Question

我正在尝试在OnCreate（）函数中声明按钮和EditTexts，调用函数findViewById（）。但是，当我尝试使用模拟器中的按钮时，应用程序失败。当我在事件处理函数中使用findViewById（）时（我使用android：onClick，因为java中的处理也没有工作），aplication工作正常。为什么我不能只在onCreate中使用findViewById（）一次？

import android.app.Activity;
import android.app.Fragment;
import android.os.Bundle;
import android.view.LayoutInflater;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.view.View.OnClickListener;
import android.view.ViewGroup;
import android.widget.Button;
import android.widget.EditText;
import android.widget.Spinner;

public class MainActivity extends Activity implements OnClickListener{

String[] names;

EditText status;
EditText par1;
EditText par2;
EditText par3;

Button b1;
Button b2;
Button b3;
Button b4;

Spinner spin;

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

    status = (EditText) findViewById(R.id.text);

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

    b1 = (Button) findViewById(R.id.b1);
    b1.setOnClickListener(new View.OnClickListener(){
        @Override
        public void onClick(View v){
            status.setText("HA"); 
        }
    });

    Button b2 = (Button) findViewById(R.id.b2);
    b2.setActivated(false);
    b2.setOnClickListener(new View.OnClickListener(){
        @Override
        public void onClick(View v){
            //Display any data about the persons 
        }
    });

    Button b3 = (Button) findViewById(R.id.b3);
    b3.setActivated(false);
    b3.setOnClickListener(new View.OnClickListener(){
        @Override
        public void onClick(View v){
            //Start the sensors lecture 
        }
    });

    Button b4 = (Button) findViewById(R.id.b4);
    b4.setActivated(false);
    b4.setOnClickListener(new View.OnClickListener(){
        @Override
        public void onClick(View v){
            //Execute the music 
        }
    }); 
}

public void treatment_button(View v){
        status = (EditText) findViewById(R.id.text);
    status.setText("Connect");
}

@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;
}

@Override
public boolean onOptionsItemSelected(MenuItem item) {
    // Handle action bar item clicks here. The action bar will
    // automatically handle clicks on the Home/Up button, so long
    // as you specify a parent activity in AndroidManifest.xml.
    int id = item.getItemId();
    if (id == R.id.action_settings) {
        return true;
    }
    return super.onOptionsItemSelected(item);
}

/**
 * A placeholder fragment containing a simple view.
 */
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;
    }
}

}

Answer 1

在oncreate（）里面你再次定义Button b1，如：

Button b1 = (Button) findViewById(R.id.b1);

将其更改为：

b1 = (Button) findViewById(R.id.b1);

当您在onCreate()中创建Button变量时，它将无法在该方法之外工作。因此，请使用您创建的Button的全局引用变量。

Answer 2

尝试这个希望它有效：

import android.app.Activity;
 import android.app.Fragment;
import android.os.Bundle;
import android.view.LayoutInflater;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.view.View.OnClickListener;
import android.view.ViewGroup;
import android.widget.Button;
import android.widget.EditText;
import android.widget.Spinner;

public class MainActivity extends Activity {

String[] names;

EditText status;
EditText par1;
EditText par2;
EditText par3;

Button b1;
Button b2;
Button b3;
Button b4;

Spinner spin;

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

status = (EditText) findViewById(R.id.text);

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

b1 = (Button) findViewById(R.id.b1);
b1.setOnClickListener(new OnClickListener() {

    @Override
    public void onClick(View v) {
        // TODO Auto-generated method stub
         status.setText("HA"); 
    }
});

 b2 = (Button) findViewById(R.id.b2);
b2.setActivated(false);
b2.setOnClickListener(new View.OnClickListener(){
    @Override
    public void onClick(View v){
        //Display any data about the persons 
    }
});

 b3 = (Button) findViewById(R.id.b3);
 b3.setActivated(false);
 b3.setOnClickListener(new View.OnClickListener(){
    @Override
    public void onClick(View v){
        //Start the sensors lecture 
    }
});

 b4 = (Button) findViewById(R.id.b4);
b4.setActivated(false);
b4.setOnClickListener(new View.OnClickListener(){
    @Override
    public void onClick(View v){
        //Execute the music 
    }
}); 
}

public void treatment_button(View v){
    status = (EditText) findViewById(R.id.text);
status.setText("Connect");
}

@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;
}

@Override
public boolean onOptionsItemSelected(MenuItem item) {
// Handle action bar item clicks here. The action bar will
// automatically handle clicks on the Home/Up button, so long
// as you specify a parent activity in AndroidManifest.xml.
int id = item.getItemId();
if (id == R.id.action_settings) {
    return true;
}
return super.onOptionsItemSelected(item);
}

 /**
 * A placeholder fragment containing a simple view.
 */
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;
  }
 }

}

在Android上使用视图的问题

2 个答案: