blocks|key|4465751|text|这在https://github.com/facebook/react-native/blob/master/docs/NativeModulesAndroid.md中并不是非常清楚，但是您可以阅读react原生发行版中的ToastModule源代码，以了解他们是如何在github.com/facebook/react-native/blob/daba14264c9f0d29c0327440df25d81c2f58316c/ReactAndroid/src/main/java/com/facebook/react/modules/toast/ToastModule.java#L31-L33中做到这一点的|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|4465752|其思想是，通过实例化github.com/facebook/react-native/blob/3b4845f93c296ed93c348733809845d587227823/local-cli/generator-android/templates/package/MainActivity.java#L28+github.com/facebook/react-native/blob/daba14264c9f0d29c0327440df25d81c2f58316c/ReactAndroid/src/main/java/com/facebook/react/shell/MainReactPackage.java#L49，主活动将在初始化程序中作为reactContext传递给从ReactInstanceManager.builder()调用的模块的MainReactPackage|4465753|entityMap|0|LINK|mutability|MUTABLE|url|https://github.com/facebook/react-native/blob/master/docs/NativeModulesAndroid.md^0|2|29|0|0|0^^$0|@$1|2|3|4|5|6|7|N|8|@]|9|@$A|O|B|P|1|Q]]|C|$]]|$1|D|3|E|5|6|7|R|8|@]|9|@]|C|$]]|$1|F|3|-4|5|6|7|S|8|@]|9|@]|C|$]]]|G|$H|$5|I|J|K|C|$L|M]]]]

It's not super clear from <a href="https://github.com/facebook/react-native/blob/master/docs/NativeModulesAndroid.md" rel="nofollow">https://github.com/facebook/react-native/blob/master/docs/NativeModulesAndroid.md</a>, but you can read the source code of the ToastModule in the react native distribution to see how they do it github.com/facebook/react-native/blob/daba14264c9f0d29c0327440df25d81c2f58316c/ReactAndroid/src/main/java/com/facebook/react/modules/toast/ToastModule.java#L31-L33

The idea is that the main activity will be passed as the reactContext in the initializer for the module called from ReactInstanceManager.builder() call in github.com/facebook/react-native/blob/3b4845f93c296ed93c348733809845d587227823/local-cli/generator-android/templates/package/MainActivity.java#L28 via the instantiation of MainReactPackage github.com/facebook/react-native/blob/daba14264c9f0d29c0327440df25d81c2f58316c/ReactAndroid/src/main/java/com/facebook/react/shell/MainReactPackage.java#L49

blocks|key|4466227|text|编辑：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|4466228|问题是getReactApplicationContext()返回的是应用程序的上下文，而不是活动。不能将应用程序上下文类型转换为活动。|4466229|这是一个简单的解决方法|4466230|因为通常在react-native中只有一个活动(主活动)，所以我们可以用MainActivity编写一个静态函数来返回该活动|4466231|private+static+Activity+mCurrentActivity+=+null;

protected+void+onCreate(Bundle+savedInstanceState)+{
++++super.onCreate(savedInstanceState);
++++mCurrentActivity+=+this;
++++...
}
...
public+static+Activity+getActivity(){
++++Activity+activity+=+new+Activity();
++++activity+=+mCurrentActivity;
++++return+activity;
}|code-block|syntax|javascript|4466232|然后从桥接模块调用MainActivity.getActivity()|offset|length|style|CODE|4466233|entityMap^0|0|0|0|0|0|9|Q|0^^$0|@$1|2|3|4|5|6|7|U|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|V|8|@]|9|@]|A|$]]|$1|D|3|E|5|6|7|W|8|@]|9|@]|A|$]]|$1|F|3|G|5|6|7|X|8|@]|9|@]|A|$]]|$1|H|3|I|5|J|7|Y|8|@]|9|@]|A|$K|L]]|$1|M|3|N|5|6|7|Z|8|@$O|10|P|11|Q|R]]|9|@]|A|$]]|$1|S|3|-4|5|6|7|12|8|@]|9|@]|A|$]]]|T|$]]

Editted:

The issue is that getReactApplicationContext() returns the context of the Application and not the Activity. You cannot typecast an Application context to an Activity. 

This is a simple workaround

Since usually, there is only one activity (Main Activity) in react-native, We can write a static function in MainActivity to return the activity

<pre><code>private static Activity mCurrentActivity = null;

protected void onCreate(Bundle savedInstanceState) {
 super.onCreate(savedInstanceState);
 mCurrentActivity = this;
 ...
}
...
public static Activity getActivity(){
 Activity activity = new Activity();
 activity = mCurrentActivity;
 return activity;
}
</code></pre>

then call <code>MainActivity.getActivity()</code> from the bridge modules

blocks|key|4466321|text|我猜ReactContextBaseJavaModule的getCurrentActivity()方法可以像下面的代码一样使用，它是从React-Native的原始代码复制过来的；|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|4466322|import+android.app.Activity;
import+com.facebook.react.bridge.ReactContextBaseJavaModule;

public+class+AwesomeModule+extends+ReactContextBaseJavaModule+{

++public+AwesomeModule(ReactApplicationContext+reactContext)+{
++++super(reactContext);
++}

++@Override
++public+String+getName()+{
++++return+"AwesomeAndroid";
++}

++private+static+final+String+ERROR_NO_ACTIVITY+=+"E_NO_ACTIVITY";
++private+static+final+String+ERROR_NO_ACTIVITY_MESSAGE+=+"Tried+to+do+the+something+while+not+attached+to+an+Activity";

++@ReactMethod
++public+void+doSomething(successCallback,+errorCallback)+{

++++final+Activity+activity+=+getCurrentActivity();

++++if+(activity+==+null)+{
++++++errorCallback(ERROR_NO_ACTIVITY,+ERROR_NO_ACTIVITY_MESSAGE);
++++++return;
++++}

++}

}|code-block|syntax|javascript|4466323|entityMap|0|LINK|mutability|MUTABLE|url|https://github.com/facebook/react-native/blob/master/ReactAndroid/src/main/java/com/facebook/react/bridge/ReactContextBaseJavaModule.java#L35-L46^0|T|K|1V|C|2|Q|0|0|0^^$0|@$1|2|3|4|5|6|7|S|8|@$9|T|A|U|B|C]|$9|V|A|W|B|C]]|D|@$9|X|A|Y|1|Z]]|E|$]]|$1|F|3|G|5|H|7|10|8|@]|D|@]|E|$I|J]]|$1|K|3|-4|5|6|7|11|8|@]|D|@]|E|$]]]|L|$M|$5|N|O|P|E|$Q|R]]]]

I guess <code>getCurrentActivity()</code> method of <a href="https://github.com/facebook/react-native/blob/master/ReactAndroid/src/main/java/com/facebook/react/bridge/ReactContextBaseJavaModule.java#L35-L46">ReactContextBaseJavaModule</a> might be used like the following code which has been copied from <code>React-Native</code> original code;

<pre><code>import android.app.Activity;
import com.facebook.react.bridge.ReactContextBaseJavaModule;

public class AwesomeModule extends ReactContextBaseJavaModule {

 public AwesomeModule(ReactApplicationContext reactContext) {
 super(reactContext);
 }

 @Override
 public String getName() {
 return "AwesomeAndroid";
 }

 private static final String ERROR_NO_ACTIVITY = "E_NO_ACTIVITY";
 private static final String ERROR_NO_ACTIVITY_MESSAGE = "Tried to do the something while not attached to an Activity";

 @ReactMethod
 public void doSomething(successCallback, errorCallback) {

 final Activity activity = getCurrentActivity();

 if (activity == null) {
 errorCallback(ERROR_NO_ACTIVITY, ERROR_NO_ACTIVITY_MESSAGE);
 return;
 }

 }

}
</code></pre>

blocks|key|4466366|text|对于0.28及之前版本，您可以使用相同的字段从ReactInstanceManagerImpl的private+@Nullable+Activity+mCurrentActivity;和0.29%2B的ReactContextBaseJavaModule获取活动。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|4466367|entityMap^0|N|O|1C|18|2R|Q|0^^$0|@$1|2|3|4|5|6|7|H|8|@$9|I|A|J|B|C]|$9|K|A|L|B|C]|$9|M|A|N|B|C]]|D|@]|E|$]]|$1|F|3|-4|5|6|7|O|8|@]|D|@]|E|$]]]|G|$]]

For 0.28 and before, you can get activity from <code>ReactInstanceManagerImpl</code> 's <code>private @Nullable Activity mCurrentActivity;</code>, 0.29+ 's <code>ReactContextBaseJavaModule</code> using the same field.

blocks|key|4466040|text|如何将activity从ReactApplication::getPackages()传递到包？|type|unstyled|depth|inlineStyleRanges|entityRanges|data|4466041|我什么都不了解。我找不到任何清晰的例子|4466042|package+com.bluetoothioexample;

import+android.app.Application;
import+android.util.Log;

import+com.facebook.react.bridge.ReactContextBaseJavaModule;

import+com.facebook.react.ReactApplication;
import+com.facebook.react.ReactInstanceManager;
import+com.facebook.react.ReactNativeHost;
import+com.facebook.react.ReactPackage;
import+com.facebook.react.shell.MainReactPackage;

import+java.util.Arrays;
import+java.util.List;

import+com.subsite.bluetoothio.BluetoothIOPackage;
import+com.oblador.vectoricons.VectorIconsPackage;

public+class+MainApplication+extends+Application+implements+ReactApplication+{

++private+final+ReactNativeHost+mReactNativeHost+=+new+ReactNativeHost(this)+{
++++@Override
++++protected+boolean+getUseDeveloperSupport()+{
++++++return+BuildConfig.DEBUG;
++++}

++++@Override
++++protected+List<ReactPackage>+getPackages()+{
++++++return+Arrays.<ReactPackage>asList(
++++++++++new+MainReactPackage(),
++++++++++new+BluetoothIOPackage(this),+//<-+How+pass+the+activity
++++++++++++++++++++++++++++++++++++++++//+from+ReactApplication+?
++++++++++new+VectorIconsPackage()
++++++);
++++}
++};

++@Override
++public+ReactNativeHost+getReactNativeHost()+{
++++++return+mReactNativeHost;
++}
}|code-block|syntax|javascript|4466043|答:您不会将活动从MainApplication传递到包。|4466044|您可以从ReactContextBaseJavaModule中调用getCurrentActivity()|4466045|entityMap^0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|O|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|P|8|@]|9|@]|A|$]]|$1|D|3|E|5|F|7|Q|8|@]|9|@]|A|$G|H]]|$1|I|3|J|5|6|7|R|8|@]|9|@]|A|$]]|$1|K|3|L|5|6|7|S|8|@]|9|@]|A|$]]|$1|M|3|-4|5|6|7|T|8|@]|9|@]|A|$]]]|N|$]]

How do you pass the activity to a package from ReactApplication::getPackages() ? 

I do not understand. I cannot find any clear examples

<pre><code>package com.bluetoothioexample;

import android.app.Application;
import android.util.Log;

import com.facebook.react.bridge.ReactContextBaseJavaModule;

import com.facebook.react.ReactApplication;
import com.facebook.react.ReactInstanceManager;
import com.facebook.react.ReactNativeHost;
import com.facebook.react.ReactPackage;
import com.facebook.react.shell.MainReactPackage;

import java.util.Arrays;
import java.util.List;

import com.subsite.bluetoothio.BluetoothIOPackage;
import com.oblador.vectoricons.VectorIconsPackage;

public class MainApplication extends Application implements ReactApplication {

 private final ReactNativeHost mReactNativeHost = new ReactNativeHost(this) {
 @Override
 protected boolean getUseDeveloperSupport() {
 return BuildConfig.DEBUG;
 }

 @Override
 protected List&lt;ReactPackage&gt; getPackages() {
 return Arrays.&lt;ReactPackage&gt;asList(
 new MainReactPackage(),
 new BluetoothIOPackage(this), //&lt;- How pass the activity
 // from ReactApplication ?
 new VectorIconsPackage()
 );
 }
 };

 @Override
 public ReactNativeHost getReactNativeHost() {
 return mReactNativeHost;
 }
}
</code></pre>

Answer: You do NOT pass Activity from MainApplication to the package.

