Java Android：requestcode值应该选择什么？

像

ActivityCompat.requestPermissions

这样的方法要求我向它们传递一个requestcode，稍后我可以在回调中测试它（在本例中是

onRequestPermissionsResult

）。我应该在requestcode中传递一些最佳实践值吗？我注意到，如果我只是输入一个随机的

int

，有时会出现如下错误：

java.lang.IllegalArgumentException: Can only use lower 8 bits for requestCode



10-25 16:47:43.652 8315-8315/? E/AndroidRuntime: FATAL EXCEPTION: main
10-25 16:47:43.652 8315-8315/? E/AndroidRuntime: Process: my package, PID: 8315
10-25 16:47:43.652 8315-8315/? E/AndroidRuntime: java.lang.RuntimeException: Unable to start activity ComponentInfo{mypackage.myactivity}: java.lang.IllegalArgumentException: Can only use lower 8 bits for requestCode
10-25 16:47:43.652 8315-8315/? E/AndroidRuntime:     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2416)
10-25 16:47:43.652 8315-8315/? E/AndroidRuntime:     at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2476)
10-25 16:47:43.652 8315-8315/? E/AndroidRuntime:     at android.app.ActivityThread.-wrap11(ActivityThread.java)
10-25 16:47:43.652 8315-8315/? E/AndroidRuntime:     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1344)
10-25 16:47:43.652 8315-8315/? E/AndroidRuntime:     at android.os.Handler.dispatchMessage(Handler.java:102)
10-25 16:47:43.652 8315-8315/? E/AndroidRuntime:     at android.os.Looper.loop(Looper.java:148)
10-25 16:47:43.652 8315-8315/? E/AndroidRuntime:     at android.app.ActivityThread.main(ActivityThread.java:5417)
10-25 16:47:43.652 8315-8315/? E/AndroidRuntime:     at java.lang.reflect.Method.invoke(Native Method)
10-25 16:47:43.652 8315-8315/? E/AndroidRuntime:     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:726)
10-25 16:47:43.652 8315-8315/? E/AndroidRuntime:     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616)
10-25 16:47:43.652 8315-8315/? E/AndroidRuntime:  Caused by: java.lang.IllegalArgumentException: Can only use lower 8 bits for requestCode
10-25 16:47:43.652 8315-8315/? E/AndroidRuntime:     at android.support.v4.app.FragmentActivity.validateRequestPermissionsRequestCode(FragmentActivity.java:799)
10-25 16:47:43.652 8315-8315/? E/AndroidRuntime:     at android.support.v4.app.ActivityCompatApi23.requestPermissions(ActivityCompat23.java:29)
10-25 16:47:43.652 8315-8315/? E/AndroidRuntime:     at android.support.v4.app.ActivityCompat.requestPermissions(ActivityCompat.java:316)
10-25 16:47:43.652 8315-8315/? E/AndroidRuntime:     at mypackage.myactivity.checkReadPhoneState(PermissionsGatewayActivity.java:48)
10-25 16:47:43.652 8315-8315/? E/AndroidRuntime:     at mypackage.myactivity.onCreate(PermissionsGatewayActivity.java:36)
10-25 16:47:43.652 8315-8315/? E/AndroidRuntime:     at android.app.Activity.performCreate(Activity.java:6237)
10-25 16:47:43.652 8315-8315/? E/AndroidRuntime:     at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1107)
10-25 16:47:43.652 8315-8315/? E/AndroidRuntime:     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2369)
10-25 16:47:43.652 8315-8315/? E/AndroidRuntime:     at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2476) 
10-25 16:47:43.652 8315-8315/? E/AndroidRuntime:     at android.app.ActivityThread.-wrap11(ActivityThread.java) 
10-25 16:47:43.652 8315-8315/? E/AndroidRuntime:     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1344) 
10-25 16:47:43.652 8315-8315/? E/AndroidRuntime:     at android.os.Handler.dispatchMessage(Handler.java:102) 
10-25 16:47:43.652 8315-8315/? E/AndroidRuntime:     at android.os.Looper.loop(Looper.java:148) 
10-25 16:47:43.652 8315-8315/? E/AndroidRuntime:     at android.app.ActivityThread.main(ActivityThread.java:5417) 
10-25 16:47:43.652 8315-8315/? E/AndroidRuntime:     at java.lang.reflect.Method.invoke(Native Method) 
10-25 16:47:43.652 8315-8315/? E/AndroidRuntime:     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:726) 
10-25 16:47:43.652 8315-8315/? E/AndroidRuntime:     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616) 

---

记录调查结果以备将来参考：

以下是来自android.support.v4.app.FragmentActivity

 /**
 * Modifies the standard behavior to allow results to be delivered to fragments.
 * This imposes a restriction that requestCode be <= 0xffff.
 */
@Override
public void startActivityForResult(Intent intent, int requestCode) {
    if (requestCode != -1 && (requestCode&0xffff0000) != 0) {
        throw new IllegalArgumentException("Can only use lower 16 bits for requestCode");
    }
    super.startActivityForResult(intent, requestCode);
}

范围

FragmentActivity

中的

startActivityForResult（）

要求请求代码为16位，这意味着范围从0到65535

---

另外，

FragmentActivity

中的

validateRequestPermissionsRequestCode

要求requestCode为16位，这意味着范围是从0到65535

尝试介于1到255之间的请求代码。这就是它的意思吗？所以从理论上讲，并行运行的请求不可能超过256个？（尽管这很可笑）我认为这个数字在现实世界中已经足够了。我们需要调用ActivityCompat.requestPermissions（）方法的权限（危险权限）不到30个。所以我认为256就足够了。不是吗？我想让我生气的是请求代码参数是int，另外，文档中没有提到8位的限制。FFSRange已更改@多谢。更新了我的答案。

@Override
public final void validateRequestPermissionsRequestCode(int requestCode) {
    // We use 16 bits of the request code to encode the fragment id when
    // requesting permissions from a fragment. Hence, requestPermissions()
    // should validate the code against that but we cannot override it as
    // we can not then call super and also the ActivityCompat would call
    // back to this override. To handle this we use dependency inversion
    // where we are the validator of request codes when requesting
    // permissions in ActivityCompat.
    if (!mRequestedPermissionsFromFragment
            && requestCode != -1 && (requestCode & 0xffff0000) != 0) {
        throw new IllegalArgumentException("Can only use lower 16 bits for requestCode");
    }
}