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RxPermissions 源碼解析

簡介

RxPermissions 是基于 RxJava 開發的用于幫助在Android 6.0 中處理運行時權限檢測的框架。在 Android 6.0 中增加了對危險權限的動態申請，而不是像 Android 6.0 之前的默認全部獲取的方式。

原始動態權限的獲取

如果按照以往的獲取權限方式的話，那么我們獲取權限一般需要有 3 個步驟，第一步是先判斷當前是否已經獲取到該權限了；第 2 步申請對應的權限；第 3 步在 Activity 或者 Fragment 中處理獲取權限的結果。具體的實現步驟如下：

step 1：判斷權限是否已經獲取。

if (ActivityCompat.shouldShowRequestPermissionRationale(this,Manifest.permission.CAMERA)) {//用于開發者提示用戶權限的用途} else {//申請權限}
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step 2:申請權限

ActivityCompat.requestPermissions(MainActivity.this,new String[]{Manifest.permission.CAMERA},REQUEST_CAMERA);
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step 3:結果處理

@Override
public void onRequestPermissionsResult(int requestCode, @NonNull String[] permissions,@NonNull int[] grantResults) {// 判斷請求碼，確定當前申請的權限if (requestCode == REQUEST_CAMERA) {//判斷權限是否申請通過if (grantResults.length == 1 && grantResults[0] == PackageManager.PERMISSION_GRANTED) {//授權成功} else {//授權失敗}} else {super.onRequestPermissionsResult(requestCode, permissions, grantResults);}
}復制代碼

RxPermissions 的簡單使用

其實 RxPermissions 的使用方式有兩種

方式 1：

RxPermissions rxPermissions = new RxPermissions(MainActivity.this);rxPermissions.request(Manifest.permission.READ_EXTERNAL_STORAGE,Manifest.permission.WRITE_EXTERNAL_STORAGE)//這里填寫所需要的權限.subscribe(new Consumer<Boolean>() {@Overridepublic void accept(Boolean aBoolean) throws Exception {if (aBoolean) {// 通過}else{// 拒絕}}});
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方式 2：結合 RxBinding 來使用

RxPermissions rxPermissions = new RxPermissions(MainActivity.this);
// Must be done during an initialization phase like onCreate
RxView.clicks(findViewById(R.id.enableCamera)).compose(rxPermissions.ensure(Manifest.permission.CAMERA)).subscribe(granted -> {// R.id.enableCamera has been clicked});復制代碼

源碼分析

整體介紹

接著我們來對這個 RxPermissions 進行一個源碼的解析，但是打開源碼的時候，我們可以發現，這個庫里面，其實就只有 3 個類：RxPermissions、RxPermissionsFragment、Permission

RxPermissions
- 最主要的實現類，利用 rxjava，為我們提供了方便權限申請的類
RxPermissionsFragment
- 是一個 fragment，主要的動態權限獲取類
Permission
- 定義的權限的 model 類

源碼分析

RxPermissions 實例創建

對于源碼的分析，我們應該先從簡單的使用入手。下面我們可以先看看實例化 RxPermissionsFragment 的時候是做了什么？

    RxPermissionsFragment mRxPermissionsFragment;public RxPermissions(@NonNull Activity activity) {mRxPermissionsFragment = getRxPermissionsFragment(activity);}復制代碼

我們可以看到，上面的代碼中，實例化 RxPermissionsFragment 的時候，里面先創建了一個 RxPermissionsFragment 的實例。我們再接著看 getRxPermissionsFragment 這個方法的實現。

    private RxPermissionsFragment getRxPermissionsFragment(Activity activity) {//  查找 RxPermissionsFragment 是否已經被添加了RxPermissionsFragment rxPermissionsFragment = findRxPermissionsFragment(activity);boolean isNewInstance = rxPermissionsFragment == null;if (isNewInstance) {rxPermissionsFragment = new RxPermissionsFragment();FragmentManager fragmentManager = activity.getFragmentManager();fragmentManager.beginTransaction().add(rxPermissionsFragment, TAG).commitAllowingStateLoss();fragmentManager.executePendingTransactions();}return rxPermissionsFragment;}復制代碼

