找不到带有findViewById()的视图 [英] Can not find a View with findViewById()

问题描述

即使ID确实存在，我也无法通过调用findViewById()来找到TextView.

I cannot find a TextView by calling findViewById(), even though the ID does exist.

OtherActivity:

public class OtherActivity extends Activity { 
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        TextView textView = (TextView)findViewById(R.ID.txt02);
        super.onCreate(savedInstanceState);//line 5
        setContentView(R.layout.other_activity);
        //textView.setText(ACCESSIBILITY_SERVICE);
        Button button = (Button)findViewById(R.ID.otherActivity_Btn);
        button.setText(R.string.otherActivityBtn);
        button.setOnClickListener(new GoBackBtnListener(this));
    }

    class GoBackBtnListener implements OnClickListener {
        OtherActivity other = null;
        public GoBackBtnListener(OtherActivity p_other) {
            other = p_other;
        }
        public void onClick(View v) {
            Intent intent = new Intent();
            intent.setClass(other, Activity01Activity.class);
            other.startActivity(intent);
        }
    }
}

我在第5行添加了一个断点，并以调试模式启动了该项目.当它在断点处停止时，我将鼠标移到了变量textView上，它为空.

I added a breakpoint at line 5, and started the project in debug mode. When it stopped at the break point, I moved the mouse to variable textView, and it was null.

other_activity布局:

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout
  xmlns:android="http://schemas.android.com/apk/res/android"
  android:orientation="vertical"
  android:layout_width="fill_parent"
  android:layout_height="fill_parent">

<TextView 
    android:id="@+ID/txt02"
    android:layout_width="fill_parent"
    android:layout_height="wrap_content"
/>

<Button 
    android:id="@+ID/otherActivity_Btn"
    android:layout_width="fill_parent"
    android:layout_height="wrap_content"
/>
</LinearLayout>

AndroidManifest.xml:

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.hp" android:versionCode="1" android:versionName="1.0">
    <uses-sdk android:minSdkVersion="4" />

    <application android:icon="@drawable/icon" android:label="@string/app_name">
        <activity android:name=".Activity01Activity" android:label="@string/app_name">
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />
                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>
        <activity android:name=".OtherActivity" android:label="@string/other"></activity>
    </application>
</manifest>

生成的R.java类:

public final class R {
    public static final class ID {
        public static final int Activity01_btn=0x7f050001;
        public static final int otherActivity_Btn=0x7f050003;
        public static final int txt01=0x7f050000;
        public static final int txt02=0x7f050002;
    }
    public static final class attr {
    }
    public static final class drawable {
        public static final int icon=0x7f020000;
    }
    public static final class layout {
        public static final int main=0x7f030000;
        public static final int other_activity=0x7f030001;
    }
    public static final class string {
        public static final int app_name=0x7f040001;
        public static final int hello=0x7f040000;
        public static final int other=0x7f040002;
        public static final int otherActivityBtn=0x7f040003;
    }
}

我认为不应找到TextView，但是为什么变量textView为空?

I don't think the TextView should not be found, but why is the variable textView null?

推荐答案

在尝试查找任何UI组件之前，必须调用setContentView(...).您正在尝试调用TextView之前.

You have to call setContentView(...) BEFORE you attempt to find any of the UI components. You're trying to find the TextView before you've called it.

将您的代码更改为此...

Change your code to this...

super.onCreate(savedInstanceState);
setContentView(R.layout.other_activity);
TextView textView = (TextView)findViewById(R.id.txt02);

这篇关于找不到带有findViewById()的视图的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！