問題描述

在完成SpEditTool的時(shí)候使用了android-gif-drawable一行代碼讓TextView中ImageSpan支持Gif，出現(xiàn)過兩次GifDrawable不刷新的現(xiàn)象

• 一次是自己限制了TextView的刷新間隔，導(dǎo)致刷新頻率很快的gif刷新了TextView還沒有刷新
• 一次是EditText刷新了但是GifDrawable沒刷新，需要setLayerType(View.LAYER_TYPE_SOFTWARE, null)才起作用

原因

跑了下android-gif-drawable，發(fā)現(xiàn)上面兩個(gè)問題的原因都是同一個(gè)

先來看下代碼

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);
        }
    }
}

這個(gè)是GifDrawable用來渲染的主要代碼，RenderTask的控制是交給GifDrawable的,GifDrawable在startAnimation()和draw()這兩個(gè)方法中去調(diào)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);
        }
    }

問題就出在這個(gè)draw()上面,Drawable的draw方法依賴于View或者ImageSpan等外部對(duì)象的調(diào)用，所以View、ImageSpan如果不刷新，RenderTask就沒有了下一次渲染的機(jī)會(huì)了，gif也就停了

EditText的問題

對(duì)于上面我說的不刷新的第一種情況大家好理解，TextView沒刷新嘛，GifDrawable按照上面的分析肯定也刷新不了

那EditText自己刷新了為啥也是draw()里面調(diào)度繪制的問題呢，而且設(shè)置了View.LAYER_TYPE_SOFTWARE就好了呢？

還是看代碼好了

GifDrawable的draw()方法是在DynamicDrawableSpan.draw()中被調(diào)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();
    }

• 順探摸瓜找到了TextLine.draw()->TextLine.drawRun()->TextLine.handleRun()->TextLine.handleReplacement()->DynamicDrawableSpan.draw()這么一條調(diào)用棧

• TextLine.draw()方法只在Layout.draw()->Layout.drawText()中調(diào)用

• 接下來只要找調(diào)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的話會(huì)調(diào)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);
        }
    }

從上面的代碼可以看到如果有離屏渲染且開啟了硬件加速,這是默認(rèn)的情況，渲染會(huì)走drawHardwareAccelerated(),反之view的LayerType為View.LAYER_TYPE_SOFTWARE的話會(huì)調(diào)用layout.draw()最終調(diào)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顯示hint的時(shí)候才會(huì)調(diào)用Layout.drawText()

結(jié)論

別看這一系列調(diào)用棧很長，簡(jiǎn)單的說就是EditText默認(rèn)狀況下（離屏渲染加硬件加速），沒有調(diào)用Layout.draw()從而導(dǎo)致GifDrawable.draw()沒走，因?yàn)镽enderTask是通過GifDrawable.draw()調(diào)度的，所以gif就停止不動(dòng)了

最后

通過上面的分析我覺得這樣的將RenderTask和Gifdrawable.draw()關(guān)聯(lián)的處理方式不太合理，所以給作者提了issue和pr，建議在Drawable的invalidateSelf()中調(diào)度下次刷新，這樣gif顯示就不會(huì)依賴于外部對(duì)象了

作者接受了我的建議，下個(gè)版本中應(yīng)該就不會(huì)出現(xiàn)這樣的問題了，碰到同樣問題又急著用的同志可以fork一個(gè)版本先自己改下

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