部分查看源码的要点总结

朴灿烈づ我的快乐病毒、 2022-05-27 13:11 170阅读 0赞

最近看了不少源码，然而看源码这种事情当时分析清楚了，下一次再看又感觉不太熟悉，毕竟Read The Fucking Source Code 嘛。所以把我感觉重要的点略微记录一下。

##### 一、在onLayout()方法中调用requestLayot() #####

[https://blog.csdn.net/litefish/article/details/53645942?utm\_source=itdadao&utm\_medium=referral][https_blog.csdn.net_litefish_article_details_53645942_utm_source_itdadao_utm_medium_referral]

这篇博文基本上已经总结比较清楚了，然而我实际测试的时候把requestLayout()放在super.onLayout()之前的时候，不会进入后续的第二次layout。一开始还不太理解，后来仔细查看源码发现在getValidLayoutRequesters()这个方法中，调用requestLayout的view在layout结束之后PFLAG\_FORCE\_LAYOUT置位，所以返回值会变为null,所以第二次layout将不会执行。但是如果这样写有一个问题，有时候设置某些属性的是在measure中实现，这样写不会进入第二次的measure,layout，会导致无法出现期望的结果。所以如果要在onLayout方法中调用requestLayot，需要写在super.onLayout()的后面。我实际测试LinearLayout中设置padding,是可以写在前面的。

##### 二、Activity的finish()源码分析 #####

[https://blog.csdn.net/zjd934784273/article/details/73930855][https_blog.csdn.net_zjd934784273_article_details_73930855]

当时看这篇文章主要是想了解下finish以及onActivityResult()的调用流程。这里总结一下吧。

主要方法是ActivityStack的resumeTopActivityInnerLocked方法，这里主要就是

{
        // Find the next top-most activity to resume in this stack that is not finishing and is
            // focusable. If it is not focusable, we will fall into the case below to resume the
            // top activity in the next focusable task.
            final ActivityRecord next = topRunningActivityLocked(true /* focusableOnly */);
    
                 // Deliver all pending results.  
                 ArrayList<ResultInfo> a = next.results;  
                 if (a != null) {  
                     final int N = a.size();  
                     if (!next.finishing && N > 0) {  
                         if (DEBUG_RESULTS) Slog.v(TAG_RESULTS,  
                                 "Delivering results to " + next + ": " + a);  
                         next.app.thread.scheduleSendResult(next.appToken, a);  
                     }  
                 }  
    
                 if (next.newIntents != null) {  
                     next.app.thread.scheduleNewIntent(next.newIntents, next.appToken);  
                 }  
    
                ......  
                 next.app.thread.scheduleResumeActivity(next.appToken, next.app.repProcState,  
                 mService.isNextTransitionForward(), resumeAnimOptions);  
     }

scheduleResumeActivity会调用onReStart–>onStart—>onResume  
所以onActivityResult以及newIntent会在这些声明周期之前执行。  
在window中添加view,并执行measure,layout之类的方法是在onResume之后执行的，所以在activity的onResume中无法获取view的宽高  
next我们通过注释知道是找到栈顶的activity，也就是接下来要显示的activity。  
next的results是在finish的时候设置的，最终方法是ActivityStack的finishActivityResultsLocked()。

private void finishActivityResultsLocked(ActivityRecord r, int resultCode, Intent resultData) {
            // send the result
            ActivityRecord resultTo = r.resultTo;
            if (resultTo != null) {
                if (DEBUG_RESULTS) Slog.v(TAG_RESULTS, "Adding result to " + resultTo
                        + " who=" + r.resultWho + " req=" + r.requestCode
                        + " res=" + resultCode + " data=" + resultData);
                if (resultTo.userId != r.userId) {
                    if (resultData != null) {
                        resultData.prepareToLeaveUser(r.userId);
                    }
                }
                if (r.info.applicationInfo.uid > 0) {
                    mService.grantUriPermissionFromIntentLocked(r.info.applicationInfo.uid,
                            resultTo.packageName, resultData,
                            resultTo.getUriPermissionsLocked(), resultTo.userId);
                }
                resultTo.addResultLocked(r, r.resultWho, r.requestCode, resultCode,
                                         resultData);
                r.resultTo = null;
            }
            else if (DEBUG_RESULTS) Slog.v(TAG_RESULTS, "No result destination from " + r);
    
            // Make sure this HistoryRecord is not holding on to other resources,
            // because clients have remote IPC references to this object so we
            // can't assume that will go away and want to avoid circular IPC refs.
            r.results = null;
            r.pendingResults = null;
            r.newIntents = null;
            r.icicle = null;
        }

如果A启动B,那么B调用finish，这里的r就是B，r.resultTo就是A，所以在A的results中加入结果，在之后A将要显示的时候就会判断results是否大于0来确认是否需要调用onActivityResult()。

[https_blog.csdn.net_litefish_article_details_53645942_utm_source_itdadao_utm_medium_referral]: https://blog.csdn.net/litefish/article/details/53645942?utm_source=itdadao&utm_medium=referral
[https_blog.csdn.net_zjd934784273_article_details_73930855]: https://blog.csdn.net/zjd934784273/article/details/73930855