背景

问题描述

在项目中使用 SwipeBackLayout 或 SlidingMenu 侧滑关闭Activity框架时，由于windowIsTranslucent这个属性设置为了true，导致按home键退到桌面在返回App时会出现两个问题。

先显示上层的Activity,再显示当前交互的Activity。（感觉闪一下）
概率出现当前Activity整个页面为透明,屏幕显示的是上一个界面的Activity,但是当前Activity并没有销毁，并且可以交互

这个是比较严重的用户体验问题，特别在小米手机上会特别明显。

过程

问题猜想

之前就出现过首页透底显示桌面的情况，是因为Theme中windowIsTranslucent = true导致这个问题，通过修改windowIsTranslucent = false属性，彻底解决了首页透底问题。

实施

方案A: 修改所有Activity Theme windowIsTranslucent = true 属性

同样的配方同样的味道替换所有所有Activity Theme 将window 改为不透明，背景颜色改为透明

    <style name="AppBaseTheme" parent="@style/Theme.AppCompat.Light.NoActionBar">
        <item name="android:windowIsTranslucent">false</item>
        <item name="android:windowBackground">@color/transparent</item>
    </style>

运行后的效果图：

闪烁透底的问题是解决了，但是侧滑框架出现了侧滑后看不到底部内容，方案A失败；

方案B：动态设置Activity Theme

在当前App退到后台时替换Activity为非透明主题，在Activity恢复到前台被点击时替换为透明主题；如何动态修改Activity Theme？


    @Override
    protected void onCreate(Bundle savedInstanceState) {
        if (current_theme!= -1){
            this.setTheme(current_theme);
        }
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        findViewById(R.id.bt_theme).setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                changeTheme(GREEN_THEME);
            }
        });
    }


    public void changeTheme(int index) {
        switch (index) {
            case DEFAULT_THEME:
                current_theme = R.style.DefaultTheme;
                break;
            case GREEN_THEME:
                current_theme = R.style.GreenTheme;
                break;
            case ORANGE_THEME:
                current_theme = R.style.OrangeTheme;
                break;
            default:
                break;
        }
    }

    protected void reload() {
        Intent intent = getIntent();
        overridePendingTransition(0, 0);
        intent.addFlags(Intent.FLAG_ACTIVITY_NO_ANIMATION);
        finish();
        overridePendingTransition(0, 0);
        startActivity(intent);
    }

其实设置主题必须在任何view创建之前，所以我们不可能在activity的onCreate之后来更改主题，如果一定要做，就只能调用setTheme()，然后调用recreate()，重新创建一个activity，并且销毁上一个activity; 所以这个方案并不可行，整个界面必须销毁重建。已知的Android theme修改方式

AndroidManifest 设置Activity Theme
在Activity setContentView执行前调用setTheme

可以通过其他方式修改Activity windowIsTranslucent 属性吗？

方案B+：反射动态设置Activity windowIsTranslucent

查阅Activity源码，看一下他是如何变成透明的

     /**
     * Convert a translucent themed Activity {@link android.R.attr#windowIsTranslucent} back from
     * opaque to translucent following a call to {@link #convertFromTranslucent()}.
     * <p>
     * Calling this allows the Activity behind this one to be seen again. Once all such Activities
     * have been redrawn {@link TranslucentConversionListener#onTranslucentConversionComplete} will
     * be called indicating that it is safe to make this activity translucent again. Until
     * {@link TranslucentConversionListener#onTranslucentConversionComplete} is called the image
     * behind the frontmost Activity will be indeterminate.
     * <p>
     * This call has no effect on non-translucent activities or on activities with the
     * {@link android.R.attr#windowIsFloating} attribute.
     *
     * @param callback the method to call when all visible Activities behind this one have been
     * drawn and it is safe to make this Activity translucent again.
     * @param options activity options delivered to the activity below this one. The options
     * are retrieved using {@link #getActivityOptions}.
     * @return <code>true</code> if Window was opaque and will become translucent or
     * <code>false</code> if window was translucent and no change needed to be made.
     *
     * @see #convertFromTranslucent()
     * @see TranslucentConversionListener
     *
     * @hide
     */
    @SystemApi
    public boolean convertToTranslucent(TranslucentConversionListener callback,
            ActivityOptions options) {
        boolean drawComplete;
        try {
            mTranslucentCallback = callback;
            mChangeCanvasToTranslucent = ActivityManager.getService().convertToTranslucent(
                    mToken, options == null ? null : options.toBundle());
            WindowManagerGlobal.getInstance().changeCanvasOpacity(mToken, false);
            drawComplete = true;
        } catch (RemoteException e) {
            // Make callback return as though it timed out.
            mChangeCanvasToTranslucent = false;
            drawComplete = false;
        }
        if (!mChangeCanvasToTranslucent && mTranslucentCallback != null) {
            // Window is already translucent.
            mTranslucentCallback.onTranslucentConversionComplete(drawComplete);
        }
        return mChangeCanvasToTranslucent;
    }
 
