Question

我正在阅读一本关于java练习的书，并且已经陷入了这种语法错误。我搜索了onSetClickListener语法错误，并且不认为我在重复问题。 Eclipse说'令牌上的语法错误'setOnClickListener“，此标记之后的标识符'。谢谢你的帮助！

package fifth.example.eventhandling;

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

public class MainActivity extends Activity implements OnClickListener{
    Button button = (Button)findViewById(R.id.button1);
    button.setOnClickListener(this);  <<ERROR HERE

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

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

    @Override
    public void onClick(View arg0) {
        TextView text = (TextView)findViewById(R.id.textmessage);
        text.setText("BUTTON HAS BEEN CLICKED. EVENT PROCESSED.");

    }

}

Answer 1

一个问题是：代码中的按钮相关代码应位于onCreate()内setContentView...

之后

    Button button = (Button)findViewById(R.id.button1);
    button.setOnClickListener(this);  <<ERROR HERE

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

应该是：

公共类MainActivity扩展Activity实现OnClickListener { 按钮按钮; //声明按钮听到

 @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        Button button = (Button)findViewById(R.id.button1);
       button.setOnClickListener(this);  <<ERROR HERE

    }

}

Answer 2

目前，您在设置Activity的布局之前尝试初始化按钮。在setContentView之后的onCreate of Activity中移动按钮初始化为：

public class MainActivity extends Activity implements OnClickListener{
    Button button ; //<<< declare  button here

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

       button = (Button)findViewById(R.id.button1);  //<<< initilze here
       button.setOnClickListener(this);   
    }

Answer 3

你的代码应该是这样的。

public class MainActivity extends Activity implements OnClickListener{


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

Button button = (Button)findViewById(R.id.button1);
button.setOnClickListener(this);  <<ERROR HERE
}

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

@Override
public void onClick(View arg0) {
    TextView text = (TextView)findViewById(R.id.textmessage);
    text.setText("BUTTON HAS BEEN CLICKED. EVENT PROCESSED.");

}

语法错误setOnClickListener

3 个答案: