java - PerformClick()方法不起作用，出现错误

Question

我有2个java类

我想在单击 btn 时单击 btntwo。

当我单击名为 btn 的按钮时，我想自动单击名为 btn 的按钮 2。 但我收到一个错误。

主要 Activity

 public class MainActivity extends AppCompatActivity {
    Button btn;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        btn =  findViewById(R.id.btn);
        btn.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
             //   Log.e("test","testone");
                final Main2Activity main2Activity = new Main2Activity();

                main2Activity.btntwo
                        .post(new Runnable(){
                            @Override
                            public void run() {
                                main2Activity.btntwo.performClick();

                            }
                        });            }
        });
    }
}

Main2Activity

public class Main2Activity extends AppCompatActivity {
    Button btntwo;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main2);
        btntwo =  findViewById(R.id.btntwo);

        btntwo.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                Log.e("test","testtwo");

            }
        });

}
}

我收到错误

2020-05-16 17:06:35.238 8529-8529/com.qarocotwo.myapplication E/AndroidRuntime: FATAL EXCEPTION: main
    Process: com.qarocotwo.myapplication, PID: 8529
    java.lang.NullPointerException: Attempt to invoke virtual method 'boolean android.widget.Button.post(java.lang.Runnable)' on a null object reference
        at com.qarocotwo.myapplication.MainActivity$1.onClick(MainActivity.java:25)
        at android.view.View.performClick(View.java:7125)
        at android.view.View.performClickInternal(View.java:7102)
        at android.view.View.access$3500(View.java:801)
        at android.view.View$PerformClick.run(View.java:27336)
        at android.os.Handler.handleCallback(Handler.java:883)
        at android.os.Handler.dispatchMessage(Handler.java:100)
        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)

为什么我会收到错误消息？ 我哪里做错了 你能帮我一下吗？

Answer 1

您在错误的位置创建了 Main2Activity 类的对象。

public class MainActivity extends AppCompatActivity {
    Button btn;
    Main2Activity main2Activity;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        btn =  findViewById(R.id.btn);
       main2Activity = new Main2Activity();

        btn.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
             //   Log.e("test","testone");

                main2Activity.btntwo
                        .post(new Runnable(){
                            @Override
                            public void run() {
                                main2Activity.btntwo.performClick();

                            }
                        });            }
        });
    }
}