执行单击()方法不起作用，我收到错误

Question

我有 2 个 java 类

当点击 btn 时，我想点击 btntwo。

当我单击名为btn的按钮时，我想自动单击名为btn two的按钮。 但是我得到一个错误。

主活动

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();
}
});            }
});
}
}

主2活动

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？ 我哪里做错了 你能帮我吗？

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();
}
});            }
});
}
}

Answer 2

这可以通过以下方法实现：

在主活动中：

btn.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
// Launch the Main2Activity using startActivity and pass the extra to 
// indicate that ‘btn’ is clicked
});

在 Main2Activity 中：

@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main2);
//get intent extras, if the extras contains an indicator which is sent 
//from MainActivity, perform click on ‘btntwo’
…
}