Question

在我的代码中，我正在从我检查过的文件夹中恢复图像，其中包含图像并且不为空。出于某种原因，当它获得壁纸管理器的setBitmap代码时，似乎停止工作并输出下面的错误。任何帮助，将不胜感激。感谢

                                                                                   Process: coolwallpaper.alexcz.coolwallpaper, PID: 15613
                                                                                    java.lang.NullPointerException: Attempt to invoke virtual method 'boolean android.graphics.Bitmap.compress(android.graphics.Bitmap$CompressFormat, int, java.io.OutputStream)' on a null object reference
                                                                                        at android.app.WallpaperManager.setBitmap(WallpaperManager.java:956)
                                                                                        at coolwallpaper.alexcz.coolwallpaper.Main$1.onClick(Main.java:54)
                                                                                        at android.view.View.performClick(View.java:5197)
                                                                                        at android.view.View$PerformClick.run(View.java:20926)
                                                                                        at android.os.Handler.handleCallback(Handler.java:739)
                                                                                        at android.os.Handler.dispatchMessage(Handler.java:95)
                                                                                        at android.os.Looper.loop(Looper.java:145)
                                                                                        at android.app.ActivityThread.main(ActivityThread.java:5951)
                                                                                        at java.lang.reflect.Method.invoke(Native Method)
                                                                                        at java.lang.reflect.Method.invoke(Method.java:372)
                                                                                        at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1400)
                                                                                        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1195)

static final File dir = new File("/data/data/coolwallpaper.alexcz.coolwallpaper/app_imageDir/");

    Button createWallpaper;
    Button setWallpaper;

    Bitmap bitmap;

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

        createWallpaper = (Button)findViewById(R.id.createWallpaper);
        setWallpaper = (Button)findViewById(R.id.set_wallpaper);

        setWallpaper.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {

                AsyncTask.execute(new Runnable() {
                    @Override
                    public void run() {
                        if (dir.isDirectory()) { // make sure it's a directory
                            for (File f : dir.listFiles()) {
                                bitmap = BitmapFactory.decodeFile(f.getAbsolutePath());
                                System.out.println(bitmap.getWidth());
                            }
                        }
                    }
                });

                WallpaperManager myWallpaperManager
                        = WallpaperManager.getInstance(getApplicationContext());
                try {
                    myWallpaperManager.setBitmap(bitmap);
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
        });

        createWallpaper.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                Intent intent = new Intent(Main.this, FractalActivity.class);
                startActivity(intent);
            }
        });

    }

Answer 1

这是因为Async Task在一个单独的线程上运行。更改壁纸的异步任务之前的代码，在后台仍然从文件加载位图时开始执行。这就是为什么setBitmap被称为包含空参数

位图从文件读取为空

1 个答案: