为什么我需要所有这些空方法来为 Glide 创建自定义文件目标？

Question

我正在使用 Glide 调整图像大小并将其保存到 Android 应用程序中的文件系统，并且我创建了一个扩展 Glide 本机的自定义 FileTarget class Target去做。

有效。耶！但是我对我必须 'define' 来满足 Target 实现的所有空方法感到有点震惊。我真正关心的是 onResourceReady...

有没有办法在不声明所有这些空方法的情况下实现这个？我应该担心他们都是这样吗？

我对 Android 有点陌生，感谢您的耐心等待。

    public static class FileTarget<T extends Bitmap> implements Target<Bitmap> {
    private final int width;
    private final int height;

    String fileName;
    Bitmap.CompressFormat format;
    int quality;

    public FileTarget(int width, int height, String fileName, Bitmap.CompressFormat format, int quality) {
        this.width = width;
        this.height = height;
        this.fileName = fileName;
        this.format = format;
        this.quality = quality;
    }

    @Override
    public void onLoadStarted(Drawable drawable) {}

    @Override
    public void onLoadFailed(Drawable drawable) {}

    @Override
    public void onLoadCleared(Drawable drawable) {}

    @Override
    public void getSize(SizeReadyCallback cb) {
        cb.onSizeReady(width, height);
    }

    @Override
    public void removeCallback(@NonNull SizeReadyCallback cb) {}

    @Override
    public void setRequest(@Nullable Request request) {}

    @Nullable
    @Override
    public Request getRequest() {
        return null;
    }

    @Override
    public void onStart() {}

    @Override
    public void onStop() {}

    @Override
    public void onDestroy() {}

    @Override
    public void onResourceReady(@NonNull Bitmap resource, @Nullable Transition<? super Bitmap> transition) {
        try {
            FileOutputStream out = new FileOutputStream(fileName);
            resource.compress(format, quality, out);
            out.flush();
            out.close();
            onFileSaved();
        } catch (IOException e) {
            e.printStackTrace();
            onSaveException(e);
        }
    }

    public void onFileSaved() {
        // do nothing, should be overriden
    }
    public void onSaveException(Exception e) {
        // do nothing, should be overriden
    }
}

Answer 1

在 Android 框架中，有一个常见的模式，即创建抽象 FooAdapter class 实现 Foo 接口中的所有方法 no-ops.

例如，考虑这个 class:

public abstract class AnimatorListenerAdapter implements Animator.AnimatorListener,
        Animator.AnimatorPauseListener {

    @Override
    public void onAnimationCancel(Animator animation) { }

    @Override
    public void onAnimationEnd(Animator animation) { }

    @Override
    public void onAnimationRepeat(Animator animation) { }

    @Override
    public void onAnimationStart(Animator animation) { }

    @Override
    public void onAnimationPause(Animator animation) { }

    @Override
    public void onAnimationResume(Animator animation) { }
}

您可以为 Glide 创建相同的东西：

public abstract class TargetAdapter<T> implements Target<T> {

    @Override
    public void onLoadStarted(Drawable drawable) {}

    @Override
    public void onLoadFailed(Drawable drawable) {}

    @Override
    public void onLoadCleared(Drawable drawable) {}

    @Override
    public void getSize(SizeReadyCallback cb) {}

    @Override
    public void removeCallback(@NonNull SizeReadyCallback cb) {}

    @Override
    public void setRequest(@Nullable Request request) {}

    @Override
    public Request getRequest() {}

    @Override
    public void onResourceReady(@NonNull T resource, @Nullable Transition<? super T> transition) {}
}

现在，当您创建 FileTarget class 时，您可以声明它 extends TargetAdapter 而不是 implements Target，并且只覆盖您关心的方法：

public static class FileTarget<T extends Bitmap> extends TargetAdapter<Bitmap> {
    // ...

    @Override
    public void getSize(SizeReadyCallback cb) {
        cb.onSizeReady(width, height);
    }

    @Nullable
    @Override
    public Request getRequest() {
        return null;
    }

    @Override
    public void onResourceReady(@NonNull Bitmap resource, @Nullable Transition<? super Bitmap> transition) {
        try {
            FileOutputStream out = new FileOutputStream(fileName);
            resource.compress(format, quality, out);
            out.flush();
            out.close();
            onFileSaved();
        } catch (IOException e) {
            e.printStackTrace();
            onSaveException(e);
        }
    }

    // ...
}

为什么我需要所有这些空方法来为 Glide 创建自定义文件目标？

Why do I need all these empty methods to create a custom file target for Glide?

java

android

image

image-resizing

android-glide