作为Activity的顶层界面视图。那么整个界面的绘制工作应该从它開始,以下我们继续跟踪源代码,看看是不是这种。
Activity在启动过程中会调用主线程ActivityThread中的方法performLaunchActivity和handleResumeActivity。在方法handleResumeActivity中会将创建的DecorView和WindowManagerImpl对象关联起来。关键源代码部分例如以下:
public final class ActivityThread { …… final void handleResumeActivity(IBinder token, boolean clearHide, boolean isForward, boolean reallyResume) { …… if (r.window == null && !a.mFinished && willBeVisible) { r.window = r.activity.getWindow(); View decor = r.window.getDecorView(); decor.setVisibility(View.INVISIBLE); ViewManager wm = a.getWindowManager(); WindowManager.LayoutParams l = r.window.getAttributes(); a.mDecor = decor; l.type = WindowManager.LayoutParams.TYPE_BASE_APPLICATION; l.softInputMode |= forwardBit; if (a.mVisibleFromClient) { a.mWindowAdded = true; wm.addView(decor, l); } } …… } }
WindowManagerImpl关键代码:
public final class WindowManagerImpl implements WindowManager { private final WindowManagerGlobal mGlobal = WindowManagerGlobal.getInstance(); …… @Override public void addView(View view, ViewGroup.LayoutParams params) { mGlobal.addView(view, params, mDisplay, mParentWindow); } …… }
WindowManagerGlobal关键代码:
public final class WindowManagerGlobal { …… public void addView(View view, ViewGroup.LayoutParams params, Display display, Window parentWindow) { …… ViewRootImpl root; View panelParentView = null; …… root.setView(view, wparams, panelParentView); …… } }
依据源代码调用关系。可得下图:
从图中。我们能够看出在ActivityThread中生成的DecorView经过WindowManagerImpl、WindowManagerGlobal,终于调用了ViewRootImpl中的setView方法。将DecorView设置赋值给了ViewRootImpl中的mView属性。
通过追踪ViewRootImpl我们发现终于调用了performTraversals方法。该方法关键代码例如以下:
private void performTraversals() { // cache mView since it is used so much below... final View host = mView; …… performMeasure(childWidthMeasureSpec, childHeightMeasureSpec); …… performLayout(lp, desiredWindowWidth, desiredWindowHeight); …… performDraw(); …… }
从上述源代码中我们能够看出。performTraversals实际上依次调用了三个关键的方法,各自是performMeasure,performLayout、performDraw。
1、方法performMeasure,内部实际上调用了mView.measure(childWidthMeasureSpec, childHeightMeasureSpec);不要忘了此处的mView正是我们传递进来的DecorView,该方法用于測量View的大小。
关键源代码例如以下:
private void performMeasure(int childWidthMeasureSpec, int childHeightMeasureSpec) { Trace.traceBegin(Trace.TRACE_TAG_VIEW, "measure"); try { mView.measure(childWidthMeasureSpec, childHeightMeasureSpec); } finally { Trace.traceEnd(Trace.TRACE_TAG_VIEW); } }
2、方法performLayout,内部实际上调用了host.layout(0, 0, host.getMeasuredWidth(), host.getMeasuredHeight());该方法用于确定视图的位置。
关键源代码例如以下:
private void performLayout(WindowManager.LayoutParams lp, int desiredWindowWidth, int desiredWindowHeight) { mLayoutRequested = false; mScrollMayChange = true; mInLayout = true; final View host = mView; …… try { host.layout(0, 0, host.getMeasuredWidth(), host.getMeasuredHeight()); mInLayout = false; int numViewsRequestingLayout = mLayoutRequesters.size(); if (numViewsRequestingLayout > 0) { …… if (validLayoutRequesters != null) { // Set this flag to indicate that any further requests are happening during …… host.layout(0, 0, host.getMeasuredWidth(), host.getMeasuredHeight()); …… } } } } finally { Trace.traceEnd(Trace.TRACE_TAG_VIEW); } mInLayout = false; }
3、方法performDraw。用于绘制视图。追踪源代码发现,终于调用了mView.draw(canvas)方法。用于绘制。
经过上述过程基本上能够确定View的绘制流程,流程图详细例如以下:
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出处:http://blog.csdn.net/jerehedu/
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posted on 2017-08-13 17:20 cynchanpin 阅读(238) 评论(0) 编辑 收藏 举报