Java 意图不起作用，单击按钮2，应用程序崩溃

我无法在活动之间切换，当我单击按钮2时，应用程序崩溃

<pre>package com.example.againtry;

    import java.util.Random;

    import android.app.Activity;
    import android.content.Intent;
    import android.os.Bundle;
    import android.view.Menu;
    import android.view.View;
    import android.widget.Button;
    import android.widget.TextView;

    public class MainActivity extends Activity {
    /** Called when the activity is first created. */
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        // Declare our View Variables and assign them the Views from the layout file

        final TextView answerLabel = (TextView) findViewById(R.id.textView1);
        Button getAnswerButton = (Button) findViewById(R.id.button1);

        getAnswerButton.setOnClickListener(new View.OnClickListener() {

    @Override
    public void onClick(View arg0) {
    // The Button was clicked, so the update the answer label with an answer

         String answer = "";
    // Randomly select one of three answers: Yes, No or May be

    // Update the label with our dynamic answer

    Random randomGenerator = new Random(); // Construct a new Random number Generator
    int randomNumber = randomGenerator.nextInt(3);
    answer = Integer.toString(randomNumber);
    // update the label with our dynamic answer

    answerLabel.setText(answer);
    }});

        Button btnSimple= (Button) findViewById(R.id.button2);
        btnSimple.setOnClickListener(new View.OnClickListener() {

    @Override
    public void onClick(View v) {

    // From One Activity to another
    Intent intent = new Intent(MainActivity.this, SendMessageActivity.class);
    startActivity(intent);

    }});
    }



    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        // Inflate the menu; this adds items to the action bar if it is present.
        getMenuInflater().inflate(R.menu.main, menu);
        return true;
    }}</pre>

MainActivity.Java

这是我的第二项活动

Button getSendButton = (Button) findViewById(R.id.button1);

在SendMessageActivity（即send_message.xml）的布局中，没有id为button1的按钮。 因此，在这样做时：

findViewById返回null，因此getSendButton.setOnClickListener/***/；抛出NullPointerException

应该是：

---

您必须将onclick分配给一个特定的按钮，我在activity\u主xml中没有看到这个按钮

只需将onclick事件添加到按钮并删除onclicklistener，它就应该可以工作了

---

要添加onclick侦听器，您可以转到designer页面，在properties中找到标记onclick。只需使用下拉菜单将onlick方法分配给该标记。

SendMessageActivity中的控件映射有错误

---

不是按钮1，而是R.id.sendButton

请张贴stacktrace。

Button getSendButton = (Button) findViewById(R.id.button1);

Button getSendButton = (Button) findViewById(R.id.sendButton);

  public class SendMessageActivity extends Activity {
@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.send_message);

    final EditText editSMS = (EditText) findViewById(R.id.editText1);
    final EditText editPhoneNum = (EditText) findViewById(R.id.phoneNum);
    Button getSendButton = (Button) findViewById(R.id.button1);