Question

我试图从视图中获取位图，因为我想模糊该位图并将其用作后续活动的背景。 Logcat给了我：

NullPointerException at android.graphics.Bitmap.createBitmap(Bitmap.java:484)

我的代码：

 @Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    // Get the view from activity_main.xml
    setContentView(R.layout.activity_splash_page);

    ProgressWheel wheel = (ProgressWheel) findViewById(R.id.progress_wheel);
    wheel.setClickable(false);

    TextView touch = (TextView) findViewById(R.id.touch_splash);
    touch.setClickable(false);

    TextView level = (TextView) findViewById(R.id.level_splash);
    level.setClickable(false);


    wheel.setProgress(0.7f);
    wheel.setClickable(true);
    touch.setClickable(true);
    level.setClickable(true);

    RelativeLayout view = (RelativeLayout)findViewById(R.id.viewtocapture);
    ImageView bmImage = (ImageView)findViewById(R.id.imageView);

    view.setDrawingCacheEnabled(true);
    // this is the important code :)
    // Without it the view will have a dimension of 0,0 and the bitmap will be null

    view.measure(View.MeasureSpec.makeMeasureSpec(0, View.MeasureSpec.UNSPECIFIED),
            View.MeasureSpec.makeMeasureSpec(0, View.MeasureSpec.UNSPECIFIED));

    view.layout(0, 0, view.getMeasuredWidth(), view.getMeasuredHeight());

    view.buildDrawingCache(true);
    view.buildDrawingCache();
    Bitmap b = Bitmap.createBitmap(view.getDrawingCache());      //Line 53
    view.setDrawingCacheEnabled(false); // clear drawing cache

    bmImage.setImageBitmap(b);


    wheel.setProgress(0.0f);

}

这里是Stacktrace / Logcat：

Caused by: java.lang.NullPointerException
        at android.graphics.Bitmap.createBitmap(Bitmap.java:484)
        at com.redstonedevelopers.status_v1.SplashPage.onCreate(SplashPage.java:53)
        at android.app.Activity.performCreate(Activity.java:5047)
        at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1094)
        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2056)       
        at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2117)
        at android.app.ActivityThread.access$700(ActivityThread.java:134)
        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1218)
        at android.os.Handler.dispatchMessage(Handler.java:99)
        at android.os.Looper.loop(Looper.java:137)
        at android.app.ActivityThread.main(ActivityThread.java:4867)
        at java.lang.reflect.Method.invokeNative(Native Method)
        at java.lang.reflect.Method.invoke(Method.java:511)
        at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1007)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:774)
        at dalvik.system.NativeStart.main(Native Method)

我尝试过以下答案：在这里：take a screenshot from the activity 在这里：NullPointerException in createBitmap() from View 在这里：android createBitmap NullPointerException

一切都无济于事。我应该做些什么来改变和/或做些什么呢？

-R

Answer 1

试试这个。
实际绘制视图时，这将启动然后你应该能够为它保存位图。

-----确保 bmImage 和视图应该是类级别，以便我们可以在ViewTreeObserver触发时使用它们。

 bmImage = (ImageView)findViewById(R.id.imageView);
 view = (RelativeLayout)findViewById(R.id.viewtocapture);
 view.getViewTreeObserver().addOnGlobalLayoutListener(new ViewTreeObserver.OnGlobalLayoutListener() {
        @SuppressWarnings("deprecation")
        @Override
        public void onGlobalLayout() {
            view.getViewTreeObserver().removeGlobalOnLayoutListener(this);
            System.out.println(view == null ? "is null" : "not null");
            Bitmap b = Bitmap.createBitmap(view.getWidth(), view.getHeight(), Bitmap.Config.ARGB_8888);                
            Canvas c = new Canvas(b);
            view.layout(view.getLeft(), view.getTop(), view.getRight(), view.getBottom());
            view.draw(c);
            bmImage.setImageBitmap(b);
        }
    });

Answer 2

在onCreate()之后，视图树不会被测量，布局和渲染。

您可以使用树视图布局观察器，如下所示。

public void onCreate(Bundle savedInstanceState)
{
     super.onCreate(savedInstanceState);

     // inflate your main layout here (use RelativeLayout or whatever your root ViewGroup type is
     LinearLayout mainLayout = (LinearLayout ) this.getLayoutInflater().inflate(R.layout.activity_splash_page, null); 

     // set a global layout listener which will be called when the layout pass is completed and the view is drawn
     mainLayout.getViewTreeObserver().addOnGlobalLayoutListener(
     new ViewTreeObserver.OnGlobalLayoutListener() {
          public void onGlobalLayout() {
               //Remove the listener before proceeding
               if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.JELLY_BEAN) {
                    mainLayout.getViewTreeObserver().removeOnGlobalLayoutListener(this);
               } else {
                    mainLayout.getViewTreeObserver().removeGlobalOnLayoutListener(this);
               }

               // do your thing here
          }
     }
 );

 setContentView(mainLayout);

Answer 3

我使用这样的代码在canvas对象上绘制视图。不确定这是否适用于您的情况。

picturePreLoad = Bitmap.createBitmap(width, height, Bitmap.Config.RGB_565);
   Canvas canvas = new Canvas(picturePreLoad);
   MyView.draw(canvas);

Answer 4

就我而言，问题在于默认情况下将位图文件复制到Drawable V24中，而不是Drawable中。为了能够同时查看两个文件夹，请在左上角将设置从 Android 更改为 Project 。

然后转到app.src.main.res，在那里您可以看到Drawable V24和Drawable。您只需要从Drawable V24中删除位图，然后将它们添加到Drawable中即可。

调用Bitmap.createBitmap时出现NullPointerException

4 个答案: