ps：flutter版本已经更新到1.2.1
引入包
在build.gradle中可以找到这个
apply from: "$flutterRoot/packages/flutter_tools/gradle/flutter.gradle"
然后我们到该目录下找到flutter.gradle
flutter.gradle
在该文件中可以找到
Path baseEnginePath = Paths.get(flutterRoot.absolutePath, "bin", "cache", "artifacts", "engine")
String targetArch = 'arm'
if (project.hasProperty('target-platform') &&
project.property('target-platform') == 'android-arm64') {
targetArch = 'arm64'
}
debugFlutterJar = baseEnginePath.resolve("android-${targetArch}").resolve("flutter.jar").toFile()
profileFlutterJar = baseEnginePath.resolve("android-${targetArch}-profile").resolve("flutter.jar").toFile()
releaseFlutterJar = baseEnginePath.resolve("android-${targetArch}-release").resolve("flutter.jar").toFile()
dynamicProfileFlutterJar = baseEnginePath.resolve("android-${targetArch}-dynamic-profile").resolve("flutter.jar").toFile()
dynamicReleaseFlutterJar = baseEnginePath.resolve("android-${targetArch}-dynamic-release").resolve("flutter.jar").toFile()
我们继续查找目录
flutter.jar
这就是flutter.jar android部分编译生成的包
在AS中直接看源码的话只能找到编译好的flutter.jar包中的.class文件，这里可以去github下载源码
flutter内核源码：
https://github.com/flutter/engine/tree/45f69ac471b47e95dfeef36e5e81597b05ed19f5/shell/platform/android
OnCreate流程
flutter初始化分为4个部分：
FlutterMain、FlutterNativeView、FlutterView和Flutter Bundle的初始化
先看下Flutter初始化的时序图（图片来源于阿里咸鱼，自己就不献丑了）
时序图
分析过android启动流程的话，知道Application先于Activity执行，在AndroidManifest.xml中可以找到FlutterApplication
public class FlutterApplication extends Application {
@Override
@CallSuper
public void onCreate() {
super.onCreate();
//初始化
FlutterMain.startInitialization(this);
}
private Activity mCurrentActivity = null;
public Activity getCurrentActivity() {
return mCurrentActivity;
}
public void setCurrentActivity(Activity mCurrentActivity) {
this.mCurrentActivity = mCurrentActivity;
}
}
先看FlutterMain的初始化：
public class FlutterMain {
...
public static void startInitialization(Context applicationContext, Settings settings) {
if (Looper.myLooper() != Looper.getMainLooper()) {
throw new IllegalStateException("startInitialization must be called on the main thread");
}
// Do not run startInitialization more than once.
if (sSettings != null) {
return;
}
sSettings = settings;
//记录初始化资源的起始时间
long initStartTimestampMillis = SystemClock.uptimeMillis();
initConfig(applicationContext);
initAot(applicationContext);
initResources(applicationContext);
//加载libflutter.so库
if (sResourceUpdater == null) {
System.loadLibrary("flutter");
} else {
sResourceExtractor.waitForCompletion();
File lib = new File(PathUtils.getDataDirectory(applicationContext), DEFAULT_LIBRARY);
if (lib.exists()) {
System.load(lib.getAbsolutePath());
} else {
System.loadLibrary("flutter");
}
}
//初始化完成时间
long initTimeMillis = SystemClock.uptimeMillis() - initStartTimestampMillis;
nativeRecordStartTimestamp(initTimeMillis);
}
}
接下来看一下MainActivity，继承自FlutterActivity，找到其的onCreate方法
public class FlutterActivity extends Activity implements FlutterView.Provider, PluginRegistry, ViewFactory {
private final FlutterActivityDelegate delegate = new FlutterActivityDelegate(this, this);
private final FlutterActivityEvents eventDelegate = delegate;
...
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
eventDelegate.onCreate(savedInstanceState);
}
}
实际上调用的是FlutterActivityDelegate的onCreate方法
public final class FlutterActivityDelegate
implements FlutterActivityEvents,
FlutterView.Provider,
PluginRegistry {
@Override
public void onCreate(Bundle savedInstanceState) {
//sdk版本大于21，即5.0，和沉浸式状态栏有关
if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.LOLLIPOP) {
Window window = activity.getWindow();
window.addFlags(LayoutParams.FLAG_DRAWS_SYSTEM_BAR_BACKGROUNDS);
window.setStatusBarColor(0x40000000);
window.getDecorView().setSystemUiVisibility(PlatformPlugin.DEFAULT_SYSTEM_UI);
}
String[] args = getArgsFromIntent(activity.getIntent());
// 1.
FlutterMain.ensureInitializationComplete(activity.getApplicationContext(), args);
flutterView = viewFactory.createFlutterView(activity);
//flutterView默认的创建结果是null，必然进入
if (flutterView == null) {
FlutterNativeView nativeView = viewFactory.createFlutterNativeView();
// 2.
flutterView = new FlutterView(activity, null, nativeView);
//界面置为全屏
flutterView.setLayoutParams(matchParent);
//flutterView为显示的主界面
activity.setContentView(flutterView);
launchView = createLaunchView();
if (launchView != null) {
addLaunchView();
}
}
if (loadIntent(activity.getIntent())) {
return;
}
String appBundlePath = FlutterMain.findAppBundlePath(activity.getApplicationContext());
if (appBundlePath != null) {
//3.
runBundle(appBundlePath);
}
}
}
assets资源已经初始化完毕，将资源路径传递给native端进行处理
public class FlutterMain {
public static void ensureInitializationComplete(Context applicationContext, String[] args) {
...
String appBundlePath = findAppBundlePath(applicationContext);
String appStoragePath = PathUtils.getFilesDir(applicationContext);
String engineCachesPath = PathUtils.getCacheDirectory(applicationContext);
nativeInit(applicationContext, shellArgs.toArray(new String[0]),
appBundlePath, appStoragePath, engineCachesPath);
sInitialized = true;
...
}
}
然后看下FlutterView是个什么
public class FlutterView extends SurfaceView implements BinaryMessenger, TextureRegistry {
...
public FlutterView(Context context, AttributeSet attrs, FlutterNativeView nativeView) {
super(context, attrs);
Activity activity = (Activity) getContext();
if (nativeView == null) {
mNativeView = new FlutterNativeView(activity.getApplicationContext());
} else {
mNativeView = nativeView;
}
dartExecutor = mNativeView.getDartExecutor();
flutterRenderer = new FlutterRenderer(mNativeView.getFlutterJNI());
mIsSoftwareRenderingEnabled = FlutterJNI.nativeGetIsSoftwareRenderingEnabled();
mMetrics = new ViewportMetrics();
mMetrics.devicePixelRatio = context.getResources().getDisplayMetrics().density;
setFocusable(true);
setFocusableInTouchMode(true);
mNativeView.attachViewAndActivity(this, activity);
mSurfaceCallback = new SurfaceHolder.Callback() {
@Override
public void surfaceCreated(SurfaceHolder holder) {
assertAttached();
mNativeView.getFlutterJNI().onSurfaceCreated(holder.getSurface());
}
@Override
public void surfaceChanged(SurfaceHolder holder, int format, int width, int height) {
assertAttached();
mNativeView.getFlutterJNI().onSurfaceChanged(width, height);
}
@Override
public void surfaceDestroyed(SurfaceHolder holder) {
assertAttached();
mNativeView.getFlutterJNI().onSurfaceDestroyed();
}
};
getHolder().addCallback(mSurfaceCallback);
mActivityLifecycleListeners = new ArrayList<>();
mFirstFrameListeners = new ArrayList<>();
// Create all platform channels
navigationChannel = new NavigationChannel(dartExecutor);
keyEventChannel = new KeyEventChannel(dartExecutor);
lifecycleChannel = new LifecycleChannel(dartExecutor);
localizationChannel = new LocalizationChannel(dartExecutor);
platformChannel = new PlatformChannel(dartExecutor);
systemChannel = new SystemChannel(dartExecutor);
settingsChannel = new SettingsChannel(dartExecutor);
// Create and setup plugins
PlatformPlugin platformPlugin = new PlatformPlugin(activity, platformChannel);
addActivityLifecycleListener(platformPlugin);
mImm = (InputMethodManager) getContext().getSystemService(Context.INPUT_METHOD_SERVICE);
mTextInputPlugin = new TextInputPlugin(this, dartExecutor);
androidKeyProcessor = new AndroidKeyProcessor(keyEventChannel, mTextInputPlugin);
androidTouchProcessor = new AndroidTouchProcessor(flutterRenderer);
sendLocalesToDart(getResources().getConfiguration());
sendUserPlatformSettingsToDart();
}
...
}
FlutterView是一个SurfaceView，那么再看其surfaceCreated方法，调用的是FlutterJNI中的native方法
@UiThread
public void onSurfaceCreated(@NonNull Surface surface) {
ensureAttachedToNative();
nativeSurfaceCreated(nativePlatformViewId, surface);
}
private native void nativeSurfaceCreated(long nativePlatformViewId, Surface surface);
也即是说flutter其实是自己绘制，然后在surfaceview上显示的，稍微深入一下来验证一下：
来找一下这个native方法，看一下里面到底做了什么，来到platform_view_android_jni.cc文件下（路径：engine/shell/platform/android/io/platform_view_android_jni.cc）
//platform_view_android_jni.cc
static const JNINativeMethod flutter_jni_methods[] = {
...
{
.name = "nativeSurfaceCreated",
.signature = "(JLandroid/view/Surface;)V",
.fnPtr = reinterpret_cast<void*>(&shell::SurfaceCreated),
},
...
