我创建的简单apk在打开时崩溃（可能是我的Java代码中的错误）

Posted 2023-01-18

我创建的简单APK在尝试启动时一直崩溃，但我不知道为什么。这是问题可能来自的代码（这是我在APK开始崩溃之前修改的最后一个代码）：

package com.example.firstapk;

import androidx.appcompat.app.AppCompatActivity;
import androidx.coordinatorlayout.widget.CoordinatorLayout;

import android.app.Activity;
import android.app.AlertDialog;
import android.content.Context;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;

import com.google.android.material.snackbar.Snackbar;

public class MainActivity extends AppCompatActivity 
    private static Button button_test;
    @Override
    protected void onCreate(Bundle savedInstanceState) 
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
            onButtonClickListener(fact_a);
    

    String fact_a = getString(R.string.Fact1);


    public void onButtonClickListener(final String fact) 
        button_test = (Button)findViewById(R.id.button2);
        button_test.setOnClickListener(
                new View.OnClickListener() 
                    @Override
                    public void onClick(View v) 
                        AlertDialog.Builder builder_test = new AlertDialog.Builder(MainActivity.this);
                        builder_test.setMessage(fact).setCancelable(true);
                        AlertDialog alert = builder_test.create();
                        alert.show();
                    
                
        );
    

提前感谢

答案

2020-05-03 16:59:55.786 13220-13220/? E/Zygote: isWhitelistProcess - Process is Whitelisted
2020-05-03 16:59:55.787 13220-13220/? E/Zygote: accessInfo : 1
2020-05-03 16:59:56.230 13220-13220/com.example.firstapk E/AndroidRuntime: FATAL EXCEPTION: main
    Process: com.example.firstapk, PID: 13220
    java.lang.RuntimeException: Unable to instantiate activity ComponentInfocom.example.firstapk/com.example.firstapk.MainActivity: java.lang.NullPointerException: Attempt to invoke virtual method 'android.content.res.Resources android.content.Context.getResources()' on a null object reference
        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3020)
        at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3257)
        at android.app.servertransaction.LaunchActivityItem.execute(LaunchActivityItem.java:78)
        at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:108)
        at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:68)
        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1948)
        at android.os.Handler.dispatchMessage(Handler.java:106)
        at android.os.Looper.loop(Looper.java:214)
        at android.app.ActivityThread.main(ActivityThread.java:7050)
        at java.lang.reflect.Method.invoke(Native Method)
        at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:494)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:965)
     Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'android.content.res.Resources android.content.Context.getResources()' on a null object reference
        at android.content.ContextWrapper.getResources(ContextWrapper.java:91)
        at android.view.ContextThemeWrapper.getResourcesInternal(ContextThemeWrapper.java:127)
        at android.view.ContextThemeWrapper.getResources(ContextThemeWrapper.java:121)
        at androidx.appcompat.app.AppCompatActivity.getResources(AppCompatActivity.java:543)
        at android.content.Context.getString(Context.java:580)
        at com.example.firstapk.MainActivity.<init>(MainActivity.java:24)
        at java.lang.Class.newInstance(Native Method)
        at android.app.AppComponentFactory.instantiateActivity(AppComponentFactory.java:69)
        at androidx.core.app.CoreComponentFactory.instantiateActivity(CoreComponentFactory.java:43)
        at android.app.Instrumentation.newActivity(Instrumentation.java:1215)
        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3008)
        at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3257) 
        at android.app.servertransaction.LaunchActivityItem.execute(LaunchActivityItem.java:78) 
        at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:108) 
        at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:68) 
        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1948) 
        at android.os.Handler.dispatchMessage(Handler.java:106) 
        at android.os.Looper.loop(Looper.java:214) 
        at android.app.ActivityThread.main(ActivityThread.java:7050) 
        at java.lang.reflect.Method.invoke(Native Method) 
        at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:494) 
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:965) 

另一答案

public class MainActivity extends AppCompatActivity 
private static Button button_test;
String fact_a;

@Override
protected void onCreate(Bundle savedInstanceState) 
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    fact_a = getString(R.string.Fact1);
    onButtonClickListener(fact_a);



public void onButtonClickListener(final String fact) 
    button_test = (Button)findViewById(R.id.button2);
    button_test.setOnClickListener(
            new View.OnClickListener() 
                @Override
                public void onClick(View v) 
                    AlertDialog.Builder builder_test = new AlertDialog.Builder(MainActivity.this);
                    builder_test.setMessage(fact).setCancelable(true);
                    AlertDialog alert = builder_test.create();
                    alert.show();
                
            
    );