巜交换上司的秘书2中文电影,繁花讲了一个什么故事,APP开发

1、View.getContext()

@ViewDebug.CapturedViewProperty
    public final Context getContext() {
        return mContext;
    }

代碼很簡單直接返回成員變量mContext，那么mContext是在哪里賦值的呢？搜索發現mContext只有一個賦值的地方:即View的構造函數中

public View(Context context) {
        mContext = context;
        //.......
}

所以getContext()返回的對象，取決于創建View時傳什么參數。一般我們創建View的方式有兩種：

1、直接通過構造new出對象。
2、通過xml解析創建View對象
第一種方式沒啥好講的，創建View時傳入什么對象，getContext()就返回什么。下面主要看下第二種方式。

2、通過xml解析創建View對象

開發中我們經常在xml中寫布局，然后在Activity的onCreate()方法中通過setContentView(int layoutId)進行布局的加載。xml中的控件是如何創建的呢？setContentView()在Activity和AppCompatActivity中是不同的。

2.1、Activity.setContentView()

###Activity.java
 public void setContentView(@LayoutRes int layoutResID) {
        getWindow().setContentView(layoutResID);
        initWindowDecorActionBar();
    }

getWindow()返回PhoneWindow的對象。所以Activity的setContentView()不過是在調用PhoneWindow()的setContentView()方法。

###PhoneWindow.java
@Override
    public void setContentView(int layoutResID) {
       if (mContentParent == null) {
            //installDecor()中創建DecorView，并將id為android.R.id.content的mContentParent添加到DecorView中。
            installDecor();
        } else if (!hasFeature(FEATURE_CONTENT_TRANSITIONS)) {
            mContentParent.removeAllViews();
        }
        if (hasFeature(FEATURE_CONTENT_TRANSITIONS)) {
            final Scene newScene = Scene.getSceneForLayout(mContentParent, layoutResID,
                    getContext());
            transitionTo(newScene);
        } else {
            mLayoutInflater.inflate(layoutResID, mContentParent);
        }
      //省略部分代碼.....
    }

代碼很簡單，如果沒有FEATURE_CONTENT_TRANSITIONS標記的話，則直接調用mLayoutInflater.inflate(layoutResID, mContentParent);加載出來。mLayoutInflater是在PhoneWindow的構造函數中創建的，PhoneWindow是在Activity中的attach()方法中創建的。

###Activity.java
final void attach(Context context, ActivityThread aThread,
            Instrumentation instr, IBinder token, int ident,
            Application application, Intent intent, ActivityInfo info,
            CharSequence title, Activity parent, String id,
            NonConfigurationInstances lastNonConfigurationInstances,
            Configuration config, String referrer, IVoiceInteractor voiceInteractor,
            Window window, ActivityConfigCallback activityConfigCallback) {
        attachBaseContext(context);

        mFragments.attachHost(null /*parent*/);

        mWindow = new PhoneWindow(this, window, activityConfigCallback);
        mWindow.setWindowControllerCallback(this);
        mWindow.setCallback(this);
        mWindow.setOnWindowDismissedCallback(this);
        mWindow.getLayoutInflater().setPrivateFactory(this);
        //省略部分代碼....
    }

所以PhoneWindow中的context就是Activity本身。

問： LayoutInflater中的mContext和PhoneWindow中的context有什么關系？
答： LayoutInflater.from(context)最終會通過調用LayoutInflater的構造函數

protected LayoutInflater(Context context) {
        mContext = context;
    }

對mContext進行賦值。所以LayoutInflater中的mContext也是Activity本身。

問：LayoutInflater中的mContext和View中的mContext是什么關系？
答：這就需要看下inflate()方法

public View inflate(XmlPullParser parser, @Nullable ViewGroup root, boolean attachToRoot) {
        //省略部分代碼...
        // Temp is the root view that was found in the xml
        final View temp = createViewFromTag(root, name, inflaterContext, attrs);
              //省略部分代碼
    }

主要看下createViewFromTag(）方法

View createViewFromTag(View parent, String name, Context context, AttributeSet attrs,
            boolean ignoreThemeAttr) {
      //省略部分代碼
        try {
            View view;
            if (mFactory2 != null) {
                view = mFactory2.onCreateView(parent, name, context, attrs);
            } else if (mFactory != null) {
                view = mFactory.onCreateView(name, context, attrs);
            } else {
                view = null;
            }

            if (view == null && mPrivateFactory != null) {
                view = mPrivateFactory.onCreateView(parent, name, context, attrs);
            }

            if (view == null) {
                final Object lastContext = mConstructorArgs[0];
                mConstructorArgs[0] = context;
                try {
                    if (-1 == name.indexOf('.')) {
                        view = onCreateView(parent, name, attrs);
                    } else {
                        view = createView(name, null, attrs);
                    }
                } finally {
                    mConstructorArgs[0] = lastContext;
                }
            }

            return view;
        } catch (InflateException e) {
            throw e;

        } catch (ClassNotFoundException e) {
            final InflateException ie = new InflateException(attrs.getPositionDescription()
                    + ": Error inflating class " + name, e);
            ie.setStackTrace(EMPTY_STACK_TRACE);
            throw ie;

        } catch (Exception e) {
            final InflateException ie = new InflateException(attrs.getPositionDescription()
                    + ": Error inflating class " + name, e);
            ie.setStackTrace(EMPTY_STACK_TRACE);
            throw ie;
        }
    }

如果mFactory2、mFactory、mPrivateFactory不會空，則調用其onCreateView()進行View的創建，繼承Activity的Activity mFactory2和mFactory均為空，而mPrivateFactory的實現類就是Activity本身，但是Activity中的onCreateView()方法直接返回null，所以會調用LayoutInflate的createView()去創建View，其中原理很簡單就是通過反射進行View的創建。此時LayoutInflater中的mContext就傳遞到View中了。

2.1.1、總結

說了這么多有點亂，總結一下Activity傳遞到View中的過程：

1、在Activity的attach方法中創建了PhoneWindow將Activity傳遞到PhoneWindow中。
2、在PhoneWindow的構造函數中創建了LayoutInflater，將Activity傳遞到LayoutInflater中。
3、通過反射創建View，傳遞到View中。
所以，在繼承Activity的頁面中通過xml加載的View的getContext()返回的對象一定是Activity。

2.2、AppCompatActivity.setContentView()

直接上源碼

###AppCompatActivity.java
public void setContentView(@LayoutRes int layoutResID) {
    this.getDelegate().setContentView(layoutResID);
}

@NonNull
public AppCompatDelegate getDelegate() {
    if (this.mDelegate == null) {
        this.mDelegate = AppCompatDelegate.create(this, this);
    }
    return this.mDelegate;
}

###AppCompatDelegate .java
public static AppCompatDelegate create(Activity activity, AppCompatCallback callback) {
        return new AppCompatDelegateImpl(activity, activity.getWindow(), callback);
    }

可以看到最終調用的是AppCompatDelegateImpl中的setContentView()

public void setContentView(int resId) {
        this.ensureSubDecor();
        ViewGroup contentParent = (ViewGroup)this.mSubDecor.findViewById(16908290);
        contentParent.removeAllViews();
        LayoutInflater.from(this.mContext).inflate(resId, contentParent);
        this.mOriginalWindowCallback.onContentChanged();
    }

主要做了3件事：

1、確保 mSubDecor 的初始化
2、從mSubDecor 中找id為android.R.id.content的contentParent
3、通過inflate將id為resId的View添加到contentParent中。

2.2.1、mSubDecor的初始化

###AppCompatDelegateImpl.java
 private void ensureSubDecor() {
        if(!this.mSubDecorInstalled) {
            this.mSubDecor = this.createSubDecor();
            //省略部分代碼。。。
            }
          //省略部分代碼。。。
    }

 private ViewGroup createSubDecor() {
     //...省略... 這部分主要針對 AppCompat 樣式檢查和適配

    // Now let's make sure that the Window has installed its decor by retrieving it
    //這句代碼很重要哦
    mWindow.getDecorView();

    final LayoutInflater inflater = LayoutInflater.from(mContext);
    ViewGroup subDecor = null;
 
    //...省略... 這部分主要針對不同的樣式設置來初始化不同的 subDecor（inflater 不同的布局 xml ）
 subDecor =inflater.inflate(XXX);

    //...省略...
    
    final ContentFrameLayout contentView = (ContentFrameLayout) subDecor.findViewById(
            R.id.action_bar_activity_content);

    final ViewGroup windowContentView = (ViewGroup) mWindow.findViewById(android.R.id.content);
    if (windowContentView != null) {
        // There might be Views already added to the Window's content view so we need to
        // migrate them to our content view
        while (windowContentView.getChildCount() > 0) {
            final View child = windowContentView.getChildAt(0);
            windowContentView.removeViewAt(0);
            contentView.addView(child);
        }

        // Change our content FrameLayout to use the android.R.id.content id.
        // Useful for fragments.
        windowContentView.setId(View.NO_ID);
        contentView.setId(android.R.id.content);

        // The decorContent may have a foreground drawable set (windowContentOverlay).
        // Remove this as we handle it ourselves
        if (windowContentView instanceof FrameLayout) {
            ((FrameLayout) windowContentView).setForeground(null);
        }
    }

    // Now set the Window's content view with the decor
    mWindow.setContentView(subDecor);

    //...省略...

    return subDecor;
}

1、通過mWindow.getDecorView();創建DecorView，并將id為android.R.id.content的ContentParent添加到DecorView中。
2、創建mSubDecor
-3 、將DecorView中的ContentParent的所有子View都添加到mSubDecor的子View contentView中，并清空ContentParent中所有子View,然后將ContentParent的id置成-1，將contentView的id置成android.R.id.content，依次來達到偷梁換柱的目的。
4、最后通過mWindow.setContentView(subDecor);將subDecor添加到DecorView中。
還記得我們要干什么嗎？當然是看繼承AppCompatActivity的Activity中的View中的Context和AppCompatActivity的關系了，我們回到AppCompatDelegateImpl的setContentView()

public void setContentView(int resId) {
        this.ensureSubDecor();
        ViewGroup contentParent = (ViewGroup)this.mSubDecor.findViewById(16908290);
        contentParent.removeAllViews();
        LayoutInflater.from(this.mContext).inflate(resId, contentParent);
        this.mOriginalWindowCallback.onContentChanged();
    }

上面分析了ensureSubDecor()做了些什么事，真正添加resId的仍然是通過
LayoutInflater.from(this.mContext).inflate(resId, contentParent);來完成的。

2.2.2、LayoutInflater.inflate()

在分析Activity的setContentView()時我們已經對inflate做了分析，最終創建View的方法是LayoutInflater的createViewFromTag()。

###LayoutInflater.java
View createViewFromTag(View parent, String name, Context context, AttributeSet attrs,
            boolean ignoreThemeAttr) {
      //省略部分代碼
        try {
            View view;
            if (mFactory2 != null) {
                view = mFactory2.onCreateView(parent, name, context, attrs);
            } else if (mFactory != null) {
                view = mFactory.onCreateView(name, context, attrs);
            } else {
                view = null;
            }

            if (view == null && mPrivateFactory != null) {
                view = mPrivateFactory.onCreateView(parent, name, context, attrs);
            }

            if (view == null) {
                final Object lastContext = mConstructorArgs[0];
                mConstructorArgs[0] = context;
                try {
                    if (-1 == name.indexOf('.')) {
                        view = onCreateView(parent, name, attrs);
                    } else {
                        view = createView(name, null, attrs);
                    }
                } finally {
                    mConstructorArgs[0] = lastContext;
                }
            }

            return view;
        } catch (InflateException e) {
            throw e;

        } catch (ClassNotFoundException e) {
            final InflateException ie = new InflateException(attrs.getPositionDescription()
                    + ": Error inflating class " + name, e);
            ie.setStackTrace(EMPTY_STACK_TRACE);
            throw ie;

        } catch (Exception e) {
            final InflateException ie = new InflateException(attrs.getPositionDescription()
                    + ": Error inflating class " + name, e);
            ie.setStackTrace(EMPTY_STACK_TRACE);
            throw ie;
        }
    }

和Activity不同的是mFactory2不為空，mFactory2是在AppCompatActivity中的onCreate()中賦值的。

###AppCompatActivity.java
 @Override
    protected void onCreate(@Nullable Bundle savedInstanceState) {
        final AppCompatDelegate delegate = getDelegate();
        delegate.installViewFactory();
        delegate.onCreate(savedInstanceState);
       //省略部分代碼...
    }

### AppcompatDelegateImpl.java
 public void installViewFactory() {
        LayoutInflater layoutInflater = LayoutInflater.from(this.mContext);
        if (layoutInflater.getFactory() == null) {
//最終調用LayoutInflater的setFactory2()
            LayoutInflaterCompat.setFactory2(layoutInflater, this);
        } else if (!(layoutInflater.getFactory2() instanceof AppCompatDelegateImpl)) {
            Log.i("AppCompatDelegate", "The Activity's LayoutInflater already has a Factory installed so we can not install AppCompat's");
        }

    }

###LayoutInflater.java
public void setFactory2(Factory2 factory) {
        if (mFactorySet) {
            throw new IllegalStateException("A factory has already been set on this LayoutInflater");
        }
        if (factory == null) {
            throw new NullPointerException("Given factory can not be null");
        }
        mFactorySet = true;
        if (mFactory == null) {
            mFactory = mFactory2 = factory;
        } else {
            mFactory = mFactory2 = new FactoryMerger(factory, factory, mFactory, mFactory2);
        }
    }

此時LayoutInflater中的mFactory和mFactory2已被賦值了，mFactory和mFactory2的實例就是AppCompatDelegateImpl，那么mPrivateFactory是何時賦值的呢？

/**
     * @hide for use by framework
     */
    public void setPrivateFactory(Factory2 factory) {
        if (mPrivateFactory == null) {
            mPrivateFactory = factory;
        } else {
            mPrivateFactory = new FactoryMerger(factory, factory, mPrivateFactory, mPrivateFactory);
        }
    }

沒找到哪里調用的，從注釋可以看出是framework調用的。通過斷點可知mPrivateFactory 的實例就是AppCompatActivity本身。下面我們看下Factory2的實現類AppCompatDelegateImpl和AppCompatActivity中的onCreateView(View parent, String name, Context context, AttributeSet attrs)方法到底做了什么？

2.2.3、AppCompatDelegateImpl的onCreateView()

public final View onCreateView(View parent, String name, Context context, AttributeSet attrs) {
        return this.createView(parent, name, context, attrs);
    }

public View createView(View parent, String name, @NonNull Context context, @NonNull AttributeSet attrs) {
       //省略...這部分創建mAppCompatViewInflater
        boolean inheritContext = false;
        if (IS_PRE_LOLLIPOP) {
            inheritContext = attrs instanceof XmlPullParser ? ((XmlPullParser)attrs).getDepth() > 1 : this.shouldInheritContext((ViewParent)parent);
        }

        return this.mAppCompatViewInflater.createView(parent, name, context, attrs, inheritContext, IS_PRE_LOLLIPOP, true, VectorEnabledTintResources.shouldBeUsed());
    }

可以看到最終會調用AppCompatViewInflater的createView()方法

final View createView(View parent, final String name, @NonNull Context context,
            @NonNull AttributeSet attrs, boolean inheritContext,
            boolean readAndroidTheme, boolean readAppTheme, boolean wrapContext) {
        final Context originalContext = context;

        // We can emulate Lollipop's android:theme attribute propagating down the view hierarchy
        // by using the parent's context
        if (inheritContext && parent != null) {
            context = parent.getContext();
        }
        if (readAndroidTheme || readAppTheme) {
            // We then apply the theme on the context, if specified
            context = themifyContext(context, attrs, readAndroidTheme, readAppTheme);
        }
        if (wrapContext) {
            context = TintContextWrapper.wrap(context);
        }

        View view = null;

        // We need to 'inject' our tint aware Views in place of the standard framework versions
        switch (name) {
            case "TextView":
                view = createTextView(context, attrs);
                verifyNotNull(view, name);
                break;
            case "ImageView":
                view = createImageView(context, attrs);
                verifyNotNull(view, name);
                break;
            case "Button":
                view = createButton(context, attrs);
                verifyNotNull(view, name);
                break;
            case "EditText":
                view = createEditText(context, attrs);
                verifyNotNull(view, name);
                break;
            case "Spinner":
                view = createSpinner(context, attrs);
                verifyNotNull(view, name);
                break;
            case "ImageButton":
                view = createImageButton(context, attrs);
                verifyNotNull(view, name);
                break;
            case "CheckBox":
                view = createCheckBox(context, attrs);
                verifyNotNull(view, name);
                break;
            case "RadioButton":
                view = createRadioButton(context, attrs);
                verifyNotNull(view, name);
                break;
            case "CheckedTextView":
                view = createCheckedTextView(context, attrs);
                verifyNotNull(view, name);
                break;
            case "AutoCompleteTextView":
                view = createAutoCompleteTextView(context, attrs);
                verifyNotNull(view, name);
                break;
            case "MultiAutoCompleteTextView":
                view = createMultiAutoCompleteTextView(context, attrs);
                verifyNotNull(view, name);
                break;
            case "RatingBar":
                view = createRatingBar(context, attrs);
                verifyNotNull(view, name);
                break;
            case "SeekBar":
                view = createSeekBar(context, attrs);
                verifyNotNull(view, name);
                break;
            default:
                // The fallback that allows extending class to take over view inflation
                // for other tags. Note that we don't check that the result is not-null.
                // That allows the custom inflater path to fall back on the default one
                // later in this method.
                view = createView(context, name, attrs);
        }

        if (view == null && originalContext != context) {
            // If the original context does not equal our themed context, then we need to manually
            // inflate it using the name so that android:theme takes effect.
            view = createViewFromTag(context, name, attrs);
        }

        if (view != null) {
            // If we have created a view, check its android:onClick
            checkOnClickListener(view, attrs);
        }

        return view;
    }

這段代碼主要為了兼容低版本，將name為TextView、ImageView等控件替換成AppCompatXXX,以TextView轉換成AppCompatTextView為例看下。

###AppCompatViewInflate.java
 @NonNull
    protected AppCompatTextView createTextView(Context context, AttributeSet attrs) {
        return new AppCompatTextView(context, attrs);
    }
###AppCompatTextView.java
public AppCompatTextView(Context context, AttributeSet attrs, int defStyleAttr) {
        super(TintContextWrapper.wrap(context), attrs, defStyleAttr);
        this.mBackgroundTintHelper = new AppCompatBackgroundHelper(this);
        this.mBackgroundTintHelper.loadFromAttributes(attrs, defStyleAttr);
        this.mTextHelper = new AppCompatTextHelper(this);
        this.mTextHelper.loadFromAttributes(attrs, defStyleAttr);
        this.mTextHelper.applyCompoundDrawablesTints();
    }

可以看到AppCompatTextView的構造函數對context進行了包裝：TintContextWrapper.wrap(context)

 public static Context wrap(@NonNull Context context) {
        if (shouldWrap(context)) {
           //省略代碼...
                TintContextWrapper wrapper = new TintContextWrapper(context);
                sCache.add(new WeakReference(wrapper));
                return wrapper;
            }
        } else {
            return context;
        }
    }

如果shouldWrap(context)返回true，則將context包裝成TintContextWrapper ，否則直接返回context。

private static boolean shouldWrap(@NonNull Context context) {
        if (!(context instanceof TintContextWrapper) && !(context.getResources() instanceof TintResources) && !(context.getResources() instanceof VectorEnabledTintResources)) {
            return VERSION.SDK_INT < 21 || VectorEnabledTintResources.shouldBeUsed();
        } else {
            return false;
        }
    }

可以看到在VERSION.SDK_INT >= 21時肯定返回false，在VERSION.SDK_INT<21時會將context包裝成TintContextWrapper。所以我們可以得出結論：

1、在Android5.0之前，會使用TintContextWrapper創建name為TextView、ImageView等控件。
2、在Android5.0及以上直接使用context即AppCompatActivity創建View。
分析完了AppCompatDelegateImpl的onCreateView()，下面看下AppComatActivity的onCreateView()。

2.2.4、AppComatActivity的onCreateView()

AppComatActivity中并沒有重寫onCreateView，而在其父類FragmentActivity做了重寫

public View onCreateView(View parent, String name, Context context, AttributeSet attrs) {
        View v = this.dispatchFragmentsOnCreateView(parent, name, context, attrs);
        return v == null ? super.onCreateView(parent, name, context, attrs) : v;
    }

可以看到對于非Fragment的控件會直接調用super.onCreateView(parent, name, context, attrs)即Activity的onCreateView()。

public View onCreateView(String name, Context context, AttributeSet attrs) {
        return null;
    }

Activity的處理很粗暴，直接return null；所以name不為TextView、ImageView等的控件，如LinearLayout，會通過反射進行創建。

2.2.5、AppCompatActivity傳遞到View的過程總結

1、創建AppCompatDelegateImpl，將AppCompatActivity賦值給mContext。
2、然后通過LayoutInflater.from(this.mContext).inflate(resId, contentParent);將AppCompatActivity傳遞給LayoutInflater。
3、在LayoutInflater中的createViewFromTag()方法中調用Factory2的實現類 AppCompatDelegateImpl中的createView()將name為TextView、ImageView等的控件替換成AppCompat開頭的控件，在Android5.0以下的創建AppCompatXX時傳遞的是TintContextWrapper。
4、對于name不為TextView、ImageView的控件依然調用LayoutInflater中的onCreateView，通過反射創建。

3、總結

1、繼承Activity的頁面中的View，getContext()直接返回Activity。
2、繼承AppCompatActivity的頁面中的View，
- 在Android5.0以下，如果name為TextView、ImageView等的控件的getContext()返回TintContextWrapper，否則則返回AppCompatActivity。
- 在Android5.0以上，直接返回AppCompatActivity。

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View.getContext()一定返回Activity嗎？

View.getContext()一定返回Activity嗎？

1、View.getContext()

2、通過xml解析創建View對象

2.1、Activity.setContentView()

2.1.1、總結

2.2、AppCompatActivity.setContentView()

2.2.1、mSubDecor的初始化

2.2.2、LayoutInflater.inflate()

2.2.3、AppCompatDelegateImpl的onCreateView()

2.2.4、AppComatActivity的onCreateView()

2.2.5、AppCompatActivity傳遞到View的過程總結

3、總結

三个男躁一个女,国精产品一区一手机的秘密,麦子交换系列最经典十句话,欧美 国产 综合 欧美 视频

View.getContext()一定返回Activity嗎？

1、View.getContext()

2、通過xml解析創建View對象

2.1、Activity.setContentView()

2.1.1、總結

2.2、AppCompatActivity.setContentView()

2.2.1、mSubDecor的初始化

2.2.2、LayoutInflater.inflate()

2.2.3、AppCompatDelegateImpl的onCreateView()

2.2.4、AppComatActivity的onCreateView()

2.2.5、AppCompatActivity傳遞到View的過程總結

3、總結

三个男躁一个女,国精产品一区一手机的秘密,麦子交换系列最经典十句话,欧美国产综合欧美视频