性能优化

面试题

1.你在项目里面是怎么优化内存的？
2.优化你是从哪几个方面入手？
3.列表卡顿的原因可能有哪些？平时是怎么优化的？
4.遇到tableview卡顿？会造成卡顿的原因有哪些？

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CPU和GPU

PerformanceOptimization_1.png

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屏幕成像原理

PerformanceOptimization_2.png

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卡顿产生的原因

PerformanceOptimization_3.png

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卡顿优化 - CPU

PerformanceOptimization_4.png

图片处理：
- (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), ^{
        // 获取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;
        });
    });
}

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卡顿优化 - GPU

PerformanceOptimization_5.png

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离屏渲染

PerformanceOptimization_6.png

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卡顿检测

PerformanceOptimization_7.png

如： LXDAppFluecyMonitor

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耗电的主要来源及优化

PerformanceOptimization_8.png

PerformanceOptimization_9.png

PerformanceOptimization_10.png

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APP的启动优化

DYLD_PRINT_STATISTICS
DYLD_PRINT_STATISTICS_DETAILS （打印的更加详细）
一般在400ms内属于正常

• App的启动

PerformanceOptimization_11.png

PerformanceOptimization_12.png

• App的启动 - dyld

PerformanceOptimization_13.png

• App的启动 - runtime

PerformanceOptimization_14.png

• App的启动 - main

PerformanceOptimization_15.png

• App的启动优化

PerformanceOptimization_16.png

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安装包瘦身

PerformanceOptimization_17.png

LSUnusedResources

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

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LinkMap

PerformanceOptimization_18.png

LinkMap