在线程中运行的 JsonReader 使应用程序崩溃

Question

我的应用程序意外崩溃，我不明白为什么。我正在使用 HttpURLConnection 来检索 json 文件，并且我正在尝试使用 JsonReader 类来读取并使用该文件。问题是应用程序在读取或对 JsonReader 实例执行任何操作后崩溃。

我已经用扫描仪读取了输入流，但这会导致类似的问题。但是，当使用扫描仪阅读时，我可以从服务器打印少量 json。因此，来自服务器的数据可能也会进入 JsonReader。

这是我的代码：

public class ConnectToServer implements Runnable {

private URL connectionUrl;
private MainActivity output;

public ConnectToServer(URL url, MainActivity mainActivity) {
    connectionUrl = url;
    output = mainActivity;
}

public void printError(String errorMessage){
    output.output(errorMessage);
}

public InputStream GetInputStream(){
    try {
        HttpURLConnection connection = (HttpURLConnection)connectionUrl.openConnection();
        InputStream inputStream = new BufferedInputStream(connection.getInputStream());
        if (inputStream == null){
            printError("Input stream is null");
        }
        return inputStream;
    } catch (IOException ex){
        printError("IO exception has been thrown");
    } catch (Exception ex){
        printError("Normal exception thrown: " + ex.getClass().getSimpleName());
    }
    return null;
}

@Override
public void run() {
    InputStream inputStream = GetInputStream();
    try {
        if (inputStream == null){
            printError("Input stream not initiated");
        } else {
            JsonReader reader = new JsonReader(new InputStreamReader(inputStream, "UTF-8"));
            printError(reader.toString());
            reader.close();
        }
    } catch (Exception ex){
        printError("Exception while printing input stream: " + ex.getClass().getSimpleName());
    }
    printError("Thread finished");
}

这将在主 UI 线程中创建的线程上运行。

public void connect(){
    output("connect started");
    boolean success = true;
    try {
        URL url = new URL("http://geonews.azurewebsites.net/api/Location");
        serverConnection = new ConnectToServer(url,this);
        Thread thread = new Thread(serverConnection);
        thread.start();
    } catch (MalformedURLException ex){
        output("Messed up the URL");
        success = false;
    }
    if (success){
        output("Thread has been started");
    } else {
        output("exception was thrown while trying to run thread");
    }
}

有人知道为什么这段代码会导致我的应用崩溃吗？即使它到达“线程完成”，它也会很快崩溃。

顺便说一句，我意识到我应该使用 AsyncTask，但我已经走上了这条路，我宁愿先走这条路。

Logcat：

06-14 22:45:00.058    4032-4052/com.tomsapps.thomas.jsonreadertestapp E/AndroidRuntime﹕ FATAL EXCEPTION: Thread-314
Process: com.tomsapps.thomas.jsonreadertestapp, PID: 4032
android.view.ViewRootImpl$CalledFromWrongThreadException: Only the original thread that created a view hierarchy can touch its views.
        at android.view.ViewRootImpl.checkThread(ViewRootImpl.java:6247)
        at android.view.ViewRootImpl.requestLayout(ViewRootImpl.java:867)
        at android.view.View.requestLayout(View.java:17364)
        at android.view.View.requestLayout(View.java:17364)
        at android.view.View.requestLayout(View.java:17364)
        at android.view.View.requestLayout(View.java:17364)
        at android.view.View.requestLayout(View.java:17364)
        at android.view.View.requestLayout(View.java:17364)
        at android.widget.RelativeLayout.requestLayout(RelativeLayout.java:360)
        at android.view.View.requestLayout(View.java:17364)
        at android.widget.TextView.checkForResize(TextView.java:6798)
        at android.widget.TextView.updateAfterEdit(TextView.java:7693)
        at android.widget.TextView.handleTextChanged(TextView.java:7709)
        at android.widget.TextView$ChangeWatcher.onTextChanged(TextView.java:9440)
        at android.text.SpannableStringBuilder.sendTextChanged(SpannableStringBuilder.java:964)
        at android.text.SpannableStringBuilder.replace(SpannableStringBuilder.java:515)
        at android.text.SpannableStringBuilder.append(SpannableStringBuilder.java:272)
        at android.text.SpannableStringBuilder.append(SpannableStringBuilder.java:33)
        at android.widget.TextView.append(TextView.java:3616)
        at android.widget.TextView.append(TextView.java:3603)
        at com.tomsapps.thomas.jsonreadertestapp.MainActivity.output(MainActivity.java:63)
        at com.tomsapps.thomas.jsonreadertestapp.ConnectToServer.printError(ConnectToServer.java:26)
        at com.tomsapps.thomas.jsonreadertestapp.ConnectToServer.run(ConnectToServer.java:74)
        at java.lang.Thread.run(Thread.java:818)

Answer 1

我相信您来自 MainActivity 的 output 方法会修改 TextView，因此会触发异常。

只能从“主”线程更改视图层次结构，在这种情况下，您可能想尝试查看 runOnUiThread，StackOverflow 上的一些资源：

• how to use runOnUiThread
• Android runOnUiThread explanation
• Android Java runOnUiThread()

希望这会有所帮助，祝你好运:)

编辑：

您可能还想使用 android Log 而不是使用 TextView 来显示错误。