Android dynamic permission application has never been easier

foreword

Note: Friends who just want to see the implementation can jump directly to the final implementation at the end

Are you still troubled by the dynamic permission application? The traditional dynamic permission application needs Activityto rewrite onRequestPermissionsResultthe method in to receive the result of user permission grant. Just imagine, if you need to apply for permissions in a sub-module, then you have to pass the results back to this module layer by layer from the module where the module is located Activity. onRequestPermissionsResultIt is quite troublesome, and the code is quite redundant and unclean. OCD.

use

In order to solve this pain point, I have encapsulated two methods for quickly and dynamically applying for permissions anytime and anywhere. Let's first take a look at how our encapsulation methods are called:

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）
    }
})
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Isn't this very simple and convenient? Both the application and the result callback are processed in one method, and it supports on-demand calling.

plan

So, how is such a convenient and easy-to-use method realized? I don’t know if you guys have noticed in your daily development. When you call it startActivityForResult, AS will prompt you that the method has been deprecated. Click it and it will tell you that you should use registerForActivityResultthe method instead. That's right, this is the function androidxprovided to us ActivityResult, and this function not only supports ActivityResultcallbacks, but also supports various callbacks such as opening documents, taking photos, selecting files, etc. It also includes the permission application we are going to talk about today

In fact, Android has already used it as the recommended method for dynamic permission application in the official document requesting runtime permissions, as shown in the following sample code:

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)
    }
}
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Speaking of this, some friends may want to question me: "You have written something that is clearly stated in the official document, and you have such a title, is it in the water article?!"

Don't worry, if you write according to the above method, it will crash directly when you actually call it:

java.lang.IllegalStateException: 
LifecycleOwner Activity is attempting to register while current state is RESUMED. 
LifecycleOwners must call register before they are STARTED.
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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。

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>() { ... };
}
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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>() { ... };
}
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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。

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)
}
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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。