}
这是jni中动态注册的方式，nativeSurfaceCreated对应了SurfaceCreated方法
//platform_view_android_jni.cc
static void SurfaceCreated(JNIEnv* env,
jobject jcaller,
jlong shell_holder,
jobject jsurface) {
fml::jni::ScopedJavaLocalFrame scoped_local_reference_frame(env);
//创建新的窗口用于显示
auto window = fml::MakeRefCounted<AndroidNativeWindow>(
ANativeWindow_fromSurface(env, jsurface));
ANDROID_SHELL_HOLDER->GetPlatformView()->NotifyCreated(std::move(window));
}
通过ANativeWindow与surfaceView进行绑定，再看NotifyCreated方法
//platform_view_android.cc
void PlatformViewAndroid::NotifyCreated(
fml::RefPtr<AndroidNativeWindow> native_window) {
if (android_surface_) {
InstallFirstFrameCallback();
android_surface_->SetNativeWindow(native_window);
}
PlatformView::NotifyCreated();
}
SetNativeWindow(native_window)与我们的window相关，继续追踪，因android_surface_是一个std::unique_ptr<AndroidSurface>（ptr是动态指针，即AndroidSurface类型）
//android_surface.h
class AndroidSurface {
public:
static std::unique_ptr<AndroidSurface> Create(bool use_software_rendering);
...
virtual bool SetNativeWindow(fml::RefPtr<AndroidNativeWindow> window) = 0;
};
}
我们找其方法实现的类
//android_surface_gi.cc
bool AndroidSurfaceGL::SetNativeWindow(
fml::RefPtr<AndroidNativeWindow> window) {
onscreen_context_ = nullptr;
if (!offscreen_context_ || !offscreen_context_->IsValid()) {
return false;
}
// Create the onscreen context.
onscreen_context_ = fml::MakeRefCounted<AndroidContextGL>(
offscreen_context_->Environment(),
offscreen_context_.get() );
if (!onscreen_context_->IsValid()) {
onscreen_context_ = nullptr;
return false;
}
if (!onscreen_context_->CreateWindowSurface(std::move(window))) {
onscreen_context_ = nullptr;
return false;
}
return true;
}
一切相关的信息都在CreateWindowSurface中
//android_context_gi.cc
bool AndroidContextGL::CreateWindowSurface(
fml::RefPtr<AndroidNativeWindow> window) {
window_ = std::move(window);
EGLDisplay display = environment_->Display();
const EGLint attribs[] = {EGL_NONE};
//创建一个通用的surface
surface_ = eglCreateWindowSurface(
display, config_,
reinterpret_cast<EGLNativeWindowType>(window_->handle()), attribs);
return surface_ != EGL_NO_SURFACE;
}
到这一步基本追踪完了，通过egl创建了一个surface_（EGLSurface）供c端使用
绘制
还记得之前在自定义控件是我们绘制圆形时使用的方法吗？
canvas.drawCircle(Offset(0, 0), 100, _paint);
深入源码一下
void drawCircle(Offset c, double radius, Paint paint) {
assert(_offsetIsValid(c));
assert(paint != null);
_drawCircle(c.dx, c.dy, radius, paint._objects, paint._data);
}
void _drawCircle(double x,
double y,
double radius,
List<dynamic> paintObjects,
ByteData paintData) native 'Canvas_drawCircle';
这里也使用了native方法，即dart调用c语言，我们也来找一下它的源码简单分析一下
Canvas_drawCircle，和jni的命名不同，这个是表示在Canvas类中的drawCircle方法
其实dart.ui包就在engine中，painting.dart文件也在其中
在canvas.cc（路径：engine/lib/ui/painting/canvas.cc）文件中找到drawCircle方法
//canvas.cc
void Canvas::drawCircle(double x,
double y,
double radius,
const Paint& paint,
const PaintData& paint_data) {
if (!canvas_)
return;
canvas_->drawCircle(x, y, radius, *paint.paint());
}
canvas_是一个SkCanvas*
//canvas.h
#include "third_party/skia/include/core/SkCanvas.h"
#include "third_party/skia/include/utils/SkShadowUtils.h"
class Canvas : public RefCountedDartWrappable<Canvas> {
...
private:
explicit Canvas(SkCanvas* canvas);
SkPictureRecorder::beginRecording,
SkCanvas* canvas_;
};
SkCanvas.h在engine工程中无法找到，不过我们能在github的skia工程中找到
void SkCanvas::drawCircle(SkScalar cx, SkScalar cy, SkScalar radius,
const SkPaint& paint) {
if (radius < 0) {
radius = 0;
}
SkRect r;
r.set(cx - radius, cy - radius, cx + radius, cy + radius);
this->drawOval(r, paint);
}
到这就不再分析下去了，flutter是通过skia引擎直接渲染的，所以在绘制速度上要比原生还快些
互调接口
- AndroidView 来调用android原生的控件(Ios使用 UiKitView)
目前还存在一些bug，感兴趣的可以查看一下flutter_webview_plugin开源库的实现源码 - EventChannel 传递和接收事件流
MethodChannel 传递和接收方法
BasicMessageChannel 传递和接收字符串
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