Android Intent 命令出错

Question

我的代码有问题。当我单击标题 "New Profile" 时，必须启动一个新的 Activity，但是当我单击时，会显示一条警告：“不幸的是 %AppName% 已停止。” .

这是 Android 监视器的日志

--------- beginning of crash
05-17 01:19:54.545 2568-2568/com.example.felipe.myappproject E/AndroidRuntime: FATAL EXCEPTION: main
   Process: com.example.felipe.myappproject, PID: 2568
   java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{com.example.felipe.myappproject/com.example.felipe.myappproject.NewProfileActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.String android.content.Context.getPackageName()' on a null object reference
       at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2327)
       at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2476)
       at android.app.ActivityThread.-wrap11(ActivityThread.java)
       at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1344)
       at android.os.Handler.dispatchMessage(Handler.java:102)
       at android.os.Looper.loop(Looper.java:148)
       at android.app.ActivityThread.main(ActivityThread.java:5417)
       at java.lang.reflect.Method.invoke(Native Method)
       at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:726)
       at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616)
    Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.String android.content.Context.getPackageName()' on a null object reference
       at android.content.ContextWrapper.getPackageName(ContextWrapper.java:133)
       at android.content.ComponentName.<init>(ComponentName.java:128)
       at android.content.Intent.<init>(Intent.java:4449)
       at com.example.felipe.myappproject.NewProfileActivity.<init>(NewProfileActivity.java:14)
       at java.lang.Class.newInstance(Native Method)
       at android.app.Instrumentation.newActivity(Instrumentation.java:1067)
       at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2317)
       at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2476) 
       at android.app.ActivityThread.-wrap11(ActivityThread.java) 
       at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1344) 
       at android.os.Handler.dispatchMessage(Handler.java:102) 
       at android.os.Looper.loop(Looper.java:148) 
       at android.app.ActivityThread.main(ActivityThread.java:5417) 
       at java.lang.reflect.Method.invoke(Native Method) 
       at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:726) 
       at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616)

这是我的 NewProfileActivity.java

public class NewProfileActivity extends AppCompatActivity {

        EditText profile, password, confirmpass;
        Intent insert = new Intent(NewProfileActivity.this, MainActivity.class);

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

        public void backMain(View v){

            startActivity(back);

        }

        public void insertData(View v) {

            profile = (EditText) findViewById(R.id.profileName);
            password = (EditText) findViewById(R.id.password);
            confirmpass = (EditText) findViewById(R.id.confirmPassword);

            insert.putExtra("profile", profile.getText().toString());
            insert.putExtra("password", password.getText().toString());
            insert.putExtra("profile", confirmpass.getText().toString());

            compare(password.getText().toString(), confirmpass.getText().toString());
        }

        public void compare(String x, String y){

            final AlertDialog alert = new AlertDialog.Builder(NewProfileActivity.this).create();

            if(x.equals(y)){
                alert.setTitle("New Profile!");
                alert.setMessage("Profile "+profile+" registered");
                alert.setButton(AlertDialog.BUTTON_NEUTRAL, "OK",
                        new DialogInterface.OnClickListener() {
                            public void onClick(DialogInterface dialog, int which) {
                                dialog.dismiss();
                            }
                        }
                );
                startActivity(insert);
            } else {
                alert.setTitle("Ops...");
                alert.setMessage("Passwords don't macth");
                alert.setButton(AlertDialog.BUTTON_NEUTRAL, "OK",
                        new DialogInterface.OnClickListener() {
                            public void onClick(DialogInterface dialog, int which) {
                                dialog.dismiss();
                            }
                        }
                );
            }
        }
    }

我找不到我做错了什么。我试图通过删除 "public void backMain(View v)" 以外的所有内容来简化代码，但我仍然遇到同样的问题。

Answer 1

根据@MikeM 的评论，您在一开始就初始化了 Intent，即使您作为参数传递的 class 也没有完全初始化。

你应该像这样使用它之前简单地初始化它：

public class NewProfileActivity extends AppCompatActivity {

    EditText profile, password, confirmpass;

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

    public void backMain(View v) {
        // startActivity(back);
    }

    public void insertData(View v) {

        profile = (EditText) findViewById(R.id.profileName);
        password = (EditText) findViewById(R.id.password);
        confirmpass = (EditText) findViewById(R.id.confirmPassword);

        compare(password.getText().toString(), confirmpass.getText().toString());
    }

    public void compare(String x, String y) {

        final AlertDialog alert = new AlertDialog.Builder(NewProfileActivity.this).create();

        if (x.equals(y)) {
            alert.setTitle("New Profile!");
            alert.setMessage("Profile " + profile + " registered");
            alert.setButton(AlertDialog.BUTTON_NEUTRAL, "OK",
                    new DialogInterface.OnClickListener() {
                        public void onClick(DialogInterface dialog, int which) {
                            dialog.dismiss();
                        }
                    }
            );
            // CODES Transferred here ====
            Intent insert = new Intent(NewProfileActivity.this, MainActivity.class);

            insert.putExtra("profile", profile.getText().toString());
            insert.putExtra("password", password.getText().toString());
            insert.putExtra("profile", confirmpass.getText().toString());
            // CODES Transferred here ====
            startActivity(insert);
        } else {
            alert.setTitle("Ops...");
            alert.setMessage("Passwords don't macth");
            alert.setButton(AlertDialog.BUTTON_NEUTRAL, "OK",
                    new DialogInterface.OnClickListener() {
                        public void onClick(DialogInterface dialog, int which) {
                            dialog.dismiss();
                        }
                    }
            );
        }
    }
}

干杯！ :D

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