就像上個文章說的，觸摸事件的傳遞機制是從外層到內層的過程。
我們想來看看這個頁面里面的層級關系：
以下我們就用what-how-why三部曲的方式來分析View的繪制過程。
由於篇幅很大，所以分幾篇來解析這個過程。
這篇主要是自定義view/viewgroup，以及從Activity到DecorView的加載過程。
1.what：怎么自定義一個View
1.1自定義View
自定義View的話，常見過程如下：
/**
* @author DemanMath
* @date 2020-02-16
*
*/
class CustomView : View {
constructor(context: Context):super(context)
constructor(context: Context,attributeSet: AttributeSet):super(context,attributeSet)
constructor(context: Context,attributeSet: AttributeSet,def:Int):super(context,attributeSet,def)
override fun onDraw(canvas: Canvas?) {
super.onDraw(canvas)
AppLog.i()
}
override fun onLayout(changed: Boolean, left: Int, top: Int, right: Int, bottom: Int) {
super.onLayout(changed, left, top, right, bottom)
AppLog.i()
}
override fun onMeasure(widthMeasureSpec: Int, heightMeasureSpec: Int) {
super.onMeasure(widthMeasureSpec, heightMeasureSpec)
AppLog.i()
}
}
三個構造方法+三個可以復寫的方法。
我們先看下這3個方法的順序：
2020-02-16 13:50:28.212 23141-23141/com.joyfulmath.androidarchitecture I/Arch_App.CustomView: onMeasure: [at (CustomView.kt:32)]
2020-02-16 13:50:28.222 23141-23141/com.joyfulmath.androidarchitecture I/Arch_App.CustomView: onMeasure: [at (CustomView.kt:32)]
2020-02-16 13:50:28.253 23141-23141/com.joyfulmath.androidarchitecture I/Arch_App.CustomView: onMeasure: [at (CustomView.kt:32)]
2020-02-16 13:50:28.255 23141-23141/com.joyfulmath.androidarchitecture I/Arch_App.CustomView: onMeasure: [at (CustomView.kt:32)]
2020-02-16 13:50:28.259 23141-23141/com.joyfulmath.androidarchitecture I/Arch_App.CustomView: onLayout: [at (CustomView.kt:27)]
2020-02-16 13:50:28.403 23141-23141/com.joyfulmath.androidarchitecture I/Arch_App.CustomView: onDraw: [at (CustomView.kt:22)]
1.2自定義ViewGroup
上代碼
package com.joyfulmath.androidarchitecture.view
import android.content.Context
import android.util.AttributeSet
import android.view.ViewGroup
import com.joyfulmath.androidarchitecture.base.AppLog
import kotlin.math.PI
import kotlin.math.cos
import kotlin.math.min
import kotlin.math.sin
/**
* @author DemanMath
* @date 2020-02-16
*
*/
class FerrisWheel:ViewGroup {
var count = 12
var a = 2*PI/count
var startA = PI/2
constructor(context: Context):super(context){
initViews()
}
constructor(context: Context,attributeSet: AttributeSet):super(context,attributeSet){
initViews()
}
constructor(context: Context,attributeSet: AttributeSet,def:Int):super(context,attributeSet,def){
initViews()
}
private fun initViews() {
for(i in 0 until count){
this.addView(CustomView(context))
}
}
override fun onLayout(changed: Boolean, l: Int, t: Int, r: Int, b: Int) {
var mViewWidth = measuredWidth
var mViewHeight = measuredHeight
AppLog.i("$mViewWidth,$mViewHeight")
var cx = mViewWidth/2
var cy = mViewHeight/2
var r = min(measuredWidth,measuredHeight)*0.5f -20
AppLog.i("r:$r,cx:$cx")
for(i in 0 until count){
var view = getChildAt(i)
var width = view.measuredWidth
var height = view.measuredHeight
var cx1 = r* sin(startA+a*i)
var cy1 = -r* cos(startA+a*i)
AppLog.i("width:$width,height:$height")
AppLog.i("cx1:$cx1,cy1:$cy1")
view.layout(cx+(cx1-width/2).toInt(),
cy+(cy1-height/2).toInt(),
cx+(cx1+width/2).toInt(),
cy+(cy1+height/2).toInt())
}
}
override fun onMeasure(widthMeasureSpec: Int, heightMeasureSpec: Int) {
measureChildren(widthMeasureSpec,heightMeasureSpec)
super.onMeasure(widthMeasureSpec, heightMeasureSpec)
}
}
效果如下：
這里override了layout方法。可見View的繪制跟他的父View只有一個關系，ViewGroup指定了子View的位置。
關於View/ViewGroup繪制的機制，在下一節討論。
2.How：View的繪制機制是什么
從上一節看出：整個繪制流程三個過程，measure，layout，draw這三個過程。
下面我們從源碼的角度來分析下是不是這個過程。
final void handleResumeActivity(IBinder token,
boolean clearHide, boolean isForward, boolean reallyResume, int seq, String reason) {
.......
// TODO Push resumeArgs into the activity for consideration
r = performResumeActivity(token, clearHide, reason);
if (r != null) {
final Activity a = r.activity;
if (localLOGV) Slog.v(
TAG, "Resume " + r + " started activity: " +
a.mStartedActivity + ", hideForNow: " + r.hideForNow
+ ", finished: " + a.mFinished);
final int forwardBit = isForward ?
WindowManager.LayoutParams.SOFT_INPUT_IS_FORWARD_NAVIGATION : 0;
// If the window hasn't yet been added to the window manager,
// and this guy didn't finish itself or start another activity,
// then go ahead and add the window.
boolean willBeVisible = !a.mStartedActivity;
if (!willBeVisible) {
try {
willBeVisible = ActivityManager.getService().willActivityBeVisible(
a.getActivityToken());
} catch (RemoteException e) {
throw e.rethrowFromSystemServer();
}
}
if (r.window == null && !a.mFinished && willBeVisible) {
r.window = r.activity.getWindow();
View decor = r.window.getDecorView();
decor.setVisibility(View.INVISIBLE);
ViewManager wm = a.getWindowManager();
WindowManager.LayoutParams l = r.window.getAttributes();
a.mDecor = decor;
l.type = WindowManager.LayoutParams.TYPE_BASE_APPLICATION;
l.softInputMode |= forwardBit;
if (r.mPreserveWindow) {
a.mWindowAdded = true;
r.mPreserveWindow = false;
// Normally the ViewRoot sets up callbacks with the Activity
// in addView->ViewRootImpl#setView. If we are instead reusing
// the decor view we have to notify the view root that the
// callbacks may have changed.
ViewRootImpl impl = decor.getViewRootImpl();
if (impl != null) {
impl.notifyChildRebuilt();
}
}
if (a.mVisibleFromClient) {
if (!a.mWindowAdded) {
a.mWindowAdded = true;
wm.addView(decor, l);
} else {
// The activity will get a callback for this {@link LayoutParams} change
// earlier. However, at that time the decor will not be set (this is set
// in this method), so no action will be taken. This call ensures the
// callback occurs with the decor set.
a.onWindowAttributesChanged(l);
}
}
// If the window has already been added, but during resume
// we started another activity, then don't yet make the
// window visible.
} else if (!willBeVisible) {
if (localLOGV) Slog.v(
TAG, "Launch " + r + " mStartedActivity set");
r.hideForNow = true;
}
// Get rid of anything left hanging around.
cleanUpPendingRemoveWindows(r, false /* force */);
// The window is now visible if it has been added, we are not
// simply finishing, and we are not starting another activity.
