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问题回顾：
在Android8.0手机上不能直接安装Apk，需要权限申请，回调后执行onActivityResult()方法，并弹出对应的dialog，这时需要判断当前Activity是否处于resume状态，通过变量来控制，但结果是这个dialog并不会弹出。
问题本质
Activity跳转到系统应用后回调onActivityResult() 先执行还是onResume()先执行？
查看源码
/**
* Called when an activity you launched exits, giving you the requestCode
* you started it with, the resultCode it returned, and any additional
* data from it. The resultCode will be
* {@link #RESULT_CANCELED} if the activity explicitly returned that,
* didn’t return any result, or crashed during its operation.
*
*
You will receive this call immediately before onResume() when your
* activity is re-starting.
*
*
This method is never invoked if your activity sets
* {@link android.R.styleable#AndroidManifestActivity_noHistory noHistory} to
* true.
*
* @param requestCode The integer request code originally supplied to
* startActivityForResult(), allowing you to identify who this
* result came from.
* @param resultCode The integer result code returned by the child activity
* through its setResult().
* @param data An Intent, which can return result data to the caller
* (various data can be attached to Intent “extras”).
*
* @see #startActivityForResult
* @see #createPendingResult
* @see #setResult(int)
*/
protected void onActivityResult(int requestCode, int resultCode, Intent data) {
}
onActivityResult()注释中有这么一句话：
You will receive this call immediately before onResume() when your activity is re-starting.
(意思是说当你的Activity重新启动时 onActivityResult() 会在onResume()之前执行)
很显然，如果你的Activity 调用了 startActivityForResult() 方法启动，回调之后会先执行 onActivityResult() ,然后执行onResume()
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