英文:
Attempt to invoke virtual method 'android.view.ViewPropertyAnimator android.widget.ImageView.animate()' on a null object reference
问题
我正在尝试制作一个简单的动画，其中的图像最初不会显示，但在出现后会从屏幕左侧旋转180度，持续一段时间。因此，我在onCreate方法中编写了以下脚本：
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
ImageView Bart = (ImageView) findViewById(R.id.bart);
Bart.animate().translationXBy(-3000);
Bart.animate().translationXBy(4000).rotation(180).setDuration(2000);
}
但由于某种原因，我收到一个错误，指示我正在尝试在空对象引用上调用虚拟方法。可能是什么问题？谢谢
英文:
I'm trying to make a simple animation with a image that iniatially it doesn't appear but after it appears rotating 180 degrees for certain a amount of seconds from the left of the screen.
So i made a script inside the onCreate method:
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
ImageView Bart = (ImageView) findViewById(R.id.bart);
Bart.animate().translationXBy(-3000);
Bart.animate().translationXBy(4000).rotation(180).setDuration(2000);
}
But for some reason i'm getting an error saying that i'm trying to invoke a virtual method on a null object reference.What could be the issue?Thanks
答案1
得分: 1
你在onCreate中没有调用setContentView()方法。
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main); // 将此行添加，使用你的布局 Id
ImageView bartImageView = (ImageView) findViewById(R.id.bart);
bartImageView.animate().translationXBy(-3000);
bartImageView.animate().translationXBy(4000).rotation(180).setDuration(2000);
}
另外，我有一些建议，变量名采用小写开头的驼峰命名法。为变量添加一些标识符，以表示它是什么，比如bartImageView或bartIV等。
英文:
You did not set setContentView() in onCreate
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main)// add this with your layout Id
ImageView bartImageView = (ImageView) findViewById(R.id.bart);
bartImageView.animate().translationXBy(-3000);
bartImageView.animate().translationXBy(4000).rotation(180).setDuration(2000);
}
Also few suggestions take variables with camelCase starting with small letter . Add some identifier to the variable which indicates what it is, like bartImageView or bartIV etc.
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