if (!r.activity.mFinished && willBeVisible
&& r.activity.mDecor != null && !r.hideForNow) {
if (r.newConfig != null) {
performConfigurationChangedForActivity(r, r.newConfig);
if (DEBUG_CONFIGURATION) Slog.v(TAG, "Resuming activity "
+ r.activityInfo.name + " with newConfig " + r.activity.mCurrentConfig);
r.newConfig = null;
}
if (localLOGV) Slog.v(TAG, "Resuming " + r + " with isForward="
+ isForward);
WindowManager.LayoutParams l = r.window.getAttributes();
if ((l.softInputMode
& WindowManager.LayoutParams.SOFT_INPUT_IS_FORWARD_NAVIGATION)
!= forwardBit) {
l.softInputMode = (l.softInputMode
& (~WindowManager.LayoutParams.SOFT_INPUT_IS_FORWARD_NAVIGATION))
| forwardBit;
if (r.activity.mVisibleFromClient) {
ViewManager wm = a.getWindowManager();
View decor = r.window.getDecorView();
wm.updateViewLayout(decor, l);
}
}
r.activity.mVisibleFromServer = true;
mNumVisibleActivities++;
if (r.activity.mVisibleFromClient) {
r.activity.makeVisible();
}
}
if (!r.onlyLocalRequest) {
r.nextIdle = mNewActivities;
mNewActivities = r;
if (localLOGV) Slog.v(
TAG, "Scheduling idle handler for " + r);
Looper.myQueue().addIdleHandler(new Idler());
}
r.onlyLocalRequest = false;
// Tell the activity manager we have resumed.
if (reallyResume) {
try {
ActivityManager.getService().activityResumed(token);
} catch (RemoteException ex) {
throw ex.rethrowFromSystemServer();
}
}
} else {
// If an exception was thrown when trying to resume, then
// just end this activity.
try {
ActivityManager.getService()
.finishActivity(token, Activity.RESULT_CANCELED, null,
Activity.DONT_FINISH_TASK_WITH_ACTIVITY);
} catch (RemoteException ex) {
throw ex.rethrowFromSystemServer();
}
}
}
2.1 關鍵是頁面繪制流程
整個的過程就是一開始講的層級關系。
第一點：performResumeActivity 比wm.addView(decor, l)先執行。所以Activity是先獲取焦點，才繪制view。
performResumeActivity->r.activity.performResume()->mInstrumentation.callActivityOnResume(this)->activity.onResume()
在performResume最后可以看到onPostResume
final void performResume() {
performRestart();
...
// mResumed is set by the instrumentation
mInstrumentation.callActivityOnResume(this);
...
onPostResume();
...
}
protected void onPostResume() {
final Window win = getWindow();
if (win != null) win.makeActive();
if (mActionBar != null) mActionBar.setShowHideAnimationEnabled(true);
mCalled = true;
}
window出現了，這個就是phonewindow。
下面我們去看docorview的過程。
//2020.02.18 phonewindow在這里獲取
if (r.window == null && !a.mFinished && willBeVisible) {
r.window = r.activity.getWindow();
//2020.02.18 docorview在這里獲取
View decor = r.window.getDecorView();
decor.setVisibility(View.INVISIBLE);
ViewManager wm = a.getWindowManager();
WindowManager.LayoutParams l = r.window.getAttributes();
a.mDecor = decor;
...
if (a.mVisibleFromClient) {
if (!a.mWindowAdded) {
a.mWindowAdded = true;
wm.addView(decor, l);
} else {
// The activity will get a callback for this {@link LayoutParams} change
// earlier. However, at that time the decor will not be set (this is set
// in this method), so no action will be taken. This call ensures the
// callback occurs with the decor set.
a.onWindowAttributesChanged(l);
}
}
我們來看下wm.addView(decor, l);這個的過程。wm的實現就是WindowManagerImpl
@Override
public void addView(@NonNull View view, @NonNull ViewGroup.LayoutParams params) {
applyDefaultToken(params);
mGlobal.addView(view, params, mContext.getDisplay(), mParentWindow);
}
mGlobal是WindowManagerGlobal， addview的核心代碼如下
root = new ViewRootImpl(view.getContext(), display);
view.setLayoutParams(wparams);
mViews.add(view);
mRoots.add(root);
mParams.add(wparams);
root.setView(view, wparams, panelParentView);
關於從ViewGroup開始的繪制流程，請看下篇。
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