Question

我使用下面的代码在android 8.1手机上检索android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());
// ...

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

我在真实电话上运行演示，发现pfd的{{1}}始终为空，因此无法获取锁屏墙纸。请帮助解决问题，谢谢。

Answer 1

我自己找到了答案，希望它可以帮助其他有相同问题的人。

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.

描述含糊不清，至少不够清晰，这是什么意思？如果您同时将照片设置为锁定屏幕和主屏幕墙纸，则两者共享同一文件，然后调用

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

pfd始终为空，那么您应该通过以下方式获取锁屏墙纸：

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

您将获得非空的pfd。 no lock-specific wallpaper has been configured.

就是这种情况

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

这是我用来检索锁屏墙纸的代码：

/**
 * 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并将其授予外部。

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上对其进行了测试。

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);
            }
        }
    }

}

manifest.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>

。

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

Answer 3

如果没有为给定的用户配置任何特定于锁的墙纸，则此方法在请求FLAG_LOCK时将返回null，而不是返回系统墙纸的图像文件。

您确定为当前用户设置了有效的锁屏墙纸吗？

 /**
     * 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，如果您希望LOCK-SCREEN壁纸，则始终为null，因为根据代码，尚不支持出厂默认的锁壁纸。

因此，根据您的情况，您可能尚未设置锁屏墙纸。只是为了进行测试，请下载任何壁纸应用程序，然后尝试设置壁纸，然后使用您之前的代码进行获取。

/**
     * 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;
        }

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

如何获得Android锁屏壁纸？

3 个答案: