Activity对DialogFragment的管理

2020-04-09 本文已影响0人 Fakecoder_Sunis

Activity 专题- Activity 如何托管 Fragment 的生命周期解析
或者你使用过 DialogFragment，DialogFragment 是一种特殊的 Fragment ，这里简单介绍下原理，其实就是 Fragment 里面封装了一个 Dialog，

public class DialogFragment extends Fragment
implements DialogInterface.OnCancelListener, DialogInterface.OnDismissListener {
Dialog mDialog;
FragmentHostCallback mHost;

//显示这个 Fragment 调用这个方法
public void show(FragmentManager manager, String tag) {
    mDismissed = false;
    mShownByMe = true;
    FragmentTransaction ft = manager.beginTransaction();
    ft.add(this, tag);
    ft.commit();
}
// 这里会创建一个默认的 dialog
@override
public LayoutInflater getLayoutInflater(Bundle savedInstanceState) {
    if (!mShowsDialog) {//如果不显示 dialog，则走普通 Fragment 流程
        return super.getLayoutInflater(savedInstanceState);
    }

    //以下是创建 dialog 的代码
    mDialog = onCreateDialog(savedInstanceState);
    switch (mStyle) {
    case STYLE_NO_INPUT:
        mDialog.getWindow().addFlags(
            WindowManager.LayoutParams.FLAG_NOT_FOCUSABLE |
            WindowManager.LayoutParams.FLAG_NOT_TOUCHABLE);
        // fall through...
    case STYLE_NO_FRAME:
    case STYLE_NO_TITLE:
        mDialog.requestWindowFeature(Window.FEATURE_NO_TITLE);
    }
    if (mDialog != null) {
        return (LayoutInflater)mDialog.getContext().getSystemService(
                   Context.LAYOUT_INFLATER_SERVICE);
    }
    //这里的 mHost 对象就是 Fragment 宿主的 Activity
    return (LayoutInflater) mHost.getContext().getSystemService(
               Context.LAYOUT_INFLATER_SERVICE);
}

//这里会对 Dialog 进行 setContentView() 操作，设置视图，getView() 方法返回的就是 你实现的 onCreateView() 返回的View
@Override
public void onActivityCreated(Bundle savedInstanceState) {
    super.onActivityCreated(savedInstanceState);

    if (!mShowsDialog) {
        return;
    }

    View view = getView();
    if (view != null) {
        if (view.getParent() != null) {
            throw new IllegalStateException(
                "DialogFragment can not be attached to a container view");
        }
        mDialog.setContentView(view);
    }
    final Activity activity = getActivity();
    if (activity != null) {
        mDialog.setOwnerActivity(activity);
    }
    mDialog.setCancelable(mCancelable);
    if (!mDialog.takeCancelAndDismissListeners("DialogFragment", this, this)) {
        throw new IllegalStateException(
            "You can not set Dialog's OnCancelListener or OnDismissListener");
    }
    if (savedInstanceState != null) {
        Bundle dialogState = savedInstanceState.getBundle(SAVED_DIALOG_STATE_TAG);
        if (dialogState != null) {
            mDialog.onRestoreInstanceState(dialogState);
        }
    }
}

// onStar() 时会调用 Dialog.show(),也就是 Activity.onStart() 的时候
@Override
public void onStart() {
    super.onStart();
    if (mDialog != null) {
        mViewDestroyed = false;
        mDialog.show();
    }
}

// onStop() 的时候会关闭 Dialog
@Override
public void onStop() {
    super.onStop();
    if (mDialog != null) {
        mDialog.hide();
    }
}

DialogFragment 内部在 getLayoutInflater() 方法的时候会创建一个 Dialog，也就是 Fragment 初始化的时候。
DialogFragment 在 onActivityCreated() 的时候，会给 Dailog 设置视图，调用了 getView() 方法，也就是返回 onCreateView() 的返回值。
onStart() 的时候会调用 dialog.show()
onStop() 的时候会调用 dialog.hide()
还可以通过重写 onCreateDialog() ，可以实现展示自定义的 Dialog.

public Dialog onCreateDialog(Bundle savedInstanceState) {
return super.onCreateDialog(savedInstanceState);
}
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这种 Dialog 的好处就是，能够通过 Fragment 监听到 Activity 的生命周期回调，从而保证，在 Activity 关闭的时候，能够确保 Dialog 是关闭的，而不会造成因 Dialog 未关闭，导致 Activity 泄漏。

Activity 如何托管 Fragment 的生命周期
除了上面提到的，DialogFragment，同样在 Glide 框架里面，也是巧妙的用了这一个原理，使得基于 Activity Context 的 Rquest 能够自动伴随 Activity 的生命周期取消，从而提高了执行效率。

这里主要通过 FragmentHostCallback 实现 Fragment 追随Activity 的生命周期，同时也是实现了 Activity 调度 Fragment 的生命周期。

先来看看这个类：

/**

Integration points with the Fragment host.
<p>
Fragments may be hosted by any object; such as an {@link Activity}. In order to
host fragments, implement {@link FragmentHostCallback}, overriding the methods
applicable to the host.
/
public abstract class FragmentHostCallback<E> extends FragmentContainer {
/*
* Called when a {@link Fragment} is being attached to this host, immediately
* after the call to its {@link Fragment#onAttach(Context)} method and before
* {@link Fragment#onCreate(Bundle)}.
*/
public void onAttachFragment(Fragment fragment) {
}

/**
- Return a {@link LayoutInflater}.
- See {@link Activity#getLayoutInflater()}.
  */
  public LayoutInflater onGetLayoutInflater() {
  return (LayoutInflater) mContext.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
  }
void doLoaderStart() {
if (mLoadersStarted) {
return;
}
mLoadersStarted = true;
```
 if (mLoaderManager != null) {
     mLoaderManager.doStart();
 } else if (!mCheckedForLoaderManager) {
     mLoaderManager = getLoaderManager("(root)", mLoadersStarted, false);
 }
 mCheckedForLoaderManager = true;
```
}

void doLoaderStop(boolean retain) {
    mRetainLoaders = retain;

    if (mLoaderManager == null) {
        return;
    }

    if (!mLoadersStarted) {
        return;
    }
    mLoadersStarted = false;

    if (retain) {
        mLoaderManager.doRetain();
    } else {
        mLoaderManager.doStop();
    }
}

void doLoaderDestroy() {
    if (mLoaderManager == null) {
        return;
    }
    mLoaderManager.doDestroy();
}
｝

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这个类的官方 API 解释就是，Fragment 可以寄宿在任何对象上，例如 Activity。为了管理 Fragment，需要实现 FragmentHostCallback 方法，重载一些关键的方法，实现对 Fragment 的管理。

这里列举一些关键的方法，具体的细节可以自行查看源码。

然后在 Activity 中，我们可以看到这样一些代码：

public class Activity {
final FragmentController mFragments = FragmentController.createController(new HostCallbacks());

@CallSuper
protected void onStart() {
    if (DEBUG_LIFECYCLE) Slog.v(TAG, "onStart " + this);
    mCalled = true;

    mFragments.doLoaderStart();

    getApplication().dispatchActivityStarted(this);
}

public View onCreateView(View parent, String name, Context context, AttributeSet attrs) {
    if (!"fragment".equals(name)) {
        return onCreateView(name, context, attrs);
    }

    return mFragments.onCreateView(parent, name, context, attrs);
}

final void performDestroy() {
    mDestroyed = true;
    mWindow.destroy();
    mFragments.dispatchDestroy();
    onDestroy();
    mFragments.doLoaderDestroy();
    if (mVoiceInteractor != null) {
        mVoiceInteractor.detachActivity();
    }
}

class HostCallbacks extends FragmentHostCallback<Activity> {
    public HostCallbacks() {
        super(Activity.this /*activity*/);
    }

    @Override
    public void onDump(String prefix, FileDescriptor fd, PrintWriter writer, String[] args) {
        Activity.this.dump(prefix, fd, writer, args);
    }

    @Override
    public boolean onShouldSaveFragmentState(Fragment fragment) {
        return !isFinishing();
    }

    @Override
    public LayoutInflater onGetLayoutInflater() {
        final LayoutInflater result = Activity.this.getLayoutInflater();
        if (onUseFragmentManagerInflaterFactory()) {
            return result.cloneInContext(Activity.this);
        }
        return result;
    }

    @Override
    public boolean onUseFragmentManagerInflaterFactory() {
        // Newer platform versions use the child fragment manager's LayoutInflaterFactory.
        return getApplicationInfo().targetSdkVersion >= Build.VERSION_CODES.LOLLIPOP;
    }

    @Override
    public Activity onGetHost() {
        return Activity.this;
    }

    @Override
    public void onInvalidateOptionsMenu() {
        Activity.this.invalidateOptionsMenu();
    }

    @Override
    public void onStartActivityFromFragment(Fragment fragment, Intent intent, int requestCode,
                                            Bundle options) {
        Activity.this.startActivityFromFragment(fragment, intent, requestCode, options);
    }

    @Override
    public void onStartIntentSenderFromFragment(Fragment fragment, IntentSender intent,
            int requestCode, @Nullable Intent fillInIntent, int flagsMask, int flagsValues,
            int extraFlags, Bundle options) throws IntentSender.SendIntentException {
        if (mParent == null) {
            startIntentSenderForResultInner(intent, fragment.mWho, requestCode, fillInIntent,
            flagsMask, flagsValues, options);
        } else if (options != null) {
            mParent.startIntentSenderFromChildFragment(fragment, intent, requestCode,
            fillInIntent, flagsMask, flagsValues, extraFlags, options);
        }
    }

    @Override
    public void onRequestPermissionsFromFragment(Fragment fragment, String[] permissions,
            int requestCode) {
        String who = REQUEST_PERMISSIONS_WHO_PREFIX + fragment.mWho;
        Intent intent = getPackageManager().buildRequestPermissionsIntent(permissions);
        startActivityForResult(who, intent, requestCode, null);
    }

    @Override
    public boolean onHasWindowAnimations() {
        return getWindow() != null;
    }

    @Override
    public int onGetWindowAnimations() {
        final Window w = getWindow();
        return (w == null) ? 0 : w.getAttributes().windowAnimations;
    }

    @Override
    public void onAttachFragment(Fragment fragment) {
        Activity.this.onAttachFragment(fragment);
    }

    @Nullable
    @Override
    public View onFindViewById(int id) {
        return Activity.this.findViewById(id);
    }

    @Override
    public boolean onHasView() {
        final Window w = getWindow();
        return (w != null && w.peekDecorView() != null);
    }
}

}
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也就是 Activity 中的内部类HostCallbacks 继承了 FragmentHostCallback ，实现了一些关键的方法，用于在 Activity 的生命周期中，回调Fragment 中对应的方法。

最终会通过 FragmentController 分发给 Fragment，我们以 onDestory() 行为为例子，进行分析：

step1:

Activity.performDestory()

final void performDestroy() {
mDestroyed = true;
mWindow.destroy();
mFragments.dispatchDestroy();
onDestroy();
mFragments.doLoaderDestroy();
if (mVoiceInteractor != null) {
mVoiceInteractor.detachActivity();
}
}
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step2：

FragmentController.dispatchDestory()

public void dispatchDestroy() {
mHost.mFragmentManager.dispatchDestroy();
}
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也就是会回调 Host 的 FragmentManager 里的方法，那么 Activity 里面的 FragmentManager 对象，其实就是 FragmentManagerImpl 类。

step3:

FragmentManagerImpl.dispatchDestory()

public void dispatchDestroy() {
mDestroyed = true;
execPendingActions();
mExecutingActions = true;
moveToState(Fragment.INITIALIZING, false);
mExecutingActions = false;
mHost = null;
mContainer = null;
mParent = null;
}
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这里进行一系列标记清楚，并且把 mHost 等引用置为 null，解除了和 Activity 之间的引用，里面还调用了 moveToState() 方法，这里对 Fragment 的状态等进行了重置，具体细节比较复杂，就不进行分析，可以理解的是，这是 Fragment 回到了，还没创建的状态。

Activity对DialogFragment的管理

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