获取 java.lang.ClassCastException：android.widget.FrameLayout$LayoutParams 无法转换为 android.widget.RelativeLayout$LayoutParams
Getting java.lang.ClassCastException: android.widget.FrameLayout$LayoutParams cannot be cast to android.widget.RelativeLayout$LayoutParams
这里我需要在运行时添加textview。首先我参考了 RelativeLayout 来获取布局参数，但不幸的是它在 RelativeLayout.LayoutParams params = (android.widget.RelativeLayout.LayoutParams)contentLayout.getLayoutParams() 抛出 ClassCastException
我也检查了 - FrameLayout to RelativeLayout ClassCastException even if there is no FrameLayout used，但没有用。因为用 FrameLayout 替换 RelativeLayout 后，我无法在 layoutParams 上添加规则。
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
TextView displayTextView = (TextView)findViewById(R.id.display_text);
ContentResolver resolver = getContentResolver();
Cursor cursor = resolver.query(UserDictionary.Words.CONTENT_URI, null, null, null, null);
cursor.moveToFirst();
displayTextView.setText("The User Dictionary contains " + cursor.getColumnCount() + " words");
RelativeLayout contentLayout = (RelativeLayout)findViewById(R.id.content_layout);
TextView columnNames = new TextView(this);
columnNames.setText("Columns: _id - frequency - word");
contentLayout.addView(columnNames);
RelativeLayout.LayoutParams params = (android.widget.RelativeLayout.LayoutParams)contentLayout.getLayoutParams();
params.addRule(RelativeLayout.ALIGN_PARENT_LEFT);
params.addRule(RelativeLayout.BELOW);
do{
TextView entry = new TextView(this);
entry.setText(cursor.getInt(cursor.getColumnIndex(UserDictionary.Words._ID)) + " - " +
cursor.getInt(cursor.getColumnIndex(UserDictionary.Words.FREQUENCY)) + " - " +
cursor.getString(cursor.getColumnIndex(UserDictionary.Words.WORD)));
entry.setLayoutParams(params);
contentLayout.addView(entry);
}while(cursor.moveToNext());
cursor.close();
}
**Getting following error** -
java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.dexter.contentpro/com.example.dexter.contentpro.MainActivity}: java.lang.ClassCastException: android.widget.FrameLayout$LayoutParams cannot be cast to android.widget.RelativeLayout$LayoutParams
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2298)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2360)
at android.app.ActivityThread.access0(ActivityThread.java:144)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1278)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:135)
at android.app.ActivityThread.main(ActivityThread.java:5221)
at java.lang.reflect.Method.invoke(Native Method)
at java.lang.reflect.Method.invoke(Method.java:372)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:899)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:694)
Caused by: java.lang.ClassCastException: android.widget.FrameLayout$LayoutParams cannot be cast to android.widget.RelativeLayout$LayoutParams
at com.example.dexter.contentpro.MainActivity.onCreate(MainActivity.java:37)
at android.app.Activity.performCreate(Activity.java:5933)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1105)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2251)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2360)
at android.app.ActivityThread.access0(ActivityThread.java:144)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1278)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:135)
at android.app.ActivityThread.main(ActivityThread.java:5221)
at java.lang.reflect.Method.invoke(Native Method)
at java.lang.reflect.Method.invoke(Method.java:372)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:899)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:694)
activity_main.xml-
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:id="@+id/content_layout"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:paddingLeft="@dimen/activity_horizontal_margin"
android:paddingRight="@dimen/activity_horizontal_margin"
android:paddingTop="@dimen/activity_vertical_margin"
android:paddingBottom="@dimen/activity_vertical_margin" tools:context=".MainActivity">
<TextView
android:id="@+id/display_text"
android:layout_width="wrap_content"
android:layout_height="wrap_content" />
</RelativeLayout>
错误是对的，你也是对的，但这是你和 android 双方的误解。你会看到当你 Inflate View 和 Parent_View 是 ViewGroup 的任何子 class 时，android return 是 View 并把它当作 View 如果你想把它当作 ViewGroup 的子 class 你将有一些 cast Excetpions... 你看，我凭经验知道这一点，但我不能给你一个有据可查的事实
回到你的问题；您尝试获取 RelativeLayout 的 Layoutparams，这是 xml 中最重要的 View，所以我认为 getLayoutParams() 应该 return null 因为它没有附加到 ViewGroup 但它不是，这意味着它附加到 FrameLayout 这是 Window 或其本身的最顶层 View。
求解
试试这个 (1)
而不是使用这条线
RelativeLayout.LayoutParams params = (android.widget.RelativeLayout.LayoutParams)
contentLayout.getLayoutParams();
使用这个
//get the layoutParams of the TextView child in the Relativelayout in
//your xml,this will automatically map to the RelativeLayout params
RelativeLayout.LayoutParams params = (android.widget.RelativeLayout.LayoutParams)
displayTextView.getLayoutParams();
或使用此(2)
仅更改您的 xml，您之前的代码将正常工作
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:paddingLeft="@dimen/activity_horizontal_margin"
android:paddingRight="@dimen/activity_horizontal_margin"
android:paddingTop="@dimen/activity_vertical_margin"
android:paddingBottom="@dimen/activity_vertical_margin"
tools:context=".MainActivity">
<RelativeLayout
android:id="@+id/content_layout"
android:layout_width="match_parent"
android:layout_height="match_parent" >
<TextView
