Question

我不知道为什么这段代码不起作用。我有TextView名为text1和Button名为button1。我想点击text1后更改button1中的文字。

我注意到程序在我评论第button1.setOnClickListener(this);行时有效，但结果没有发生。

 package com.example.testowaniefragmentow;

    import android.os.Bundle;
    import android.support.v4.app.Fragment;
    import android.support.v7.app.ActionBarActivity;
    import android.view.LayoutInflater;
    import android.view.View;
    import android.view.View.OnClickListener;
    import android.view.ViewGroup;
    import android.widget.Button;
    import android.widget.TextView;

    public class MainActivity extends ActionBarActivity implements OnClickListener {

        TextView text1;
        @Override
        protected void onCreate(Bundle savedInstanceState) {
            super.onCreate(savedInstanceState);
            setContentView(R.layout.activity_main);

            Button button1 = (Button) findViewById(R.id.button_B1);
            button1.setOnClickListener(this);
            TextView text1 = (TextView) findViewById(R.id.textview_text);


            if (savedInstanceState == null)
            {
                getSupportFragmentManager().beginTransaction().add(R.id.container, new PlaceholderFragment()).commit();
            }

        }

        public static class PlaceholderFragment extends Fragment {

            public PlaceholderFragment() {

            }


            @Override
            public View onCreateView(LayoutInflater inflater, ViewGroup container,
                    Bundle savedInstanceState) {
                View rootView = inflater.inflate(R.layout.fragment_main, container,false);
                return rootView;

            }
        }

        @Override
        public void onClick(View v) {

            switch (v.getId()) {
            case R.id.button_B1:
                text1.setText("Text has been changed");
                break;

            default:
                break;
            }


        }

    }

Answer 1

更改

setContentView(R.layout.activity_main);

到

setContentView(R.layout.fragment_main);

希望有所帮助......

或

正如迈克所说，将fragment_main.xml的全部内容复制到activity_main.xml ..

Answer 2

您错误地定义了TextView。您的代码中有两个文本TextView。一个在MainActivity类中，第二个是onCreate方法的局部变量。所以在你的onClicklistener中，当你尝试为text1设置文本时，它实际上没有被初始化。请在MainActivity类和onCreate方法中更改您的代码，如下所示，并保持一致。

 //declare the view and button here.
 TextView text1;
 Button button1;

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


        //initialise the view and button here but do not declare it again or else they will become local variable
        button1 = (Button) findViewById(R.id.button_B1);
        button1.setOnClickListener(this);
        text1 = (TextView) findViewById(R.id.textview_text);


        if (savedInstanceState == null)
        {
            getSupportFragmentManager().beginTransaction().add(R.id.container, new PlaceholderFragment()).commit();
        }

    }

Answer 3

试试这个兄弟：

button1.setOnClickListener（new View.OnClickListener（）{

        @Override
        public void onClick(View v) {
            // TODO Auto-generated method stub
            switch (v.getId()) {
        case R.id.button_B1:
            text1.setText("Text has been changed");
            break;

        default:
            break;
        }
        }
    });

Android中的OnClickListener，没有错误，但应用程序停止

3 个答案: