Android - Imageview 片段滞后

Question

您好，我有一个滑动视图，其中包含使用片段的相应选项卡。第一个视图仅包含大约 1.91mb 大小的全高清图像。

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical" >

<ImageView
    android:id="@+id/imageView1"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:contentDescription="@string/my_picture"
    android:src="@drawable/image1" />

</LinearLayout>

现在，当我从第 1 页滑到第 2 页或以其他方式滑动时，动画似乎真的很滞后。

public class SectionsPagerAdapter extends FragmentPagerAdapter {

    public SectionsPagerAdapter(FragmentManager fm) {
        super(fm);
    }

    @Override
    public Fragment getItem(int position) {
        Fragment fragment = null;

        switch(position) {
        case 0:
            fragment = new Tab_one();
            break;
        case 1:
            fragment = new Tab_two();
            break;
        case 2:
            fragment = new Tab_three();
            break;
        default:
            fragment = new Tab_one();
            break;
        }
        return fragment;
    }

    @Override
    public int getCount() {
        return 3;
    }

    @Override
    public CharSequence getPageTitle(int position) {
        Locale l = Locale.getDefault();
        switch (position) {
        case 0:
            return getString(R.string.title_section1).toUpperCase(l);
        case 1:
            return getString(R.string.title_section2).toUpperCase(l);
        case 2:
            return getString(R.string.title_section3).toUpperCase(l);
        }
        return null;
    }
}
}

所以从 page1（仅包含 imageview）到 page2（包含一些带有信息的 textview）的转换是滞后的。有人可以帮我吗？文件大小是否会促进滞后？

Answer 1

您的图像大小并不重要，您的图像分辨率很重要，因为例如以ARGB_8888 格式显示图像，每个像素将占用 4 个字节，因此快速分析将产生：

不同尺寸的图片：

image: 1024 * 768 * 4 = 2MB 
image: 1920 * 1080* 4 = 6MB
image: 1280 * 720 * 4 = 3MB

在您的计算机中，所有这些都可能小于 1 MB。那你该怎么办？你必须缩小你的图像，然后分配给你的图像视图，看看

public static int calculateInSampleSize(
            BitmapFactory.Options options, int reqWidth, int reqHeight) {
    // Raw height and width of image
    final int height = options.outHeight;
    final int width = options.outWidth;
    int inSampleSize = 1;

    if (height > reqHeight || width > reqWidth) {

        final int halfHeight = height / 2;
        final int halfWidth = width / 2;

        // Calculate the largest inSampleSize value that is a power of 2 and keeps both
        // height and width larger than the requested height and width.
        while ((halfHeight / inSampleSize) > reqHeight
                && (halfWidth / inSampleSize) > reqWidth) {
            inSampleSize *= 2;
        }
    }

    return inSampleSize;
}

public static Bitmap decodeSampledBitmapFromResource(Resources res, int resId,
        int reqWidth, int reqHeight) {

    // First decode with inJustDecodeBounds=true to check dimensions
    final BitmapFactory.Options options = new BitmapFactory.Options();
    options.inJustDecodeBounds = true;
    BitmapFactory.decodeResource(res, resId, options);

    // Calculate inSampleSize
    options.inSampleSize = calculateInSampleSize(options, reqWidth, reqHeight);

    // Decode bitmap with inSampleSize set
    options.inJustDecodeBounds = false;
    return BitmapFactory.decodeResource(res, resId, options);
}

Loading Large Bitmaps Efficiently

你可以使用decodeSampledBitmapFromResource(Resources res, int resId, int reqWidth, int reqHeight)来加载你的图片。