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做学徒时，一家公司告诉我为 Jelly-bean 开发一个应用程序，但现在他们突然想把我的一些工作移植到 froyo 上。

我想重新开始，但我什至无法开始，更改TextView文本会让我失望nullPointerException：

package com.videopleyer22ics;

import android.os.Bundle;
import android.app.Activity;
import android.view.Menu;
import android.widget.TextView;

    public class MainActivity extends Activity
    {
        TextView tv1;

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

            tv1 = (TextView) findViewById(R.id.texto1);

            setContentView(R.layout.activity_main);

            tv1.setText("Text changed");
        }

        @Override
        public boolean onCreateOptionsMenu(Menu menu) {
            // Inflate the menu; this adds items to the action bar if it is present.
            getMenuInflater().inflate(R.menu.activity_main, menu);
            return true;
        }

}

这是 Logcat 转储

02-11 14:52:34.058: E/AndroidRuntime(510): FATAL EXCEPTION: main
02-11 14:52:34.058: E/AndroidRuntime(510): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.videopleyer22ics/com.videopleyer22ics.MainActivity}: java.lang.NullPointerException
02-11 14:52:34.058: E/AndroidRuntime(510):  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2663)
02-11 14:52:34.058: E/AndroidRuntime(510):  at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2679)
02-11 14:52:34.058: E/AndroidRuntime(510):  at android.app.ActivityThread.access$2300(ActivityThread.java:125)
02-11 14:52:34.058: E/AndroidRuntime(510):  at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2033)
02-11 14:52:34.058: E/AndroidRuntime(510):  at android.os.Handler.dispatchMessage(Handler.java:99)
02-11 14:52:34.058: E/AndroidRuntime(510):  at android.os.Looper.loop(Looper.java:123)
02-11 14:52:34.058: E/AndroidRuntime(510):  at android.app.ActivityThread.main(ActivityThread.java:4627)
02-11 14:52:34.058: E/AndroidRuntime(510):  at java.lang.reflect.Method.invokeNative(Native Method)
02-11 14:52:34.058: E/AndroidRuntime(510):  at java.lang.reflect.Method.invoke(Method.java:521)
02-11 14:52:34.058: E/AndroidRuntime(510):  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:868)
02-11 14:52:34.058: E/AndroidRuntime(510):  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:626)
02-11 14:52:34.058: E/AndroidRuntime(510):  at dalvik.system.NativeStart.main(Native Method)
02-11 14:52:34.058: E/AndroidRuntime(510): Caused by: java.lang.NullPointerException
02-11 14:52:34.058: E/AndroidRuntime(510):  at com.videopleyer22ics.MainActivity.onCreate(MainActivity.java:54)
02-11 14:52:34.058: E/AndroidRuntime(510):  at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1047)
02-11 14:52:34.058: E/AndroidRuntime(510):  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2627)
02-11 14:52:34.058: E/AndroidRuntime(510):  ... 11 more

我只是不知道该怎么做，因为它在 ICS 上运行良好，我需要帮助。您知道将 ICS 项目移植到 froyo 的方法吗？我不介意从头再来一次。

4

1 回答 1

6

setContentView()交换和的顺序findViewById()。您正试图TextView在主布局膨胀之前找到。

于 2013-02-11T16:10:43.160 回答