Android动态权限申请从未如此简单
作者：dreamgyf
juejin.cn/post/7225516176171188285
1. 前言
大家是否还在为动态权限申请感到苦恼呢？传统的动态权限申请需要在 Activity 中重写 onRequestPermissionsResult 方法来接收用户权限授予的结果。试想一下，你需要在一个子模块中申请权限，那得从这个模块所在的 Activity 的 onRequestPermissionsResult 中将结果一层层再传回到这个模块中，相当的麻烦，代码也相当冗余和不干净，逼死强迫症。
2. 使用
为了解决这个痛点，我封装出了两个方法，用于随时随地快速的动态申请权限，我们先来看看我们的封装方法是如何调用的：
activity.requestPermission(Manifest.permission.CAMERA, onPermit = {
//申请权限成功 Do something
}, onDeny = { shouldShowCustomRequest ->
//申请权限失败 Do something
if (shouldShowCustomRequest) {
//用户选择了拒绝并且不在询问，此时应该使用自定义弹窗提醒用户授权（可选）
}
})
这样是不是非常的简单便捷？申请和结果回调都在一个方法内处理，并且支持随用随调。
3. 方案
那么，这么方便好用的方法是怎么实现的呢？不知道小伙伴们在平时开发中有没有注意到过，当你调用 startActivityForResult 时，AS会提示你该方法已被弃用，点进去看会告诉你应该使用 registerForActivityResult 方法替代。没错，这就是 androidx 给我们提供的 ActivityResult 功能，并且这个功能不仅支持 ActivityResult 回调，还支持打开文档，拍摄照片，选择文件等各种各样的回调，同样也包括我们今天要说的权限申请
其实 Android 在官方文档“请求运行时权限”中就已经将其作为动态权限申请的推荐方法了：https://developer.android.com/training/permissions/requesting
如下示例代码所示：
val requestPermissionLauncher =
registerForActivityResult(RequestPermission()
) { isGranted: Boolean ->
if (isGranted) {
// Permission is granted. Continue the action or workflow in your
// app.
} else {
// Explain to the user that the feature is unavailable because the
// feature requires a permission that the user has denied. At the
// same time, respect the user's decision. Don't link to system
// settings in an effort to convince the user to change their
// decision.
}
}
when {
ContextCompat.checkSelfPermission(
CONTEXT,
Manifest.permission.REQUESTED_PERMISSION
) == PackageManager.PERMISSION_GRANTED -> {
// You can use the API that requires the permission.
}
shouldShowRequestPermissionRationale(...) -> {
// In an educational UI, explain to the user why your app requires this
// permission for a specific feature to behave as expected, and what
// features are disabled if it's declined. In this UI, include a
// "cancel" or "no thanks" button that lets the user continue
// using your app without granting the permission.
showInContextUI(...)
}
else -> {
// You can directly ask for the permission.
// The registered ActivityResultCallback gets the result of this request.
requestPermissionLauncher.launch(
Manifest.permission.REQUESTED_PERMISSION)
}
}
说到这里，可能有小伙伴要质疑我了：“官方文档里都写明了的东西，你还特地写一遍，还起了这么个标题，是不是在水文章？！”
莫急，如果你遵照以上方法这么写的话，在实际调用的时候会直接发生崩溃：
java.lang.IllegalStateException:
LifecycleOwner Activity is attempting to register while current state is RESUMED.
LifecycleOwners must call register before they are STARTED.
这段报错很明显的告诉我们，我们的注册工作必须要在 Activity 声明周期 STARTED 之前进行（也就是 onCreate 时和 onStart 完成前），但这样我们就必须要事先注册好所有可能会用到的权限，没办法做到随时随地有需要时再申请权限了，有办法解决这个问题吗？答案是肯定的。
4. 绕过生命周期检测
想解决这个问题，我们必须要知道问题的成因，让我们带着问题进到源码中一探究竟：
public final <I, O> ActivityResultLauncher<I> registerForActivityResult(
@NonNull ActivityResultContract<I, O> contract,
@NonNull ActivityResultCallback<O> callback) {
return registerForActivityResult(contract, mActivityResultRegistry, callback);
}
public final <I, O> ActivityResultLauncher<I> registerForActivityResult(
@NonNull final ActivityResultContract<I, O> contract,
@NonNull final ActivityResultRegistry registry,
@NonNull final ActivityResultCallback<O> callback) {
return registry.register(
"activity_rq#" + mNextLocalRequestCode.getAndIncrement(), this, contract, callback);
}
public final <I, O> ActivityResultLauncher<I> register(
@NonNull final String key,
@NonNull final LifecycleOwner lifecycleOwner,
@NonNull final ActivityResultContract<I, O> contract,
@NonNull final ActivityResultCallback<O> callback) {
Lifecycle lifecycle = lifecycleOwner.getLifecycle();
if (lifecycle.getCurrentState().isAtLeast(Lifecycle.State.STARTED)) {
throw new IllegalStateException("LifecycleOwner " + lifecycleOwner + " is "
+ "attempting to register while current state is "
+ lifecycle.getCurrentState() + ". LifecycleOwners must call register before "
+ "they are STARTED.");
}
registerKey(key);
LifecycleContainer lifecycleContainer = mKeyToLifecycleContainers.get(key);
if (lifecycleContainer == null) {
lifecycleContainer = new LifecycleContainer(lifecycle);
}
LifecycleEventObserver observer = new LifecycleEventObserver() { ... };
lifecycleContainer.addObserver(observer);
mKeyToLifecycleContainers.put(key, lifecycleContainer);
return new ActivityResultLauncher<I>() { ... };
}
我们可以发现，registerForActivityResult 实际上就是调用了 ComponentActivity 内部成员变量的 mActivityResultRegistry.register 方法，而在这个方法的一开头就检查了当前 Activity 的生命周期，如果生命周期位于STARTED后则直接抛出异常，那我们该如何绕过这个限制呢？
其实在 register 方法的下面就有一个同名重载方法，这个方法并没有做生命周期的检测：
public final <I, O> ActivityResultLauncher<I> register(
@NonNull final String key,
@NonNull final ActivityResultContract<I, O> contract,
@NonNull final ActivityResultCallback<O> callback) {
registerKey(key);
mKeyToCallback.put(key, new CallbackAndContract<>(callback, contract));
if (mParsedPendingResults.containsKey(key)) {
@SuppressWarnings("unchecked")
final O parsedPendingResult = (O) mParsedPendingResults.get(key);
mParsedPendingResults.remove(key);
callback.onActivityResult(parsedPendingResult);
}
final ActivityResult pendingResult = mPendingResults.getParcelable(key);
if (pendingResult != null) {
mPendingResults.remove(key);
callback.onActivityResult(contract.parseResult(
pendingResult.getResultCode(),
pendingResult.getData()));
}
return new ActivityResultLauncher<I>() { ... };
}
找到这个方法就简单了，我们将 registerForActivityResult 方法调用替换成 activityResultRegistry.register 调用就可以了
当然，我们还需要注意一些小细节，检查生命周期的 register 方法同时也会注册生命周期回调，当 Activity 被销毁时会将我们注册的 ActivityResult 回调移除，我们也需要给我们封装的方法加上这个逻辑，最终实现就如下所示。
5. 最终实现
private val nextLocalRequestCode = AtomicInteger()
private val nextKey: String
get() = "activity_rq#${nextLocalRequestCode.getAndIncrement()}"
fun ComponentActivity.requestPermission(
permission: String,
onPermit: () -> Unit,
onDeny: (shouldShowCustomRequest: Boolean) -> Unit
) {
if (ContextCompat.checkSelfPermission(this, permission) == PackageManager.PERMISSION_GRANTED) {
onPermit()
return
}
var launcher by Delegates.notNull<ActivityResultLauncher<String>>()
launcher = activityResultRegistry.register(
nextKey,
ActivityResultContracts.RequestPermission()
) { result ->
if (result) {
onPermit()
} else {
onDeny(!ActivityCompat.shouldShowRequestPermissionRationale(this, permission))
}
launcher.unregister()
}
lifecycle.addObserver(object : LifecycleEventObserver {
override fun onStateChanged(source: LifecycleOwner, event: Lifecycle.Event) {
if (event == Lifecycle.Event.ON_DESTROY) {
launcher.unregister()
lifecycle.removeObserver(this)
}
}
})
launcher.launch(permission)
}
fun ComponentActivity.requestPermissions(
permissions: Array<String>,
onPermit: () -> Unit,
onDeny: (shouldShowCustomRequest: Boolean) -> Unit
) {
var hasPermissions = true
for (permission in permissions) {
if (ContextCompat.checkSelfPermission(
this,
permission
) != PackageManager.PERMISSION_GRANTED
) {
hasPermissions = false
break
}
}
if (hasPermissions) {
onPermit()
return
}
var launcher by Delegates.notNull<ActivityResultLauncher<Array<String>>>()
launcher = activityResultRegistry.register(
nextKey,
ActivityResultContracts.RequestMultiplePermissions()
) { result ->
var allAllow = true
for (allow in result.values) {
if (!allow) {
allAllow = false
break
}
}
if (allAllow) {
onPermit()
} else {
var shouldShowCustomRequest = false
for (permission in permissions) {
if (!ActivityCompat.shouldShowRequestPermissionRationale(this, permission)) {
shouldShowCustomRequest = true
break
}
}
onDeny(shouldShowCustomRequest)
}
launcher.unregister()
}
lifecycle.addObserver(object : LifecycleEventObserver {
override fun onStateChanged(source: LifecycleOwner, event: Lifecycle.Event) {
if (event == Lifecycle.Event.ON_DESTROY) {
launcher.unregister()
lifecycle.removeObserver(this)
}
}
})
launcher.launch(permissions)
}
6. 总结
其实很多实用技巧本质上都是很简单的，但没有接触过就很难想到，我将我的开发经验分享给大家，希望能帮助到大家。