在 getRxPermissionsFragment() 這個方法中，首先是先查找當前是否已經添加了這個 rxPermissionsFragment 的實例，如果已經添加，那么直接返回已經添加的實例，如果沒有添加過的話，那么就重新再創建一個 RxPermissionsFragment 實例并提交；

    private RxPermissionsFragment findRxPermissionsFragment(Activity activity) {return (RxPermissionsFragment) activity.getFragmentManager().findFragmentByTag(TAG);}
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到此，rxPermissionsFragment 的實例化已經完成，接著我們需要看看 request 這個方法中實現了什么。

request 方法

    public Observable<Boolean> request(final String... permissions) {return Observable.just(TRIGGER).compose(ensure(permissions));}
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    static final Object TRIGGER = new Object();
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從上面的代碼中，我們可以看到，request 方法中需要傳入的參數是一個權限的數組，返回值是 Observable 對象。Observable.just(TRIGGER) 是快捷創建一個 Observable 的方式，由于 TRIGGER 是一個空的 Object 對象，所以 TRIGGER 就是一個占位符而已，Observable.just(TRIGGER) 創建的是一個 Observable,之后通過 compose 將 Observable 轉化為 Observable 并返回。在 compose 中需要的參數是一個 ObservableTransformer，那么我們接著看 ensure() 這個方法。

ensure(permissions);

public <T> ObservableTransformer<T, Boolean> ensure(final String... permissions) {// 創建一個Transformer對象返回return new ObservableTransformer<T, Boolean>() {@Overridepublic ObservableSource<Boolean> apply(Observable<T> o) {//request(o, permissions) 方法返回 Observable<Permission> 對象return request(o, permissions)// 將 Observable<Permission> 轉換為 Observable<Boolean>，在這里會等待所有的權限都返回了一次性發射數據。.buffer(permissions.length).flatMap(new Function<List<Permission>, ObservableSource<Boolean>>() {@Overridepublic ObservableSource<Boolean> apply(List<Permission> permissions) throws Exception {// 如果permissions為空那么直接返回Observable.empty();if (permissions.isEmpty()) {// Occurs during orientation change, when the subject receives onComplete.// In that case we don't want to propagate that empty list to the// subscriber, only the onComplete.return Observable.empty();}// Return true if all permissions are granted.for (Permission p : permissions) {if (!p.granted) {return Observable.just(false);}}return Observable.just(true);}});}};}復制代碼

在 ensure 的這個方法中，最終會返回的是 ObservableTransformer<T, Boolean> 對象。接著我們看看 ObservableTransformer 的匿名實現類里面的 apply 方法，這里實現的就是將 Observable 轉換為 Observable 的操作。我們對 apply 這個方法里面的代碼進行簡化一下。

return request(o,permissions).buffer(permissions.length).flatMap(new Function<List<Permission>, ObservableSource<Boolean>>{});
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request() 方法返回 Observable 對象
buffer(len) 操作符將一個 Observable 變換為 Observable<List>，原來的 Observable 正常發射數據，變換產生的 Observable 發射這些數據的緩存集合。buffer 將數據緩存到一個集合當中，然后在適當(比如：所有請求的權限結果都返回了）的時機一起發送。
flatMap() 方法將 Observable<List> 轉化為 Observable

request(o, permissions);

    private Observable<Permission> request(final Observable<?> trigger, final String... permissions) {if (permissions == null || permissions.length == 0) {throw new IllegalArgumentException("RxPermissions.request/requestEach requires at least one input permission");}return oneOf(trigger, pending(permissions)).flatMap(new Function<Object, Observable<Permission>>() {@Overridepublic Observable<Permission> apply(Object o) throws Exception {return requestImplementation(permissions);}});}復制代碼

