java - android 位图空指针异常

Question

这是我的java类(class)。为什么我得到一个空指针？不是很好吗？就像我初始化了一切一样。显示的错误是

Caused by: 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

public class Screenshot extends Activity{
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        Bitmap bitmap = takeScreenshot();
        saveBitmap(bitmap);
    }
    public Bitmap takeScreenshot() {
        View rootView = findViewById(android.R.id.content).getRootView();
        rootView.setDrawingCacheEnabled(true);
        return rootView.getDrawingCache();
    }
    public void saveBitmap(Bitmap bitmap) {
        File imagePath = new File(Environment.getExternalStorageDirectory() + "/screenshot.png");
        FileOutputStream fos;
        try {
            fos = new FileOutputStream(imagePath);
            bitmap.compress(Bitmap.CompressFormat.JPEG, 100, fos);
            fos.flush();
            fos.close();
        } catch (FileNotFoundException e) {
            Log.e("GREC", e.getMessage(), e);
        } catch (IOException e) {
            Log.e("GREC", e.getMessage(), e);
        }
    }
}

Answer 1

您的位图为空。根据日志，您正在尝试访问 null 对象上的 t 'boolean android.graphics.Bitmap.compress 方法。因此位图肯定是空的。

您也可以尝试此代码来获取位图:

View v1 = getWindow().getDecorView().getRootView();
        v1.setDrawingCacheEnabled(true);
        Bitmap bitmap = Bitmap.createBitmap(v1.getDrawingCache());
        v1.setDrawingCacheEnabled(false);