public class MainActivity extends ActionBarActivity {
Button btn_wr;
TextView editText1;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
btn_wr = (Button)this.findViewById(R.id.button1);
editText1 = (TextView)this.findViewById(R.id.editText1);
if (savedInstanceState == null) {
getSupportFragmentManager().beginTransaction()
.add(R.id.container, new PlaceholderFragment())
.commit();
}
}
private String getDataFromText() {
return this.editText1.getText().toString();
}
private boolean isExternalStorageWritable() {
String state = Environment.getExternalStorageState();
if (Environment.MEDIA_MOUNTED.equals(state)) {
return true;
}
return false;
}
private void writeToFile(String fileName, String content) {
boolean flag = false;
File file;
FileOutputStream fos = null;
if (isExternalStorageWritable())
file = new File(Environment.getExternalStorageDirectory(), fileName);
else
file = new File("/" + fileName);
try {
fos = new FileOutputStream(file);
fos.write(content.getBytes());
flag = true;
} catch (FileNotFoundException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} finally {
try {
fos.close();
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
System.out.println("===>write ok? " + flag);
}
public void writeToFile(View v) {
writeToFile("hello", getDataFromText());
}
04-04 14:58:36.010: E/AndroidRuntime(10002): FATAL EXCEPTION: main
04-04 14:58:36.010: E/AndroidRuntime(10002): java.lang.IllegalStateException: Could not execute method of the activity
04-04 14:58:36.010: E/AndroidRuntime(10002): at android.view.View$1.onClick(View.java:3598)
04-04 14:58:36.010: E/AndroidRuntime(10002): at android.view.View.performClick(View.java:4203)
04-04 14:58:36.010: E/AndroidRuntime(10002): at android.view.View$PerformClick.run(View.java:17549)
04-04 14:58:36.010: E/AndroidRuntime(10002): at android.os.Handler.handleCallback(Handler.java:725)
04-04 14:58:36.010: E/AndroidRuntime(10002): at android.os.Handler.dispatchMessage(Handler.java:92)
04-04 14:58:36.010: E/AndroidRuntime(10002): at android.os.Looper.loop(Looper.java:137)
04-04 14:58:36.010: E/AndroidRuntime(10002): at android.app.ActivityThread.main(ActivityThread.java:5068)
04-04 14:58:36.010: E/AndroidRuntime(10002): at java.lang.reflect.Method.invokeNative(Native Method)
04-04 14:58:36.010: E/AndroidRuntime(10002): at java.lang.reflect.Method.invoke(Method.java:511)
04-04 14:58:36.010: E/AndroidRuntime(10002): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:793)
04-04 14:58:36.010: E/AndroidRuntime(10002): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:560)
04-04 14:58:36.010: E/AndroidRuntime(10002): at dalvik.system.NativeStart.main(Native Method)
04-04 14:58:36.010: E/AndroidRuntime(10002): Caused by: java.lang.reflect.InvocationTargetException
04-04 14:58:36.010: E/AndroidRuntime(10002): at java.lang.reflect.Method.invokeNative(Native Method)
04-04 14:58:36.010: E/AndroidRuntime(10002): at java.lang.reflect.Method.invoke(Method.java:511)
04-04 14:58:36.010: E/AndroidRuntime(10002): at android.view.View$1.onClick(View.java:3593)
04-04 14:58:36.010: E/AndroidRuntime(10002): ... 11 more
04-04 14:58:36.010: E/AndroidRuntime(10002): Caused by: java.lang.NullPointerException
04-04 14:58:36.010: E/AndroidRuntime(10002): at com.example.sdtest.MainActivity.getDataFromText(MainActivity.java:41)
04-04 14:58:36.010: E/AndroidRuntime(10002): at com.example.sdtest.MainActivity.writeToFile(MainActivity.java:84)
04-04 14:58:36.010: E/AndroidRuntime(10002): ... 14 more
04-04 14:58:36.025: D/dalvikvm(10002): GC_CONCURRENT freed 198K, 10% free 3795K/4172K, paused 1ms+2ms, total 22ms

空指针异常引起的
调用目标异常
执行方法异常
先看看哪里空指针了
大约是84行 你找找

双击log定位一下，也有可能是非法参数导致的

v7包我一直不会用……

你好，你看一下这行：
04-04 14:58:36.010: E/AndroidRuntime(10002): Caused by: java.lang.NullPointerException
cause by，后面跟的语句就是你程序出错的原因。这里说的是因为空指针异常，你打开LogCat界面，在cause by这行，后面应该有引起空指针的语句。双击进入这条语句，然后再依次往下查找就行了