You call getCurrentActivity() from within your ReactContextBaseJavaModule

blocks|key|4466422|text|使用UI线程上下文获取活动/窗口/装饰视图|type|unstyled|depth|inlineStyleRanges|entityRanges|data|4466423|在您的类文件中，导入包括...|4466424|import+android.view.WindowManager;
import+android.view.Window;
import+android.view.View;|code-block|syntax|javascript|4466425|在你的类构造函数中...|4466426|private+static+ReactApplicationContext+reactContext;
MyModule(ReactApplicationContext+context)+{
++super(context);
++reactContext+=+context;
}|4466427|然后在类方法中...|4466428|@ReactMethod
public+void+doSomethingRequiringWindow()+{
++//+get+access+to+current+UI+thread+first
++reactContext.getCurrentActivity().runOnUiThread(new+Runnable()+{
++++@Override
++++public+void+run()+{
++++++Window+window+=+reactContext
+++++++.getCurrentActivity().getWindow();
++++++View+decorView+=+reactContext
+++++++.getCurrentActivity().getWindow().getDecorView();
++++++//+you+have+access+to+main+ui+thread+so+you+can+effect
++++++//+immediate+behavior+on+window+and+decorView
++++}
++});
}|4466429|entityMap^0|0|0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|S|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|T|8|@]|9|@]|A|$]]|$1|D|3|E|5|F|7|U|8|@]|9|@]|A|$G|H]]|$1|I|3|J|5|6|7|V|8|@]|9|@]|A|$]]|$1|K|3|L|5|F|7|W|8|@]|9|@]|A|$G|H]]|$1|M|3|N|5|6|7|X|8|@]|9|@]|A|$]]|$1|O|3|P|5|F|7|Y|8|@]|9|@]|A|$G|H]]|$1|Q|3|-4|5|6|7|Z|8|@]|9|@]|A|$]]]|R|$]]

<h1>Get Activity / Window / Decor View with UI Thread context</h1>
In your class file imports include...
<pre><code>import android.view.WindowManager;
import android.view.Window;
import android.view.View;
</code></pre>
In your class constructor...
<pre><code>private static ReactApplicationContext reactContext;
MyModule(ReactApplicationContext context) {
 super(context);
 reactContext = context;
}
</code></pre>
Then in for class methods...
<pre><code>@ReactMethod
public void doSomethingRequiringWindow() {
 // get access to current UI thread first
 reactContext.getCurrentActivity().runOnUiThread(new Runnable() {
 @Override
 public void run() {
 Window window = reactContext
 .getCurrentActivity().getWindow();
 View decorView = reactContext
 .getCurrentActivity().getWindow().getDecorView();
 // you have access to main ui thread so you can effect
 // immediate behavior on window and decorView
 }
 });
}
</code></pre>

blocks|key|4466462|text|对于自定义UI组件，您可以在构造函数中获取上下文，然后可以通过context.getCurrentActivity()获取活动|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|4466463|entityMap^0|V|S|0^^$0|@$1|2|3|4|5|6|7|H|8|@$9|I|A|J|B|C]]|D|@]|E|$]]|$1|F|3|-4|5|6|7|K|8|@]|D|@]|E|$]]]|G|$]]

For custom UI component, you can get the context in the constructor, and later you can get the activity by <code>context.getCurrentActivity()</code>

I'm attempting to bridge over the Android functionality of keeping the screen on to React Native. I figured I could do this with a simple module, however I don't know how to get access to the current Android Activity from said module.

I need the Activity reference so I can call <code>.getWindow().addFlags(WindowManager.LayoutParams.FLAG_KEEP_SCREEN_ON);</code> on it

I tried to get the activity via casting like so <code>((Activity)getReactApplicationContext().getBaseContext())</code>, but this throws a "cannot be cast to Android.app.Activity" error

How to access Activity from a React Native Android module?

React Native

Android

我试图跨越Android的功能，让屏幕保持在React Native上。我想我可以用一个简单的模块来做这件事，但是我不知道如何从这个模块访问当前的Android活动。我需要活动引用，以便可以对其调用.getWindow().addFlags(WindowManager.LayoutParams.FLAG_KEEP_SC...

问如何从React Native Android模块访问Activity？
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