前言
上一篇文章,笔者详细讲述了View三大工作流程的第一个,Measure流程,如果对测量流程还不熟悉的读者可以参考一下上一篇文章。测量流程主要是对View树进行测量,获取每一个View的测量宽高,那么有了测量宽高,就是要进行布局流程了,布局流程相对测量流程来说简单许多。那么我们开始对layout流程进行详细的解析。
ViewGroup的布局流程
上一篇文章提到,三大流程始于ViewRootImpl#performTraversals方法,在该方法内通过调用performMeasure、performLayout、performDraw这三个方法来进行measure、layout、draw流程,那么我们就从performLayout方法开始说,我们先看它的源码:
private void performLayout(WindowManager.LayoutParams lp, int desiredWindowWidth, int desiredWindowHeight) { mLayoutRequested = false; mScrollMayChange = true; mInLayout = true; final View host = mView; if (DEBUG_ORIENTATION || DEBUG_LAYOUT) { Log.v(TAG, "Laying out " + host + " to (" + host.getMeasuredWidth() + ", " + host.getMeasuredHeight() + ")"); } Trace.traceBegin(Trace.TRACE_TAG_VIEW, "layout"); try { host.layout(0, 0, host.getMeasuredWidth(), host.getMeasuredHeight()); // 1 //省略... } finally { Trace.traceEnd(Trace.TRACE_TAG_VIEW); } mInLayout = false; }