在 request 這個方法里面，其實 oneOf() 和 pending() 方法我們可以忽略的，主要的話，我們應該關注 requestImplementation(final String... permissions) 這個方法，在這個方法里面，主要實現了權限的請求。

requestImplementation

@TargetApi(Build.VERSION_CODES.M)private Observable<Permission> requestImplementation(final String... permissions) {List<Observable<Permission>> list = new ArrayList<>(permissions.length);List<String> unrequestedPermissions = new ArrayList<>();// In case of multiple permissions, we create an Observable for each of them.// At the end, the observables are combined to have a unique response.for (String permission : permissions) {mRxPermissionsFragment.log("Requesting permission " + permission);if (isGranted(permission)) {// Already granted, or not Android M// Return a granted Permission object.// 權限已經被同意或者不是 Android 6.0 以上版本，創建一個 同意的 Permission 對象。list.add(Observable.just(new Permission(permission, true, false)));continue;}if (isRevoked(permission)) {// 權限被拒絕，返回一個 拒絕的 Permission 對象。list.add(Observable.just(new Permission(permission, false, false)));continue;}PublishSubject<Permission> subject = mRxPermissionsFragment.getSubjectByPermission(permission);// 如果 subject 不存在，那么創建一個 subject。if (subject == null) {unrequestedPermissions.add(permission);subject = PublishSubject.create();mRxPermissionsFragment.setSubjectForPermission(permission, subject);}list.add(subject);}// 還未提起申請的權限進行申請if (!unrequestedPermissions.isEmpty()) {String[] unrequestedPermissionsArray = unrequestedPermissions.toArray(new String[unrequestedPermissions.size()]);requestPermissionsFromFragment(unrequestedPermissionsArray);}// 嚴格按照順序發射數據return Observable.concat(Observable.fromIterable(list));}復制代碼

onRequestPermissionsResult()

@TargetApi(Build.VERSION_CODES.M)public void onRequestPermissionsResult(int requestCode, @NonNull String permissions[], @NonNull int[] grantResults) {super.onRequestPermissionsResult(requestCode, permissions, grantResults);if (requestCode != PERMISSIONS_REQUEST_CODE) return;boolean[] shouldShowRequestPermissionRationale = new boolean[permissions.length];for (int i = 0; i < permissions.length; i++) {shouldShowRequestPermissionRationale[i] = shouldShowRequestPermissionRationale(permissions[i]);}onRequestPermissionsResult(permissions, grantResults, shouldShowRequestPermissionRationale);}void onRequestPermissionsResult(String permissions[], int[] grantResults, boolean[] shouldShowRequestPermissionRationale) {for (int i = 0, size = permissions.length; i < size; i++) {log("onRequestPermissionsResult  " + permissions[i]);// Find the corresponding subjectPublishSubject<Permission> subject = mSubjects.get(permissions[i]);if (subject == null) {// No subject foundLog.e(RxPermissions.TAG, "RxPermissions.onRequestPermissionsResult invoked but didn't find the corresponding permission request.");return;}// 發射權限申請結果mSubjects.remove(permissions[i]);boolean granted = grantResults[i] == PackageManager.PERMISSION_GRANTED;subject.onNext(new Permission(permissions[i], granted, shouldShowRequestPermissionRationale[i]));subject.onComplete();}}復制代碼

RxJava 操作符

Observable.just()

just 操作符是將一個對象轉化為 Observable 的操作符。這個對象可以是一個數字、字符串或者是數組對象等，是 RxJava 中快速創建一個 Observable 對象的操作符。如果有 subscriber 訂閱的話，那么會依次調用 onNext() 和 OnComplete() 方法。所以這里只是創建了一個 Observable 對象，方便后續的調用。

compose(Transformer)操作符

compose 操作符是對 Observable 對象的整體轉化。例如：通過 Transformer，我們可以將 Observable 對象轉換成 Observable 對象了。

    public static ObservableTransformer<String,Boolean> getTransformer(){return new ObservableTransformer<String, Boolean>() {@Overridepublic ObservableSource<Boolean> apply(Observable<String> upstream) {return upstream.flatMap(new Function<String, ObservableSource<Boolean>>() {@Overridepublic ObservableSource<Boolean> apply(String s) throws Exception {return Observable.just(true);}});}};}
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/*** 線程切換* @return*/public static <T> ObservableTransformer<T,T> getScheduler(){return new ObservableTransformer<T, T>() {@Overridepublic ObservableSource<T> apply(Observable<T> upstream) {return upstream.subscribeOn(Schedulers.io()).observeOn(AndroidSchedulers.mainThread());}};}復制代碼

buffer 操作符

buffer 操作符將一個 Observable 變換為另一個，原來的 Observable 正常發射數據，變換產生的 Observable 發射這些數據的緩存集合。buffer將數據緩存到一個集合當中，然后在適當的時機一起發送。 buffer(count) 以列表(List)的形式發射非重疊的緩存，每一個緩存至多包含來自原始Observable的count項數據（最后發射的列表數據可能少于count項）

例如：緩存 2 個數據之后，再發送數據（調用 buffer(count) 函數）

                Observable.just(1,2,3,4,5,6).buffer(2).subscribe(integers -> {Log.i(TAG, "accept size: "+integers.size());for (Integer integer : integers) {Log.i(TAG, "accept: "+integer);}});
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輸出結果

2018-12-14 11:16:28.452 28126-28126/com.luwei.lwbaselib I/LwBaseActivity: accept size: 2
2018-12-14 11:16:28.452 28126-28126/com.luwei.lwbaselib I/LwBaseActivity: accept: 1
2018-12-14 11:16:28.453 28126-28126/com.luwei.lwbaselib I/LwBaseActivity: accept: 2
2018-12-14 11:16:28.453 28126-28126/com.luwei.lwbaselib I/LwBaseActivity: accept size: 2
2018-12-14 11:16:28.453 28126-28126/com.luwei.lwbaselib I/LwBaseActivity: accept: 3
2018-12-14 11:16:28.453 28126-28126/com.luwei.lwbaselib I/LwBaseActivity: accept: 4
2018-12-14 11:16:28.453 28126-28126/com.luwei.lwbaselib I/LwBaseActivity: accept size: 2
2018-12-14 11:16:28.453 28126-28126/com.luwei.lwbaselib I/LwBaseActivity: accept: 5
2018-12-14 11:16:28.453 28126-28126/com.luwei.lwbaselib I/LwBaseActivity: accept: 6
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例如：緩存 3 個數據，再發送數據，每次移動 1 步

                Observable.just(1,2,3,4).buffer(3,1).subscribe(integers -> {Log.i(TAG, "accept size: "+integers.size());for (Integer integer : integers) {Log.i(TAG, "accept: "+integer);}});
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輸出結果

2018-12-14 11:24:31.455 29164-29164/com.luwei.lwbaselib I/LwBaseActivity: accept size: 3
2018-12-14 11:24:31.455 29164-29164/com.luwei.lwbaselib I/LwBaseActivity: accept: 1
2018-12-14 11:24:31.455 29164-29164/com.luwei.lwbaselib I/LwBaseActivity: accept: 2
2018-12-14 11:24:31.455 29164-29164/com.luwei.lwbaselib I/LwBaseActivity: accept: 3
2018-12-14 11:24:31.455 29164-29164/com.luwei.lwbaselib I/LwBaseActivity: accept size: 3
2018-12-14 11:24:31.455 29164-29164/com.luwei.lwbaselib I/LwBaseActivity: accept: 2
2018-12-14 11:24:31.455 29164-29164/com.luwei.lwbaselib I/LwBaseActivity: accept: 3
2018-12-14 11:24:31.455 29164-29164/com.luwei.lwbaselib I/LwBaseActivity: accept: 4
2018-12-14 11:24:31.456 29164-29164/com.luwei.lwbaselib I/LwBaseActivity: accept size: 2
2018-12-14 11:24:31.456 29164-29164/com.luwei.lwbaselib I/LwBaseActivity: accept: 3
2018-12-14 11:24:31.456 29164-29164/com.luwei.lwbaselib I/LwBaseActivity: accept: 4
2018-12-14 11:24:31.456 29164-29164/com.luwei.lwbaselib I/LwBaseActivity: accept size: 1
2018-12-14 11:24:31.456 29164-29164/com.luwei.lwbaselib I/LwBaseActivity: accept: 4
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concat 操作符

是接收若干個Observables，發射數據是有序的，不會交叉。

Subject

作為 Observable 和 Observer 之間的橋梁
可以當做 Observable
可以當做 Observer

PublishSubject

繼承至 Subject，它的 Observer 只會接收到 PublishSubject 被訂閱之后發送的數據。示例代碼如下；我們只會接收到 publishSubject3 和 publishSubject4；

                PublishSubject<String> publishSubject = PublishSubject.create();publishSubject.onNext("publishSubject1");publishSubject.onNext("publishSubject2");publishSubject.subscribe(new Consumer<String>() {@Overridepublic void accept(String s) throws Exception {Log.i(TAG, "accept: "+s);}});publishSubject.onNext("publishSubject3");publishSubject.onNext("publishSubject4");復制代碼

執行結果

2018-12-14 11:33:18.168 29916-29916/com.luwei.lwbaselib I/LwBaseActivity: accept: publishSubject3
2018-12-14 11:33:18.168 29916-29916/com.luwei.lwbaselib I/LwBaseActivity: accept: publishSubject4
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舉一反三

可以看到，在 RxPermissions 這個獲取權限的開源框架中，往 Activity 中添加了一個空的 Fragment，這個 fragment 才是用來發起申請權限和處理權限的請求，最后再將結果返回，這樣子就避免了我們發送請求之后，還需要在 onRequestPermissionsResult 中進行處理，并判斷 requestCode 等繁瑣操作。想到這里，我們平時使用 startActivityForResult 時，我們也可以同樣采用這樣的思路來簡化我們的請求。

同樣的，我們采用添加空白的 fragment，來做 startActivityForResult 請求，主要的實現類有 SimpleForResult 和 SimpleOnResultFragment，ActivityResultInfo 是請求 model，接下我們先看代碼。

SimpleForResult


/*** @Author: chenjianrun* @Time: 2018/12/7* @Description:   避免調用 startActivity 時，需要 onActivityResult 處理的類*/
public class SimpleForResult {private static final String TAG = "SimpleForResult";private SimpleOnResultFragment mSimpleOnResultFragment;public SimpleForResult(AppCompatActivity activity) {mSimpleOnResultFragment = getOnResultFragment(activity.getSupportFragmentManager());}public SimpleForResult(Fragment fragment){mSimpleOnResultFragment = getOnResultFragment(fragment.getChildFragmentManager());}private SimpleOnResultFragment getOnResultFragment(FragmentManager fragmentManager) {SimpleOnResultFragment simpleOnResultFragment = findSimpleOnResultFragment(fragmentManager);if (simpleOnResultFragment == null) {simpleOnResultFragment = new SimpleOnResultFragment();fragmentManager.beginTransaction().add(simpleOnResultFragment, TAG).commitAllowingStateLoss();fragmentManager.executePendingTransactions();}return simpleOnResultFragment;}private SimpleOnResultFragment findSimpleOnResultFragment(FragmentManager fragmentManager) {return (SimpleOnResultFragment) fragmentManager.findFragmentByTag(TAG);}public Observable<ActivityResultInfo> startForResult(Intent intent) {return mSimpleOnResultFragment.startForResult(intent);}public Observable<ActivityResultInfo> startForResult(Class<?> clazz) {Intent intent = new Intent(mSimpleOnResultFragment.getActivity(), clazz);return startForResult(intent);}public void startForResult(Intent intent, Callback callback) {mSimpleOnResultFragment.startForResult(intent, callback);}public void startForResult(Class<?> clazz, Callback callback) {Intent intent = new Intent(mSimpleOnResultFragment.getActivity(), clazz);startForResult(intent, callback);}public interface Callback {void onActivityResult(int requestCode, int resultCode, Intent data);}
}復制代碼

SimpleOnResultFragment


/*** @Author: chenjianrun* @Time: 2018/12/7* @Description:    真正調用 startActivity 和處理 onActivityResult 的類。*/
public class SimpleOnResultFragment extends Fragment {private static Map<Integer, PublishSubject<ActivityResultInfo>> mSubjects = new HashMap<>();private static Map<Integer, SimpleForResult.Callback> mCallbacks = new HashMap<>();public SimpleOnResultFragment() {}@Overridepublic void onCreate(Bundle savedInstanceState) {super.onCreate(savedInstanceState);setRetainInstance(true);}public Observable<ActivityResultInfo> startForResult(final Intent intent) {int requestCode = generateRequestCode();PublishSubject<ActivityResultInfo> subject = PublishSubject.create();mSubjects.put(requestCode, subject);startActivityForResult(intent, requestCode);return subject;}public void startForResult(Intent intent, SimpleForResult.Callback callback) {int requestCode = generateRequestCode();mCallbacks.put(requestCode, callback);startActivityForResult(intent, requestCode);}@Overridepublic void onActivityResult(int requestCode, int resultCode, Intent data) {super.onActivityResult(requestCode, resultCode, data);//rxjava方式的處理PublishSubject<ActivityResultInfo> subject = mSubjects.remove(requestCode);if (subject != null) {subject.onNext(new ActivityResultInfo(requestCode, resultCode, data));subject.onComplete();}//callback方式的處理SimpleForResult.Callback callback = mCallbacks.remove(requestCode);if (callback != null) {callback.onActivityResult(requestCode, resultCode, data);}}private int generateRequestCode(){Random random = new Random();for (;;){int code = random.nextInt(65536);if (!mSubjects.containsKey(code) && !mCallbacks.containsKey(code)){return code;}}}
}
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ActivityResultInfo

package com.luwei.util.forresult;import android.content.Intent;/*** @Author: chenjianrun* @Time: 2018/12/7* @Description:*/
public class ActivityResultInfo {private int requestCode;private int resultCode;private Intent data;public ActivityResultInfo(int requestCode, int resultCode, Intent data) {this.requestCode = requestCode;this.resultCode = resultCode;this.data = data;}public int getRequestCode() {return requestCode;}public void setRequestCode(int requestCode) {this.requestCode = requestCode;}public ActivityResultInfo(int resultCode, Intent data) {this.resultCode = resultCode;this.data = data;}public int getResultCode() {return resultCode;}public void setResultCode(int resultCode) {this.resultCode = resultCode;}public Intent getData() {return data;}public void setData(Intent data) {this.data = data;}
}復制代碼

簡單使用示例

簡單的 Activity 調用

// 簡化調用 startActivityForResult 及避免在 onActivityResult 中處理繁瑣的結果SimpleForResult simpleForResult = new SimpleForResult(this);simpleForResult.startForResult(ToastActivity.class).subscribe((resultInfo) -> {if (resultInfo.getData() != null) {ToastUtils.showLong(resultInfo.getData().getStringExtra("result"));}});
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調用攝像頭

    /*** 打開攝像頭*/private void openCamera() {try {mTmpFile = FileUtils.createTmpFile(this);} catch (IOException e) {e.printStackTrace();}simpleForResult.startForResult(getOpenCameraIntent(this, mTmpFile)).subscribe((resultInfo -> {if (resultInfo.getResultCode() == RESULT_OK) {mHeadUrl = mTmpFile.getAbsolutePath();ImageLoaderUtils.loadCircleImage(this, ivHeader, mHeadUrl);// 裁剪(如果沒有要求可裁剪，也可以不要）startPictureZoom(mTmpFile);}}));}/*** 獲取打開照相機的 intent，適配 Android 7.0* @param activity* @param mTmpFile* @return*/public static Intent getOpenCameraIntent(Activity activity,File mTmpFile){Intent intent = new Intent(MediaStore.ACTION_IMAGE_CAPTURE);if (intent.resolveActivity(activity.getPackageManager()) != null) {if (mTmpFile != null && mTmpFile.exists()) {if (Build.VERSION.SDK_INT >= 24) {// 適配 Android 7.0intent.putExtra(MediaStore.EXTRA_OUTPUT,FileProvider.getUriForFile(activity, activity.getPackageName()+".provider",mTmpFile));} else {intent.putExtra(MediaStore.EXTRA_OUTPUT, Uri.fromFile(mTmpFile));}} else {Toast.makeText(activity, me.nereo.image_selector.R.string.error_image_not_exist, Toast.LENGTH_SHORT).show();}} else {Toast.makeText(activity, me.nereo.image_selector.R.string.msg_no_camera, Toast.LENGTH_SHORT).show();}return intent;}復制代碼