android - 同一 Activity 上有多个按钮

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What is a NullPointerException, and how do I fix it?

(12个答案)

在17天前关闭。

首先，让我感谢您的关注。我仍然对开发非常陌生，但是现在我成功地拥有了一个不错的启动屏幕，正在努力进行注册和登录 Activity ，以在按下按钮后显示出来。下面的代码适用于登录 Activity ，但是按下注册按钮后，我的应用程序崩溃了。我怀疑自己在做一些愚蠢的事情，但是我尝试了几种方法来介绍这些按钮并使它们起作用，但似乎什么也没有。
单击SignUpBtn时的Logcat

2020-09-18 11:32:21.732 1217-2251/? I/HwResolverManager: isMultiScreenCollaborationEnabled: Operate settings exception! 
2020-09-18 11:32:28.474 30804-30804/com.example.doadventuresv30 I/BlockMonitor: dispatchingThrewException In MainThread
2020-09-18 11:32:28.474 30804-30804/com.example.doadventuresv30 I/QarthLog: [PatchStore] createDisableExceptionQarthFile
2020-09-18 11:32:28.475 30804-30804/com.example.doadventuresv30 E/AndroidRuntime: FATAL EXCEPTION: main
    Process: com.example.doadventuresv30, PID: 30804
    java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.doadventuresv30/com.example.doadventuresv30.SignUpActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.TextView.setOnClickListener(android.view.View$OnClickListener)' on a null object reference
        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3895)
        at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:4074)
        at android.app.servertransaction.LaunchActivityItem.execute(LaunchActivityItem.java:91)
        at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:149)
        at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:103)
        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2473)
        at android.os.Handler.dispatchMessage(Handler.java:110)
        at android.os.Looper.loop(Looper.java:219)
        at android.app.ActivityThread.main(ActivityThread.java:8347)
        at java.lang.reflect.Method.invoke(Native Method)
        at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:513)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1055)
     Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.TextView.setOnClickListener(android.view.View$OnClickListener)' on a null object reference
        at com.example.doadventuresv30.SignUpActivity.initActions(SignUpActivity.java:59)
        at com.example.doadventuresv30.SignUpActivity.onCreate(SignUpActivity.java:30)
        at android.app.Activity.performCreate(Activity.java:8085)
        at android.app.Activity.performCreate(Activity.java:8073)
        at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1320)
        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3868)
        at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:4074) 
        at android.app.servertransaction.LaunchActivityItem.execute(LaunchActivityItem.java:91) 
        at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:149) 
        at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:103) 
        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2473) 
        at android.os.Handler.dispatchMessage(Handler.java:110) 
        at android.os.Looper.loop(Looper.java:219) 
        at android.app.ActivityThread.main(ActivityThread.java:8347) 
        at java.lang.reflect.Method.invoke(Native Method) 
        at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:513) 
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1055) 
2020-09-18 11:32:28.573 2157-2381/? I/HwPacketFilterBypass: isAllowSendSmartCureToChr false, no exceptions occur, dropCnt:0
2020-09-18 11:32:31.597 1217-1822/? W/AwareLog: AwareMem_MemoryUtils: trim Memory illegal arg exception, proc:30209 userId:-2 level:40 fromIAware:true
2020-09-18 11:32:38.212 13449-13912/? I/SmartChgBase/Arb_HidlParam: Apply Skipped: IsApplyExcept return true. [moduleName:NightChargeAi, param:soc_control, detailsWithValue:source=trigger;event=heartbeat;chargestatus=start;value=1 95 100 1 0;]

public class SplashActivity extends AppCompatActivity {

    private ImageView iconImageView;
    private Button SignUpBtn, LoginBtn;

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

        SignUpBtn = findViewById(R.id.SignUpBtn);
        SignUpBtn.setOnClickListener((v) ->{
            Intent intent = new Intent(SplashActivity.this, SignUpActivity.class);
            startActivity(intent);
        }
        LoginBtn = findViewById(R.id.LoginBtn);
        LoginBtn.setOnClickListener((v) ->{
            Intent in = new Intent(SplashActivity.this, LoginActivity.class);
            startActivity(in);
        });
    }
}


public class SignUpActivity extends AppCompatActivity {

    TextView createTextView;
    LinearLayout facebookLinearLayout, twitterLinearLayout, googlePlusLinearLayout;
    Button registerButton;
    ImageView bgImageView;
    Button forgotButton;

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

        initDataBindings();

        initActions();

    }

    //region Init Functions
    private void initUI() {

        forgotButton = findViewById(R.id.forgotButton);

        facebookLinearLayout = findViewById(R.id.facebookLinearLayout);
        twitterLinearLayout = findViewById(R.id.twitterLinearLayout);
        googlePlusLinearLayout = findViewById(R.id.googlePlusLinearLayout);

        registerButton = findViewById(R.id.registerButton);

        bgImageView = findViewById(R.id.bgImageView);

    }

    private void initDataBindings() {
        int id = R.drawable.lightbg;
        Utils.setImageToImageView(getApplicationContext(), bgImageView, id);
    }

    private void initActions() {
        forgotButton.setOnClickListener(view -> {
            Toast.makeText(getApplicationContext(), "Clicked Forgot Password", Toast.LENGTH_SHORT).show();
        });

        createTextView.setOnClickListener(view -> {
            Toast.makeText(getApplicationContext(), "Clicked Create Account", Toast.LENGTH_SHORT).show();
        });

        facebookLinearLayout.setOnClickListener(view -> {
            Toast.makeText(getApplicationContext(), "Clicked Facebook", Toast.LENGTH_SHORT).show();
        });

        twitterLinearLayout.setOnClickListener(view -> {
            Toast.makeText(getApplicationContext(), "Clicked Twitter", Toast.LENGTH_SHORT).show();
        });

        googlePlusLinearLayout.setOnClickListener(view -> {
            Toast.makeText(getApplicationContext(), "Clicked Google Plus", Toast.LENGTH_SHORT).show();
        });

        registerButton.setOnClickListener(view -> {
            Toast.makeText(getApplicationContext(), "Clicked Sign Up", Toast.LENGTH_SHORT).show();
        });

    }
    //endregion
}

最佳答案

createTextView为空。用findViewById()初始化它。

关于android - 同一 Activity 上有多个按钮，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/63951086/

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