 /**
     * Convert a translucent themed Activity {@link android.R.attr#windowIsTranslucent} to a
     * fullscreen opaque Activity.
     * <p>
     * Call this whenever the background of a translucent Activity has changed to become opaque.
     * Doing so will allow the {@link android.view.Surface} of the Activity behind to be released.
     * <p>
     * This call has no effect on non-translucent activities or on activities with the
     * {@link android.R.attr#windowIsFloating} attribute.
     *
     * @see #convertToTranslucent(android.app.Activity.TranslucentConversionListener,
     * ActivityOptions)
     * @see TranslucentConversionListener
     *
     * @hide
     */
    @SystemApi
    public void convertFromTranslucent() {
        try {
            mTranslucentCallback = null;
            if (ActivityManager.getService().convertFromTranslucent(mToken)) {
                WindowManagerGlobal.getInstance().changeCanvasOpacity(mToken, true);
            }
        } catch (RemoteException e) {
            // pass
        }
    }

可以看到这个两个Api就是将Activity转化为投透明和非透明通过 ActivityManager.getService() 和 WindowManagerGlobal.getInstance().changeCanvasOpacity()修改Window透明属性;

convertToTranslucent //将当前Activity Window 设置为透明
convertFromTranslucent //将当前 Activity Window 设置为非透明

由于是系统Api 并有 @hide 标注正常是无法调用的，可以通过反射来调用；反射调用如下：

	/**
	 * Convert a translucent themed Activity
	 * 将Activity 改为透明
	 */
	public static void convertActivityToTranslucent(Activity activity) {
		long timeMillis = SystemClock.currentThreadTimeMillis();
		if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.LOLLIPOP) {
			convertActivityToTranslucentAfterL(activity);
		} else {
			convertActivityToTranslucentBeforeL(activity);
		}
		FxLog.d("convertActivity :  convertActivityToTranslucent  time = " + (SystemClock.currentThreadTimeMillis() - timeMillis));
	}

	/**
	 * Calling the convertToTranslucent method on platforms before Android 5.0
	 */
	public static void convertActivityToTranslucentBeforeL(Activity activity) {
		try {
			Class<?>[] classes = Activity.class.getDeclaredClasses();
			Class<?> translucentConversionListenerClazz = null;
			for (Class clazz : classes) {
				if (clazz.getSimpleName().contains("TranslucentConversionListener")) {
					translucentConversionListenerClazz = clazz;
				}
			}
			Method method = Activity.class.getDeclaredMethod("convertToTranslucent",
					translucentConversionListenerClazz);
			method.setAccessible(true);
			method.invoke(activity, new Object[] {
					null
			});
		} catch (Throwable t) {
		}
	}

	/**
	 * Calling the convertToTranslucent method on platforms after Android 5.0
	 */
	private static void convertActivityToTranslucentAfterL(Activity activity) {
		try {
			Method getActivityOptions = Activity.class.getDeclaredMethod("getActivityOptions");
			getActivityOptions.setAccessible(true);
			Object options = getActivityOptions.invoke(activity);

			Class<?>[] classes = Activity.class.getDeclaredClasses();
			Class<?> translucentConversionListenerClazz = null;
			for (Class clazz : classes) {
				if (clazz.getSimpleName().contains("TranslucentConversionListener")) {
					translucentConversionListenerClazz = clazz;
				}
			}
			Method convertToTranslucent = Activity.class.getDeclaredMethod("convertToTranslucent",
					translucentConversionListenerClazz, ActivityOptions.class);
			convertToTranslucent.setAccessible(true);
			convertToTranslucent.invoke(activity, null, options);
		} catch (Throwable t) {
		}
	}

性能问题的思考

这样的反射是否对性能有损耗呢？在调用时做了耗时测试在日志打印中可以看到性能完全不会受影响；

为了进一步优化并减少反射调用，仅在用户触发侧滑、侧滑完全闭合时修改Activity透明属性

	public void setWindowToTranslucent(boolean translucent) {
		if (isTranslucentWindow == translucent || !isSlidingEnabled()){
			return;
		}
		isTranslucentWindow = translucent;
		if (isTranslucentWindow) {
			convertActivityToTranslucent(((Activity) getContext()));
		} else {
			convertActivityFromTranslucent(((Activity) getContext()));
		}
	}

稳定性问题的思考

由于是系统Api 在不同版本会略有不同，做了版本区分。并对反射Api做了try/catch保护，在反射Api调用异常的情况下，不会对App功能有影响。原Activity windowIsTranslucent 属性不变

总结

设置windowIsTranslucent =true 后，退后台再打开App时上层的Activity 会被再次绘制
Activity 替换主题的两种方式

AndroidManifest 设置Activity Theme
在Activity setContentView执行前调用setTheme

Activity 源码分析

convertToTranslucent //将当前Activity Window 设置为透明
convertFromTranslucent //将当前 Activity Window 设置为非透明

反射调用

思考

1.在9.0后 @hide Api 通过反射是无法调用，后续是解决方案 2.除了修改windowIsTranslucent 还没有有其他的解决方案？ 3.如何从根源思考、解决问题