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一、需求分析
前几篇博客中，和大家分享了关于React Native For Android 的一系列内容，以及React Native第三方库的使用技巧。今天和大家分享的内容可以算是React Native基于最新版本实现JsBundle预加载，界面秒开优化功能延伸。
本篇博客围绕的依然是如何加载RN界面，在JsBundle加载优化这篇博客中，我们从源码角度分析了如何实现快速加载RN界面，RN界面的加载在ReactActivity的onCreate中完成，实则是通过ReactDelegate委托类的onCreate来实现。在ReactDelegate的onCreate方法中，系统调用loadApp来加载RN根视图，在loadApp方法中通过createRootView创建视图（new ReactRootView()），并启动设置到Activity的ContentView（DecoerView）上。
二、视图加载
ReactRootView rootView = new ReactRootView(activity);
rootView.startReactApplication(
((ReactApplication) activity.getApplication()).getReactNativeHost().getReactInstanceManager(),
componentName,
null); 此时当我们加载出ReactRootView后，就可以将其添加到我们Activity或者Fragment布局。但是此时会发现一个问题，如果RN中视图控件有交互功能，例如单击事件，此时这些功能都失效了。百思不得姐后，查看源码会发现交互的功能都由ReactDelegate来实现，所以我们单纯加载ReactRootView只是显示了视图，但是交互是不行的。如何解决呢？
三、功能实现
上面我们分析了整个RN视图加载的流程，那么如何在现有Activity布局中加载RN界面呢？原理依然要从创建设置ReactRootView来解决。RN的新版本对设置创建ReactRootView进行了封装，使得我们只需要重写getMainComponentName方法返回RN注册名称即可。这就使得我们不能直接控制ReactRootView的创建和设置。所以依然要采用重写ReactDelegate的方式来解决。
public class MyReactDelegate {
private final Activity mActivity;
private ReactRootView mReactRootView;
private Callback mPermissionsCallback;
private final String mMainComponentName;
private PermissionListener mPermissionListener;
private final int REQUEST_OVERLAY_PERMISSION_CODE = 1111;
private DoubleTapReloadRecognizer mDoubleTapReloadRecognizer;
public PreLoadReactDelegate(Activity activity, @Nullable String mainComponentName) {
this.mActivity = activity;
this.mMainComponentName = mainComponentName;
}
public void onCreate() {
boolean needsOverlayPermission = false;
if (getReactNativeHost().getUseDeveloperSupport() && Build.VERSION.SDK_INT >= Build.VERSION_CODES.M) {
// Get permission to show redbox in dev builds.
if (!Settings.canDrawOverlays(mActivity)) {
needsOverlayPermission = true;
Intent serviceIntent = new Intent(Settings.ACTION_MANAGE_OVERLAY_PERMISSION, Uri.parse("package:" + mActivity.getPackageName()));
mActivity.startActivityForResult(serviceIntent, REQUEST_OVERLAY_PERMISSION_CODE);
}
}
if (mMainComponentName != null && !needsOverlayPermission) {
mReactRootView = new ReactRootView(mActivity);
mReactRootView.startReactApplication(
getReactInstanceManager(),
mMainComponentName,
null);
}
// 3.将RootView设置到Activity布局
mActivity.setContentView(R.layout.acty_rn);
((FrameLayout)mActivity.findViewById(R.id.rn_contaner)).addView(mReactRootView);
}
mDoubleTapReloadRecognizer = new DoubleTapReloadRecognizer();
}
public void onResume() {
if (getReactNativeHost().hasInstance()) {
getReactInstanceManager().onHostResume(mActivity, (DefaultHardwareBackBtnHandler)mActivity);
}
if (mPermissionsCallback != null) {
mPermissionsCallback.invoke();
mPermissionsCallback = null;
}
}
public void onPause() {
if (getReactNativeHost().hasInstance()) {
getReactInstanceManager().onHostPause(mActivity);
}
}
public void onDestroy() {
if (mReactRootView != null) {
mReactRootView.unmountReactApplication();
mReactRootView = null;
}
if (getReactNativeHost().hasInstance()) {
getReactInstanceManager().onHostDestroy(mActivity);
}
}
public boolean onNewIntent(Intent intent) {
if (getReactNativeHost().hasInstance()) {
getReactInstanceManager().onNewIntent(intent);
return true;
}
return false;
}
public void onActivityResult(int requestCode, int resultCode, Intent data) {
if (getReactNativeHost().hasInstance()) {
getReactInstanceManager().onActivityResult(mActivity, requestCode, resultCode, data);
} else {
// Did we request overlay permissions?
if (requestCode == REQUEST_OVERLAY_PERMISSION_CODE && Build.VERSION.SDK_INT >= Build.VERSION_CODES.M) {
if (Settings.canDrawOverlays(mActivity)) {
if (mMainComponentName != null) {
if (mReactRootView != null) {
throw new IllegalStateException("Cannot loadApp while app is already running.");
}
mReactRootView = new ReactRootView(mActivity);
mReactRootView.startReactApplication(
getReactInstanceManager(),
mMainComponentName,
null);
mActivity.setContentView(mReactRootView);
}
}
}
}
}
public boolean onBackPressed() {
if (getReactNativeHost().hasInstance()) {
getReactInstanceManager().onBackPressed();
return true;
}
return false;
}
public boolean onRNKeyUp(int keyCode) {
if (getReactNativeHost().hasInstance() && getReactNativeHost().getUseDeveloperSupport()) {
if (keyCode == KeyEvent.KEYCODE_MENU) {
getReactInstanceManager().showDevOptionsDialog();
return true;
}
boolean didDoubleTapR = Assertions.assertNotNull(mDoubleTapReloadRecognizer)
.didDoubleTapR(keyCode, mActivity.getCurrentFocus());
if (didDoubleTapR) {
getReactInstanceManager().getDevSupportManager().handleReloadJS();
return true;
}
}
return false;
}
public void requestPermissions(String[] permissions, int requestCode, PermissionListener listener) {
mPermissionListener = listener;
mActivity.requestPermissions(permissions, requestCode);
}
public void onRequestPermissionsResult(final int requestCode, final String[] permissions, final int[] grantResults) {
mPermissionsCallback = new Callback() {
@Override
public void invoke(Object... args) {
if (mPermissionListener != null && mPermissionListener.onRequestPermissionsResult(requestCode, permissions, grantResults)) {
mPermissionListener = null;
}
}
};
}
/**
* 获取 Application中 ReactNativeHost
* @return
*/
private ReactNativeHost getReactNativeHost() {
return MainApplication.getInstance().getReactNativeHost();
}
/**
* 获取 ReactInstanceManager
* @return
*/
private ReactInstanceManager getReactInstanceManager() {
return getReactNativeHost().getReactInstanceManager();
}
} 核心依然是修改了onCreate中方法，我们在设置根布局时，不是直接设置ReactRootView，而是加载我们自己的Activity布局，然后将RN布局作为子布局添加到Activity布局，这样就可以实现在现有Activity布局中嵌入RN布局了。
