android2.1版本下android.webkit.WebView.getSettings的NullPointerException问题

在做腾讯微博的第三方登录的时候,由于要兼容2.2以下的版本,不得已使用了oauth2.0和oauth1两种授权机制来处理。要用oauth1,用http协议,只有自己定义webview了。但是在使用2.1的sdk测试该webview的时候,出现了一个ANR。大概的错误日志如下:

01-01 22:56:38.063: E/AndroidRuntime(15404): java.lang.NullPointerException
01-01 22:56:38.063: E/AndroidRuntime(15404): 	at android.webkit.WebView.getSettings(WebView.java:2759)
01-01 22:56:38.063: E/AndroidRuntime(15404): 	at android.webkit.WebView.onWindowFocusChanged(WebView.java:3585)
01-01 22:56:38.063: E/AndroidRuntime(15404): 	at android.view.View.dispatchWindowFocusChanged(View.java:3731)
01-01 22:56:38.063: E/AndroidRuntime(15404): 	at android.view.ViewGroup.dispatchWindowFocusChanged(ViewGroup.java:657)
01-01 22:56:38.063: E/AndroidRuntime(15404): 	at android.view.ViewGroup.dispatchWindowFocusChanged(ViewGroup.java:661)
01-01 22:56:38.063: E/AndroidRuntime(15404): 	at android.view.ViewGroup.dispatchWindowFocusChanged(ViewGroup.java:661)
01-01 22:56:38.063: E/AndroidRuntime(15404): 	at android.view.ViewGroup.dispatchWindowFocusChanged(ViewGroup.java:661)
01-01 22:56:38.063: E/AndroidRuntime(15404): 	at android.view.ViewGroup.dispatchWindowFocusChanged(ViewGroup.java:661)
01-01 22:56:38.063: E/AndroidRuntime(15404): 	at android.view.ViewRoot.handleMessage(ViewRoot.java:1822)
01-01 22:56:38.063: E/AndroidRuntime(15404): 	at android.os.Handler.dispatchMessage(Handler.java:99)
01-01 22:56:38.063: E/AndroidRuntime(15404): 	at android.os.Looper.loop(Looper.java:123)
01-01 22:56:38.063: E/AndroidRuntime(15404): 	at android.app.ActivityThread.main(ActivityThread.java:4367)
01-01 22:56:38.063: E/AndroidRuntime(15404): 	at java.lang.reflect.Method.invokeNative(Native Method)
01-01 22:56:38.063: E/AndroidRuntime(15404): 	at java.lang.reflect.Method.invoke(Method.java:521)
01-01 22:56:38.063: E/AndroidRuntime(15404): 	at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:860)
01-01 22:56:38.063: E/AndroidRuntime(15404): 	at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:618)
01-01 22:56:38.063: E/AndroidRuntime(15404): 	at dalvik.system.NativeStart.main(Native Method)

空指针,WebSettings webSettings = webView.getSettings();是在onCreate()方法中处理的,按理说不会出现空指针的啊?一开始,onPageStarted()方法中的代码如下,这段代码在2.1以上的版本上跑是没有问题的。

public void onPageStarted(final WebView view, String url, Bitmap favicon) {
	if (url.indexOf("xxxxx") != -1) {
		view.destroyDrawingCache();
		view.destroy();
		finish();
	}
	super.onPageStarted(view, url, favicon);
}

纠结了老半天,后来看了一下WebView的destroy()的文档。如下:

Destroy the internal state of the WebView. This method should be called after the WebView has been removed from the view system. No other methods may be called on a WebView after destroy.

原来是在destroy()方法后面调用了finish,导致ANR。具体的原因不详,但从文档中应该可以看出是提前调用了destroy()方法导致WebViewClient后续的方法中出现了空指针。

解决办法就是将destroy()方法放在WebViewClient的onPageFinished()方法中,而onPageStarted方法中只做finish()的操作。如下:

WebViewClient client = new WebViewClient(){
	@Override
	public void onPageStarted(final WebView view, String url, Bitmap favicon) {
		if (url.indexOf("xxxxx") != -1) {
		//...
			finish();
		}
		super.onPageStarted(view, url, favicon);
	}

	@Override
	public void onPageFinished(WebView view, String url)
	{
		if (url.indexOf("xxxxx") != -1) {
			view.destroyDrawingCache();
			view.destroy();
		}
		super.onPageFinished(view, url);
	}
};

纠结了老半天的问题,在此记录一下。Oauth2.0和Oauth1一起使用,也真够烦的。




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