面試題

1.你在項目里面是怎么優化內存的？
2.優化你是從哪幾個方面入手？
3.列表卡頓的原因可能有哪些？平時是怎么優化的？
4.遇到tableview卡頓？會造成卡頓的原因有哪些？

CPU和GPU

PerformanceOptimization_1.png

屏幕成像原理

PerformanceOptimization_2.png

卡頓產生的原因

PerformanceOptimization_3.png

卡頓優化 - CPU

PerformanceOptimization_4.png

圖片處理：
- (void)image{
    UIImageView *imageView = [[UIImageView alloc] init];
    imageView.frame = CGRectMake(100, 100, 100, 56);
    [self.view addSubview:imageView];
    self.imageView = imageView;

    dispatch_async(dispatch_get_global_queue(0, 0), ^{
        // 獲取CGImage
        CGImageRef cgImage = [UIImage imageNamed:@"timg"].CGImage;

        // alphaInfo
        CGImageAlphaInfo alphaInfo = CGImageGetAlphaInfo(cgImage) & kCGBitmapAlphaInfoMask;
        BOOL hasAlpha = NO;
        if (alphaInfo == kCGImageAlphaPremultipliedLast ||
            alphaInfo == kCGImageAlphaPremultipliedFirst ||
            alphaInfo == kCGImageAlphaLast ||
            alphaInfo == kCGImageAlphaFirst) {
            hasAlpha = YES;
        }

        // bitmapInfo
        CGBitmapInfo bitmapInfo = kCGBitmapByteOrder32Host;
        bitmapInfo |= hasAlpha ? kCGImageAlphaPremultipliedFirst : kCGImageAlphaNoneSkipFirst;

        // size
        size_t width = CGImageGetWidth(cgImage);
        size_t height = CGImageGetHeight(cgImage);

        // context
        CGContextRef context = CGBitmapContextCreate(NULL, width, height, 8, 0, CGColorSpaceCreateDeviceRGB(), bitmapInfo);

        // draw
        CGContextDrawImage(context, CGRectMake(0, 0, width, height), cgImage);

        // get CGImage
        cgImage = CGBitmapContextCreateImage(context);

        // into UIImage
        UIImage *newImage = [UIImage imageWithCGImage:cgImage];

        // release
        CGContextRelease(context);
        CGImageRelease(cgImage);

        // back to the main thread
        dispatch_async(dispatch_get_main_queue(), ^{
            self.imageView.image = newImage;
        });
    });
}

卡頓優化 - GPU

PerformanceOptimization_5.png

離屏渲染

PerformanceOptimization_6.png

卡頓檢測

PerformanceOptimization_7.png

如： LXDAppFluecyMonitor

耗電的主要來源及優化

PerformanceOptimization_8.png

PerformanceOptimization_9.png

PerformanceOptimization_10.png

APP的啟動優化

DYLD_PRINT_STATISTICS
DYLD_PRINT_STATISTICS_DETAILS （打印的更加詳細）
一般在400ms內屬于正常

• App的啟動

PerformanceOptimization_11.png

PerformanceOptimization_12.png

• App的啟動 - dyld

PerformanceOptimization_13.png

• App的啟動 - runtime

PerformanceOptimization_14.png

• App的啟動 - main

PerformanceOptimization_15.png

• App的啟動優化

PerformanceOptimization_16.png

安裝包瘦身

PerformanceOptimization_17.png

LSUnusedResources

https://www.jetbrains.com/objc/

LinkMap

PerformanceOptimization_18.png

LinkMap