我有2个Java类
我想单击btn时单击btntwo。
当我单击名为btn的按钮时，我要自动单击名为btn的按钮两个。但是我得到一个错误。
主要活动
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();
}
}); }
});
}
}
Main2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");
}
});
}
}
我遇到错误
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)
为什么我会出错？我在哪里做错了请你帮我吗？
这可以通过以下方式实现：
在MainActivity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’
…
}
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