[英]How to set “custom” option to View
我試圖在我的類中設置擴展LinearLayout
類中的選項,在帶有(Context , AttributeSet)
公共構造函數中,我使用TypedArray
接受屬性, TypedArray
雖如此,我使用Builder
方法創建了一個類,並將參數設置為使用該類View
(在公共構造函數中),如果我在setContentView(..)
之前調用Builder
,那么可以,如果以后再調用NullPointerException
。
現在的問題是,在將布局設置為MainActivity
之后,如何更改View
類的“屬性”?
在簡單的代碼中,如下所示:
MainActivity進入onCreate(..):
MyBuilder.set(new MyBuilder.Builder()
.setParam(...)
.setEtc(...)
.build());
setContentView(...);
MyObject obj = (MyObject) findViewById(R.id.myObject);
//MyObject.java get param from MyBuilder.java and use it for setup MyObject
//Works!
這是我想要的:
setContentView(...);
//Do various op
MyBuilder.set(new MyBuilder.Builder()
.setParam(...)
.setEtc(...)
.build());
MyObject obj = (MyObject) findViewById(R.id.myObject);
//Params to MyObject is set after setContentView()
//With this flow I get NullPointerException in MyObject.java in reference to MyBuilder.java
現在可以進行簡單的流程說明:
這是我想要的:
這是logcat:
java.lang.RuntimeException: Unable to start activity ComponentInfo{it.michelelacorte.lib/it.michelelacorte.lib.MainActivity}: android.view.InflateException: Binary XML file line #56: Binary XML file line #56: Error inflating class it.michelelacorte.lib.MyObject
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2434)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2494)
at android.app.ActivityThread.access$900(ActivityThread.java:157)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1356)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:148)
at android.app.ActivityThread.main(ActivityThread.java:5527)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:730)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:620)
Caused by: android.view.InflateException: Binary XML file line #56: Binary XML file line #56: Error inflating class it.michelelacorte.lib.MyObject
at android.view.LayoutInflater.inflate(LayoutInflater.java:539)
at android.view.LayoutInflater.inflate(LayoutInflater.java:423)
at android.view.LayoutInflater.inflate(LayoutInflater.java:374)
at android.support.v7.app.AppCompatDelegateImplV7.setContentView(AppCompatDelegateImplV7.java:256)
at android.support.v7.app.AppCompatActivity.setContentView(AppCompatActivity.java:109)
at it.michelelacorte.lib.MainActivity.onCreate(MainActivity.java:114)
at android.app.Activity.performCreate(Activity.java:6272)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1108)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2387)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2494)
at android.app.ActivityThread.access$900(ActivityThread.java:157)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1356)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:148)
at android.app.ActivityThread.main(ActivityThread.java:5527)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:730)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:620)
Caused by: android.view.InflateException: Binary XML file line #56: Error inflating class it.michelelacorte.lib.MyObject
at android.view.LayoutInflater.createView(LayoutInflater.java:645)
at android.view.LayoutInflater.createViewFromTag(LayoutInflater.java:764)
at android.view.LayoutInflater.createViewFromTag(LayoutInflater.java:704)
at android.view.LayoutInflater.rInflate(LayoutInflater.java:835)
at android.view.LayoutInflater.rInflateChildren(LayoutInflater.java:798)
at android.view.LayoutInflater.rInflate(LayoutInflater.java:838)
at android.view.LayoutInflater.rInflateChildren(LayoutInflater.java:798)
at android.view.LayoutInflater.inflate(LayoutInflater.java:515)
at android.view.LayoutInflater.inflate(LayoutInflater.java:423)
at android.view.LayoutInflater.inflate(LayoutInflater.java:374)
at android.support.v7.app.AppCompatDelegateImplV7.setContentView(AppCompatDelegateImplV7.java:256)
at android.support.v7.app.AppCompatActivity.setContentView(AppCompatActivity.java:109)
at it.michelelacorte.lib.MainActivity.onCreate(MainActivity.java:114)
at android.app.Activity.performCreate(Activity.java:6272)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1108)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2387)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2494)
at android.app.ActivityThread.access$900(ActivityThread.java:157)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1356)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:148)
at android.app.ActivityThread.main(ActivityThread.java:5527)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:730)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:620)
Caused by: java.lang.reflect.InvocationTargetException
at java.lang.reflect.Constructor.newInstance(Native Method)
at android.view.LayoutInflater.createView(LayoutInflater.java:619)
at android.view.LayoutInflater.createViewFromTag(LayoutInflater.java:764)
at android.view.LayoutInflater.createViewFromTag(LayoutInflater.java:704)
at android.view.LayoutInflater.rInflate(LayoutInflater.java:835)
at android.view.LayoutInflater.rInflateChildren(LayoutInflater.java:798)
at android.view.LayoutInflater.rInflate(LayoutInflater.java:838)
at android.view.LayoutInflater.rInflateChildren(LayoutInflater.java:798)
at android.view.LayoutInflater.inflate(LayoutInflater.java:515)
at android.view.LayoutInflater.inflate(LayoutInflater.java:423)
at android.view.LayoutInflater.inflate(LayoutInflater.java:374)
at android.support.v7.app.AppCompatDelegateImplV7.setContentView(AppCompatDelegateImplV7.java:256)
at android.support.v7.app.AppCompatActivity.setContentView(AppCompatActivity.java:109)
at it.michelelacorte.lib.MainActivity.onCreate(MainActivity.java:114)
at android.app.Activity.performCreate(Activity.java:6272)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1108)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2387)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2494)
at android.app.ActivityThread.access$900(ActivityThread.java:157)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1356)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:148)
at android.app.ActivityThread.main(ActivityThread.java:5527)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:730)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:620)
Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'float it.michelelacorte.lib.MyBuilder.getRadius()' on a null object reference
at it.michelelacorte.lib.MyObject.<init>(MyObject.java:90)
at java.lang.reflect.Constructor.newInstance(Native Method)
at android.view.LayoutInflater.createView(LayoutInflater.java:619)
at android.view.LayoutInflater.createViewFromTag(LayoutInflater.java:764)
at android.view.LayoutInflater.createViewFromTag(LayoutInflater.java:704)
at android.view.LayoutInflater.rInflate(LayoutInflater.java:835)
at android.view.LayoutInflater.rInflateChildren(LayoutInflater.java:798)
at android.view.LayoutInflater.rInflate(LayoutInflater.java:838)
at android.view.LayoutInflater.rInflateChildren(LayoutInflater.java:798)
at android.view.LayoutInflater.inflate(LayoutInflater.java:515)
at android.view.LayoutInflater.inflate(LayoutInflater.java:423)
at android.view.LayoutInflater.inflate(LayoutInflater.java:374)
at android.support.v7.app.AppCompatDelegateImplV7.setContentView(AppCompatDelegateImplV7.java:256)
at android.support.v7.app.AppCompatActivity.setContentView(AppCompatActivity.java:109)
at it.michelelacorte.lib.MainActivity.onCreate(MainActivity.java:114)
at android.app.Activity.performCreate(Activity.java:6272)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1108)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2387)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2494)
at android.app.ActivityThread.access$900(ActivityThread.java:157)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1356)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:148)
at android.app.ActivityThread.main(ActivityThread.java:5527)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:730)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:620)
您使用setContentView()
設置的XML資源包含標簽<it.michelelacorte.lib.MyObject .../>
。 然后,在構造函數MyObject.<init>()
,獲取MyBuilder
實例並使用它來設置布局。
但是,由於僅在設置內容視圖之后才初始化MyBuilder
,因此您只會得到一個null
實例,從而得到一個NullPointerException
。
而是在MyObject
創建設置方法
public void setup() {
MyBuilder builder = MyBuilder.get();
if (builder != null) {
// setup view with builder
} else {
// setup view defaults
}
}
處理這個並在onCreate()
適當地調用它
MyObject obj = (MyObject) findViewById(R.id.myObject);
obj.setup();
和構造函數本身
public MyObject() {
super(...);
setup();
}
您可以使用LayoutInflater
類的createView
方法來實現。
方法簽名是createView(name, prefix, attrs)
,其中attrs
是AttributeSet
實例
這是有關此方法的一些簡短文檔, 有關LinearLayout的更多信息
參數 :
返回值 :
view
,或者為null。 拋出 :
嘗試以這種方式使用它
LayoutInflater inflater = (LayoutInflater) getSystemService(Context.LAYOUT_INFLATER_SERVICE);
inflater.createView(name, prefix, attrs);
您想在MainActivity
使用它,所以我確定在定義LayoutInflater
時不會發生任何問題
但是,如果您對此有任何疑問,請評論此帖子,我將指導您如何做到這一點。
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