android:id="@+id/display_text"
android:layout_width="wrap_content"
android:layout_height="wrap_content" />
</RelativeLayout>
</RelativeLayout>
这里我需要在运行时添加textview。首先我参考了 RelativeLayout 来获取布局参数，但不幸的是它在 RelativeLayout.LayoutParams params = (android.widget.RelativeLayout.LayoutParams)contentLayout.getLayoutParams() 抛出 ClassCastException
我也检查了 - FrameLayout to RelativeLayout ClassCastException even if there is no FrameLayout used，但没有用。因为用 FrameLayout 替换 RelativeLayout 后，我无法在 layoutParams 上添加规则。
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
TextView displayTextView = (TextView)findViewById(R.id.display_text);
ContentResolver resolver = getContentResolver();
Cursor cursor = resolver.query(UserDictionary.Words.CONTENT_URI, null, null, null, null);
cursor.moveToFirst();
displayTextView.setText("The User Dictionary contains " + cursor.getColumnCount() + " words");
RelativeLayout contentLayout = (RelativeLayout)findViewById(R.id.content_layout);
TextView columnNames = new TextView(this);
columnNames.setText("Columns: _id - frequency - word");
contentLayout.addView(columnNames);
RelativeLayout.LayoutParams params = (android.widget.RelativeLayout.LayoutParams)contentLayout.getLayoutParams();
params.addRule(RelativeLayout.ALIGN_PARENT_LEFT);
params.addRule(RelativeLayout.BELOW);
do{
TextView entry = new TextView(this);
entry.setText(cursor.getInt(cursor.getColumnIndex(UserDictionary.Words._ID)) + " - " +
cursor.getInt(cursor.getColumnIndex(UserDictionary.Words.FREQUENCY)) + " - " +
cursor.getString(cursor.getColumnIndex(UserDictionary.Words.WORD)));
entry.setLayoutParams(params);
contentLayout.addView(entry);
}while(cursor.moveToNext());
cursor.close();
}
**Getting following error** -
java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.dexter.contentpro/com.example.dexter.contentpro.MainActivity}: java.lang.ClassCastException: android.widget.FrameLayout$LayoutParams cannot be cast to android.widget.RelativeLayout$LayoutParams
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2298)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2360)
at android.app.ActivityThread.access0(ActivityThread.java:144)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1278)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:135)
at android.app.ActivityThread.main(ActivityThread.java:5221)
at java.lang.reflect.Method.invoke(Native Method)
at java.lang.reflect.Method.invoke(Method.java:372)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:899)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:694)
Caused by: java.lang.ClassCastException: android.widget.FrameLayout$LayoutParams cannot be cast to android.widget.RelativeLayout$LayoutParams
at com.example.dexter.contentpro.MainActivity.onCreate(MainActivity.java:37)
at android.app.Activity.performCreate(Activity.java:5933)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1105)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2251)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2360)
at android.app.ActivityThread.access0(ActivityThread.java:144)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1278)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:135)
at android.app.ActivityThread.main(ActivityThread.java:5221)
at java.lang.reflect.Method.invoke(Native Method)
at java.lang.reflect.Method.invoke(Method.java:372)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:899)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:694)
activity_main.xml-
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:id="@+id/content_layout"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:paddingLeft="@dimen/activity_horizontal_margin"
android:paddingRight="@dimen/activity_horizontal_margin"
android:paddingTop="@dimen/activity_vertical_margin"
android:paddingBottom="@dimen/activity_vertical_margin" tools:context=".MainActivity">
<TextView
android:id="@+id/display_text"
android:layout_width="wrap_content"
android:layout_height="wrap_content" />
</RelativeLayout>
错误是对的，你也是对的，但这是你和 android 双方的误解。你会看到当你 Inflate View 和 Parent_View 是 ViewGroup 的任何子 class 时，android return 是 View 并把它当作 View 如果你想把它当作 ViewGroup 的子 class 你将有一些 cast Excetpions... 你看，我凭经验知道这一点，但我不能给你一个有据可查的事实
回到你的问题；您尝试获取 RelativeLayout 的 Layoutparams，这是 xml 中最重要的 View，所以我认为 getLayoutParams() 应该 return null 因为它没有附加到 ViewGroup 但它不是，这意味着它附加到 FrameLayout 这是 Window 或其本身的最顶层 View。
求解
试试这个 (1)
而不是使用这条线
RelativeLayout.LayoutParams params = (android.widget.RelativeLayout.LayoutParams)
contentLayout.getLayoutParams();
使用这个
//get the layoutParams of the TextView child in the Relativelayout in
//your xml,this will automatically map to the RelativeLayout params
RelativeLayout.LayoutParams params = (android.widget.RelativeLayout.LayoutParams)
displayTextView.getLayoutParams();
或使用此(2)
仅更改您的 xml，您之前的代码将正常工作
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:paddingLeft="@dimen/activity_horizontal_margin"
android:paddingRight="@dimen/activity_horizontal_margin"
android:paddingTop="@dimen/activity_vertical_margin"
android:paddingBottom="@dimen/activity_vertical_margin"
tools:context=".MainActivity">
<RelativeLayout
android:id="@+id/content_layout"
android:layout_width="match_parent"
android:layout_height="match_parent" >
<TextView
android:id="@+id/display_text"
android:layout_width="wrap_content"
android:layout_height="wrap_content" />
</RelativeLayout>
</RelativeLayout>