Question

点击图片后，我试图创建一个活动链接。我无法运行该应用程序。它显示“ App保持关闭”。我在网上搜索过，认为这是空指针异常。即使是我也找不到解决方案。

public class MainActivity extends AppCompatActivity {

    private Button button1;
    protected void onCreate(Bundle savedInstanceState) {

        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity1);

        button1=findViewById(R.id.letsgo);
        button1.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                openActivity1();
            }
        });
    }
    public void openActivity1(){
        Intent intent=new Intent(this,MainActivity2.class);
        startActivity(intent);
    }
}

LOGCAT

at android.os.Handler.dispatchMessage(Handler.java:107)
        at android.os.Looper.loop(Looper.java:214)
        at android.app.ActivityThread.main(ActivityThread.java:7356)
        at java.lang.reflect.Method.invoke(Native Method)
        at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:492)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:930)
     Caused by: java.lang.ClassCastException: androidx.appcompat.widget.AppCompatImageButton cannot be cast to android.widget.Button
        at com.example.app3.MainActivity.onCreate(MainActivity.java:21)
        at android.app.Activity.performCreate(Activity.java:7802)
        at android.app.Activity.performCreate(Activity.java:7791)
        at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1299)
        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3245)
        at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3409) 
        at android.app.servertransaction.LaunchActivityItem.execute(LaunchActivityItem.java:83) 
        at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:135) 
        at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:95) 
        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2016) 
        at android.os.Handler.dispatchMessage(Handler.java:107) 
        at android.os.Looper.loop(Looper.java:214) 
        at android.app.ActivityThread.main(ActivityThread.java:7356) 
        at java.lang.reflect.Method.invoke(Native Method) 
        at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:492) 
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:930)

Answer 1

将private Button button1更改为private ImageButton button1

Answer 2

您输入了错误的类。如果要使用Button，则导入Button，如果要使用ImageButton，则导入ImageButton。尝试检查导入的类是否正确

如何修复'com.example.app15.MainActivity.onCreate'错误

2 个答案: