Question

我写了一个android程序，在主活动中有两个按钮：“login”，“regstration”。两个按钮都在布局中创建。问题是活动无法得到它们。之后：

Button mLoginButoon;
....
mLoginButoon = (Button)findViewById(R.string.login);

mLoginButoon为空。

这是代码： MainActivity：

    package com.example.forum.controlers;

import com.example.forum.R;
import com.example.forum.R.id;
import com.example.forum.R.layout;
import com.example.forum.R.menu;

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

public class MainActivity extends Activity {
    private Button mRegisterButoon;
    private Button mLoginButoon;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        Object o = null;
        setContentView(R.layout.activity_main);
        o = this.findViewById(android.R.id.content);
        mLoginButoon = (Button)findViewById(R.string.login);
        mLoginButoon.setOnClickListener(new View.OnClickListener() {
            public void onClick(View v) {
                startActivity(new Intent(MainActivity.this, LoginActivity.class));
            }
        });
        mRegisterButoon = (Button)findViewById(R.string.register);
        mRegisterButoon.setOnClickListener(new View.OnClickListener() {
            public void onClick(View v) {
                startActivity(new Intent(MainActivity.this, LoginActivity.class));
            }
        });
    }

    @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);
    }
}

这是activity_main布局：

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:paddingBottom="@dimen/activity_vertical_margin"
android:paddingLeft="@dimen/activity_horizontal_margin"
android:paddingRight="@dimen/activity_horizontal_margin"
android:paddingTop="@dimen/activity_vertical_margin"
tools:context="com.example.forum.controlers.MainActivity" >

<TextView
    android:id="@+id/textView1"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:text="@string/welcome_to_my_forum" />

<LinearLayout
    android:id="@+id/linearLayout1"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:layout_alignLeft="@+id/textView1"
    android:layout_below="@+id/textView1"
    android:layout_marginTop="34dp"
    android:background="?android:attr/selectableItemBackground"
    android:orientation="horizontal" >

    <Button
        android:id="@+id/login"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="@string/login" />

    <Button
        android:id="@+id/register"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="@string/register" />
</LinearLayout>

Answer 1

(Button)findViewById(R.string.login);

R.string？改为使用R.id.login：

(Button)findViewById(R.id.login);

Answer 2

您引用的是字符串资源而不是ID，例如您使用R.string.login代替R.id.login

更改

mLoginButoon = (Button)findViewById(R.string.login);

以

mLoginButoon = (Button)findViewById(R.id.login);

和

mRegisterButoon = (Button)findViewById(R.string.register);

到

mRegisterButoon = (Button)findViewById(R.id.register);

活动无法从布局中获取按钮

2 个答案: