AndroidStudio - CompileError: (App keeps stopping) -> RuntimeException: Unable to instantiate activity

Question

我突然遇到一个问题，Android Studio 不想再编译我的项目了。 VD 已启动且未指定其他语法错误，但应用程序不断关闭。即使我创建一个新项目并在那里更改一些东西，也没有任何效果。

我已经搜索了错误，但不明白具体是指哪些设置，因为没有人指定任何内容。我比较新，所以如果有人能以一种易于理解和详细的方式向我解释这一点，我将非常高兴 - 谢谢！

E/AndroidRuntime: FATAL EXCEPTION: main
    Process: kuehl.leon.tictactoe, PID: 2719
    java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{kuehl.leon.tictactoe/kuehl.leon.tictactoe.MainActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'android.view.Window$Callback android.view.Window.getCallback()' on a null object reference
        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2718)
        at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2892)
        at android.app.ActivityThread.-wrap11(Unknown Source:0)
        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1593)
        at android.os.Handler.dispatchMessage(Handler.java:105)
        at android.os.Looper.loop(Looper.java:164)
        at android.app.ActivityThread.main(ActivityThread.java:6541)
        at java.lang.reflect.Method.invoke(Native Method)
        at com.android.internal.os.Zygote$MethodAndArgsCaller.run(Zygote.java:240)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:767)
     Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'android.view.Window$Callback android.view.Window.getCallback()' on a null object reference
        at android.support.v7.app.AppCompatDelegateImplBase.<init>(AppCompatDelegateImplBase.java:117)
        at android.support.v7.app.AppCompatDelegateImplV9.<init>(AppCompatDelegateImplV9.java:149)
        at android.support.v7.app.AppCompatDelegateImplV11.<init>(AppCompatDelegateImplV11.java:29)
        at android.support.v7.app.AppCompatDelegateImplV14.<init>(AppCompatDelegateImplV14.java:54)
        at android.support.v7.app.AppCompatDelegateImplV23.<init>(AppCompatDelegateImplV23.java:31)
        at android.support.v7.app.AppCompatDelegateImplN.<init>(AppCompatDelegateImplN.java:31)
        at android.support.v7.app.AppCompatDelegate.create(AppCompatDelegate.java:198)
        at android.support.v7.app.AppCompatDelegate.create(AppCompatDelegate.java:183)
        at android.support.v7.app.AppCompatActivity.getDelegate(AppCompatActivity.java:519)
        at android.support.v7.app.AppCompatActivity.findViewById(AppCompatActivity.java:190)
        at kuehl.leon.tictactoe.MainActivity.<init>(MainActivity.java:13)
        at java.lang.Class.newInstance(Native Method)
        at android.app.Instrumentation.newActivity(Instrumentation.java:1173)
        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2708)
        at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2892) 
        at android.app.ActivityThread.-wrap11(Unknown Source:0) 
        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1593) 
        at android.os.Handler.dispatchMessage(Handler.java:105) 
        at android.os.Looper.loop(Looper.java:164) 
        at android.app.ActivityThread.main(ActivityThread.java:6541) 
        at java.lang.reflect.Method.invoke(Native Method) 
        at com.android.internal.os.Zygote$MethodAndArgsCaller.run(Zygote.java:240) 
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:767)

我只想让我的东西再次正确编译！

Answer 1

此错误表明您在调用 setContentView() 之前调用了 findViewById()。

有没有可能你正在做那样的事情？

public class MainActivity extends AppCompatActivity {

    TextView label = (TextView) findViewById(R.id.label);

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
    }
}

如果您可以分享您的 activity 代码，将有助于确定问题。

AndroidStudio - CompileError: (App keeps stopping) -> RuntimeException: Unable to instantiate activity

AndroidStudio - CompileError: (App keeps stopping) -> RuntimeException: Unable to instantiate activity

java

android-studio

kotlin

compilation

runtimeexception