1

如何从中获取值TextView并将其存储在 a 中String？在这里，我试图创建一个具有 TextView 值的字符串并将其写入文件。

下面的代码显示了运行时错误：

package com.ralley.par2;
import java.io.File;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.OutputStreamWriter;

import android.app.Activity;
import android.os.Bundle;
import android.widget.EditText;
import android.widget.TextView;
import android.widget.Toast;

    public class Par2Activity extends Activity {
        /** Called when the activity is first created. */
        @Override
        public void onCreate(Bundle savedInstanceState) {
            super.onCreate(savedInstanceState);
            TextView txtData1;

            txtData1 = (TextView) findViewById(R.id.txtData1);

            try {
            File myFile = new File("/sdcard/mysdfile.txt");

                myFile.createNewFile();
                FileOutputStream fOut = new FileOutputStream(myFile);
                OutputStreamWriter myOutWriter = 
                                        new OutputStreamWriter(fOut);
                String s = txtData1.getText().toString();
                myOutWriter.write(s);
                myOutWriter.close();
                fOut.close();
                Toast.makeText(getBaseContext(),
                        "Done writing SD 'mysdfile.txt'",
                        Toast.LENGTH_SHORT).show();

            } 


            catch (IOException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
        }
    }

日志错误： 

12-06 16:51:47.794: D/AndroidRuntime(3291): Shutting down VM
12-06 16:51:47.794: W/dalvikvm(3291): threadid=1: thread exiting with uncaught exception (group=0x40015560)
12-06 16:51:47.814: E/AndroidRuntime(3291): FATAL EXCEPTION: main
12-06 16:51:47.814: E/AndroidRuntime(3291): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.ralley.par2/com.ralley.par2.Par2Activity}: java.lang.NullPointerException
12-06 16:51:47.814: E/AndroidRuntime(3291):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1647)
12-06 16:51:47.814: E/AndroidRuntime(3291):     at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1663)
12-06 16:51:47.814: E/AndroidRuntime(3291):     at android.app.ActivityThread.access$1500(ActivityThread.java:117)
12-06 16:51:47.814: E/AndroidRuntime(3291):     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:931)
12-06 16:51:47.814: E/AndroidRuntime(3291):     at android.os.Handler.dispatchMessage(Handler.java:99)
12-06 16:51:47.814: E/AndroidRuntime(3291):     at android.os.Looper.loop(Looper.java:123)
12-06 16:51:47.814: E/AndroidRuntime(3291):     at android.app.ActivityThread.main(ActivityThread.java:3683)
12-06 16:51:47.814: E/AndroidRuntime(3291):     at java.lang.reflect.Method.invokeNative(Native Method)
12-06 16:51:47.814: E/AndroidRuntime(3291):     at java.lang.reflect.Method.invoke(Method.java:507)
12-06 16:51:47.814: E/AndroidRuntime(3291):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:839)
12-06 16:51:47.814: E/AndroidRuntime(3291):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:597)
12-06 16:51:47.814: E/AndroidRuntime(3291):     at dalvik.system.NativeStart.main(Native Method)
12-06 16:51:47.814: E/AndroidRuntime(3291): Caused by: java.lang.NullPointerException
12-06 16:51:47.814: E/AndroidRuntime(3291):     at com.ralley.par2.Par2Activity.onCreate(Par2Activity.java:30)
12-06 16:51:47.814: E/AndroidRuntime(3291):     at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1047)
12-06 16:51:47.814: E/AndroidRuntime(3291):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1611)
12-06 16:51:47.814: E/AndroidRuntime(3291):     ... 11 more
12-06 16:52:04.874: I/Process(3291): Sending signal. PID: 3291 SIG: 9
4

1 回答 1

5

目前，在从 Current Activity 布局获取 UI 元素之前，您没有为 Activity 设置布局，因此setContentView 用于将 Activity 的布局设置为：

 public class Par2Activity extends Activity {
        /** Called when the activity is first created. */
        @Override
        public void onCreate(Bundle savedInstanceState) {
            super.onCreate(savedInstanceState);
            setContentView(R.layout.main); ///<<<<<<<Set layout here for Activity
           //....your code here....
于 2013-01-26T05:58:16.837 回答