android - getWindowManager() 返回 Null？

Question

我有一个动画类，当我需要将图像从某个地方移动到另一个时，我从主类调用它...但问题是当我调用它时，它变成了 NullPointerException。这是我的代码:

public class Animation extends Activity{

ImageView image;
int width;
int fromXDelta;
AnimationSet animation = new AnimationSet(true);
TranslateAnimation translateAnimation = null;

Animation(View main) {
    image = (ImageView) main.findViewById(R.id.logo);
    fromXDelta = image.getLeft();
            // this line gives me error:
    width = getWindowManager().getDefaultDisplay().getWidth(); 
}

public void animateToLeft () {      
    translateAnimation = new TranslateAnimation(0, -fromXDelta, 0, 0);
    translateAnimation.setDuration(1000);
    animation.addAnimation(translateAnimation);
    animation.setAnimationListener(new AnimationListener() {

        public void onAnimationEnd(android.view.animation.Animation v) {
            // TODO Auto-generated method stub
            image.clearAnimation();
            v.reset();
            image.layout(0, 0, image.getWidth(), image.getHeight());                
        }

        public void onAnimationRepeat(android.view.animation.Animation arg0) { }
        public void onAnimationStart(android.view.animation.Animation arg0) { }

    });

    image.startAnimation(animation);
}

public void animateToRight () {     
    translateAnimation = new TranslateAnimation(fromXDelta, width - image.getWidth() - fromXDelta , 0, 0);
    translateAnimation.setDuration(1000);
    animation.addAnimation(translateAnimation);
    animation.setAnimationListener(new AnimationListener() {

        public void onAnimationEnd(android.view.animation.Animation v) {
            // TODO Auto-generated method stub
            image.clearAnimation();
            v.reset();
            image.layout(width - image.getWidth(), 0, width, image.getHeight());                
        }

        public void onAnimationRepeat(android.view.animation.Animation arg0) { }
        public void onAnimationStart(android.view.animation.Animation arg0) { }

    });

    image.startAnimation(animation);
}

public void animateToEx (int control) {     

    if(control == 0) {
        // left to ex point
        translateAnimation = new TranslateAnimation(fromXDelta, width - image.getWidth() - fromXDelta , 0, 0);
    } else if(control == 2) {
        // right to ex point
        translateAnimation = new TranslateAnimation(fromXDelta, width - image.getWidth() - fromXDelta , 0, 0);
    }

    translateAnimation.setDuration(1000);
    animation.addAnimation(translateAnimation);
    animation.setAnimationListener(new AnimationListener() {

        public void onAnimationEnd(android.view.animation.Animation v) {
            // TODO Auto-generated method stub
            image.clearAnimation();
            v.reset();
            image.layout(width - image.getWidth(), 0, width, image.getHeight());                
        }

        public void onAnimationRepeat(android.view.animation.Animation arg0) { }
        public void onAnimationStart(android.view.animation.Animation arg0) { }

    });

    image.startAnimation(animation);
}

 }

提前致谢。

Answer 1

我认为您做的不对...您需要阅读 Activity 的文档及其生命周期。您定义的构造函数永远不会调用...使用 onCreate 而不是您的构造函数...