findViewById返回null的WebView [英] findViewById returns null for WebView

问题描述

我想建立一个Android应用程序，刚刚由一个网页视图中。我从 Android开发人员网站并修改了它的例子。但是，因为它看起来简单，findViewById每次调用导致空指针。
在java文件：

I'm trying to build an android app, which just consists of a webview. I took the example from android dev site and modified it. But as simple as it looks, every call to findViewById results in a null pointer. The .java file:

    public class MainActivity extends Activity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        WebView webView = (WebView) findViewById(R.id.webview);
        // returns null pointer 
        webView.loadUrl("file:///android_asset/index.html");

        setContentView(webView);
    }
}

布局文件：

<LinearLayout 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"
    android:orientation="horizontal"
    tools:context=".MainActivity" >

    <WebView
        android:id="@+id/webview"
        android:layout_width="fill_parent"
        android:layout_height="fill_parent" />

</LinearLayout>

和我把下面的行到清单：

And I put following line into the manifest:

<uses-permission android:name="android.permission.INTERNET" />

我很疑惑...

I'm puzzled ...

推荐答案

更改为

public class MainActivity extends Activity {
@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.mylayout); // muylayout is your layout.xml
    WebView webView = (WebView) findViewById(R.id.webview);
    // returns null pointer 
    webView.loadUrl("file:///android_asset/index.html");
}
}

您需要调用 findViewById 前将布局到活动的内容。 findViewById 查找与充气当前布局提供的ID景色。

You need to set the content of your layout to the activity before calling findViewById. findViewById looks for a view with the id provided in the current layout inflated.

这篇关于findViewById返回null的WebView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！