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/*
* Copyright (C) 2020 The Android Open Source Project
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package com.android.systemui.util;
import android.content.Context;
import android.content.res.Resources;
import android.view.View;
import android.view.View.OnAttachStateChangeListener;
/**
* Utility class that handles view lifecycle events for View Controllers.
*
* Implementations should handle setup and teardown related activities inside of
* {@link #onViewAttached()} and {@link #onViewDetached()}. Be sure to call {@link #init()} on
* any child controllers that this uses. This can be done in {@link #onInit()} if the
* controllers are injected, or right after creation time of the child controller.
*
* Tip: View "attachment" happens top down - parents are notified that they are attached before
* any children. That means that if you call a method on a child controller in
* {@link #onViewAttached()}, the child controller may not have had its onViewAttach method
* called, so it may not be fully set up.
*
* As such, make sure that methods on your controller are safe to call _before_ its {@link #init()}
* and {@link #onViewAttached()} methods are called. Specifically, if your controller must call
* {@link View#findViewById(int)} on its root view to setup member variables, do so in its
* constructor. Save {@link #onViewAttached()} for things that can happen post-construction - adding
* listeners, dynamically changing content, or other runtime decisions.
*
* @param <T> View class that this ViewController is for.
*/
public abstract class ViewController<T extends View> {
protected final T mView;
private boolean mInited;
private OnAttachStateChangeListener mOnAttachStateListener = new OnAttachStateChangeListener() {
@Override
public void onViewAttachedToWindow(View v) {
ViewController.this.onViewAttached();
}
@Override
public void onViewDetachedFromWindow(View v) {
ViewController.this.onViewDetached();
}
};
protected ViewController(T view) {
mView = view;
}
/**
* Call immediately after constructing Controller in order to handle view lifecycle events.
*
* Generally speaking, you don't want to override this method. Instead, override
* {@link #onInit()} as a way to have an run-once idempotent method that you can use for
* setup of your ViewController.
*/
public void init() {
if (mInited) {
return;
}
onInit();
mInited = true;
if (isAttachedToWindow()) {
mOnAttachStateListener.onViewAttachedToWindow(mView);
}
addOnAttachStateChangeListener(mOnAttachStateListener);
}
/**
* Run once when {@link #init()} is called.
*
* Override this to perform idempotent, one-time setup that your controller needs. It will
* be called before {@link #onViewAttached()}.
*/
protected void onInit() {}
protected Context getContext() {
return mView.getContext();
}
protected Resources getResources() {
return mView.getResources();
}
public boolean isAttachedToWindow() {
return mView != null && mView.isAttachedToWindow();
}
/** Add an OnAttachStateListener to the view. Does nothing if the view is null. */
public void addOnAttachStateChangeListener(View.OnAttachStateChangeListener listener) {
if (mView != null) {
mView.addOnAttachStateChangeListener(listener);
}
}
/**
* Called when the view is attached and a call to {@link #init()} has been made in either order.
*/
protected abstract void onViewAttached();
/**
* Called when the view is detached.
*/
protected abstract void onViewDetached();
}
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