问题描述

在完成SpEditTool的时候使用了android-gif-drawable一行代码让TextView中ImageSpan支持Gif，出现过两次GifDrawable不刷新的现象

• 一次是自己限制了TextView的刷新间隔，导致刷新频率很快的gif刷新了TextView还没有刷新
• 一次是EditText刷新了但是GifDrawable没刷新，需要setLayerType(View.LAYER_TYPE_SOFTWARE, null)才起作用

原因

跑了下android-gif-drawable，发现上面两个问题的原因都是同一个

先来看下代码

class RenderTask extends SafeRunnable {

    RenderTask(GifDrawable gifDrawable) {
        super(gifDrawable);
    }

    @Override
    public void doWork() {
        final long invalidationDelay = mGifDrawable.mNativeInfoHandle.renderFrame(mGifDrawable.mBuffer);
        if (invalidationDelay >= 0) {
            mGifDrawable.mNextFrameRenderTime = SystemClock.uptimeMillis() + invalidationDelay;
            if (mGifDrawable.isVisible() && mGifDrawable.mIsRunning && !mGifDrawable.mIsRenderingTriggeredOnDraw) {
                mGifDrawable.mExecutor.remove(this);
                mGifDrawable.mRenderTaskSchedule = mGifDrawable.mExecutor.schedule(this, invalidationDelay, TimeUnit.MILLISECONDS);
            }
            if (!mGifDrawable.mListeners.isEmpty() && mGifDrawable.getCurrentFrameIndex() == mGifDrawable.mNativeInfoHandle.getNumberOfFrames() - 1) {
                mGifDrawable.mInvalidationHandler.sendEmptyMessageAtTime(mGifDrawable.getCurrentLoop(), mGifDrawable.mNextFrameRenderTime);
            }
        } else {
            mGifDrawable.mNextFrameRenderTime = Long.MIN_VALUE;
            mGifDrawable.mIsRunning = false;
        }
        if (mGifDrawable.isVisible() && !mGifDrawable.mInvalidationHandler.hasMessages(MSG_TYPE_INVALIDATION)) {
            mGifDrawable.mInvalidationHandler.sendEmptyMessageAtTime(MSG_TYPE_INVALIDATION, 0);
        }
    }
}

这个是GifDrawable用来渲染的主要代码，RenderTask的控制是交给GifDrawable的,GifDrawable在startAnimation()和draw()这两个方法中去调度下一次渲染

    void startAnimation(long lastFrameRemainder) {
        if (mIsRenderingTriggeredOnDraw) {
            mNextFrameRenderTime = 0;
            mInvalidationHandler.sendEmptyMessageAtTime(MSG_TYPE_INVALIDATION, 0);
        } else {
            cancelPendingRenderTask();
            mRenderTaskSchedule = mExecutor.schedule(mRenderTask, Math.max(lastFrameRemainder, 0), TimeUnit.MILLISECONDS);
        }
    }

public void draw(@NonNull Canvas canvas) {
        final boolean clearColorFilter;
        if (mTintFilter != null && mPaint.getColorFilter() == null) {
            mPaint.setColorFilter(mTintFilter);
            clearColorFilter = true;
        } else {
            clearColorFilter = false;
        }
        if (mTransform == null) {
            canvas.drawBitmap(mBuffer, mSrcRect, mDstRect, mPaint);
        } else {
            mTransform.onDraw(canvas, mPaint, mBuffer);
        }
        if (clearColorFilter) {
            mPaint.setColorFilter(null);
        }

        if (mIsRenderingTriggeredOnDraw && mIsRunning && mNextFrameRenderTime != Long.MIN_VALUE) {
            final long renderDelay = Math.max(0, mNextFrameRenderTime - SystemClock.uptimeMillis());
            mNextFrameRenderTime = Long.MIN_VALUE;
            mExecutor.remove(mRenderTask);
            mRenderTaskSchedule = mExecutor.schedule(mRenderTask, renderDelay, TimeUnit.MILLISECONDS);
        }
    }

问题就出在这个draw()上面,Drawable的draw方法依赖于View或者ImageSpan等外部对象的调用，所以View、ImageSpan如果不刷新，RenderTask就没有了下一次渲染的机会了，gif也就停了

EditText的问题

对于上面我说的不刷新的第一种情况大家好理解，TextView没刷新嘛，GifDrawable按照上面的分析肯定也刷新不了

那EditText自己刷新了为啥也是draw()里面调度绘制的问题呢，而且设置了View.LAYER_TYPE_SOFTWARE就好了呢？

还是看代码好了

GifDrawable的draw()方法是在DynamicDrawableSpan.draw()中被调用的

    @Override
    public void draw(Canvas canvas, CharSequence text,
                     int start, int end, float x, 
                     int top, int y, int bottom, Paint paint) {
        Drawable b = getCachedDrawable();
        canvas.save();
        
        int transY = bottom - b.getBounds().bottom;
        if (mVerticalAlignment == ALIGN_BASELINE) {
            transY -= paint.getFontMetricsInt().descent;
        }

        canvas.translate(x, transY);
        b.draw(canvas);
        canvas.restore();
    }

• 顺探摸瓜找到了TextLine.draw()->TextLine.drawRun()->TextLine.handleRun()->TextLine.handleReplacement()->DynamicDrawableSpan.draw()这么一条调用栈

• TextLine.draw()方法只在Layout.draw()->Layout.drawText()中调用

• 接下来只要找调用了Layout.draw()的地方

TextView.onDraw()方法

    @Override
    protected void onDraw(Canvas canvas) {
            ...
        if (mEditor != null) {
            mEditor.onDraw(canvas, layout, highlight, mHighlightPaint, cursorOffsetVertical);
        } else {
            layout.draw(canvas, highlight, mHighlightPaint, cursorOffsetVertical);
        }
            ..
    }
...

如果是EditText的话会调用Editor.onDraw()方法

    void onDraw(Canvas canvas, Layout layout, Path highlight, Paint highlightPaint,
            int cursorOffsetVertical) {
        ...
        if (mTextView.canHaveDisplayList() && canvas.isHardwareAccelerated()) {
            drawHardwareAccelerated(canvas, layout, highlight, highlightPaint,
                    cursorOffsetVertical);
        } else {
            layout.draw(canvas, highlight, highlightPaint, cursorOffsetVertical);
        }
    }

从上面的代码可以看到如果有离屏渲染且开启了硬件加速,这是默认的情况，渲染会走drawHardwareAccelerated(),反之view的LayerType为View.LAYER_TYPE_SOFTWARE的话会调用layout.draw()最终调用到GifDrawable.draw()

看下drawHardwareAccelerated()

    private void drawHardwareAccelerated(Canvas canvas, Layout layout, Path highlight,
            Paint highlightPaint, int cursorOffsetVertical) {
        ...
        } else {
            // Boring layout is used for empty and hint text
            layout.drawText(canvas, firstLine, lastLine);
        }
    }

只在EditText显示hint的时候才会调用Layout.drawText()

结论

别看这一系列调用栈很长，简单的说就是EditText默认状况下（离屏渲染加硬件加速），没有调用Layout.draw()从而导致GifDrawable.draw()没走，因为RenderTask是通过GifDrawable.draw()调度的，所以gif就停止不动了

最后

通过上面的分析我觉得这样的将RenderTask和Gifdrawable.draw()关联的处理方式不太合理，所以给作者提了issue和pr，建议在Drawable的invalidateSelf()中调度下次刷新，这样gif显示就不会依赖于外部对象了

作者接受了我的建议，下个版本中应该就不会出现这样的问题了，碰到同样问题又急着用的同志可以fork一个版本先自己改下

Fix GifDrawable invalidation. Rework of #511. Fixes #510.