java.lang.NullPointerException:尝试调用虚拟方法长类
所以我要做的是,我有一个用户名,一个userprofileimage和postmg 我试图将这些值插入到SQLdatabase中,我首先将图像转换为字节数组,然后插入到数据库中,但我发现了一个错误 java.lang.NullPointerException:尝试调用虚拟方法“long” 空对象上的Classes.DBController.addRecord(Classes.posts)“” 参考资料 这是我的密码 主要活动java.lang.NullPointerException:尝试调用虚拟方法长类,java,android,Java,Android,所以我要做的是,我有一个用户名,一个userprofileimage和postmg 我试图将这些值插入到SQLdatabase中,我首先将图像转换为字节数组,然后插入到数据库中,但我发现了一个错误 java.lang.NullPointerException:尝试调用虚拟方法“long” 空对象上的Classes.DBController.addRecord(Classes.posts)“” 参考资料 这是我的密码 主要活动 public class Main2Activity extend
public class Main2Activity extends AppCompatActivity {
DBController db;
ListView datalist;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main2);
}
public void test(View v) {
Bitmap bm = BitmapFactory.decodeResource(getResources(), R.drawable.download);
ByteArrayOutputStream stream = new ByteArrayOutputStream();
bm.compress(Bitmap.CompressFormat.PNG, 100, stream);
byte[] nimg = stream.toByteArray();
Bitmap bm1 = BitmapFactory.decodeResource(getResources(), R.drawable.bc);
ByteArrayOutputStream stream1 = new ByteArrayOutputStream();
bm1.compress(Bitmap.CompressFormat.PNG, 100, stream1);
byte[] nimg1 = stream.toByteArray();
posts obj = new posts();
obj.setUsername("gitesh");
obj.setUserProfileImg(nimg);
obj.setPostImg(nimg1);
long result = db.addRecord(obj);
if(result==-1) {
Log.d("error","error");
}
else {
datalist = (ListView) findViewById(R.id.listview);
db = new DBController(this);
List<posts> contacts = db.getAll();
Adapter adp = new Adapter(this, R.layout.activity_main, contacts);
datalist.setAdapter(adp);
}
}
}
似乎从未实例化过
db
在onCreate
方法中,您需要具有以下内容:
db = new DBController(this);
在为变量赋值之前,尝试对其运行方法时,您认为会发生什么情况?建议:将所有
findViewById
和活动的任何其他初始化都放在onCreate
中。您成功地放置了db=newdbcontroller(此)代码>在else
语句中,但不是在它之外使用db
之前。谢谢,我得到了,但我在datalistno中得到了null,你得到了null,因为你在访问db时没有实例化它。是的,这个问题已经解决了,但现在没有找到listview,datalist对象在调试模式下显示为null
05-23 23:16:29.034 2900-2900/com.example.gitesh.timeline E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.example.gitesh.timeline, PID: 2900
java.lang.IllegalStateException: Could not execute method for android:onClick
at android.support.v7.app.AppCompatViewInflater$DeclaredOnClickListener.onClick(AppCompatViewInflater.java:293)
at android.view.View.performClick(View.java:5207)
at android.view.View$PerformClick.run(View.java:21168)
at android.os.Handler.handleCallback(Handler.java:746)
at android.os.Handler.dispatchMessage(Handler.java:95)
at android.os.Looper.loop(Looper.java:148)
at android.app.ActivityThread.main(ActivityThread.java:5443)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:728)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:618)
Caused by: java.lang.reflect.InvocationTargetException
at java.lang.reflect.Method.invoke(Native Method)
at android.support.v7.app.AppCompatViewInflater$DeclaredOnClickListener.onClick(AppCompatViewInflater.java:288)
at android.view.View.performClick(View.java:5207)
at android.view.View$PerformClick.run(View.java:21168)
at android.os.Handler.handleCallback(Handler.java:746)
at android.os.Handler.dispatchMessage(Handler.java:95)
at android.os.Looper.loop(Looper.java:148)
at android.app.ActivityThread.main(ActivityThread.java:5443)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:728)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:618)
Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'long Classes.DBController.addRecord(Classes.posts)' on a null object reference
at com.example.gitesh.timeline.Main2Activity.test(Main2Activity.java:45)
at java.lang.reflect.Method.invoke(Native Method)
at android.support.v7.app.AppCompatViewInflater$DeclaredOnClickListener.onClick(AppCompatViewInflater.java:288)
at android.view.View.performClick(View.java:5207)
at android.view.View$PerformClick.run(View.java:21168)
at android.os.Handler.handleCallback(Handler.java:746)
at android.os.Handler.dispatchMessage(Handler.java:95)
at android.os.Looper.loop(Looper.java:148)
at android.app.ActivityThread.main(ActivityThread.java:5443)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:728)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:618)
db = new DBController(this);