如何获得安卓锁屏壁纸？

Question

我使用下面的代码来检索安卓 8.1 手机上的安卓锁屏壁纸：

WallpaperManager manager = WallpaperManager.getInstance(getActivity());
ParcelFileDescriptor pfd = manager.getWallpaperFile(WallpaperManager.FLAG_LOCK);
if (pfd == null) // pfd is always null for FLAG_LOCK, why?
    return;
Bitmap lockScreenWallpaper = BitmapFactory.decodeFileDescriptor(pfd.getFileDescriptor());
// ...

我已经授予READ_EXTERNAL_STORAGE权限并预先设置了锁屏壁纸。

我在真机上运行demo，发现pfd对于FLAG_LOCK总是为空，所以无法获取锁屏壁纸。请帮忙解决问题，谢谢。

Answer 1

我自己找到了答案，希望对有同样问题的人有所帮助。

getWallpaperFile 的官方文档说：If no lock-specific wallpaper has been configured for the given user, then this method will return null when requesting FLAG_LOCK rather than returning the system wallpaper's image file.

描述模糊，至少不够清楚，是什么意思？如果你将一张照片设置为锁屏和主屏壁纸，两者共享同一个文件，那么通过调用

ParcelFileDescriptor pfd = wallpaperManager.getWallpaperFile(WallpaperManager.FLAG_LOCK);

pfd 将永远为空，那么你应该通过这种方式获取锁屏壁纸：

if (pfd == null)
    pfd = wallpaperManager.getWallpaperFile(WallpaperManager.FLAG_SYSTEM);

你会得到非空的pfd。就是这样no lock-specific wallpaper has been configured.

相反，lock-specific wallpaper has been configured 如果直接将照片设置为锁屏壁纸，wallpaperManager.getWallpaperFile(WallpaperManager.FLAG_SYSTEM) 将返回非空值。

这是我用来检索锁屏壁纸的代码：

/**
 * please check permission outside
 * @return Bitmap or Drawable
 */
public static Object getLockScreenWallpaper(Context context)
{
    WallpaperManager wallpaperManager = WallpaperManager.getInstance(context);
    if (Build.VERSION.SDK_INT >= 24)
    {
        ParcelFileDescriptor pfd = wallpaperManager.getWallpaperFile(WallpaperManager.FLAG_LOCK);
        if (pfd == null)
            pfd = wallpaperManager.getWallpaperFile(WallpaperManager.FLAG_SYSTEM);
        if (pfd != null)
        {
            final Bitmap result = BitmapFactory.decodeFileDescriptor(pfd.getFileDescriptor());

            try
            {
                pfd.close();
            }
            catch (Exception e)
            {
                e.printStackTrace();
            }

            return result;
        }
    }
    return wallpaperManager.getDrawable();
}

不要忘记在清单文件中添加READ_EXTERNAL_STORAGE 并在外部授予它。

Answer 2

我正在测试的代码与您的相似。我已经在三星 A5 和 LG Nexus 5X 上进行了测试。

MainActivity.java

import android.Manifest;
import android.annotation.SuppressLint;
import android.app.WallpaperManager;
import android.content.pm.PackageManager;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.os.Build;
import android.os.Bundle;
import android.os.ParcelFileDescriptor;
import android.support.v4.app.ActivityCompat;
import android.support.v4.content.ContextCompat;
import android.support.v7.app.AppCompatActivity;
import android.widget.ImageView;

public class MainActivity extends AppCompatActivity {

    public static final int REQUEST_CODE_EXTERNAL_STORAGE = 5;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        String permission = Manifest.permission.WRITE_EXTERNAL_STORAGE;
        if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.JELLY_BEAN) {
            permission = Manifest.permission.READ_EXTERNAL_STORAGE;
        }

        if (ContextCompat.checkSelfPermission(this, permission) != PackageManager.PERMISSION_GRANTED) {
            ActivityCompat.requestPermissions(this, new String[]{permission}, REQUEST_CODE_EXTERNAL_STORAGE);
        } else {
            retrieveLockScreenWallpaper();
        }
    }

    @Override
    public void onRequestPermissionsResult(int requestCode, String permissions[], int[] grantResults) {
        switch (requestCode) {
            case REQUEST_CODE_EXTERNAL_STORAGE: {
                if (grantResults.length > 0 && grantResults[0] == PackageManager.PERMISSION_GRANTED) {
                    retrieveLockScreenWallpaper();
                }
            }
        }
    }

    @SuppressLint("MissingPermission")
    private void retrieveLockScreenWallpaper() {
        if (android.os.Build.VERSION.SDK_INT >= android.os.Build.VERSION_CODES.N) {
            WallpaperManager manager = WallpaperManager.getInstance(getApplicationContext());
            ParcelFileDescriptor descriptor = manager.getWallpaperFile(WallpaperManager.FLAG_LOCK);
            if (descriptor != null) {
                Bitmap bitmap = BitmapFactory.decodeFileDescriptor(descriptor.getFileDescriptor());
                ((ImageView) findViewById(R.id.imageView)).setImageBitmap(bitmap);
            }
        }
    }

}

ma​​nifest.xml

<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="aminography.com.lockscreenapplication">

    <uses-permission android:name="android.permission.READ_EXTERNAL_STORAGE" />
    <uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" />

    <application

        ...

    </application>

</manifest>

.

在 LGE Nexus 5X（Android 8.1.0，API 27）上的结果：

Answer 3

如果没有为给定用户配置锁特定壁纸，则在请求 FLAG_LOCK 时此方法将返回 null 而不是返回系统壁纸的图像文件。

您确定为当前用户设置了有效的锁屏壁纸吗？

 /**
     * Get an open, readable file descriptor to the given wallpaper image file.
     * The caller is responsible for closing the file descriptor when done ingesting the file.
     *
     * <p>If no lock-specific wallpaper has been configured for the given user, then
     * this method will return {@code null} when requesting {@link #FLAG_LOCK} rather than
     * returning the system wallpaper's image file.
     *
     * @param which The wallpaper whose image file is to be retrieved.  Must be a single
     *     defined kind of wallpaper, either {@link #FLAG_SYSTEM} or
     *     {@link #FLAG_LOCK}.
     *
     * @see #FLAG_LOCK
     * @see #FLAG_SYSTEM
     */
    public ParcelFileDescriptor getWallpaperFile(@SetWallpaperFlags int which) {
        return getWallpaperFile(which, mContext.getUserId());
    }

WallpaperManager openDefaultWallpaper 中有一个类似的功能，如果你想要 LOCK-SCREEN 壁纸，你总是会得到 null，因为根据代码，工厂默认锁壁纸尚不支持。

所以在您的情况下，您可能没有设置锁屏壁纸。 只是为了测试，下载任何壁纸应用程序，并尝试设置壁纸，然后使用您之前的代码来获取它。

/**
     * Open stream representing the default static image wallpaper.
     *
     * If the device defines no default wallpaper of the requested kind,
     * {@code null} is returned.
     *
     * @hide
     */
    public static InputStream openDefaultWallpaper(Context context, @SetWallpaperFlags int which) {
        final String whichProp;
        final int defaultResId;
        if (which == FLAG_LOCK) {
            /* Factory-default lock wallpapers are not yet supported
            whichProp = PROP_LOCK_WALLPAPER;
            defaultResId = com.android.internal.R.drawable.default_lock_wallpaper;
            */
            return null;
        }

您可以在http://androidxref.com/8.1.0_r33/xref/frameworks/base/core/java/android/app/WallpaperManager.java#openDefaultWallpaper查看代码